Polymer Chemistry A Practical Approach (Practical Approach Series)

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ThePracticalApproachinChemistrySeriesSERIESEDITORSL.M.HarwoodC.J.MoodyDepartmentofChemistryDepartmentofChemistryUniversityofReadingUniversityofExeter ThePracticalApproachinChemistrySeriesOrganocopperreagentsEditedbyRichardJ.K.TaylorMacrocyclesynthesisEditedbyDavidParkerHigh-pressuretechniquesinchemistryandphysicsEditedbyWilfriedB.HolzapfelandNeilS.IsaacsPreparationofalkenesEditedbyJonathanM.J.WilliamsTransitionmetalsinorganicsynthesisEditedBySusanE.Gibson(néeThomas)Matrix-isolationtechniquesIanR.DunkinLewisacidreagentsEditedbyHisashiYamamotoOrganozincacidreagentsEditedbyPaulKnochelandPhilipJonesAminoacidderivativesEditedbyGrahamC.BarrettAsymmetricoxidationreactionsEditedbyTsutomuKatsukiNitrogen,oxygenandsulfurylidechemistryEditedbyJ.StephenClarkOrganophosphorusreagentsEditedbyPatrickJ.MurphyPolymerchemistryEditedbyFredJ.Davis PolymerChemistryAPracticalApproachEditedbyFREDJ.DAVISTheSchoolofChemistry,TheUniversityofReading,UK1 1GreatClarendonStreet,OxfordOX26DPOxfordUniversityPressisadepartmentoftheUniversityofOxford.ItfurtherstheUniversity’sobjectiveofexcellenceinresearch,scholarship,andeducationbypublishingworldwideinOxfordNewYorkAucklandBangkokBuenosAiresCapeTownChennaiDaresSalaamDelhiHongKongIstanbulKarachiKolkataKualaLumpurMadridMelbourneMexicoCityMumbaiNairobiSãoPauloShanghaiTaipeiTokyoTorontoOxfordisaregisteredtrademarkofOxfordUniversityPressintheUKandincertainothercountriesPublishedintheUnitedStatesbyOxfordUniversityPressInc.,NewYork©OxfordUniversityPress2004ThemoralrightsoftheauthorhavebeenassertedDatabaserightOxfordUniversityPress(maker)Firstpublished2004Allrightsreserved.Nopartofthispublicationmaybereproduced,storedinaretrievalsystem,ortransmitted,inanyformorbyanymeans,withoutthepriorpermissioninwritingofOxfordUniversityPress,orasexpresslypermittedbylaw,orundertermsagreedwiththeappropriatereprographicsrightsorganization.EnquiriesconcerningreproductionoutsidethescopeoftheaboveshouldbesenttotheRightsDepartment,OxfordUniversityPress,attheaddressaboveYoumustnotcirculatethisbookinanyotherbindingorcoverandyoumustimposethissameconditiononanyacquirerAcataloguerecordforthistitleisavailablefromtheBritishLibraryLibraryofCongressCataloginginPublicationData(Dataavailable)ISBN0198503091(Hbk)10987654321TypesetbyNewgenImagingSystems(P)Ltd.,Chennai,IndiaPrintedinGreatBritainonacid-freepaperbyBiddlesLtd,King’sLynn TomywifeJacqueline,mychildrenCharlie,William,Gracie,andBriony,andtomylatemotherMrsJosephineP.Davis Thispageintentionallyleftblank PrefaceItissometimesinceLaurenceHarwoodsuggestedtometheideaofthisvolumeofthePracticalApproachinOrganicChemistryseries,andwhilstinitiallyIcouldseethevalueofsuchacontribution,asthesubsequentdelayinproductiontestifies,Ihavehadsomedifficultyintransposingthistopictoarelativelysmalltext.Therearemanyscientificpublicationsdevotedentirelytotheareaofpolymersynthesis,withtensofthousandpagesdevotedtothetopicinthescientificliteratureeveryyearIhavefocusedonthoseaspectsofthetopicwhichIfindinteresting,andconsequentlytherearecertainlymanyomissions.Ihope,however,thattheexamplesIhaveincludedwillgiveaflavourofwhatcanbeachieved(generallywithoutrecoursetohighlyspe-cializedequipment)intermsofthedevelopmentofnovelmacromolecularsystems.AswithallthevolumesinthePracticalApproachSeries,thisbookaimstoprovideadetailedandaccessiblelaboratoryguidesuitableforthosenewtotheareaofpolymersynthesis.Theprotocolscontainedwithinthismanuscriptprovideinformationaboutsolventpurification,equipmentandreactionconditions,andlistsomepotentialproblemsandhazards.ThelatterpointisparticularlyimportantandinmostinstancesIhavereferredtothemanufacturers’safetydatasheet(MSDS,whichcompaniessuchasMerckandAldrichprovideon-line);however,oftenthesevaryindetailfromsource-to-sourceandfromtime-to-time,andofcourselocalrulesalwaysmusttakeprecedance.Iamparticularlyindebtedtothecontributorstothisworkfortheirexcel-lenteffortsandpromptresponsestomyrequests.Iamalsogratefultomypostgraduatestudents,particularlyDarioCastiglioneandVidhuMahendraforcheckingsomeoftheexperimentaldetails,andtomycolleagueatReadingDrWayneHayesforhisconstantenthusiasmandadvice.FredJ.DavisReadingDecember2003 Thispageintentionallyleftblank ContentsContributorsxiiiAbbreviationsxvii1.Polymercharacterization1IanL.Hosier,AlunS.Vaughan,GeoffreyR.Mitchell,JintanaSiripitayananon,andFredJ.Davis1.Introduction12.Syntheticroutestopolymers23.Molecularweightdetermination44.Compositionandmicrostructure75.Opticalmicroscopy96.Electronmicroscopy117.Analyticalmicroscopy148.Scanningprobemicroscopy169.Thermalanalysis1810.Molecularrelaxationspectroscopy2111.X-rayandneutronscatteringmethods2412.Conclusions32References332.Generalproceduresinchain-growthpolymerization43NajibAragrag,DarioC.Castiglione,PaulR.Davies,FredJ.Davis,andSangdilI.Patel1.Introduction432.Free-radicalchainpolymerization443.Anionicpolymerization674.Ring-openingpolymerizationsinitiatedbyanionicreagents835.Coordinationpolymers906.Conclusions95References95 Contents3.Controlled/‘living’polymerizationmethods99WayneHayesandSteveRannard1.Introduction992.Covalent‘living’polymerization:grouptransferpolymerization1013.Controlledfree-radicalpolymerizationsmediatedbynitroxides1094.Controlledfree-radicalpolymerizations:atomtransferfree-radicalpolymerizations(ATRP)andaqueousATRP116References1234.Step-growthpolymerization—basicsanddevelopmentofnewmaterials126ZhiqunHe,EricA.Whale,andFredJ.Davis1.Introduction1262.Thesynthesisofanaromaticpolyamide1273.Preparationofamain-chainliquidcrystallinepoly(esterether)withaflexibleside-chain1304.Non-periodiccrystallizationfromaside-chainbearingcopolyester1355.Acomparisonofmeltpolymerizationofanaromaticdi-acidcontaininganethyleneglycolspacerwithpolymerizationinasolventanddispersioninaninorganicmedium138References1435.Theformationofcyclicoligomersduringstep-growthpolymerization145AbderrazakBenHaida,PhilipHodge,andHowardM.Colquhoun1.Introduction1452.Synthesisandextractionofcyclicoligomersofpoly(etherketone)1463.Synthesisofsomesulfone-linkedparacyclophanesfrommacrocyclicthioethers1524.Summary156References156x Contents6.Thesynthesisofconductingpolymersbasedonheterocycliccompounds158DavidJ.Walton,FredJ.Davis,andPhilipJ.Langley1.Introduction1582.Electrochemicalsynthesis1593.Synthesisofpolypyrrole1634.Synthesisofpolyaniline1785.Synthesisofpolythiophene1816.Conclusions186References1867.Someexamplesofdendrimersynthesis188DonaldA.Tomalia1.Introduction1882.Excessreagentmethod1903.Protection–deprotectionmethod193References1998.Newmethodologiesinthepreparationofimprintedpolymers201CameronAlexander,NicoleKirsch,andMichaelWhitcombe1.Introduction2012.Sacrificialspacerapproach2033.Preparationofbacteria-imprintedpolymers210References2149.Liquidcrystallinepolymers215SangdilI.Patel,FredJ.Davis,PhilipM.S.Roberts,CraigD.Hasson,DavidLacey,AlanW.Hall,AndreasGreve,andHeinoFinkelmann1.Introduction2152.Synthesisofanacrylate-basedliquidcrystalpolymer2173.Thehydrosilylationreaction:ausefulprocedureforthepreparationofavarietyofside-chainpolymers225xi Contents4.Photochemicalpreparationofliquidcrystallineelastomerswithamemoryofthealignedcholestericphase2295.Definingpermanentmemoryofmacroscopicglobalalignmentinliquidcrystalelastomers2346.Summary244References244Index246xii ContributorscameronalexanderSchoolofPharmacyandBiomedicalSciences,UniversityofPortsmouth,WhiteSwanRoad,Portsmouth,PO12DT,UKnajibaragragTheDepartmentofChemistry,TheUniversityofReading,Whiteknights,Reading,Berkshire,RG66AD,UKabderrazakbenhaidaDepartmentofChemistry,UniversityofManchester,OxfordRoad,Manchester,M139PL,UKdarioc.castiliglioneTheDepartmentofChemistry,TheUniversityofReading,Whiteknights,Reading,BerkshireRG66AD,UKhowardcolquhounTheDepartmentofChemistry,TheUniversityofReading,Whiteknights,Reading,BerkshireRG66AD,UKpaulr.daviesSchoolofChemistry,TheUniversityofReading,Whiteknights,Reading,BerkshireRG66AD,UKfredj.davisSchoolofChemistry,TheUniversityofReading,Whiteknights,Reading,BerkshireRG66AD,UKheinofinkelmannInstitutfürMakromoleculareChemie,UniversitätFreiburg,Stefan-Meier-Strasse31,FreiburgD-79104,GermanyandreasgreveInstitutfürMakromoleculareChemie,UniversitatFreiburg,Stefan-Meier-Strasse31,FreiburgD-79104,Germanyalanw.hallTheDepartmentofChemistry,TheUniversityofHull,Kingston-upon-Hull,CottinghamRoad,HullHU67RX,UKcraigd.hassonJJThomsonPhysicalLaboratory,POBox220,Whiteknights,ReadingRG66AF,UK ContributorswaynehayesTheDepartmentofChemistry,TheUniversityofReading,Whiteknights,Reading,BerkshireRG66AD,UKzhiqunheInstituteofOptoelectronicTechnology,BeijingJiaotongUniversity,Beijing100044,ChinaphiliphodgeDepartmentofChemistry,UniversityofManchester,OxfordRoad,Manchester,M139PL,UKianl.hosierSchoolofElectronicsandComputerScience,UniversityofSouthampton,SO171BJ,UKnicolekirschBioorganicandBiophysicalChemistryLaboratory,DepartmentofChemistryandBiomedicalSciences,UniversityofKalmar,SE-39182Kalmar,Swedengeoffreyr.mitchellJJThomsonPhysicalLaboratory,POBox220,Whiteknights,ReadingRG66AF,UKphilipj.langleySchoolofChemistry,TheUniversityofReading,Whiteknights,Reading,BerkshireRG66AD,UKsangdili.patelSchoolofChemistry,TheUniversityofReading,Whiteknights,Reading,BerkshireRG66AD,UKphilipm.s.robertsJJThomsonPhysicalLaboratory,POBox220,Whiteknights,ReadingRG66AF,UKdavidlaceyTheDepartmentofChemistry,TheUniversityofHull,Kingston-upon-Hull,CottinghamRoad,HullHU67RX,UKsteverannardUnileverResearchPortSunlightLaboratory,QuarryRoadEast,Bebington,Wirral,CH633JW,UKjintanasirpitayananonBiopolymersResearchUnit,DepartmentofChemistry,FacultyofScience,ChiangMaiUniversity,50200,Thailandxiv Contributorsdonalda.tomaliaMichiganMolecularInstitute,1910WestSt.AndrewsRoad,Midland,MI48640–2696,USAaluns.vaughanSchoolofElectronicsandComputerScience,UniversityofSouthampton,SO171BJ,UKdavidj.waltonSchoolofScienceandtheEnvironment,CoventryUniversity,PrioryStreet,CoventryCV15FB,UKerica.whaleJRATechnologyLtd,JRAHouse,TaylorsClose,Marlow,BuckinghamshireSL71PR,UKmichaelj.whitcombeInstituteofFoodResearch,NorwichResearchPark,Colney,Norwich,NR47UA,UKxv Thispageintentionallyleftblank AbbreviationsAFMatomicforcemicroscopyAIBN2,2
-AzobisisobutyronitrileATRPatomtransferfree-radicalpolymerizationBHT2,6-Di-t-butylphenolCCDchargecoupleddeviceCFIcontactforceimagingCLSMconfocallaserscanningmicroscopyDBEdibutyletherDICdifferentialinterferencecontrastDMFdimethylformamideDMSOdimethylsulfoxideDMTAdynamicmechanicalthermalanalysisDPdegreeofpolymerizationDSCdifferentialscanningcalorimetryDTAdifferentialthermalanalysisDVBdivinylbenzeneEELSelectronenergylossspectroscopyEGDMAethyleneglycoldimethacrylateFTIR+A28Fouriertransforminfra-red.GPCgelpermeationchromatographyGTPgrouptransferpolymerizationHPLChighperformanceliquidchromatographyIRinfra-redLCSTlowercriticalsolutiontemperatureLEDLightemittingdiodeLSCELiquidsinglecrystallineelastomerLSMLaserscanningmicroscopeMALDI-TOFmatrix-assistedlaserdesorptionionization—timeofflightMAOmethylaluminoxaneMBPImethylenebis(phenlyisocynate)MDSCModulatedDSCMHTBO1-methyl-4-hydroxymethyl-2,6,7-trioxabicyclo-[2,2,2]-octaneMIPMolecularlyimprintedpolymersMOPS(3-[N]-morpholino)propylsulfonicacidNIPAN-IsopropylacrylamideNMPN-methylpyrrolidoneNMRnuclearmagneticresonance AbbreviationsPAApoly(allylamine)PAMAMpoly(amidoamine)PEEKpoly(etheretherketone)PEKpoly(etherketone)PETPolyethyleneterephthalatePHBpoly(hydroxybutyrate)PMMApolymethylmethacrylatePPVpoly(phenylenevinylene)PPTSPyridine-p-toluenesulfonatePTFEpoly(tetrafluoroethylene)PVCpolyvinlychloridePVF2poly(vinylidenefluoride)RAFTreversibleadditionfragmentationchaintransferROMPring-openingmetathesispolymerizationSCEstandardcalomelelectrodeSECsizeexclusionchromatography(GPC)SEMscanningelectronmicroscopySPMscanningprobemicroscopySTEMscanningtransmissionelectronmicroscopySTMscanningtunnellingmicroscopyTASHF2tris(dimethylamino)sulfoniumbifluorideTBABBtetra-n-butylammoniumbibenzoateTEMtransmissionelectromicroscopyTEMPO2,2,6,6-Tetramethylpiperidinyl-1-oxyTHFtetrahydrofuranTLCthinlayerchromatographyUV–VisUltraviolet–Visiblexviii 1PolymercharacterizationIANL.HOSIER,ALUNS.VAUGHAN,GEOFFREYR.MITCHELL,JINTANASIRIPITAYANANON,andFREDJ.DAVIS1.IntroductionPolymerscienceis,ofcourse,drivenbythedesiretoproducenewmaterialsfornewapplications.Thesuccessofmaterialssuchaspolyethylene,polypropylene,andpolystyreneissuchthatthesematerialsaremanufacturedonahugescaleandareindeedubiquitous.Thereisstillamassivedrivetounderstandthesematerialsandimprovetheirpropertiesinordertomeetmaterialrequirements;however,increasinglypolymersarebeingappliedtoawiderangeofproblems,andcertainlyintermsofdevelopingnewmaterialsthereismuchmoreemphasisoncontrol.Suchcontrolcanbecontrolofmolecularweight,forexample,theproductionofpolymerswithahighlynarrowmolecularweightdistributionbyanionicpolymerization.1Thecon-trolofpolymerarchitectureextendsfromblockcopolymerstoothernovelarchitecturessuchasladderpolymersanddendrimers(seeChapter7).2,3Cyclicsystemscanalsobeprepared4,5(seeChapter5),usuallythesearelowermolecularweightsystems,althoughthesealsomightbeexpectedtobethenaturalconsequenceofstep-growthpolymerizationathighconversion.6Polymersareusedinawiderangeofapplications,ascoatings,asadhesives,asengineeringandstructuralmaterials,forpackaging,andforclothingtonameafew.Akeyfeatureofthesuccessandversatilityofthesematerialsisthatitispossibletobuildinpropertiesbycarefuldesignofthe(largely)organicmoleculesfromwhichthechainsarebuiltup.Forexample,rigidaromaticmoleculescanbeusedtomakehigh-strengthfibres,themosthigh-profileexampleofthisbeingKevlar®;rigidmoleculesofthistypeareoftenmadebysimplestep-growthpolymerization7andofferparticularsyntheticchallengesasoutlinedinChapter4.Thereisnowanincreasingdemandforhighlyspecializedmaterialsforuseinforexampleopticalandelectronicapplicationsandpolymershavebeensingledoutashavingparticularpotentialinthisregard.Forexample,thereisconsiderableinterestinthedevelopmentofpolymerswithtargetedopticalpropertiessuchassecond-orderopticalnon-linearity,8andinconductingpolymers(seeChapter6)aselectrodematerials,9 I.L.Hosieretal.asaroutetowardssupercapacitors10andaselectroluminescentmaterials.11Polymericmaterialscanalsobeusedasanelectrolyteinthedesignofcom-pactbatteries.12Aparticularfeatureofpolymersisthepossibilityoflinkingtogetherseparatechainstoformnetworks.Suchcross-linkscanbeintroducedbycopolymerizationofamonofunctionalmonomersuchasstyrenewithadifunctionalmonomersuchasdivinylbenzene.13Ifthedegreeofcross-linkingishigh,theresultingnetworkbecomesratherrigidandintractable.Aparticu-larlyimportantfeatureofthisisthatthenetworkproducedinteractsonlyslightlywithsolvents;asaconsequencethematerialcanbereadilyseparatedfromorganicsolutions.Suchmaterialsareincreasinglyimportantinarangeofareas:theseincludepolymer-supportedreactions,suchasthoseinpeptidesynthesis,14combinatorialchemistry,15andcatalysis;16andmolecularsep-arationwhereimprintedpolymersofferapowerfulroutetohighlyspecificseparation.17ExamplesofroutestoimprintedpolymersareincludedinChapter8.Lightlycross-linkedmaterialshavealsoattractedconsiderableinterest,sincethepotentialforreversibledeformationintroducesthepossi-bilityofanumberofnovelproperties.Suchmaterialsincludesolventswollensystems(wetgels)18,19andliquidcrystallineelastomers;20theformersystemsareoftenrathersimpletoprepare,whilethelattermaybeformedfromquitecomplexmonomers21(asoutlinedinChapter9).2.SyntheticroutestopolymersWiththevastcommercialimportanceofpolymersitisperhapsnotsurprisingthattherehavebeenhugedevelopmentsinsyntheticmethodology.Thescopeofthefieldissuchthatitisimpossibletoprovideacomprehensivereviewofallthesedevelopmentshere,butafewexamplesmightservetoillustratethearea.Free-radicalpolymerizationremainsapopularsyntheticmethod,butevenwithinthesimplicityofthissystemtherehavebeenmajordevelopments,forexample,theuseofsupercriticalCOasasolvent22hashugepotential.The2developmentofpolymer-supportedreagentshasnecessitatedatailoringofsuspensionpolymerizations,13,23tosuitparticularneeds,forexample,topro-ducemacroporousresins,i.e.resinswhichhaveawell-definedstructureeveninthedrystate.Emulsionpolymerizationshaveevenbeenundertakeninspace24toproduceextremelyuniform10mspheres.Perhapsthemostexcit-ingdevelopmentintheareaoffree-radicalpolymerchemistryistheintroduc-tionofcontrolintofree-radicalpolymerization;initiallyMoad25andlaterothers26havedevelopedawayofcontrollingfree-radicalpolymerizationsusingstablenitroxideradicals.27AtomTransferFreeRadicalPolymerization(ATRP)28isamorerecent29analogousmethodinvolvingstableradicalinter-mediates.Aparticularlyinterestingfeatureofthislattertechniqueisitsadapta-tiontohydrophilicmonomersinaqueoussystems,thusprovidinglivingpolymerswiththeablitytotoleratethepresenceofwater.302 1:PolymercharacterizationThedevelopmentofATRPhassupplementedratherthansupersededanionicpolymersintermsofcontrolofpolymerstructure;anionicpolymerizationisstillthemethodofchoiceforpreparingpolymerswithnarrowmolecularweightdistributionandcontrolledstructures.Thisislargelybecausethewayinwhichpolymericchainsmaybeproducedthatdonotundergoterminationiswellunderstood.31Thereis,however,clearlyacomplexrelationshipbetweenthesolvent,themonomer,andthecounterionspresentandanumberoftech-niquessuchasligatedanionicpolymerizationhavedeveloped,inthiscasetoensurethegrowingchainsareliving.32Blockcopolymersareparticularlyimportant,33forexample,triblockcopolymersmayactasthermoplasticelas-tomers.Thestyrene–butadiene–styrenecopolymeriscommerciallyimportant,butothersystemsincludeliquidcrystallinethermoplasticelastomers.34Star-shapedpolymerscanbemadebycouplingtheanionicchainendswithanotherreactiveunit35(e.g.SiCl);alternativelypolymerswithfunctionalendgroups4canbemadebyreactingtheanionwithsimplemoleculessuchasCO2toformanacidterminatedchain.36Otherpopularmethodsofproducinglivingpoly-mersincludecationicpolymerization37andgroup-transferpolymerization.38,39Organometallicchemistryhasplayedanimportantroleinimprovingsyntheticmethodologyinpolymerscience,40giventhesuccessofclassicalZiegler–Nattacatalyticsystems,41,42itmighthavebeenthoughtthatatleastforbulkpolymersthesyntheticproblemshadbeenlargelysolved.However,thedevelopmentofmetallocenecatalysts43hasclearlyshownthatthisisnotthecase.44Theapplicationofthesecatalyststosystemssuchaspolyethyleneandpolypropylenehasprovedofimmenseimportance,allowingtheformationofnewmaterials45suchasaformofpolypropylene,whichactsasathermoplasticelastomer.46Ofcourse,metallocenesarenottheonlyinorganicpolymerizationcatalystsunderinvestigation47andthisisprovingaparticularlyfruitfulareafororganometallicchemists.Anotherwell-knownorganometallic-catalysedpoly-merizationisthering-openingmetathesispolymerization(ROMP).48,49Oneparticularlyattractivefeatureofthisisthatthecatalysts(oftenruthenium-based)50arenotonlyhighlyactivebutalsocompatiblewithmostfunctionalgroupsandeasytouse.51ROMPhasfoundapplicationinanumberofareas,butaparticularlyinterestingoneisthepreparationofpolyacetylenebyaprecursorroutereferredtoasthe‘Durhamroute’.52Intheorganometallicexamplescitedabove,polymerizationoccursbyachain-growthmechanism.Increasingly,highlyefficientorganometalliccoup-lingreactionssuchastheStillereaction,53theSuzukireaction,54,55andothers56arebeingusedforC–Cbondformationinpolymericreactions.Thesepolycondensationshavebeenusedparticularlytoformhighlyconjugatedaromaticpolymers,forexample,theSuzukireactioncanbeusedtoformpolyphenylene.57Therearevariousorganometallicroutestoformpolythio-phenes.58,59Theseareparticularlyusefulforunsymmetricalthiophenessincetheyprovidefargreatercontroloftheregiochemistrythanelectrochemicalorsimplechemicaloxidation.3 I.L.Hosieretal.Thisbookislargelyconcernedwithpolymersynthesis,andinthefollowingchaptersarangeofbothcommonandmorespecializedsyntheticmethodsusedtoproducemacromolecularsystemsisgiven.However,itmustbenotedthatpolymersareunlikesimplelowmolecularweightmaterialsinthattheyarenotbuilt-upfromasinglestructure,butratheramixtureofsimilarmateri-alsdiffering,forexample,inthenumberofmonomerunitsattachedtothechain,orthestereochemistryaroundastereogeniccarbonatom.Thus,char-acterizationisoftensomethingofastatisticalexercise.Inaddition,becauseofthehugeinterestinpolymersasmaterials,oftenmoredetailedinformationaboutpropertiessuchasorientation,thermalcharacteristics,andmorphologyarerequired.Inthefollowingsectionssomeofthemethodsusedtocharacterizepolymersaredescribed.3.MolecularweightdeterminationItisimportantthatthemolecularweightcharacteristicsofpolymerscanbeaccuratelydetermined.60Ofcourse,theprecisemolecularweightdeterminedwilldependonthetechniqueused,thustechniquesthatrelyonthemeasure-mentofcolligativeproperties,suchasosmoticpressure,countthenumberofmoleculesinsolutionand,therefore,givethenumberaveragemolecularweightMn(Eqn(1)),whileothertechniques,mostnotably,lightscatteringprovideanaveragevaluebasedontheweightfractionsofmoleculesofagivenmass,togivetheweightaveragemolecularmassMw(Eqn(2)).Asimpleandcommonlyusedtechniqueforassessingthemolecularweightofapolymerisviscometry.Inthistechnique,thetimeismeasuredforadilutesolutionofpolymertoflowthroughacapillary.Throughmeasuringthetimesatvariouspolymerconcentrationsandcomparingwiththetimeobtainedfortheneatsolvent,itispossibletoobtainavaluefortheintrinsicviscosity(orlimitingviscositynumber)[
],whichcanberelatedtothemolecularweightusingtheMark–Houwink–Sakuradarelationship(Eqn(3));whereMistheviscosityaveragemolecularweight(eqn(4))andKandaareconstants.Interestingly,thevalueforaisdetermineddirectlybypolymer–solventinteractions,forexample,inathetasolvent61ais0.5,forrod-likepolymersthevaluecanbecloseto1.0;thus,likegelpermeationchromatography(GPC)themeasuredmolecularweightisrelatedtothehydrodynamicvolumeofthemolecules62.
i0NiMiMn(1)
i0Ni2
i0NiMiMn(2)
i0NiMi4 1:Polymercharacterization[
]KMa(3)1/aNM1a
i0iiMn(4)
i0NiMiThereisarangeoftechniquesusedtodeterminethemolecularweight,includingthetwocitedabove,63,64butthemostcommonmethodisGPC(orsize-exclusionchromatography,SEC).65,66Thischromatographictech-niqueisbaseduponsize-exclusionphenomenaandenablestheseparationandassessmentofpolydispersesystems,suchaspolymersandmulti-componentbiologicalsamples.67Inthismethod,polymersareseparatedbyvirtueoftheirhydrodynamicvolume.Thetechniqueinvolvespassingasolutionofthepoly-merthroughacolumnpackedwithaporoussolidphase(oftenpolystyrenecross-linkedwithdivinylbenzene);smallmoleculescanaccesstheseporesrathermoreeasilythanlargermolecules,asaconsequence,theselargermoleculesareelutedfirst.Thetechniquedoesnotgiveabsolutevalues,butrathergivesrelativeones;andthereforerequirescalibrationwithaseriesofpolymersofknownmolecularweight.Sincethetechniquereliesonthesizeofthepolymerinsolution,boththesolventandthetypeofpolymerareimport-ant.Thusdataobtainedforpolystyreneinchloroformdoesnotexactlymatchdataforpolystyrenedissolvedintetrahydrofuran(THF).Similarlyasampleofpoly(methylmethacrylate)inTHFshouldnotstrictlybecomparedwithpolystyrenestandards.Ofcourse,whensynthesizingnovelpolymersitisnotpossibletohavematchingstandards,andconsiderableefforthasbeenspentfindingsolutionstothisproblem.OnesolutionthatisparticularlypopularistheuseofGPCinconjunctionwithaviscositydetector,amethodknownasuniversalcalibration.68Thistechniquemakesuseofabroadlylinearrela-tionshipbetweentheelutionvolumeandtheproductoftheintrinsicviscosityandmolecularweight.MorerecentlyGPCsystemsfittedwithlightscatteringdetectorshavebecomemorepopular.69Oneparticularlyimportantfeatureofthismethodisthatitprovidesagoodindicationofthedistributionofmolecularweightswithinthesample.Figures1.1and1.2illustratethis.Theformershowstracesobtainedfromfirst-andsecond-generationdendrimersamples,70whichareessentiallymonodispersebyMatrix-assistedlaserdes-orptionionization-timeofflight(MALDI-TOF)(infacttheGPChasinsuffi-cientresolutiontoprovideanaccuratepictureofthemolecularweightdistributioninthesesamples).Figure1.2,incontrast,showsthemolecularweightdistributionobtainedfromanattempttoformastyrene–acrylatediblockcopolymerusinganionicpolymerization(seeChapter2).Notonlyisthepolydispersityindexratherlarge(at2.96),butalsotheshapeofthecurveisnotwhatmightbeexpectedfromahomogeneoussample;clearlytherehasbeensomeprobleminthepreparationhere.5 I.L.Hosieretal.15010050002000400060008000Mol.wt.Fig.1.1GPCdataobtainedfrompolyaromaticdendrimerspossessingarepetitiveamide–estercouplingsequence.1.51.0M/logwd0.50100100010000100000Mol.wt.Fig.1.2GPCdataobtainedfromanattempttoformastyrene–acrylatediblockcopolymerusinganionicpolymerization.Boththepolydispersityindex(2.96)andtheshapeofthecurvesuggestthatthedesiredhomogeneousproducthasnotbeenformed.MALDI-TOF71,72massspectralanalysisisbecomingincreasinglyimportantasamethodforthedeterminationofmolecularweightsofsyntheticpolymers,sinceincomparisontotraditionalmethods(suchasGPC),theresultscanbeobtainedinafewminutes.Inthesimplestterms,themacromoleculeisdis-persedinaUV-absorbingmatrix,andbecomesvolatilizedwhensubjectedtoapulseoflaserenergy;thevolatileparticlesarethenionizedandsubsequently6 1:Polymercharacterization110001000090008000700060005000Intensity40003000200010000300040005000600070008000Mass(m/z)Fig.1.3SpectrumobtainedusingMALDI-TOFofasampleofpolystyreneusingadithranolmatrixwithsilvertrifluoroacetateadded.(Thepeakmassesarefromthepolymerchainscombinedwithasilverion.)acceleratedbyanelectricfieldtothedetector.Themassesaredeterminedbythetimeofflight.Thus,thistechniqueisaverypowerfulanalyticaltool,allow-ingchemistsaccesstomolecularweightdatain‘realtime’ratherthanprovid-ingroutinepost-polymerizationcharacterization.73Inaddition,thetechniqueprovidesdirectaccesstomolecularweightdataratherthanaveragevaluesthatneedtobecomparedwithsuitablestandards(asisthecaseforGPC).Thesoft-ionizationmayalsoallowthedirectobservationofdifferentendgroups.However,samplepreparationhasproventobethekeysteptothesuccessoftheanalyses74andparticularcareneedstobetakeninthechoiceofmatrix.However,excellentresultscanbeobtainedascanbeseeninFigure1.3.4.Compositionandmicrostructure1Hand13CNMRarevitaltoolsforthecharacterizationofpolymericmaterials.Solid-stateNMRisfrequentlyusedtostudysuchsystems,butthebriefdiscussionherewillbeconfinedtoNMRinsolution.751HNMRprovidesinformationrelatingtocomposition.Thisisparticularlyimportantforcopolymerswheresuchinformationmay,forexample,beusedtodeterminereactivityratios76and,forvinylpolymers,cangiveanimmediateindica-tionofthepresenceofunreactedmonomer.Insomecases,forexample,7 (a)HeterotacticIsotacticSyndiotactic121.5120.0119.52001000(b)AmArAAmAmAPmArPArAmPPrArPAmArPArArAAmamPPmPmPArArP125120Fig.1.4(a)NMRspectraofpoly(acylonitrile)showingthenitrileregion.Thecomplexpatternarisesasaconsequenceofthevariousconfigurationsaroundthenitrilegroup.Thusthepolymertacticitycanbeascertained.(b)NMRspectruminthe13Cregionofacrylonitrile(A)/2-vinylpyridine(P)copolymer(70:30feedstockconcentration).Thesignalsatlowfieldcor-respondtoAAAtriads,thoseatslightlyhigherfieldcorrespondtoAAPtriads,andthoseatevenhigherfieldcorrespondtoPAPtriads.8 1:Polymercharacterizationpoly(methylmethacrylate),thetacticityofthepolymercanbereadilyestab-lishedfromthe1HNMRalone.77However,itisoftenfoundthatlinewidthsinthe1Hspectrumarerelativelylargecomparedwithdifferencesinchemicalshiftfordifferentstructuralfeatures.Insuchcases,detailsabouttacticitymaybeobtainedfromthe13CNMRspectrum.Thus,Figure1.4(a)showsthenitrileresonancefromasampleofpolyacrylonitrile;thevariousstereochem-icalarrangementscanberesolvedandassignedtovariouspentadsequences.Incontrast,featuresfromthepolymerbackboneofapolyacrylatemaynotbesoapparent.78ForcopolymersystemsNMRisusednotonlytodeterminecompositionsandthustherelativereactivityofthetwomonomers,76butalsotodeterminemonomersequenceswithinthechains.79Thisenablesonetodistinguishbetween,forexample,ablockandanalternatingcopolymerandmayberead-ilyrelatedtothereactivityratios.80Figure1.4(b)showsthenitrileregionofthe13CNMRspectrumobtainedfromacopolymerofacrylonitrileand2-vinylpyridine(seeChapter2,Protocol4).Quantificationofsuchmicrostructuralfeaturesrequiresparticularcaresinceintegratedintensitiesin13CNMRdependnotonlyonthenumberofmoleculescontainingaparticulararrange-ment,butalsoonthenatureoftheenvironment.Thatbeingsaid,thesimilarityofmostoftheenvironmentspresentinsuchmicrostructuralvariationsaresuchthatintegratedintensitiescanbeusedtoestablishthepresenceofvarioussequencesofcomonomerunits.81,82NMRisnot,ofcourse,theonlyanalyticaltechniqueusedtoestablishthecompositionandmicrostructureofpolymericmaterials.Othersinclude75,66ultraviolet–visiblespectroscopy(UV–Vis),Ramanspectroscopy,andinfra-red(IR)spectroscopy.IRandRamanspectroscopyareparticularlyuseful,whenbyvirtueofcross-linking(see,e.g.Chapter9),orthepresenceofrigidaromaticunits(seeChapter4),thematerialneithermeltsnordissolvesinanysolventsuitableforNMR.Thedevelopmentofmicroscopybasedonthesespectroscopicmethodsnowmakessuchanalysisrelativelysimple(seebelow).Spaceprecludesadetailedaccountoftheseandmanyothertech-niquesfamiliartotheorganicchemist.Insteadwefocusfortheremainderofthechapteronsomeofthetechniquesusedtocharacterizethephysicalpropertiesofpolymericmaterials.5.OpticalmicroscopyTheopticalmicroscopeisasophisticatedinstrumentcapableofprovidingimageswitharesolutionoftheorderof1m,molecularinformationviabire-fringence,andchemicalinformationviacolourchangesorthroughtheuseofspecificdyes.Whenthesefactorsarecombinedwithrelativeeaseofsamplepreparation(c.f.electronmicroscopy)andpurchasecost,opticalmicroscopyisapowerfultechniqueforthestudyofmanymaterials,particularlythosethattransmitinthevisibleregionofthespectrum.9 I.L.Hosieretal.50µmFig.1.5Polarizedtransmittedlightopticalmicrograph.AlamellaraggregateofthelongchainalkaneC294H590isshown,surroundedbyquenchedmaterial.Intransmittedlightmicroscopy,abeamoflightpassesthroughatransparentmedium,andthismaychangeitinanumberofways.Theamplitudemaybemodifiedfromplacetoplaceasaresultofvariationsinabsorptionorscatteringcharacteristics,andthiscanbeexploitedtoformanimageusingbrightanddarkfieldmicroscopy.Inthesetechniques,itisspatialvariationsintheampli-tudeofthelightenteringtheobjectivelensthatresultsdirectlyinimagecon-trast.Whentransparentthinfilmsamplesareexamined,includingpolymers,thestructureswithinthemcanresult,notinspatialvariationsintheamplitudeofthetransmittedbeambut,rather,spatialvariationsinphaseand,con-sequently,suchphaseobjectsarenotvisibletothenakedeye.Inphasecontrastmicroscopy,thesephasedifferencesareconvertedintoamplitudecontrastrenderingphaseobjectvisible.Possiblythemostwidelyusedtransmissiontechniqueforthestudyofpolymersispolarizedlightmicroscopy(Figure1.5).Thisexploitsthefactthatpolymermoleculesareintrinsicallyanisotropicstruc-turesand,therefore,undermanycircumstances,giverisetoopticallyanisotropicmaterials.Whenabeamofplanepolarizedlightpassesthroughsuchasystem,itspolarizationstatewill,ingeneral,bealtered.Inthecaseofcrystallineorliquidcrystallinematerials,themolecularanisotropygivesrisedirectlytobirefringentmaterials.Thestudyofpolymericspherulitesisanareathathasexploitedtheattributesofpolarizedlightmicroscopyformanydecades.83–85Otherexamplesincludeflowingpolymersolutions,shearedpoly-mermelts,andglassyartefactsthatareexposedtoamechanicalstress.Ingeneral,alltheabovetechniquescanalsobeused,withvaryingdegreesofsuccess,inreflectedaswellastransmittedmodes.Althoughtheleastpromisingofthesewouldappeartobepolarizedlightmicroscopy,sincethisrequiresthatthebeampassthroughthespecimen,polarizingtechniquescanbepowerful.Forexample,ifthesampleisrelativelythin,incidentilluminationcanbeusedalongwithareflectingsubstratetoproducepolarizedlightimages.However,10 1:Polymercharacterizationthetrueutilityofreflectedlightmicroscopyconcernssamplesthataretoothickortoohighlyabsorbingtobesuitedtotransmissiontechniques,butwherethesurfacetopographycontainsusefulstructuralinformation.Indifferentialinter-ferencecontrast(DIC)microscopy,thesurfaceofthesampleisilluminatedbytwodisplacedpolarizedbeams,which,onrecombination,interferewithoneanother.Ifthesurfaceisilluminatedwithwhitelight,theaboveresultsinsurfacetopography(thelocalgradient≡rateofchangeofopticalpathdiffer-ence)canbevisualizedasopticalinterferencecolours.FormoredetailsontheaboveimagingmodesandmorespecializedopticaltechniquesthereaderisreferredtoAppliedpolymerlightmicroscopybyD.A.Hemsley.866.ElectronmicroscopyElectronmicroscopycanbedividedintotwoareas;transmissionelectronmicroscopy(TEM)involvingthinspecimensandthescanningelectronmicroscope(SEM)involvingbulksamples.87However,wheneverapolymerisexposedtoabeamofelectrons,energyisdissipatedinthespecimen,bondsarebroken,andpermanentchemicalandphysicalchangesresult.88–91Theextenttowhichtheseeffectspreventexaminationisthenlargelyamatterofthematerialitselfandinformationrequired.92–94ForTEM,abasicrequirementisthatthespecimenissufficientlythinfortransmissionoftheelectronbeam(100nm).Thus,intrinsicallythinspecimens95–99canbeexamineddirectly,orafterdispersionuponasupportfilm,but,generally,thegeometryofthesamplemustbechanged.Forpolymers,ultramicrotomy100isthemostdirectmeansofachievingthis,butthecuttingprocesscanbefarfromstraightforward,involvingappreciabledeformationofthespecimen.Alternativetechniquesincludecastingfilmsfromsolution,101insitucrystallization,102mechanicalelongation,103andfragmentation.93IntheTEM,imagecontrastdependsuponvariationsinatomicnumber(Z-contrast),variationsinthickness(thicknesscontrast)andBraggdiffraction(diffractioncontrast).Inthecaseofpolymers,itisthefirstofthesethatismostwidelyexploited.Inmaterialssuchasconductingpolymersandcertainblends,compositionalvariationscanleadtomeaningfulcontrast.104,105Elsewhere,imagecontrastcanbeinducedbychemicaltreatmentofthespecimen,andmanydifferentstainshavealsobeendevelopedtothisend.Alloftheserelyupontheincorporationofelectron-denseelementsintothestructureatparticularsites,eitherthroughspecificchemicalreactionsorjustphysicalabsorption.Consequently,imagecontrastmayreflectchemicalvariationswithinthespecimenorjustthelocalphysicalstructure(amorphouscomparedwithcrystals).However,whilestainingisaprovenapproach,itisnotwithoutitsproblems;theaggressivenatureofmostreagentscanresultinartefacts106and,wherestructuralfeaturesaresmallerthanthethicknessoftheTEMspecimen,imagescanbedifficulttointerpret.Commonpolymericstains11 I.L.Hosieretal.1000ÅFig.1.6TEMimageofaRuO4-stainedthinfilmofanatacticpolystyrene/KratonG1650blendcontaining30%polystyrene.Swollenstyrenedomainscanbeseenwithintheblockcopoly-mertogetherwiththelargerphase-separatedpolystyreneregions.includeosmiumtetroxide(OsO4)(whichiswidelyappliedtounsaturatedblockcopolymers107andrubbermodifiedsystems108),rutheniumtetroxide(RuO)4(aversatilestainthathasbeenappliedwithsuccesstomanydifferentpolymertypes109–112),chlorosulfonicacid(ameansofstainingethylene-basedsystems113)andphosphotungsticacid(whichtendstobeusedinconjunctionwithsystemscontainingpolyamides114).Wherethechemistryofthepolymerisinappropriate,additionalpriortreatmentofthespecimencanbeemployedtomodifyitinsomeway;electronirradiation115andchemicalpre-treatments116havebeenusedwithsuccess,ashasnegativestaining117–119(Figure1.6).Analternativemeansofgeneratingathinspecimeninwhichthelocaltrans-missionoftheincidentelectronbeamvariesinrelationtostructuralfeaturesissurfacereplication.Althoughnumerousvariantsexist,replicationinvolvestheobliqueevaporationofsomeelectron-densemetalontothesamplesurface,so-calledshadowing(togiveimagecontrast),followedbytheproductionofathin,transparentsupportfilm(typicallycarbon).Inthisway,surfacetopographyistranslatedviathenon-uniformdistributionofshadowmetalintoimagecontrast.Althoughfracturingthesamplecanbeasimplemeansofproducingsurfacetexturethatisrelatedtounderlyingstructure,fracturesurfacescanalsocontainfractographyfeatureswhichcanbemisinterpreted,120,121canbepronetobias,122andareoftentooroughtoallowtheproductionofgoodqualityreplicas.123Etchinghaslongbeenusedtorevealstructuralfeaturesinmetallurgy124toremovematerialfromthespecimeninsuchawaythatsurfacereliefdevelops,whichissimplyrelatedtotheunderlyingmicrostructure.Inthecaseofpolymers,etchingprocedurescanbedividedintoanumberofdistinctclasses.Insolventetching,onecomponentofthemicrostructureisdissolved,leavingtheotherpreservedinitsoriginalform.Althoughtherearemanyexamplesofsolventsbeingusedtotreatsinglecomponentpolymersystemsin12 1:Polymercharacterizationordertoexposestructuraldetails,125thepropensityforpolymerstoswellmeansthatthisapproachismostsafelyappliedtoblendsystems.126Afsharietal.127describedaninterestingstudyofpolypropylene/polyamide6fibresystems,inwhichformicacidwasusedtoremovethenylonfibresfromthepolypropylenematrix,decalinwasusedtodissolvethepolypropylenematrix,leavingthefibres,whilstafluorescentdyewasusedinconjunctionwithlaserscanningconfocalmicroscopytostudythefibresinsitu.Incontrasttoselectivedissolu-tion,chemicaletchinginvolvesmaterialdegradationandthesubsequentremovalofmolecularfragmentsfromthesamplesurface.Truechemicaletchantsincludechromicacidandrelatedcompoundsforsystemscontainingpolyolefinsorpoly(vinylidenefluoride)(PVF);128–130sodiumethoxide/ethanolforpoly-2imides,131polyurethanes,andpoly(ethyleneoxide);132aqueousmethylamineforpoly(hydroxybutyrate)(PHB);133anumberofaminesforpoly(ethyl-eneterephthalate)anditsblends;134andstrongaqueousbases135,136anddiethyl-enetriamine137,138forsystemscontainingpolycarbonates.However,themostversatileproceduresarebaseduponoxidativeetchingwithmanganese.Theso-calledpermanganicetchantsnowformafamilyofreagentswhosechemistrycanbevariedtosuitparticularapplications;130,139ofwhichpolyolefinsareanareaofparticularsuccess.Asinthecaseofstaining,etchingalsoinvolvesexpos-ingthespecimentoreagentsthatarecapableofinducingartifacts.140,141Consequently,wheneveraspecimenisexposedtosuchaggressivereagents,independentcorroborationoftheresultsisessential.113,122,128,137,142Forfurtherdetailsoftheabovetechniques,seethereviewarticlesonsolventandchromictreatments143andpermanganicreagents.144IntheSEManarrow(10nm)primaryelectronbeamoftheorderof10keVinenergyisscannedacrossthesurfaceofthespecimenandanimageisbuiltuppixelbypixel(Figure1.7).Sinceitisessentialthatthechargedepositedonthesamplesurfacebytheelectronbeamisabletoleakaway,forinsulatingpolymers,itisusuallydesirabletocoatthespecimenwithaconductingfilm10µmFig.1.7SEMimageofthesurfaceofanelectrochemicallypolymerizedfilmofpolypyrrolep-toluenesulfonate.13 I.L.Hosieretal.priortoexamination;sputtercoatingwithgoldandchromiumarecommonlyusedproceduresandeachhasitsmerits.145,146Althoughmanyprocessesoccurwithinthesample,forimagingpurposesitisconvenienttoconsidertwoprocesses;lowenergysecondaryelectronemissions(30eV)andhighenergybackscatteredelectrons(10keV).87,147Sincetheproductionofbackscatteredelectronsisdependentuponthelocalatomicnumber,147thesecanprovideameansofimagingcompositionalvariationswithinthesurface.148,149Nevertheless,itissecondaryelectronemissionandsurfacetopographythatismostwidelyusedforimaging,throughthedirectexamina-tionoftheexternalsurfaceofthesample118,149ortheproductionofaninter-nalfracturesurface.120,150,151Theetchingtechniquesdescribedabovecanalsobenaturallyexploited,andwithouttheneedforsuccessfulreplicapro-duction.Thatis,theSEMcansuccessfullyexamineetchedsurfacesthataretoofriableortooroughtogivegoodreplicasforTEMwork.152Forexample,conductingpolymersareextremelysusceptibletoattackbypermanganicreagents153and,consequently,thephasestructureofablendcontainingsuchapolymercanbeimagedclearlyafteretchingawaytheconductingnetworktoleaveaporoussurface.AsimilarresultaroseduringstudiesinvolvingtheenzymaticdegradationofPHB.154AlthoughstainingismostcommonlyusedinconjunctionwithTEMimages,ithasalsobeenusedinalimitednumberofstudiestoenhancecontrastintheSEM.Forexample,polyethylene/carbonfibrecompositesweretreatedwithchlorosulfonicacidsuchthat,inbackscat-teredSEMimages,thefibresappearedlightagainstthestainedpolyethylenematrix.155Backscatteredelectronsimaginghasalsobeenuseddirectlytoexaminesuitablystainedpolymericsystems.156,157However,whenasuffi-cientlylowacceleratingvoltageisusedtoproducetheprimarybeam(1kV),SEMtechniquescanalsoproduceexcellentimagesofthephasestructureofstainedblendsandblockcopolymers.156,158,159ThebookbySawyerandGrubb119providesamoredetailedaccountofelectronmicroscopyofpolymersandinparticular,anexcellentoverviewofthedifferentsamplepreparationtechniquesthathavebeendevised.7.AnalyticalmicroscopyTheaboveaccountofopticalandelectronmicroscopyfocusedentirelyuponimaging.However,theenergydistributionoftheemergentradiationalsocontainsusefulinformation.IntheTEM,abeamofmonochromaticelectronsentersthesample,someofwhich,undergoinelasticscattering.Electronenergylossspectroscopy(EELS)initsvariousguises160isparticularlywellsuitedtolow-Zsystems,suchasmostpolymers.Inthisway,informationontheelementalcompositionofthesamplecanbeobtainedintheconventionalTEMor,usingmorespecializedinstrumentation,elementalmapscanbegenerated,byenergyfilteringthebrightfieldimage.161,162Inelasticscatteringwithinthesampleresultsintheproductionofsecondaryelectrons,asabove,andX-rays,whichincludecharacteristiclinesthatreflecttheelemental14 1:Polymercharacterizationcompositionofthesamplematerial.Inadditiontoidentifyingthechemicalcompositionofunknownspecimens,energydispersivespectrometry(EDS)canalsobeusedinconjunctionwiththescanningtransmissionelectronmicroscopy(STEM)modestodisplaythespatialdistributionofdifferentelementswithinthesample.InSTEM,asmallelectronprobeispositioneduponthespecimensuchthatelementmapsarebuiltuppixelbypixel.SimilarapproachescanbeappliedintheSEM,althoughtheresultingdatacanincludeartefactsthatresultfromthepreciseinteractionsbetweentheelectrons,X-rays,andthesample.Consequently,intheSEM,EDSisbestdescribedasasemi-quantitativetechnique,particularlywhenthesamplesurfaceisrough.Infra-red(IR)andFourierTransforminfra-red(FTIR)techniquesarewidelyusedtostudypolymericmaterials.Asatechniqueforlocalanaly-sis,theutilityofIRspectroscopyis,however,limitedbyacombinationofphysicalandpracticalfactors.First,thetheoreticalresolutionofanopticalsystem,outsidethenear-fieldregime,willbedeterminedbythewavelengthoftheradiationinvolved.163Inthisrespect,IRisnotideal.Second,instrumen-tally,IRmicroscopyislimitedbytherequirementforopticalelementsthatreflectand/ortransmitoverthewavelengthrangeofinteresttomanipulatetheprobebeam,andtheneedforefficientdetection.Theformerismosteasilymetsimplybytheuseofmasksthatdeterminewhichregionofthesampleistobeinterrogated.WhileitispossibletoperformIRmicroscopyinreflection,trans-missionisoftenpreferableongroundsofsensitivity.However,sincepolymersabsorbheavilyatparticularregionswithintheinfra-red,thisreturnsustothesameproblemsofoptimumgeometryandsamplepreparation,asdiscussedaboveinconnectionwithTEM(Figure1.8).Ramanmicroscopyavoidsmanyofthedifficultiesdescribedabove.Thesamplecanbeinterrogatedusingalaseroperatinginthevisibleornear-infra-redregionsofthespectrum,suchthatboththeincidentandscatteredradia-tioncanbemanipulatedusingamodifiedopticalmicroscope.Thewavelengthsinvolved,beingmuchshorterthanIR,meanthatthelateralspatialresolutionisalsoimproved.However,theRamaneffectisaweakone;thisrequirestheuseofefficientdetectorsandmeansthatfluorescencecanswamptheweakRamansignal,particularlyinthecaseofagedordegradedspecimens.Practically,Ramanmicroscopycanbeperformedintwoways.Thesamplecanbeilluminatedusingamonochromatic(laser)source,asinconventionalopticalmicroscopy,andthereflectedortransmittedbeamcanbepassedthroughanopticalfilter,whichtransmitsonlythosewavelengthsthatareofinterest,toformafinalimage.Alternatively,thelasercanbefocusedontothesamplesuchthatdataareacquiredfromasinglepoint;imagesarethenbuiltuppixelbypixel.Aprincipaladvantageofthelatterapproachisthatitprovidesthepotentialforconfocaloptics,110–113,164althoughthetruenatureofconfocalRamanmicroscopyisatopicofconsiderabledebate165despiteitswide-spreaduseinthestudyofpolymerfilmsandlaminates.16615 I.L.Hosieretal.1600140012001000800Counts60040020001600140012001000800600400Wavenumber(cm–1)Fig.1.8ConfocalRamanspectrumobtainedfromaheat-sealedcompositesilk/Paraloid72B/silkcrepelinesample.Inart-conservationpolymers,suchaspoly(butylmethacrylate)areusedtoconsolidatefragileantiquetextiles.Herethelateralresolutionofthetechniquehasbeencombinedwiththeconfocalopticstodecouplethespectrumoftheadhesivefromthoseoftheothercomponents.8.ScanningprobemicroscopyComparedwiththeabovetechniques,theoriginsofscanningprobemicro-scopies(SPMs)arerelativelyrecent.In1982,Binnigetal.167describedthefirstscanningtunnellingmicroscope(STM),inwhichabiasvoltageisappliedbetweenanatomicallysharptipandaconductingsample.Providedthesep-arationbetweenthesampleandthetipisoftheorderof0.1nm,acurrentflowsbetweenthemduetoquantummechanicaltunnellingand,sincethisisverystronglydependentuponseparation,atopographicimageofthesurfacecanbeobtainedbyscanningthetipacrossthesampleandmonitoringitsverticalpositionatconstantscanningcurrent.Theresultingimages,poten-tially,haveatomicresolutionbutthiswilldependuponsurfaceroughness.Nevertheless,theabovedoesillustratethebasicprinciplesoftheapproach;apointprobeisscannedacrossasurfaceunderconditionswhereitisoperatinginthenear-fieldregime.Sincetheearly1980s,thenumberofvariantstotheabovethathavebeendevelopedaremanifoldand,therefore,onlyabriefintroductiontothetechniqueispossiblehere.ToexploitthepotentialofSTMfully,thesampleneedstobebothflatandconducting,andhenceitisnotwidelyusedforthestudyofpolymers.However,avariantofthetechniquehasbecomeverywidelyused—atomicforcemicroscopy(AFM).Inmanyways,AFMisderivedfromsurfaceprofilometry,168inwhichastylusisscannedacrossthe16 1:Polymercharacterizationsurfaceofa(non-conducting)specimentobuildupatopographicmap.Whenanatomicallysharptipisbroughtclose(1nm)toasurface,interactionforcesresultand,ifthetipismountedattheendofacantilever,thecantileverwilldeflect.Atitsmostsimplelevel,theresultisaprofilometerwithhighspatialandforceresolution(Figure1.9).Forthestudyofnon-conductingsamplesthemechanicalinteractionbetweentheprobetipandthespecimencanbeexploitedinmanyways.(a)(b)Fig.1.9AFMtappingmodeimagesofaspherulitictextureinisotactpolypropylene.Thesamplewascrystallizedtocompletionat145Candsubjectedtopermanganicetchingpriortoexamination.Image(a)showstopographywhile(b)containsphaseinformation.Scalebars5m.17 I.L.Hosieretal.Theseincludecontactforceimaging(CFI)mode,inwhichthetipisscannedacrossthesamplesurfaceatconstantforce,tappingmodeinwhichthetiposcillatesclosetothesurfaceenablingeithertheforcesorphaserelationshipsbetweenloadanddisplacementtobeusedtoformtheimage,andlocalforcespectroscopyorforce/volumeimaginginwhichthevariationofforcewithtip/sampleseparationatapointcanbeusedtostudylocalinteractions.ThesimplicityofsamplepreparationisthemajoradvantageofAFMoverTEM,forexample,forthedetailedstudyoflamellarstructure.Coupledwithpermanganicetching,theAFMisnowrecognizedasapowerfultoolforthecharacterizationofpolymericmaterials.169–171Inparticular,AFMlendsitselftothestudyofnucleationandgrowthphenomenonwheretherequirementforahighvacuuminconventionalelectronmicroscopyprohibitstheuseofhightemperaturesandhas,todate,beenappliedsuccessfullytoalargevarietyofdifferentpolymers.170Theuniqueabilitytoimageinthreedimensionsallowsstructuralinformationsuchaslamellarthickness171tobeextractedandthedirectimagingofcomplexstructuresincludingnanocomposites.155,172Inthefinalexample,itispossibletomodifythechemicalnatureofthetiptoexplorespecificinteractions,173forexample,singlepolymerloadextensioncurveshavebeenexploredby,first,usingthetiptodetachsomemolecules,reattachthemelsewhereand,finally,monitortheforceastheyareextended.173–175Indeed,anotheruseofAFMisasameansofmovingatomsandmoleculestobuildstructures.Recentdevelopmentsincludeanovelhigh-speedimagingsystem.176Insituationswheretheelectricalpropertiesofamaterialareofinterest,arangeofSPMshavebeendevelopedtoexploredifferenteffects.Weisendanger177providesamorecomprehensivesummaryofthemultitudeofdifferentSPMtechniquesthanispossiblehere.9.ThermalanalysisDifferentialscanningcalorimetry(DSC)constitutesoneofthemostwidelyusedtechniquesforthestudyofpolymers,particularlythosesystemsthatcrystallize.AlthoughthetermDSCisusedinconjunctionwithmanydifferentinstruments,fundamentally,thesecanbedividedintotwocategories;heatflowinstrumentsbasedupondifferentialthermalanalysis(DTA)andthosewhicharetruepowercompensatedinstruments.InDTA,thetemperatureofthesampleiscomparedwiththatofaninertreferenceasbotharesubjectedto,ideally,identicalthermalprogrammes.Toillustratetheprinciples,consideranexperimenttoinvestigatethemeltingbehaviourofamaterial.Inthis,heatissuppliedtoboththesampleandthereferenceand,asaconsequence,thetemperatureofeachwillrise.Asthesamplemelts,thethermalenergysuppliedbytheinstrumentnolongerraisesitstemperaturebut,rather,providesthenecessaryenthalpyoffusion.Sincethetemperatureoftheinertreferencewillcontinuetorisethroughoutthisprocess,thetemperaturedifferencebetweenthesampleandthereference18 1:Polymercharacterizationchangesandapeakintheoutputsignalresults.Insuchaninstrument,theoutputsignaltakestheformoftemperaturedifferenceasafunctionoftime(atconstantheatingratethisiseasilyconvertedtotemperature)and,there-fore,transitiontemperaturescanbeobtainedeasily,whereasthermodynamicparametersmustbededucedthroughaknowledgeofspecificheatcapacities,thermalconductivities,etc.178InpowercompensatedDSCs,thesampleandthereferenceareheatedseparately,andthenitisthedifferenceinthepowerrequiredtomaintainthemat,theoretically,thesametemperaturethroughoutthethermalcyclethatisrecorded.Thatis,theoutputtakestheformofthepowerdifferenceasafunctionoftime,enablingenthalpiesoffusion,specificheatcapacities,etc.tobeobtainedrelativelyeasily.Inpractice,thefeedbackcontrolbetweenthesampleandthereferencetemperaturesensorsandheaterswillnecessarilyintroducesomeerrors179andithas,therefore,beensuggestedthatpowercompensatedcalorimeterssufferfrommanyofthesameproblemsexperiencedbyheatflowinstruments.178Whilethisisqual-itativelytrue,quantitatively,theproblemsareverymuchless.Despitethetheoreticaladvantagesofthepowercompensatedapproach,theassociatedinstrumentationismuchmorecomplexand,therefore,therearecircumstanceswherethesimplicityofDTAhasmuchtorecommendit.DTArequiresjusttwothermocouplesandcan,therefore,beusedunderdemandingconditions.Forexample,high-pressureDTAexperimentshavebeenusedextensivelytogeneratephasediagramsofpolyethyleneandrelatedlowmolarmasscompounds180–182—high-pressureDSCisrathermorecomplex.183,184Crystallinepolymerspresentparticularproblemsforthermalanalysis,sincetheyareneverpresentinathermodynamicequilibriumstate.Theques-tion,therefore,isnot,istheexperimentinvasive,butrather,howinvasiveisit?Wheremultiplemeltingpeaksareobserved,185–187twopossibleinterpreta-tionscanbeproposed:eachpeakrepresentsaparticularcomponentwithintheinitialmaterial;oneormoreofthepeaksareadirectresultofstructuralchangesthathaveoccurredduringthecourseoftheDSCscanitself.Forexample,inpolyethyleneterephthalate(PET),thisissuehasanextensivehistory;188,189inpolyethyleneblends,multiplepeaksareanecessaryfeatureofthesystem,buthere,co-crystallizationanddynamicreorganizationwithintheDSCcanresultinparticularlycomplexformsofbehaviour.190,191Nevertheless,nowherehasthetopicofDSC-inducedchangesbeendebatedmoreextensivelythaninconnectionwithpoly(etheretherketone)(PEEK)—seeRef.192forexample.192Ultimately,thisproblemisentirelytodowiththetimescaleoftheexperimentrelativetothekineticsofsamplereorganiza-tionand,therefore,reducingtheformer,willreducetheimpactofthelatter.Whilehigh-speedDSCmaybedesirable,eveninpowercompensatedinstru-ments,therearelimitstowhichthiscanbepracticallyrealized.Recently,ithasbeensuggestedthatasimpleexpedienttoovercomethisinvolvesreducingthethermalinertiaofthetotalsample;thatis,thesampleplusitsencapsula-tionsystem.193Replacingconventionalsamplecans(mass10mg)with19 I.L.Hosieretal.Tc=124°CEndothermicTc=118°C90100110120130140Temperature/°CFig.1.10DSCtracesshowingtheeffectofcrystallizationtemperatureonthemeltingbehaviourofanucleatedpolyethyleneblend(20%high-densityand80%low-densitypolyethylene).Inthiscase,allthepeaksrepresentspecificlamellarpopulationswithineachsystem.piecesofaluminiumfoil(mass100g)andsimilarlyreducingthesamplemasscanhaveadramaticeffect.OtherprocessesthathavebeenstudiedbyDSC/DTAincludethecurekineticsofthermosettingpolymers194andthermaldegradation,boththroughthedirectmeasurementoftheassociatedexothermicpeaks195,196andthroughassociatedchangesinotherthermalcharacteristicsofthespecimen.196,197However,neitheroftheseisentirelywithoutrisktotheinstrumentsince,inboth,damagingspeciesmayescapefromtheDSCcan(Figure1.10).Inthecaseofglassysystems,DSCcanalsobeusedtoexaminethediscon-tinuityinthespecificheatcapacitythatisassociatedwiththeglasstransition.198However,thistransitionisgenerallybroadandweakand,therefore,inferringTginthiswaycanbedifficult;also,differentauthorschoosetoidentifyTgindifferentways.198,199Asinthecaseofcrystallinepolymers,polymerglassesarealsoneveratequilibriumand,therefore,theformofthetransitionthatis20 1:Polymercharacterizationobservedinpracticewilldependuponexperimentalconditions,thewaytheglasswaspreparedandsubsequentphysicalageing.Inparticular,theso-calledenthalpyrelaxationpeaksareseenafterageingandcareshouldbetakennottomisinterprettheseasfirst-orderthermodynamictransitions.199–201TemperaturemodulatedDSC(MDSC)202–204isanothertechniquethathasprovedusefulinthestudyoftheglasstransition194–196,205,206where,ithasbeenclaimed,theapproachiscapableofprovidingbetterresolutionandsensitivitythanconventionalDSC.207Inthis,amodulatedtemperatureprogrammeissuperimposedupontheconventionalheatingrampandtheresultingheatflowsareinterpretedintermsoftwoheatcapacities;anin-phasestorageheatcapacityandanout-of-phasekineticheatcapacity.Varioustheoreticalprocedures208,209havebeenproposedforthisandthereislittledoubtthattheapproachcanprovideinformationthatiscomplementarytoconventionalDSC.210However,thetechniquedoesinvolveslowtempera-turescans(cf.high-speedDSCabove)andtheauthorsfeelthatthereareareaswheretheadditionaldataarenot,atpresent,easytointerpret.10.MolecularrelaxationspectroscopyInMDSC,thebasisofthetechniqueinvolvesexaminingtheresponseofasystemtoanoscillatingthermalstimulus.Asdescribedabove,theresultisparametersthatcharacterizethein-phaseandout-of-phaseresponseofthesystem.Indynamicmechanicalthermalanalysis(DMTA),anoscillatorystrainisappliedtoasampleandtheresultingstressesaredeterminedasafunctionoffrequency,temperature,orboth.Sincepolymersareviscoelasticsolids,thestresswillgenerallybeoutofphasewiththestrain,soleadingtothreeparameters:therealstoragemodulus;theimaginarylossmodulus;andtan,theratioofthelossmodulustothestoragemodulus.Foranin-depththeoreticalaccountofthetechnique,seethereviewbyGradinetal.211Usingtheaboveapproach,awiderangeofdifferentcomplexmodulicanbeobtained,dependinguponthegeometryoftheexperiment.Commontestingmodesincludetensile(filmsandfibres),shearsandwichandparallel-platetorsion(softsolidsandviscousmelts),compression,three-pointbendanddualcantilever(bulksamples).However,theaccurateacquisitionofabsolutemechanicalparametersinthiswayisnottrivial,particularlyinsystems,likepolymers,whichcreep.Forexample,intensileandcompressionmodes,thestrainmustneverpassthroughzero.Forthisreason,dualcantilever,inwhichabeamofmaterialisflexedaboutzerodeformation,isattractiveinthatnooffsethastobeapplied.However,endeffectsandclampingconditionsarestillimportant—particularlywherethetemperaturerangeofinterestcanapprecia-blychangethecharacteristicsofthematerial.Also,eachmodeisonlysuitableoveralimitedrangeofmechanicalresponse,wherethisincludesbothmaterialpropertiesandsamplegeometry.Consequently,thetrueutilityofDMTAisasameansofdeterminingchangesinthemechanicalbehaviourofamaterialas21 I.L.Hosieretal.afunctionoftemperatureorfrequency.DMTAhas,therefore,beenusedwidelytostudycrosslinking,212theeffectsofadditivesandfillers213andexposuretoenvironmentalfactorssuchaswaterandotherlowmolarmasscompounds.214,215Reference215isinterestingfromthetechnicalperspective,inthattheauthorsemployedfreetorsionaloscillationstostudytheeffectofvariouspenetrantmoleculesonthe-relaxationprocessinalkalinepolycapro-lactam.Inthecaseofnano-compositestheextentoftheinterfaciallayerscanresultinsignificantlyalteredchainrelaxationdynamics.216Inthecaseofamorphousmaterials,theprimaryrelaxationprocessisassociatedwithTgand,forthesesystems,istermedasthe-relaxation.Asdescribedabove,thechangeintheheatcapacityassociatedwithTgcanberelativelysmalland,therefore,DSCisnotideallysuitedtothestudyoftheglasstransition.Conversely,inDMTA,Tgiseasilydetected,sinceitisassoci-atedwithalargechangeinthemechanicalproperties.AttemperaturesbelowTg,molecularmotionisrelatedtomolecularsegmentsorside-groups,processeswhichcanleadtoanumberofsecondaryrelaxationpeaksintan;conven-tionally,thesearesequentiallyindicated,,etc.withdecreasingtempera-ture.Inthecaseofpolymethylmethacrylate(PMMA),forexample,the-transitionhasbeenshowntobeassociatedwithside-chainmotionsoftheestergroupswhilethe-and-relaxationsinvolvemotionofthemethylgroupsattachedtothemainchainandthesidechain,respectively.217Inblendsystems,thepresenceofasingleglasstransitionistakentoindicatemiscibilityand,therefore,thestudyofthe-transitionisparticularlyimportant.However,sinceDMTAcannotresolvephaseslessthan~5nminsize,218miscibility,inthiscontext,doesnotnecessarilyimplymiscibilityonthemolecularscale.Nevertheless,relativelybroadandweaktransitionsarereadilydetectedbyDMTAand,therefore,miscibilitycanbeexploredwiththistech-niquewithmuchgreatersensitivitythanispossiblebyDSC.ExamplesofmisciblesystemswherethisapproachhasbeenemployedincludePEEK/poly(etherimide)219andPVF/PMMA.220Innylon/polystyrene2ionomerblendsystems,miscibilitydependsonthecounterion218,221whileininterpenetratingnetworksystems,theextentofcrosslinkingiscritical.222Systemswheretwodistinctglasstransitionshavebeenobservedincludepoly[(S)-lactide]/poly[(R,S)-3-hydroxybutyrate]223andPEEK/poly(ethersulfone).224However,inboththesecases,smallshiftsinbehaviourwithblendcompositionarereported,suggestingpartialmiscibilityofthetwocomponents.Incrystallinepolymers,theprincipalrelaxationprocessisassociatedwithmelting.Inpolyethylene,;-,and-transitionshavebeenidentifiedand,par-ticularlyinhigh-densitypolyethylene,the-transitionhasbeensub-dividedintoand
.Inethylene-basedpolymers,the-transitionsat120Cisgenerallyassociatedwiththeamorphousphase,inparticular,with‘crankshaft’motionofmethylenesequences.211,225However,baseduponstudiesofsolutiongrownlamellae,ithasalsobeensuggestedthatthismaythenbeassociatedwith22 1:Polymercharacterizationdefectswithinthecrystals.226Thestrengthofthe-transitionsisfoundtovarywithbranchcontentand,therefore,isgenerallyassociatedwiththemotionofside-groupswithinamorphousareasoratlamellarfoldsurfaces.Indeed,Wooetal.227,228havesuggestedthat,inultra-low-densitypolyethylenes,the-relaxationmayprovideanindicationofthetypeandnumberofbranchpoints;wheresidegroupsundergohydrogenbonding,thisthenhasamarkedeffectonthe-relaxation.228Inhigh-densitypolyethylene,thetemperatureofthe-and
-processescorrelateswiththemeltingtransitionandthereforetheserelaxationsareassociatedwiththecrystallinestructure.The-processvarieswithcrystalthickness,suggestingthatitisalsoassociatedwithfoldsurfaces,while
hasbeenassignedtoslipatlamellarboundaries.229Inpolytetrafluroethylene(PTFE),the-,-,and-transitionsarelocatedatabout127,30–100,and97C,respectively.230The-transitionisfoundtodecreasewithincreasingcrystallinityandhas,therefore,beenassociatedwiththeamor-phousphase(specificallyTg);the-transitionbehavesinasimilarmanner.Inthissystem,theintermediate-transitionincreasesandbroadenswithcrys-tallinity,suggestingthatitisrelatedtoacrystallinerelaxation.211Ingeneral,producingamechanisticinterpretationofanobservedrelaxationprocessesisfarfromstraightforward.Indeed,theconventionofreferringtotheobservedpeaksintanas,,,etc.withdecreasingtemperature,whatevertheirmolecularorigin,meansthatthesignificanceofeachofthesetermscanvaryenormouslyfrommaterialtomaterial,asintheaboveexamples.Practically,DMTAislimitedtolowfrequencies(uptotensofhertz)and,consequently,providesinformationaboutrelativelyslowprocesses.Dielectricspectroscopyisarelatedapproachinwhichanalternatingelectricfieldisappliedtoasampleandthecomplexpermittivityisthenobtainedfromphaseandamplitudemeasurementsofcurrentandvoltage;again,itispossibletoconsiderdatainthefrequencydomain,thetemperaturedomain,orevenasfrequency/temperaturecontourmaps.230,231SeeRefs.230and232foratheo-reticalaccountoftheunderlyingphysics.Theapproachcanprovideinformationinthefrequencyrange102–1011Hz232bycouplingtheappliedelectricfieldwithdipolesinthesystemand,assuch,themolecularprobe(moleculardipolemoment)iswelldefined.This,however,immediatelypresentsalimitationinthatthetechniqueisnotwellsuitedtonon-polarpolymerssuchaspolyethyleneandPTFE.Insuchmaterials,dielectricspectroscopytendstoprovidedirectinformationaboutimpuritiesordegradationsinceitisnecessarytodecoratethepolymertorendercertainrelaxationsdetectable.233Inpolyethylene,deliberateoxidationorchlorinationcanbeusedtoeffectsuitablechanges.AsinDMTA,dielectricspectroscopycanalsobeusedtostudybothimposedfactors;suchasadditives,234degradation,235andpenetrantmolecules,236andintrinsicmolecularprocesses.Inthelattercase,anumberofdistinctdielectricrelaxationsaregenerallyobserved,whicharelabeled,,,etc.withdecreasingtemperature;inthecaseofNafionperfluorocar-boxylatepolymers,forexample,specific
,,,,and-relaxationshave23 I.L.Hosieretal.beenobserved.237Inthecaseofamorphouspolymers,the-transitionisgenerallyobservedsomewhataboveTg,asmeasuredbyDSCorDMTA.Theoriginofthisisthedifferentexperimentalfrequenciesinvolvedineachtechnique—thehigherthefrequency,thehighertheapparentrelaxationtemperature.Nevertheless,the-transitionisrelatedtoTgand,consequently,itischaracterizedbyaverymarkedincreaseinrelaxationtimewithdecreas-ingtemperature.Fromamolecularperspective,itinvolvesmicro-Brownianmotionofchains,andanumberofspecificmodelshavebeenproposed.232The-relaxationisassociatedwithlocalmolecularmotionsandisgenerallybroaderthanthe,reflectingboththemoietyinvolvedanditsenvironment.Indeed,eveninmiscibleblends,multiple-processescanbeobserved.238Inmodifiedpolyethylene,effectssimilartoDMTAareseen.Althoughitisacceptedthatthe-relaxationisrelatedtothecrystallinephase,anumberofdifferentmodelshavebeenproposedand,consequently,itspreciseinterpretationisunclear.239The-relaxationhasalargeactivationenergyandisregardedasananalogueofthe-relaxationseeninamorphoussystems.232The-relaxation,whichisextremelybroadinthefrequencydomain,hasbeenattributedvariouslytothecrystallinephaseandtochainendsandbrancheswithinamorphousregions.240Inothersemi-crystallinesystems,specificmolecularinterpretationshavebeenproposedforthemultiplerelaxa-tionprocessesthatareseen.232Aparticularareaofinterestinsemi-crystallinesystemsistherigidamorphousphasethatisimaginedtoexistbetweencrystallineandamorphousregions.238Inconclusion,althoughDMTAanddielectricspectroscopyinvolveverydifferentstimuli,theinformationtheyprovideiscomplementaryandsimilarbasicprinciplesapplytoboth.Consequently,thepaircanbeusedintandem241toprovideamorecomprehensivepictureofthemolecularrelaxationprocessesthatoccurwithinpolymericmaterials.11.X-rayandneutronscatteringmethodsX-rayscatteringmethodsprovidearoutetounambiguouslydeterminingthebasicstructuralcharacteristicsofpolymericmaterials.ThepenetrationofX-raysmeansthatthesetechniquesarenotrestrictedtothinfilms,asinthecaseofIRspectroscopy,oropticallytransparentmaterials,asinthecaseofopticalmicroscopy.Complexmaterialsincludingfilledpolymers,compos-ites,andotheropticallyopaquesamples,suchassemi-crystallinepolymers,canbestudiedwithease.Moreover,thesamplepreparationrequiredforX-rayscatteringtechniquesisoftenminimal.Wide-angleX-rayscatteringtechniquescanprovidedirectinformationonkeyfeaturessuchascrystallinity,preferredorientation,phaseidentificationandcompositionalanalysis.242,243Moredetailedanalysiscanyielddetailsoflocalchainconformationsandpackingarrangementsinbothcrystallineanddisorderedpolymers.24424 1:PolymercharacterizationStructureandscattering|Q|=4
sin()/IncidentbeamScatteredbeam2|Q|<0.1Å–1–1–1–1~1Å>2Å>8Å2*<2°~15°~30°>160°Morphology,IntersegmentChainsegments,lamellarthicknesscorrelations,BondscrystalplanesinhomogenitiescrystalplanesCCCCCCSmallanglescatteringWide-anglescattering*calculatedusingCuKradiationFig.1.11AschematicofthescalesofstructureaccessiblethroughX-rayandneutronscatter-ingprocedures.Small-angleX-rayscatteringtechniquesprovidearoutetoinformationatalargerscale,particularlyinmulti-phasematerialssuchassemi-crystallinepolymers,blockcopolymers,andblends.Quantitativedetailsoncrystallinelamellarsizeoronpreferredorientationarejusttwoexamplesofthestruc-turalparameterswhichcanbeobtainedusingthispowerfultechnique.242,243Figure1.11providesaschematicoftherangeofinformationthatisavailablefromscatteringtechniques.Scatteringdataisoftenreportedintermsofthemagnitudeofthescatteringvector|Q|whichdependsbothuponthescatteringangle2andtheincidentwavelengthasindicatedinFigure1.11.Thescatter-ingvectorprovidesanexperiment-independentscaleincontrasttoordinatessuchasthescatteringangle.Moreover,itallowsdataobtainedthroughneutronscatteringprocedurestobecomparedwithX-rayscatteringdata.X-raysarescatteredbytheelectronsaroundeachatomicnucleusand,there-fore,thestrengthofscatteringdependsontheatomicnumber.ThismeansthatforpolymerscontainingrelativelyhighatomicnumberelementssuchasCl,F,P,orSi,theresultantscatteringsignalisdominatedbycorrelationsbetweenatomsofthoseelements.TheX-rayscatteringfrompolyvinylchloride(PVC)isagoodexampleofthishigh-Zdomination.DuetothevariouschaindefectspresentinPVC,theClatomsaredispersedinaratherdisorderedmannerandthishasinhibiteddetailedstructuralanalysis.FormostpolymerscontainingonlyC,H,N,orO,thiseffectisnotpresent.Moreover,thelowatomicnumbercompositionmeansthatX-raytransparencyishighandexperimentscanbeperformedusingtransmissiongeometrywithsamplethicknessesfrom0.1to2.0mm.Transmissiongeometryfacilitatesconsiderablythestudyofanisotropyandthedeploymentofsmall-angleX-rayscatteringtechniques.25 I.L.Hosieretal.18000160001400012000)10000(QI800060001.01.21.41.61.84000Q(Å–1)200000123456Q(Å–1)Fig.1.12Wide-angleX-rayscatteringpatternforpoly-capralactoneobtainedatroomtemper-atureusingatransmissionX-raydiffractometer.245Theinsetillustrateshowthetotalscattering(points)canbedecomposedintocrystalline(fulllines)andamorphous(brokenline)compon-ents.Thedottedlinerepresentsthesumofthecrystallineandamorphouscomponents.Conversely,theuseofparafocusingreflectionpowderdiffractometerswidelyusedinotherareasofmaterialssciencecanleadtominorcomplications.Essentially,thesampledoesnotabsorbsufficientlyforittoappeartobe‘infin-itelythick’asinthecaseofmetalsandthiswillleadtomodificationtotheintensityvalueswhichwillneedtobecorrectedbeforeinterpretation.Figure1.12showsawide-angleX-rayscatteringpatternforpoly-capralactoneobtainedatroomtemperatureusingatransmissionX-raydiffractometer.245Thispatternistypicalofmanysemi-crystallinehydrocarbonbasedpolymers.ThesharppeaksatQ~1.52,1.66,2.1,etc.(Å1)arisefromthecrystallinephase,whilstthemuchbroaderpeaksbeneaththesesharppeaksarisefromthenon-crystallineortheso-calledamorphousphase.Wecanobtainvaluesfortheso-calledd-spacings,thatis,thespacingbetweenthecrystallineplanesthroughd2/Q0whereQ0isthepositionofaparticularpeak.ThisisBragg’slaw.ThebreadthofthepeaksQprovidesinformationonthecorrelationlength(lc)forthatstructure,inessence,thesizeofthecrystal,throughlc2/Q.IfweareabletoseparateoutthecontributionsintheX-rayscatteringpatternfromthecrystallineandtheamorphousphaseswecanusetheratiooftheintegratedsecondmomentofthecrystallinescatteringtothetotalscatteringasameasureofthecrystallinityofthatsample.243Usingnon-linearleastsquarespeakfitting26 1:Polymercharacterizationprocedures,itisfairlystraightforwardtoidentifythecontributionsfromthecrystallinephase,whileprovidinganadequaterepresentationoftheamorphousphaseisgenerallymoredifficult.Usingthescatteringfromasampleinthemeltasamodelfortheamorphousscatteringoftenleadstocomplicationsduetothetemperaturedependenceofthescattering.However,inmostcases,reliableandconsistentresultsforthedegreeofcrystallinitycanbeobtainedifsufficientcareistakeninthepeakfittingprocedure.TheinsettoFigure1.12showsanexampleofthisanalysis.Thecrystallineandamorphouscomponentsofthescatteringcanbeseendirectly.Analysisofthecurvesyieldsacrystallinityoftheorderof40%.Theabsenceofsharppeaksinawide-angleX-rayscatteringpatternisasimpleandstraightforwardtestforthelackofacrystallinestructure.Non-crystallinepolymerssuchasatacticpolystyreneoratacticPMMAexhibitrathercharacteristicX-rayscatteringpatterns246andwherethisisthecase,itmaybepossibletocarryoutidentificationandcompositionalanalysisfromtheX-rayscatteringpatterns.Asafirstapproximation,wecanusethepositionofthediffusepeaksinanamorphouspatterntoderivetherealspacelengthscalegivingrisetothatpeakthroughamodifiedBragg’slawrk2/Q0wherethevalueofkdependsonthenatureofthestructuralunitsbutusuallyliesintherange1–1.2.244Materialswhichexhibitapreferredorientationineithertheamorphousorcrystallinephasesreflectthisinthewide-angleX-raypattern.Figure1.13showsthewide-angleX-raypatternforameltspunmonofilamentfibreofpoly-capralactoneobtainedusingatransmissionsystemequippedwithanFig.1.13Wide-angleX-raypatternofameltspunfibreofpoly-caprolactone.Thefibreaxisisvertical.TheintensespotsontheequatorcorrespondtoQ~1.5Å1.27 I.L.Hosieretal.X-raysensitivechargecoupleddevice(CCD)detector.ThisexperimentalarrangementallowsdatatobeobtainedrapidlyintensofsecondsbutwitharestrictedQrange.Thehighdegreeofpreferredorientationofthecrystalsisimmediatelyobvious.Moreover,thesymmetryofthepatternenablesustolocatethedirectionofpreferredorientation,notsurprisinglyinthiscaseitisparalleltothefibreaxis.Theazimuthalbreadthofthepeakscanbeusedasameasureofthedegreeofpreferredorientationandstraightforwardproced-uresareavailabletoyieldthecompleteorientationdistributionfunction.EvenwithinthelimitedQrangeoftheX-raypatternshowninFigure1.13,thereisconsiderablymoreinformationinthepatternthaninFigure1.12.Thereareveryintensepeaksontheequatorialsectionandanumberofmuchweakerpeakslyingontheso-calledlayerlines.Thespacingbetweenthelayerlinesyieldsthelengthoftherepeatingstructureinthecrystalalongthefibreaxis.Suchscatteringdatafromfibrescanbeusedtodeterminetheconformationofthechainsinthecrystalsandotherdetailsofthecrystalstructure.247Figure1.14showsthesmall-angleX-rayscatteringpatternfromthesamepoly-caprolactonefibresstudiedinFigure1.13takenusingbeam-line16.1Fig.1.14Small-angleX-raypatternofameltspunfibreofpoly-caprolactone.Thefibreaxisisvertical.TheQrangeisfrom0.1to0.1Å1forbothhorizontalandverticaldirections.28 1:PolymercharacterizationattheDaresburysynchrotronsource.245SimilarpatternscanbeobtainedusinglaboratoryX-raysourcesbutrequireasubstantiallylongerdataaccumulationtime.Thehighlevelofpreferredorientationisimmediatelyvisible.Theintensepeaksarisefromthesegregatedamorphousandcrys-tallinestructureinwhichthincrystalssandwichtheamorphousmaterial.Thescatteringvectorcorrespondingtothepeaks(Q0)canbeusedtocalculatethelongperiod(lp),thatis,thelengthscaleofthisalternatingstructurethroughlp2/Q0.Ifweknowthedegreeofcrystallinity,forexample,fromawide-angleX-rayscatteringstudy,wecanusethistocalculatethethicknessofthecrystallineandamorphouscomponents.ThehorizontalscatteringstreakinFigure1.14arisesfromelongatedvoidsinthefibre.Blockcopolymersexhibitpatternsatsmallanglewhicharecharacteristicofthemorphology,thatis,lamellar,columns,spheres,etc.242Somepolymersmaybeofparticularinterestinthattheyexhibitliquidcrystalphases.X-rayscatteringinconjunctionwiththermalanalysisandopticalmicroscopyprovidesapowerfultooltoidentifynematicandsmecticphases.248Usuallytheinformationofinterestliesattheboundaryofsmall-angleandwide-anglescatteringregimesandidentificationisgreatlyfacilit-atedifmacroscopicallyalignedsamplesareavailable,forexample,throughtheuseofmagneticfields.NeutronscatteringproceduresfollowinbroadoutlineX-rayscatteringtechniques.Clearlysuchstudiescanonlybecarriedoutatspecialistnationalorinternationalfacilities.249Asaconsequence,neutronscatteringexperimentsarefocusedinobtainingdatanotavailablewithothertechniques.Forpoly-mers,neutronscatteringtechniquesoffertwodistinctadvantages.250ThefirstisthatdataoveramuchlargerQrangecanbeeasilyobtained,forexample,usingGEMorSANDALSattheUKISISpulsedneutronfacilitybroadQdata(equivalenttowide-angle)canbeobtainedwithQvaluesfrom0.1to50Å1.Dataoverthisextendedrangeisparticularlyusefulindetailedstudiesofthelocalarrangementsofdisorderedpolymers.251Thesecondadvantagecentresonthefactthathydrogenhasadifferentneutronscatteringcross-sectiontodeuterium.250Thiscanbewidelyexploitedinboth‘wide-angle’and‘low-angle’techniques.Hydrogenhasalargeincoherentcross-sectionwhichleadstoasubstantialbackgroundwhichcon-tainsnousefulstaticstructureinformation.Itis,however,widelyusedinthestudyofdynamics.ThebroadQneutronscatteringdataforaper-deuteratedpolymerwillhaveasimilarappearancetoawide-angleX-rayscatteringpattern,althoughthefall-offofintensitywithQismuchlesspronouncedthaninthecaseofanX-rayscatteringpattern.Figure1.15showsbroadQneutronscatteringdataobtainedusingGEMatISIS,thelowestcurveisobtainedforper-deuteratedpolyethyleneinthemeltphaseandthesubsequentcurvesaresnapshotstakenoversuccessivetimeperiodsafterquenchingthesampletoanintermediatetemperatureinordertofollowtheisothermalcrystallization29 I.L.Hosieretal.81.21.00.86)0.6(tl1100.40.24)0.0(QS–0.2–199991999929999399992time(s)0–223456Q(Å–1)Fig.1.15BroadQneutronscatteringforasampleofper-deuteratedlinearpolyethylene.Thelowestcurvecorrespondstothemeltstateandthesuccessivecurvescorrespondtosnapshotstakenattimeintervalsfollowingquenchingfromthemelt(160Cto129C).Theinsetshowshowtheintensityofthefirstsharpcrystallinepeakincreaseswithtimeduringthecrystallizationprocess.process.252Theinsetshowsthedevelopmentoftheintensityofthefirstcrystallinepeakwithtimeduringtheearlystagesofcrystallization.Thefirstcurveistypicalofmanydisorderedpolymersinthatitcontainsaseriesofratherdiffusepeaks.Thefirstisusuallyassociatedwithinter-segmentalcorrelationswhileathighQthescatteringarisesfromcorrelationswithinasegment.251Despitethediffusenatureofthescattering,considerablestruc-turalinformationcanbeobtainedusingadvancedcomputationalmodellingprocedurestightlycoupledtothescatteringdata.251Figure1.16showsthebroadQneutronscatteringdatarecordedforthinfilmsofper-deuteratedpolypyrroledopedwithtoluenesulfonate.253Thediffusenatureofthepeaksshowsthatthestructureishighlydisordered.However,thesefilmsexhibitasubstantiallevelofpreferredorientationascanbeseenbycomparingthescatteringrecordedwiththescatteringvectorperpendiculartothefilmthicknessandparalleltothefilm.Bycomparingthescatteringforfilmspreparedusingper-deuteratedtoluenesulfonatewiththosepreparedwiththeequivalenthydrogencontainingcompound,quantitativedetailsofthelocationofthedopantwithinthefilmwereobtained.Essentially,thefilmexhibitsalayeredstructurewithmoreorlessalternatinglayersofpolypyrroleanddopant.25330 1:PolymercharacterizationQperp.+Qpar.7)6–1+++++++5++++Neutrons(Å++4+++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++3+++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++2012345678910MomentumtransferQ(Å–1)Fig.1.16BroadQneutronscatteringforasampleofper-deuteratedpolypyrroledopedwithdeuteratedtoluenesulfonate.ThefulllineshowsthedataforQperpendiculartothefilmsurfaceandthepointsshowthedataforQparalleltothefilmsurface.Wecanexploitmixturesofper-deuteratedandper-hydrogenatedpoly-mersinsmall-angleneutronscatteringmeasurementstorevealinformationontheconfigurationofindividualchainsaswellasassembliesofchainsinthecaseofphaseseparatingblends,blockcopolymers,andotherinhomo-genoussystems.250,254Thisistheclassicpolymersciencetechniquewhichhasunderpinnedmuchofourcurrentunderstandingofthestructureonthescaleoftheradiusofgyration.254Figure1.17showsanexampleofsmall-angleneutronscatteringdatarecordedusingD22attheInstitutLaueLangevinforasampleofper-deuteratedpolyethylenewith10%ofper-hydrogenatedpolyethylene.255Thesampleismoltenandhasbeensubjectedtoacontrolleddeformation(3times)usingachanneldie.Theflowaxisishorizontalandthesquareinthecentreoftheintensescatteringcorrespondstothebeamstoparea.Thebeamstoppreventstheveryintensezeroanglebeamsaturatingthedetector.ThescatteringisclearlyanisotropicandtheintensityfallsofflessquicklywithQinthedirectionnormaltotheflowaxiscomparedtothedirectionparalleltotheflowaxis.Therateoffall-offoftheintensityisrelatedtotheradiusofgyrationofthechaininthatdirection.Quantitativeanalysisofthedatarevealsanextensionofthechainsinthedirectionofflowby20%witharadiusofgyrationinthatdirectionof200Å.31 I.L.Hosieretal.1.13e+30.0254760.021990.01583.70.010.00535.1γ0–114.7cm–0.0056.17–0.012.59–0.0151.09–0.020.455–0.0250.191–0.0100.010.020.030.04q(Å–1)xFig.1.17Small-angleneutronscatteringpatternforasampleofper-deuteratedlightlybranchedpolyethylenecontaining10%ofhydrogencontaininglinearpolyethylene.Thesampleismoltenandhasjustbeensubjectedtodeformationinachanneldie.Theflowaxisishorizontalandtheeffectiveextensionratiois
3.12.ConclusionsThischaptergivessomeexamplesoftherangeoftechniquesavailableforthecharacterizationofpolymericmaterials.Itisbynomeansanexhaustive,andofnecessitybrief,butitdoesservetoillustratesomeofthechallengesfacedbythepolymerscientist,andtheneedforinteractionsacrosstheboundariesoftraditionalscientificdisciplines.Thesituationisparticularlycomplicatedbecausesubtlechangesinchemicalcompositioncanoftenhavemarkedinfluenceonthemacroscopicpropertiesofpolymerandsuchsmalldiffer-encesmaybeparticularlychallengingtomonitoratamolecularlevelusingtechniqueslikeNMR.However,ultimatelythekeytodevelopingmaterialswithdesirablepropertiesiscontrolthroughsynthesis.Inthediscussionthatfollows,manyroutestomacromolecularmaterialsaredescribed.Ineverycasethelevelofcontroloverstructureisdeterminedbytheintendedapplica-tion.Thus,forcross-linkedpolystyrenebeadsparticlesizemaybeimportant,forablockcopolymerproducedbyanionicchain-growthpolymerizationthesizeoftheblocksmaybeacrucialfeature,anddendrimersareoftendesignedtobesinglemonodispersesystems.Itistobehopedthatthefollowingaccount,whilebynomeanscomplete,willgivethereaderaflavourofthemethodsofconstructingmacromoleculesandmacromolecularsystems.32 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2Generalproceduresinchain-growthpolymerizationNAJIBARAGRAG,DARIOC.CASTIGLIONE,PAULR.DAVIES,FREDJ.DAVIS,andSANGDILI.PATEL1.IntroductionThischapterisintendedtoprovideageneralintroductiontothelaboratorytechniquesusedinpolymersynthesis,byfocusingonsomerelativelywell-knownpolymerizationsthatoccurbychain-growthprocesses.Inthiswaysomeofthemorecommonlyusedproceduresinpolymerchemistryaredescribed.Duetothenatureoftheintermediatesproduced,1suchasfreerad-icals,carbanions,carbocations,togetherwitharangeoforganometallicspecies,thetechniquesofteninvolvehandlingcompoundsinthecompleteabsenceofoxygenandmoisture.Becauseofthisthebestresultsmayrequirequitesophisticatedequipmentandglassware;2however,itisourintentiontoshowthatthegeneralproceduresareaccessibletoanyreasonablyequippedlaboratory,andindeedsomeofthetechniquesaresuitableforuseinanundergraduateteachinglaboratory.3–5Chain-growthpolymerizationinvolvesthesequentialstep-wiseadditionofmonomertoagrowingchain.Usually,themonomerisunsaturated,almostalwaysaderivativeofethene,andmostcommonlyvinylic,thatis,amono-substitutedethane,1particularlywherethegrowingchainisafreeradical.Forsuchmonomers,thepolymerizationprocessisclassifiedbythewayinwhichpolymerizationisinitiatedandthusthenatureofthepropagatingchain,namelyanionic,cationic,orfreeradical;polymerizationbycoordina-tioncatalystisgenerallyconsideredseparatelyasthenatureofthegrowingchain-endmaybelessclearandcoordinationmaybringaboutasubstantiallevelofcontrolnotpossiblewithothermethods.6HXHH1Structure1 N.Aragragetal.Ring-openingpolymerizationsexhibitmanyofthefeaturesofchain-growthpolymerization,butmayalsoshowsomeofthefeaturesexpectedfromstep-growthpolymerizations.7However,itisprobablyfairtosaythatfromaprac-ticalpointofviewthetechniquesinvolvedarerathersimilarorthesameasthoseusedinchain-growthprocessesandconsequentlysomeexamplesofring-openingprocessesareprovidedhere.Itisparticularlyinstructivetoconsidertherequirementsofchain-growthcomparedtostep-growthprocessesintermsofthedemandsforreagentpurityandreactionconditions.Inbothcasesmonomerpurityisofthehighestimportance,butitshouldberememberedthatforachain-growthprocessonlyatinyfraction(depending,ofcourse,onthemolecularweight)ofmonomermoleculesreactwithinitiatorandconsequentlythereisthepoten-tialformassiveinhibitionofthereactionbytracesofimpurities,theclassicexamplebeingtheinhibitionoffree-radicalchain-growthpolymerizationbysmallquantitiesofphenoliccompounds.Indeed,useismadeofthispropertyinthestabilizationofmonomersandcompoundssuchas2areaddedtocom-mercialmonomersamplestopreventpolymerizationpriortouse.Theseneedtoberemovedpriortouse;videinfra.Waterandoxygenmayalsoneedtoberemovedandoftenthisnecessitatestheuseofvacuumlinesandotherequip-mentusedtypicallyforair-andmoisture-sensitivematerials.Inthecaseofstep-growthpolymerization,thecrucialneedistoavoidthepresenceofmonofunctionalunitsthatcancapthepolymerizationandofcourseanyunknownmaterialthatmightinadvertentlyeffectthestoichiometry—herehighmolecularweightsareonlypossibleathighconversionsasdictatedbyCarother’sequation(seeChapter4).OHCH32Structure22.Free-radicalchainpolymerizationThisisperhapsthemostwell-knownmethodofpolymerization,andasthenameimplies,involvesthecontinuousadditionofmonomerunitstoagrowingfree-radicalchain.8Thegeneralmechanismofthisprocessinrelationtothepolymer-izationofavinylmonomerisshowninScheme1.AsScheme1shows,initiationisatwo-stageprocessinwhich,firstafreeradicalisformed,andsecondthisradicaladdsontoamonomerunit.Thesecondstageisessentiallythesamefor44 2:Generalproceduresinchain-growthpolymerizationalltherelatedprocesses;however,thefirststepcanbeachievedinavarietyofways;andthetypeofinitiatordependsonthenatureofthepolymerizationexperiment.Inalaboratory,2,2
-azo-bisisobutyronitrile(AIBN),inasealedtubeisusuallytheinitiatorofchoiceforthisandotherfree-radicalprocessespre-sumablybecauseoftheconvenienttimescaleofitsdecomposition(Scheme2)ofabout18hat60C.Morecommonlyusedinanindustrialsettingareperoxidesand,inanaqueousormixedenvironment,inorganicinitiatorssuchaspersulfateandotherredoxsystems.Electromagneticradiation,usuallyvisibleorultravioletlightbutoccasionallyhigherenergyradiationssuchasX-and-raysarealsoofsomeimportance,9photoinitiatorsoftenbeingusedtocurepreformedpolymerchainsbythepolymerizationofpendantpolymerizableside-groups.10*Someexamplesoffree-radicalinitiatorsincommonusearelistedinTable2.1.11,12Insomecases,polymerizationapparentlyoccursintheabsenceofanyaddedini-tiator;herepolymerizationisinducedbyadventitiousfree-radicalproduction.†Thepropagationstepis,ofcourse,thecoreoftheprocess,butasinallchain-growthprocesses,itisthenumberofmonomerunitsthatareaddedforeachinitiatormoleculethatdeterminesthemolecularweightofthefinalmaterial.Inthecaseoffree-radicalpolymerizationthisiscontrolledbyconsideringtheprocessesinvolvedinterminatingthegrowingchain;oftentheseinvolveradical–radicalcombinationsandhighmolecularweightsarefavouredbykeepingtheconcentrationoffreeradicalslow.Intheidealcase,thatis,wherethereisnochaintransfer,thenumberaveragedegreeofpolymerizationisrelatedtotheini-tiatorconcentrationbyeqn(1).[Monomer]xn(1)Initiator•InitiatorR••RHXR+CH2CHXCH2C••RCCH2CHX+H2CHXRCH2CHXCH2CHX••CHX+XCHCHXCHXScheme1Mechanismoffree-radicalpolymerization.*Itmustalsobenotedherethatnotallphotoinitiatorsinitiatefree-radicalpolymerization,forexample,theuseofoniumsaltsasphotoinitiatorsisbasedontheirabilitytoinitiatecationicpolymerizationprocesses.†Abottleofstyreneleftuntouchedforlongperiodswillbefoundtohavepolymerizedeventhoughtheinhibitorhasnotbeenremoved;monomerfromwhichtheinhibitorhasbeenremovedhasanevenshortershelf-life.Forthisreason,itissuggestedthatstyreneisdisposedofafter12–18monthsandthatwiththeinhibitorremovedusedimmediately.45 N.Aragragetal.CNCNCNCH3NNCH32CH3•+N2CH3CH3CH3Scheme2ThermaldecompositionoftheinitiatorAIBN.Table2.1Examplesoffree-radicalinitiatorsincommonuseThermalfree-radicalSolventT(C)k(s1)t(s)t(h)d1/21/2initiatorsa2,2
-AzobisisobutyronitrileBenzene502.201063.1510587.52(AIBN)bBenzene703.201052.171046.02Benzene1001.501034.621020.131,1
-Azobis(cyclohexane-Benzene806.501061.0710529.62carbonitrile)Benzene955.401051.281043.56Benzene1021.301045.331031.48BenzoylperoxidecBenzene602.001063.4710596.27Benzene782.301053.011048.37Benzene1005.001041.391030.39tert-ButylperoxideBenzene807.801088.891062468.47Benzene1008.801077.88105218.80Benzene1303.001052.311046.42DodecanoylperoxideBenzene404.901071.41106392.94(lauroylperoxide)Benzene609.201067.5310420.93Benzene853.801041.821030.51PotassiumpersulfateWater806.901051.001042.790.1MNaOH509.501077.30105202.670.1MNaOH603.201062.1710560.170.1MNaOH809.201057.531032.090.1MNaOH903.501041.981030.55Photoinitiators
max(nm)Transparentregion(nm)Acetophenone242360–450280Anthraquinone250390–450270325Benzophenone250380–450Triarylsulfonium300370–450hexafluoroantimonatesaltsTriarylsulfonium298380–450hexafluorophosphatesaltsaHazardinformationisprovidedinthetextwhereinitiatorsareused;butitshouldbenotedthatfreeradicalinitiatorsoftenpresentariskofexplosion.bAIBNisnowbecomingdifficulttoobtain.1,1
-Azobis(cyclohexanecarbonitrile)isoftenpromotedasanalternative.cDecomposestogivephenylradicals.46 2:Generalproceduresinchain-growthpolymerizationItisoftenfoundthatthemolecularweightofthematerialisratherhigherthanisconvenient;insuchcaseschain-transferagentsmaybeused.Commonchain-transferagentsinuseincludethiolsandhalogenoalkanes;andinsomecasesthesolventmaybeusedtocontrolmolecularweight[e.g.bothtolueneandtetrahydrofuran(THF)mayactinthisway].Aconvenientsourceofdataontheeffectivenessofchain-transferagentsisgivenbythePolymerHandbook.11Theuseoffunctionalizedchain-transferagentssuchas2-mercaptoethanolcanleadtomonofunctionalpolymers,13asshowninScheme3;thesecanbesubsequentlyreactedtoform,forexample,ablockcopolymer.CO2MeCH•2+HOCH2CH2SHMeCO2MeCH2H+HOCH2CH2S•MeCO2MeCH2CO2MeMeHOCH2CH2S•HOCH2CH2SCH2•MeCO2MeCH2COCO2Me2MeMeHOCH2CH2SCH2CH2•MeMeScheme3Chain-transferprocesswith2-mercaptoethanoltogiveahydroxyl-terminatedpolymer.2.1Generalproceduresinfree-radicalpolymerizationAlthoughthepresenceofwaterisgenerallynotanissueinfree-radicalchainpolymerization(indeedwatermaybeasuitablemediumforpolymer-izationasinProtocols5–7)unlike,forexample,chain-growthpolymeriza-tioninitiatedbyanionicspecies,itisalwaysadvisabletousesolventsofthehighestpurityandthiswillgenerallyincludesomeelementofpre-drying.Ingeneral,solventsshouldbedistilled,particularlyasanumberofsuitablesolventsforpolymerizationreactionscontainstabilizerswhichusu-allyservetomopupfreeradicalsandthereforeinhibitthepolymerization47 N.Aragragetal.process.Itisusuallyadvisabletopre-drysolventsoftenwithcalciumhydride(seebelow)andthendistilthemfromanotherdryingagent.LiAlH4isnotnowadaysafavouredreagentinthislattercapacity.Etherealsolventsarenotusuallysuitableforfree-radicalprocesses(unlessarestrictedmolecu-larweightisrequired*).However,wheretheyareused,theyaregener-allydriedonamixtureofsodiumandbenzophenoneunderanitrogenatmosphere;thedeepbluecolourofthesodiumbenzophenoneketylindicat-ingthatthesolventisdry.Thisketylalsoactstoremoveoxygen.ThedemandfordryTHFinmanylaboratoriesissuchthatasemi-permanentsolvent-stillisrequired.Itisimportantthattheusersrememberthepossibil-ityanddangerofperoxidebuild-upinsuchsystemsandregularlytestforthese.Thisisdonebyadding1mLofthesolventto1mLofa10%(w/v)solutionofsodiumiodideinaceticacid;ayellowcolourindicatesperoxidespresent,butinlowconcentrations;abrowncolourhighconcentrations.†Inanycase,astillshouldbedismantledregularlyandcleaned.Solvent-stillsareaclearfireriskandshouldnotbeusedwithoutappropriateprecau-tionsandshouldbecarefullymonitoredduringuse.Someinforma-tionaboutcommonsolventsusedbothforpolymerizationandinthepreparationandpurificationofcommonmonomersislistedinTable2.2.ThelistisnotexhaustiveandthereaderisreferredtotheexcellentbookbyPerrinandArmarego,14andsomeexcellenttextbooksonpracticalchemistry.15–17Aftermonomerandsolventpurity(particularlytheremovalofinhibitors),perhapsthemostcrucialfactorindeterminingthesuccessofafree-radicalpolymerizationprocessistheabsenceofoxygen.Oxygenis,ofcourse,highlyreactivetowardsfreeradicalsandhasadetrimentaleffectonpolymer-izations.Forthisreason,free-radicalpolymerizationsneedtobeperformedunderanaerobicconditions.Solutionorbulkpolymerizationstendtobeper-formedinpolymerizationtubessuchastheoneshowninFigure2.1.Suchtubesmaybesealedusingaflameinwhichcaseitisusuallydesireabletopreparethemwithaconstrictionnearthetop.Forlessvolatilemonomersandsolvents,particularlywhereonlysmallvolumesarebeingused,itissufficienttosealthetubeusinga‘Young’stap’makingthewholeprocessmuchmoreconvenient.Evenunderthesecircumstancesitisimportanttotreatsuchtubeswithconsiderablerespect,largeunexpectedchangesinpressurewillcausethemtoshatterexplosivelyandablastscreenshouldbeplaced*Themethyleneunitattachedtotheetherealoxygenisparticularlyreactivetowardsradicalattackandthuschain-transferprocesseswouldbeexpectedtosubstantiallyreducethemolecularweightofthefinalpolymer.Somereductionisnoticedbutboththissolventandtoluenecanbeusedforfree-radicalpolymer-ization(andnotethesuccessfulpolymerizationofbenzylacrylateinProtocol1).†Peroxidesmybedestroyedbytreatingthesolventwithaconcentratedsolutionofferroussulfate.48 2:Generalproceduresinchain-growthpolymerizationTable2.2SomepropertiesandpurificationmethodsofcommonsolventsSolventBoilingpointaPurificationmethodHazards18Tetrahydrofuran65Pre-driedoverCaHHighlyflammable,bmay2(THF)thendriedoverNaformperoxides,anddistilledfromNairritatingtoeyesandwithbenzophenonerespiratorysystemDiethylether35AswithTHFabove;Extremelyflammable,diethylethermayformperoxidessufficientlydryforthepreparationofGrignardreagentscanbeobtainedbystandingonsodiumwireToluene111ThesesolventscanbeHighlyflammable,driedwithcalciumharmfulbyinhalationhydridethendistilled;Benzene80alternatively,theycanCaution:Cancersuspectbetreatedastheagent,highlyflammable,etherialsolventabovetoxicbyinhalationChlorobenzene131.7RelativelypureFlammable,harmfulbychlorobenzenecaninhalationbepreparedbywashingwithH2SO4thendryingwithsodiumbicarbonate,followedbydryingwithCaCl2thendistillationfromP2O5Hexane68.7DistillationandstoringHighlyflammable,over4AmolecularharmfulbyinhalationandsievesisusuallysuitableincontactwiththeskinforthesesolventsPentane36.1HighlyflammablePetroleumetherVariousExtremelyflammableorhighlyflammableChloroform61ChloroformcanbeHarmfulbyinhalation,simplypurifiedbypotentialcarcinogenpassingthroughacolumnofbasicaluminatoremovetheethanol,whichisaddedasastabilizer.Chloroformmustbestoredinthedarktoavoidthephotochemicalgenerationofphosgene49 N.Aragragetal.Table2.2ContinuedSolventBoilingpointaPurificationmethodHazards18Dichloromethane40DrydichloromethaneHarmfulbyinhalation,canbeobtainedbypotentialcarcinogenpre-dryingwithCaCl2followedbydistillationfromCaH2Dimethylformamide153DriedbystirringoverHarmfulincontactwith(DMF)calciumhydrideforskin,irritatingtoeyes24h,thendistilledunderreducedpressureDimethylsulfoxide190DriedovernightoverHarmfuliftaken(DMSO)CaO,thendriedinternally,irritatingtooverCaH2theneyesdistilledatreducedpressureAcetonitrile80DriedovermolecularHighlyflammable,toxicsieveandbystirringbyinhalationincontactoverCaH2,thenwithskinandifdistilledfromCaH2swallowedMethanol65EthanolormethanolHighlyflammable,toxiccangenerallybedriedbyinhalationandusing4AmolecularifswallowedsievefollowedbyEthanol79distillation;forHighlyflammablemorerigorousdryingthesolventscanbetreatedwithmagnesiumandiodineEthylacetate77WashedwithNa2CO3HighlyflammableandthenwithsaturatedNaCl,distilledfromCaH2aCat760mmHgunlessotherwisestated.bAflammableliquidisgenerallyconsideredtobeonewithaflashpointbelow55Cbutabove21C;ahighlyflammableliquidisonewithaflashpointabove0Candbelow21C;anyliquidwithaflashpointlowerthan0Candaboilingpointlowerthan35Cmustbelabelledextremelyflammable.Thesearethedefinitionsusedherebutitshouldbenotedthatthetermextremelyflammableissometimesusedforliquidswithaflashpointbelow32C.betweenthetubeandtheoccupantsofthelaboratory.Forsystemswherestirringisrequired,suchasinemulsionandsuspensionpolymerizations,eitheracontinuousstreamofnitrogenisbubbledthroughthesolution,ortheapparatusisevacuatedandnitrogenadmittedintothesystem,whichisthenmaintainedunderaheadofnitrogen.Afewyearsago,thislatterprocess50 2:Generalproceduresinchain-growthpolymerizationFig.2.1Polymerizationtubeforfree-radicalpolymerizationofgram-scalesamples.mayhavebeenperformedusingaballooncontainingnitrogenconnectedtoathree-waytap,nowadaysmostworkersprefertheversatilityofadoublemanifoldsystem,whichprovidesaccesstobothaninertgassupplyandthevacuumpump.Atypicalset-upforthisisshowninFigure2.2.Themanifoldconsistsoftwoglasstubeswithtaps,whichallowoneortheothertubetobeconnectedtothereactionvessel.Onesectionofthemani-foldisconnectedtoasourceofdrynitrogenatoneendandagasbubblerattheother.Theothersectionisconnectedtothevacuumpump.Com-mercialnitrogenandargonaresufficientlydryforthereactionsdes-cribedhere,butitisnormaltoplaceadryingtubecontainingsilicagelbetweenthecylinderandthemanifoldalthoughelaborate‘dryingtrains’aretobeavoided.17Itisalsoimportanttobeabletomaintainasmoothgentleflowofinertgasandforthisreasonthecylinderisconnectedtothesystemviaaneedlevalve,whichallowscarefulregulationofthegasflow.Theexamplesprovidedbelowareintendedtoillustratesomeofthetechniquesavailableforproducingpolymersbyfree-radicalchain-growthpolymerization.Inthefirstexampleweillustratehowamonomermaybepreparedandpurifiedpriortothepolymerizationprocess.Thefreeze–pump–thawprocessforremovingoxygenfromthesolutionisageneraltechnique,andapplicabletoawiderangeofprocesseswherefreeradicalsaregenerated.51 N.Aragragetal.BubblerVacuumlineventInertgasinTovacuumThree-wayhighvacuumtapVacuumtrapDouble-obliquehighvacuumtapsFig.2.2Doublemanifoldsystemdesignedtoprovideasourceofinertgasandreducedpressure.Protocol1.Preparationandpolymerizationofbenzylacrylate(Scheme4)Caution!Carryoutallproceduresinawell-ventilatedfume-hood,wearappro-priatedisposablegloves,alab-coat,andsafetyglasses.Allvacuum-lineworkshouldbeperformedwhilestandingbehindaprotectivePerspexscreen.Checkallglasswareforstarcracksbeforeusewithanyreducedpressuresystem.Neveruseflat-bottomedflaskswithrotaryevaporators.OHOO(Et)3N+THFClOOOAIBNOOnScheme4Preparationandpolymerizationofbenzylacrylate.52 2:Generalproceduresinchain-growthpolymerizationEquipment●Dualmanifold(nitrogen/vacuum)●Lab-jack●Vacuumsource●Polymerizationtube●Sourceofdrynitrogen●Dewarcontainingliquidnitrogen●Thermostattedwater-bath●Single-neckedround-bottomedflask(250mL)foruse●Funnelonrotaryevaporator●Buchnerfilterapparatus●Sintered-glassfunnel●Erlenmeyerflasks(250mL)●Three-neckedround-bottomedflask(250mL)●Refluxcondenser●Teflon®-coatedmagneticstirrerbar●Hotplatestirrer●Ice–salt-bath●Separatingfunnel●Apparatusfordistillationatreducedpressure:four●Round-bottomedflask(500mL)single-neckedround-bottomedflasks(50mL),●Vacuumovencondenser,thermometer,airbleed,‘pig-type’●Droppingfunnelreceiver-adapter,Claisenstill-head,andthermometer●RotaryevaporatorMaterials●Acryloylchloride,11.30mL,0.14molFlammable,causesseverburns;avoidcontactwitheyes,skin,andrespiratorysystem●AIBN,0.010g,6.1105molToxic,harmful,explosive,highlyflammable●Benzylalcohol,9.60mL,0.09molflammable,severeirritant●THF,100mLhighlyflammable,mayformperoxides,irritatingtoeyesandrespiratorysystem●Methanol,ca.200mLhighlyflammable,toxicbyinhalationandifswallowed●2,6-Di-tert-butyl-4-methylphenoltrace,harmful,irritantca.10mg●Triethylamine,19.40mL,0.13molhighlyflammable,irritatingtoeyes,skin,andrespiratorysystem●Dichloromethane,ca.70mLharmfulbyinhalation,potentialcarcinogen●Chlorobenzene,20mLflammable,harmfulbyinhalation●Hexaneforchromatographyhighlyflammable,harmfulbyinhalationandincontactwiththeskin●Diethyletherforchromatographyextremelyflammable,mayformperoxides●Silicagelforflashchromatographyharmfulbyinhalation,irritatingtorespiratorysystem●Liquidnitrogenforcoolingextremelycoldliquid,vapourcancauserapidsuffocationMethodStep1:preparationofbenzylacrylate1.Toathree-neckedround-bottomedflask(250mL)equippedwitharefluxcondenser,adroppingfunnel,andamagneticstirrerbar,addbenzylalcohol(9.60mL,0.09mol).AdddryTHF(60mL)afollowedby2,6-di-tert-butyl-4-methylphenol(trace,ca.10mg)bandstiruntilallthesolidhasdissolved.Finally,triethylamine(19.40mL,0.13mol)isaddedandtheflaskcooledtoca.5Cusinganice–saltbath.2.Acryloylchloride(11.30mL,0.14mol)cisdissolvedinTHF(40mL)andthesolutionplacedinthedroppingfunnel.Thesolutionisthenaddeddrop-wisetothestirredbenzylalcoholsolution,overabout10minensuringthatthetemperaturedoesnotexceed5C.Thesolutionisthenallowedtowarmtoroomtemperatureandstirredfor24h.3.After24h,thesolutionistransferredtoa500mLround-bottomedflaskandtheTHFremovedontherotaryevaporatortoyieldayellowsolid.Thissolidisthendissolvedindichloromethane(50mL)andwashedwithwater(50mL)53 N.Aragragetal.Protocol1.Continuedinaseparatingfunnel.Thedichloromethane(lower)layeristhenrun-offintoanErlenmeyerflask(250mL)anddriedwithanhydroussodiumsulfate(suf-ficienttobecomefreeflowingwhenthesolutionisswirled).Thissolutionisthenfilteredundergravitythroughaflutedfilterpaperintoaconicalfunnelplacedinthesingle-neckedround-bottomedflask(250mL)toremovethedryingagentandthedichloromethaneisthenremovedfromthisredorganiclayerontherotaryevaporator,toleavearedliquid.4.Benzylacrylateisthenpurifiedbydistillationatreducedpressure(b.p.130–140Cat20mmHg)toyieldacolourlessliquid.dThisisfurtherpurifiedbycolumnchromatography(onsilicagel)etogivethemonomerin69%yield.fStep2:Polymerizationofbenzylacrylate5.Placethebenzylacrylate(2g,0.012mol)andAIBN(0.010g,6.1105mol)inapolymerizationtubetheaddchlorobenzene(20mL).Aprotectivenet-tingsleeveisthenplacedoverthetubetominimizedangerfromglass,shouldthetubeshatter.AttachthetubetothemanifoldandclosetheYoung’stapatthetopofthetube.6.PlacethepolymerizationtubeintotheDewarcontainingliquidnitrogen,usingthelab-jacktoraisetheDewartothecorrectposition,waitforthesolutiontofreeze(evaporationoftheliquidnitrogenbecomeslessrapid)andevacuatethemanifoldbyclosingthenitrogensupplyandopeningthevacuumtap.7.Openthetaptothepolymerizationtubeandallowtheairtobepumpedoutofthetube,withtheliquidnitrogenDewarstillinplace.Afterafewminutestheairwillberemovedfromthesystem(generallythiscanbedetectedbythesoundofthepump).Closethetaponthepolymerizationtube,theuppertap,andtheaccesstothepump.8.RemovethenitrogenDewarfromunderthepolymerizationtubeandallowthesystemtowarmtoroomtemperature.Anysuddencontactwiththepolymerizationtubeatthisstagemaycausethetubetoshatter.9.AllownitrogenintothesystembyopeningtheN2inlettap;thencarefullyopentheuppertapandthenthelowertapinsequence,beingparticularlycarefultoensurethatasuddeninfluxofairdoesnotcausethetubetobecomedetachedfromthemanifold.10.Repeatsteps6–9twomoretimestoensurecompleteremovalofoxygenfromthesystem.11.Whennitrogenhasbeenpassedintothesystemforathirdtime,placethepolymerizationtubeintotheliquidnitrogenDewarandevacuatethemani-foldbyclosingthenitrogensupplyandopeningthevacuumtap.12.ClosetheYoung’staponthepolymerizationtubeandwarmtoroomtem-perature.Placethetubeinathermostattedwater-bathat55Cfor18h.54 2:Generalproceduresinchain-growthpolymerization13.After18h,removethetubefromthewater-bathandallowtocooltoroomtemperature.Pourthecooledsolutionintoaflaskcontainingcooled(0C)methanol.Thesolidpolymeriscollected,dried,andthenfurtherpurifiedbytwicedissolvingindichloromethane(typically1gin10mL)andre-precipitatingintomethanol.Finally,thepolymerisdriedinavacuumovenat40C.PossibleproblemsPolymerizationwillbeobviousbythemarkedincreaseinviscosityofthesolu-tion,ifthisisnotapparentthenitispossiblethatatraceofinhibitorremainsinthemonomer(thisisnotlikelyinthiscase).Eitherre-purifythemonomerorincreasethequantityofinitiatorandleavethepolymerizationforalongerperiod(thislatterprocedureisnottoberecommendedifanycontrolofthemolecularweightisrequired).Filtrationofthecrudepolymermayprovedifficultasresidualsolventmayactasaplasticiserandtheresultantsoftpolymermayblockthefilterfunnel.Insuchcases,thesolutioncontainingtheprecipitatedpolymercanbeallowedtostandandthesupernatantliquidcanbedecanted.aSeeTable2.2.bThisinhibitsfree-radicalpolymerizationbothduringthereactionandthefinaldistillation.cAcryloylchloridecanbeobtainedcommercially,butcaremustbetakenwhenstoringthematerial,andinanycaseitshouldnotbestoredforlongperiods(sinceanexothermicpolymerizationmayoccur);acryloylchloridecanbereadilypreparedbyheatingacrylicacidwithexcessbenzoylchlorideanddistillationofthevolatilecomponent.dTheapparatusfordistillationatreducedpressureisdescribedinRef.17,itisrecommendedthatarel-ativelysmall-scaleapparatusisused:50mLflasksandglasswarewith14/23joints.Thejointsshouldallbegreasedusingvacuumgrease.TheflaskcontainingthebenzylacrylateisfittedwiththeClaisenstill-head,thecondenser,thethermometer,andthe‘pig-type’receiver-adapter.Theremainingthreeflasksareattachedtothisadapter(specialclipsareavailabletopreventtheseflasksfallingoff).Anair-bleedispulledfromaglasspipettebygraspingbothendsofthepipetteandheatingthethinend(sufficientlyfarawayfromyourhandtoavoidburning);whentheglasssoftens,thepipetteisquicklyremovedfromtheheatandbothhandspulledapart.TheresultantcapillaryisadjustedtotherightsizeandthenplacedintheClaisenheadusingascrewadaptersuchthatitisjustabovethebottomoftheflask.Thereceiver-adapterisconnectedtothewateraspiratorandavacuumapplied,thedistillationflaskisthenheatedusinganoil-bath(ahotairgunmaybemoresuitableinsomecircumstances)andthemiddlefractionofthedistilledmaterialcollected(caution!—neverdistiltodryness).eTheeluentusedwasamixtureofdichloromethaneandcarbontetrachloride,asuitablealternativeisamixtureofhexaneanddiethylether.f1HNMR(400MHz;CDCl;MeSi):7.40(5H,m,aromaticH),6.45(1H,dd,J17.2,J1.5,3
H),6.16H343
23
3(1H,dd,J2,310.4,J2,3
,1.5,2-H),5.83(1H,dd,J3,3
,1.5,J3,210.4,3-H),5.25(2H,s,4-H).Structuralstudiesofpolymermaterialsoftenuseneutronscatteringtech-niques.Insuchcircumstancestheuseofdeuteratedchainscanbenecessarybecauseitovercomesproblemsassociatedwithinelasticscattering.Inthisexample,acommercialsampleofpolystyrene-d7ispolymerizedinsuchawayastomaximizeyieldduetothehighcostofthemonomer.Thereislittleadvan-tageinpolymerizingstyreneinsolutionunlesslargequantitiesarerequired(whereheattransferbecomesaproblem).Polystyrenecanbepolymerizedinthe55 N.Aragragetal.bulkattemperaturesabove100Cwithoutanyaddedinitiator,butundersuchcircumstancesthemolecularweightmayberatherhigh.Controlofthemolecu-larweightandlowerpolymerizationtemperaturescanbeachievedusinginitia-tors.Usuallybenzoylperoxideistheinitiatorofchoice,however,wehavefoundthatAIBNworkswellandthatistheonedescribedhere.Protocol2.Bulkpolymerizationofstyrene-d7(Scheme5)Caution!Carryoutallproceduresinawell-ventilatedfume-hood,wearappro-priatedisposablegloves,alab-coat,andsafetyglasses.Allvacuum-lineworkshouldbeperformedwhilestandingbehindaprotectivePerspexscreen.Neveruseflat-bottomedflaskswithrotaryevaporators.AIBNScheme5PolymerizationofstyreneinitiatedbyAIBN.Equipment●Dualmanifold(nitrogen/vacuum)●Lab-jack●Vacuumsource●Polymerizationtube●Sourceofdrynitrogen●Dewarcontainingliquidnitrogen●Thermostattedwater-bath●Beaker(500mL)●Separatingfunnel●Vacuumoven●Erlenmeyerflasks(250mL)●Apparatusforfiltrationunderreducedpressure:●FunnelBuchnerfunnel,flask,andwateraspiratorMaterials●Sodiumhydroxidesolution(1M)causessevereburns●Magnesiumsulfatedonotbreathdust,avoidcontactwithskinandeyes●Styrene-d7,2g,19mmolflammable,irritatingtoeyesandrespiratorysystem●AIBN,0.032g,0.2mmoltoxic,harmful,explosive,highlyflammable●Methanol,ca.300mLhighlyflammable,toxicbyinhalationandifswallowed●Dichloromethane,45mLharmfulbyinhalation,potentialcarcinogen●Liquidnitrogenforcooling.extremelycoldliquid,vapourcancauserapidsuffocationMethod1.Thestyreneisfreedofinhibitorsbyshakingwithsodiumhydroxideinasep-aratingfunnel.Itisthendriedwithmagnesiumsulfatea.Aprotectivenettingsleeveisthenplacedoverthetubetominimizedangerfromglassshouldthetubeshatter.AttachthetubetothemanifoldandclosetheYoung’stapatthetopofthetube.2.Styrene-d7(2g,19mmol)isaddedtoapolymerizationtube(Figure2.2)andAIBN(0.032g,0.2mmol)isthenadded.56 2:Generalproceduresinchain-growthpolymerization3.Themonomerandinitiatorarethendegassedusingthefreeze–pump–thawtechniquedescribedinProtocol1(steps6–11).Thetubecontainingthedegassedmonomeristhenplacedinathermostattedwater-bathat55Cforabout15h.Afterthistimethestyrenehasbeenconvertedintoaglassysolidlumpofpolystyreneatthebottomofthetube.4.Theglassypolymerisdissolvedbyaddingdichloromethane(15mL)andallow-ingtostandfor2h.Thehighlyviscoussolutionisthenallowedtodropslowlyintoaflaskcontainingcoldmethanol.Thesolidpolymeriscollected,dried,andthenfurtherpurifiedbytwicedissolvingindichloromethane(15mL)andre-precipitatingintomethanol.Finally,thepolymerisdriedinavacuumovenat40C.aStyrenecanbepurifiedbydistillationatreducedpressure,butitdoesexhibitamarkedtendencytobumpandwithasmallsamplesuchasusedherelossesmayberathersignificant.2.2CopolymerizationTheintroductionofasecondmonomerintoafree-radicalpolymerizationisausefultooltomodifythepropertiesoftheresultantpolymer.Suchanapproachmayofferadvantagesovertheblendingofthetwopolymerssincethelatterproceduredoesnotguaranteeamisciblematerialduetothepoorentropyofmixingoflargemolecules.Onesimpleapplicationofcopolymerizationmightbetheintroductionofchemicalreactiveunitstoallowtheincorporationofotherunitsfollowingpolymerization.Twoexamplesmightbetheincorpora-tionofchromophorescontainingnitrocompoundstogeneratealiquidcrys-tallinecompoundwithspecificopticalpropertiesortheintroductionofhydroxylorotherunitstoprovidesiteforsubsequentcross-linking.WeshallseeinChapter9howthisapproachcanbeusefulinprovidingmaterialsthatdisplayapermanentmemoryoftheirorientationatthetimeofcross-linking.Forfree-radicalcopolymerstheincorporationofasecondmonomerisnotstraightforward.ThecompositionofthefinalcopolymerisdeterminedbythekineticsinawayfirstdescribedbyDorstal19butlaterelaboratedbyAlfrey,20MayoandWalling21,andothers.ThekineticmodelassumesthatthekineticsdependsontheendgroupoftheradicalchainandthenewmonomerinawaycommonlydescribedformonomersM1andM2asshowninScheme6.M1•+M1M1•k11M1•+M2M2•k12M2•+M1M1•k21M2•+M2M2•k22Scheme6Reactionsoccurringinacopolymerization;inthesimplestmodel,thereactivityofthepropagatingchainisconsideredtobedependentonlyontheterminalmonomerunit.57 N.Aragragetal.Table2.3SometypicaldataforreactivityratiosM1M2r1r2ConditionsStyreneAcrylonitrile0.40.0460CStyreneMaleicanhydride0.040.0160CStyreneMethylmethacrylate0.520.4660CMethylmethacrylateStyrene0.460.4260CAcrylonitrileMethylmethacrylate0.151.2280CThemonomerreactivityratiosr1(k11/k12)andr2(k22/k21)(Table2.3)reflecttherelativerateconstantsforagivenradicaladdingtoitsprecursormonomerandtothealternative.Ifthemonomersareverysimilarforexampletwoslightlydifferentacrylatesthenthevaluesofr1andr2areclosetoequalandunity.Insuchacase,thecompositionofthepolymerisequaltothecom-positionofthefeedstockatallstagesofthepolymerization.Ifontheotherhand,thevaluesarebothsmallasinthecaseofmaleicanhydrideandstyrenetheneachmonomerisreluctanttoreactwithitself;theresultisanalternatingcopolymer.Protocol3.Preparationofapoly(styrene–acrylicacid)copolymerbyfree-radicalpolymerization(Scheme7)Caution!Carryoutallproceduresinawell-ventilatedfume-hood,wearappro-priatedisposablegloves,alab-coat,andsafetyglasses.Allvacuum-lineworkshouldbeperformedwhilestandingbehindaprotectivePerspexscreen.+AIBNOOHHOOScheme7Acopolymerformedfromstyreneandacrylicacid.Equipment●Dualmanifold(nitrogen/vacuum)●Lab-jack●Vacuumsource●Polymerizationtube●Sourceofdrynitrogen●Dewarcontainingliquidnitrogen●Thermostattedwater-bath●Beaker(500mL)●Apparatusforfiltrationunderreducedpressure:●Erlenmeyerflasks(250mL)Buchnerflask,sintered-glass●Vacuumovenfunnel,andwateraspirator58 2:Generalproceduresinchain-growthpolymerizationMaterials●Acrylicacid,1.7mL,25mmolflammable,causesburns●Styrene,25.55mL,223mmolflammable,irritatingtoeyesandrespiratorysystem●AIBN,0.41g,2.5mmoltoxic,harmful,explosive,highlyflammable●Methanol,ca.150mLhighlyflammable,toxicbyinhalationandifswallowed●Acetone,ca.20mLhighlyflammable●Petroleumether60/80,ca.300mLhighlyflammable●LiquidnitrogenforcoolingExtremelycoldliquid,vapourcancauserapidsuffocationMethodPreparation:Styreneandacrylicacidshouldbepurifiedtoremoveinhibitorspriortouse.Bothmaybedistilledunderreducedpressure,butstyrenecanbewashedwithadiluteaqueoussolutionofpotassiumcarbonate.1.Placestyrene(25.55mL,223mmol),acrylicacid(1.7mL,25mmol),andAIBN(0.41g,2.5mmol)inapolymerizationtube.Aprotectivenettingsleeveisthenplacedoverthetubetominimizedangerfromglassshouldthetubeshatter.AttachthetubetothemanifoldandclosetheYoung’stapatthetopofthetube.2.PlacethepolymerizationtubeintotheliquidnitrogenDewarandevacuatethemanifoldbyclosingthenitrogensupplyandopeningthevacuumtap.3.Oncefrozen,openthetaptothepolymerizationtubeandallowtheairtobepumpedoutofthetube,withtheliquidnitrogenDewarstillinplace.Afterafewminutestheairwillberemovedfromthesystem(generallythiscanbedetectedbythesoundofthepump).Closethetaponthepolymerizationtube,theuppertap,andtheaccesstothepump.4.RemovethenitrogenDewarfromunderthepolymerizationtubeandallowthesystemtowarmtoroomtemperature.Anysuddencontactwiththepolymerizationtubeatthisstagemaycausethetubetoshatter.5.AllownitrogenintothesystembyopeningtheN2inlettap;thencarefullyopentheuppertapandthenthelowertapinsequence,beingparticularlycarefultoensurethatasuddeninfluxofgasdoesnotcausethetubetobecomedetachedfromthemanifold.6.Repeatsteps2–5twomoretimestoensurecompleteremovalofoxygenfromthesystem.7.Whennitrogenhasbeenpassedintothesystemforathirdtime,placethepolymerizationtubeintotheliquidnitrogenDewarandevacuatethemani-foldbyclosingthenitrogensupplyandopeningthevacuumtap.8.ClosetheYoung’staponthepolymerizationtubeandwarmtoroomtem-perature.Placethetubeinathermostattedwater-bathat55Cfor1hr.a9.Removethetubefromthewater-bathandallowtocooltoroomtemperature.10.Pourtheviscoussolutiondrop-wiseinto150mLmethanolcontainedinabeaker(500mL)cooledinice.Dissolvethepolymerinasmallquantityofasuitablesolvent(nomorethan10mLpergrampolymer),inthiscaseacetone,andprecipitatefromasuitablenon-solventforthepolymer(inthiscase,petroleumether60/80).59 N.Aragragetal.Protocol3.Continued11.Dissolvethepolymeronceagaininasuitablesolventandre-precipitate.Collectthewhitepolymerbyfiltrationatthewaterpumpusingacleandrysintered-glassfunnelanddrythesampleinthevacuumovenat60Cfor24h.aItisimportantthatthepolymerizationnotbeallowedtoproceedtohighyieldsincethedifferentreac-tivitiesofthetwomonomerswillresult(inmostcasesatleast)inachangingcompositionasafunctionoftimeasoneofthemonomersisdepletedmorerapidlythantheother.Polymerizationisnotalwaysthefinalchemicaltransformationinaprocessandthereareanumberofcommercialprocessesthatrelyonmanipulationofapreformedpolymerbackbone.Polyvinylalcohol,forexample,cannotbemadedirectlyfromthemonomer(whichistheenolformofacetaldehyde),andismadeinsteadbyhydrolysisofpoly(vinylacetate).Poly(acrylonitrile)isofparticularinterestsincetherearesomeimportantcommercialconsequencesofitspyrolysis;inparticular,heatingtohightemperaturesintheabsenceofoxygenresultsinaprocessknownasgraphitization.Ifthisprocessisper-formedonpoly(acrylonitrile)fibresunderstressthentheresultingcarbonfibresexhibitaveryhighmodulusandexcellentheatresistance.Theyfindpar-ticularuseincompositematerials.Theunderlyingchemistryofthepyrolysisprocessiscomplex,butitisclearthatthe1,3-relationshipbetweenneighbour-ingnitrileunitsfacilitatescyclization,andtheresultingladderstructurelosesnitrogenintheformofHCNandN2asoutlinedinScheme8.Thefollowingexample,describesthecopolymerizationofacrylonitrilewith2-vinylpyridine.Subsequentpyrrolysisresultsintheformationofanelectricallyconductivematerial,inspiteofthepresenceofthecomonomerunits;whenthecopolymerisheatedsufficientlyfortheformationofahighlyconjugatedstructurebutnotatasufficientlyhightemperatureforgraphitizationtooccur,thenthereisanexcessofnitrogeninthethermallyrestructuredproduct.Thismayfinduseaselectrodematerialinrechargeablepowercells.22AIBNCN+NCNN400°CCNConductingmaterialNScheme8Copolymerizationofstyreneand2-vinylpyridineandthermalrestructuringtoformaconductingmaterial.60 2:Generalproceduresinchain-growthpolymerizationProtocol4.Thermalrestructuringofacopolymerofacrylonitrileand2-vinylpyridineCaution!Carryoutallproceduresinawell-ventilatedfume-hood,wearappro-priatedisposablegloves,alab-coat,andsafetyglasses.Allvacuum-lineworkshouldbeperformedwhilestandingbehindaprotectivePerspexscreen.Equipment●Dualmanifold(nitrogen/vacuum)●Lab-jack●Sourceofdrynitrogen●Vacuumsource●Thermostattedwater-bath●Polymerizationtube●Vacuumoven●Dewarcontainingliquidnitrogen●Apparatusforfiltrationunderreduced●Beaker(500mL)pressure:Buchnerflask,sintered-glass●Erlenmeyerflasks(250mL)funnel,andwateraspirator●TubefurnaceMaterials●Acrylonitrile,2.00g,37mmolhighlyflammable,toxicbyinhalation,incontactwithskinandifswallowed●2-Vinylpyridine,1.70g,16mmolflammable,harmfulbyinhalationandskincontact●2,6-Di-tert-butyl-4-methylphenoltrace,ca.20mgharmful,irritant●AIBN,0.044g,0.24mmoltoxic,harmful,explosive,highlyflammable●Chlorobenzene,20mLflammable,harmfulbyinhalation●Methanol,ca.1Lhighlyflammable,toxicbyinhalationandifswallowed●Dichloromethane,ca.150mLharmfulbyinhalation,potentialcarcinogen●Diethylether,ca.100mLextremelyflammable,mayformperoxides●Liquidnitrogenforcooling.extremelycoldliquid,vapourcancauserapidsuffocationMethodPreparation:Acrylonitrileispurifiedbypre-dryingovercalciumhydride(24h),thendistilledinthepresenceofatraceof2,6-di-tert-butyl-p-cresolunderanitro-genatmosphere(b.p.78C,760mmHg).2-Vinylpyridineisdistilledunderreducedpressurewithatrace2,6-di-tert-butyl-p-cresolandusedimmediatelytoavoidpolymerizationduringstorage.1.Placeacrylonitrile(2.00g,37mmol),2-vinylpyridine(1.70g,16mmol)andAIBN(0.044g,0.24mmol)inapolymerizationtube.Finallychlorobenzene(20mL)isadded.Aprotectivenettingsleeveisthenplacedoverthetubetominimizedangerfromglassshouldthetubeshatter.AttachthetubetothemanifoldandclosetheYoung’stapatthetopofthetube.2.Steps2–7ofProtocol3arerepeatedandthepolymerizationtubeisplacedinathermostatedwater-bathat50Candthemixtureallowedtopolymerizefor48h.3.ThepolymertubeisallowedtocooltoroomtemperatureandthevacuumreleasedbyopeningtheYoung’stap;thepartialsolubleandtheswollenpolymeraispouredintoabeaker(1L)containingandexcessofmethanol(400mL).Thematerialiscollectedthenswollenindichloromethane(ca.50mL)andthenprecipitatedintomethanol(500mL),andonceagainthesolidcollected.Finally,afurtherportionofdichloromethaneisaddedandthe61 N.Aragragetal.Protocol4.Continuedpolymerprecipitatedintodiethylether.Thepolymeristhendriedinavacuumovenat50Cfor48h.Polymerspreparedinthiswayshowlittleevidenceofanyunreactedmonomerorsolventinthefinalproduct.b4.Pyrrolysisofthesampleisperformedinatubefurnace.cAsampleofthepolymer(ca.1g)isplacedinacrucibleandmountedinthefurnace.Theendsofthefurnacearesealedsavefortheinletfortheinertgassupplyandthegasoutletpipewhichmustbeventedintothefume-hood.Thesampleisthenheatedattherequiredtemperature(e.g.400Cfor3h)andallowedtocooltoroomtemperatureunderanitrogenatmosphere.aPoly(acylonitrile)issolubleinDMFbutnotinsolventssuchasdichloromethane.DMFisnotasuitablesolventtouseinsolventpurificationnotleastbecauseremovingitfromthefinalpolymerislikelytobedifficult.Increasingthe2-vinylpyridineconcentrationimprovessolubilityindichloromethane.bUnlikethepreviousexample,themonomersarepolymerizedtohighyield.This,ofcourse,meansthattheuptakeofmonomersisclosetotheirrelativeconcentrationsintheinitialfeedstock;however,ofcoursethecompositionofthepolymerintheinitialstagesofthepolymerizationislikelytobedifferenttothatformedwhenmonomersbecomedepletedindifferingamounts.Inthisparticularexampleaclearindicationoftheaveragemicrostructureinthepolymercanbeobtainedusing13CNMR(seeChapter1).Thesequencedistributionsandcompositionofthepolymerscanbecalculatedusingthereactivityratios.23cAttemperaturesbelow500Cborosilicateglass(Pyrex®)apparatusmaybeused,butparticularcareneedstobetakentoensurethatthetemperatureatthesampleisknown.Thereactionisexothermicsoitmaybedifficulttocontroltemperatureswithlargersamples.2.3SmartactuatorsusingN-isopropylacrylamidegelsN-Isopropylacrylamide(NIPA)gelshavebeeninvestigatedextensivelyfortheirdynamicpropertiesaswellastheexpectedswellingpropertiesfoundcommonlyamongstcross-linkedpolymers.Amongstthenovelanduniquecharacteristicsarethoseobservedduringchangesintheexternalconditionsofthegel.Forexample,thegelcanswellorshrinkbyafactorofseveralhundredonchangesintemperature.Suchpropertieshavebeenattributedtoaphasetransition,commonlyreferredtoasthelowercriticalsolutiontemperature(LCST).24WheninaqueoussolutionabovetheLCST,thepolymerexhibitsphaseseparationwherethedensityandporesizeofthenetworkexhibitlarge-scalefluctuations.Theforcesactingonthegelduringthetransitionaretheelasticity,theaffinityofthepolymerchainstooneanotherandthehydrogenionpressure.25Intheexamplebelow,thepolymerizationofNIPAandcross-linkingreactioniscarriedoutinonestep.Ammoniumpersulfateisusedasthefree-radicalinitiatoralongwithN,N,N,N-tetramethylethylenediamine,andthecross-linkingisachievedwiththeuseofN,N
-methylenebisacrylamideThinrodsofthegelcanbeobtainedbyplacingglasstubesinthepolymeriza-tionmixture;thegelcanbereadilyremovedfromthese‘moulds’usinghotwater.62 2:Generalproceduresinchain-growthpolymerizationProtocol5.Synthesisofcross-linkedpoly(N-isopropylacrylamide)(Scheme9)Caution!Carryoutallproceduresinawell-ventilatedfume-cupboard,wearappropriatedisposablegloves,alaboratorycoat,andsafetyglasses.NHCH3NHNHTEMED+OCHOO(NH4)2(SO4)2NHONHO3CH3CH3NHOScheme9SynthesisofahighlyabsorbentnetworkbycopolymerizationofNIPAandN,N
-methylenebisacrylamide.Equipment●Beaker(100mL)●Refrigerator(setbetween0and5C)●Glasscapillaries(5mmdiameter,30mmlength)●Scalpel*Care*Materialsa●NIPA,5.0g,44mmolharmful,toxic,irritant●N,N
-Methylenebisacrylamide,77mg,0.5mmolharmful●N,N,N,N-Tetramethylethylenediamine,58mg,0.5mmolcorrosive,flammable●Ammoniumpersulfate,25mg,0.1mmolharmful,irritant,sensitizer,oxidant●Water,deionized,50mL●n-Hexane,200mLhighlyflammable,harmfulbyinhalationandincontactwiththeskinMethod1.DissolveNIPA(5.0g,44mmol)andN,N
-methylenebisacrylamide(77mg,0.5mmol)inaglassbeaker(100mL)withdeionizedwater(50mL).AddN,N,N,N-tetramethylethylenediamine(58mg,0.5mmol)andimmersethedesirednumberofglasscapillaries(~30)inthesolution.2.Addammoniumpersulfate(25mg,0.1mmol)andimmediatelyplacethebeakerinarefrigeratoratabout2C.Leavethesolutiontostandatthistem-peraturefor20h.3.Removetheglasscapillariesfromthebulkofthegelbycuttingaroundthemwiththeuseofascalpel.Holdtheindividualglasscapillariesunderrunningtapwater(hot)toremovethegelcylindersfromwithin.4.Washthegelswithcopiousamountsofwaterusingasoak–decantmethodandleavethemtostand(inwater)for24h.Afterthistimewashthegelsagainwithwater,hexane(200mL),andfinally,water(usingthesamesoak–decantmethod).aNIPA(5.0g)isrecrystallizedpriortousefromn-hexane(60mL)anddriedinavacuumovenat50C.63 N.Aragragetal.2.4SuspensionandemulsionpolymerizationOnalaboratoryscale,styreneisperfectlysuitedtobulkpolymerization,particularlywhen,asabove,onlyacoupleofgramsofmaterialarerequired.Onalargerscale,however,anumberofdifficultiesmaybeencountered,forexample,thepolymermustbepurified,inparticulartoremoveunreactedmonomer—re-precipitationislessthansatisfactoryinthisregardsinceitintro-ducesthesubsequentneedtoremoveboththesolventandtheprecipitatingmedium.Themaindifficulty,however,isthattheexothermicnatureofmostpolymerizationreactionsgenerallynecessitatesheattransferinordertoavoidlocalizedheatinggivingaratherinhomogeneousproduct(having,e.g.aratherlargepolydispersityandpossiblysomedegradation).Althoughperformingthereactioninsolutiondoesovercomethisproblemthisintroducestheneedtoremovethesolvent(itmayalsobethecasethatthegrowingpolymerchainsprecipitatefromsolutionathighermolecularweights).Analternativeapproachtopolymerizationistosuspendthemonomerassmalldropletsinanon-solvent(thisusuallymeanswaterbutothersystemscanbeused).Thedropletstypicallyhavediametersrangingfrom100to5000mandaggregationispreventedbyacombinationofstirringandstabilizers[theseincludepoly(vinylalcohol),gelatin,avarietyofcellulosederivatives,andthesodiumsaltofpoly(acrylicacid)].Insuchsystemstheinitiatorismisciblewiththemonomerphase,sothesystemcanberegardedasalargenumberofsmall-scalebulkpolymerizations.Thereisaparticularproblemwithagglomerationifthebeadsbecomesticky,anditisnotsurprisingthatthisfindsmostusecommerciallyintheproductionofglassypolymerssuchaspolystyreneandpolyacrylonitrile.Suspensionpolymerizationfindsparticularuseinthepreparationofpolymerbeadsforpolymersupportedreactions,andtherearespeciallydesignedreactorsavailable.26Thesemaybealsousedtoformlarger-sizedpolymerparticlesthatarealsomonodispersebyatechniqueknownasseededsuspensionpolymerization.27,28Thefollow-ingexamplewasprovidedbyDrM.WhitcombeoftheInstituteforFoodResearchinNorwich.29Protocol6.Formationofpolystyrenebeadscross-linkedwithdivinylbenzenebysuspensionpolymerizationCaution!Carryoutallproceduresinawell-ventilatedfume-cupboard,wearappropriatedisposablegloves,alab-coat,andsafetyglasses.Allvacuum-lineworkshouldbeperformedwhilestandingbehindaprotectivePerspexscreen.Equipment●Dualmanifold(nitrogen/vacuum)●Resinkettle(250mL)●Sourceofdrynitrogen●Droppingfunnel64 2:Generalproceduresinchain-growthpolymerization●Mechanicalstirrer●Condenser●Nitrogeninlet●Hotplate●Oil-bath●Vacuumoven●CentrifugeMaterials●Sodiumhydroxide(1M)causessevereburns●Magnesiumsulfatedonotbreathdust,avoidcontactwithskinandeyes●Styrene,0.2g,2mmolflammable,irritatingtoeyesandrespiratorysystem●Methanol,ca.500mLhighlyflammable,toxicbyinhalationandifswallowed●Water,deionized,100mL●Divinylbenzene,4.8g,36mmolirritant●AIBN,0.1g,0.6mmolharmful,irritant●Poly(vinylalcohol)(87–89%hydrolysed,MW85000–146000),7gcombustible,irritantMethodPreparation:Thestyreneisfreedofinhibitorsbyshakingwithsodiumhydroxidesolutioninaseparatingfunnel,itisthendriedwithmagnesiumsulfate.aDivinylbenzeneisfreedfrominhibitorinasimilarway.bDeionizedwaterispurgedwithinertgasforanhourpriortotheexperiment.1.Inaresinkettle(250mL)equippedwithamechanicalstirrer,condenser,drop-pingfunnel,andnitrogeninlet,poly(vinylalcohol)(7g,87–89%hydrolysed,MW85000–146000)cisdissolvedinwater(100mL)bystirringat90–95C.2.Themixtureiscooledtoroomtemperatureanddivinylbenzene(4.8g,36mmol),styrene(0.2g,2mmol),andAIBN(0.1g,0.6mmol)areplacedintheflask.dThemixtureisstirredat650rpmunderagentlestreamofnitrogenwhilethetemperatureisraisedto65C.3.Thepolymerizationisallowedtoproceedunderagentlestreamofnitrogenandwithvigorousstirringfor24h.4.Themixtureiscooledtoroomtemperatureandthepolystyrenebeadsarewashedbyrepeatedsedimentationfromwaterat10Cinacentrifugeat13000rpmfor30min.Finally,thebeadsaredriedinavacuumovenat80Covernight.aStyrenecanbepurifiedbydistillationatreducedpressure,butitdoesexhibitamarkedtendencytobumpandwithasmallsamplesuchasusedherelossesmaybesignificant.bForexample,Whitcombeetal.suggest(Chapter8)theremovalofinhibitorbywashingthedivinyl-benzenewithdilutesodiumhydroxidesolution(0.1M)inaseparatingfunnel,followedbywashingwithwater,thenwithsaturatedbrine,anddryingtheorganiclayerovercalciumchloride.cOtherdispersingagentsincludepolyacrylicacid,gelatin,methylcellulose,zincoxide,andkaolin.dTherearemanypossiblereagentcombinationsforsuchpolymersandthestyrene/divinylbenzeneratiomustbetailoredtosuitindividualneeds[benzoylperoxideisoftenusedasaninitiatorforsus-pensionpolymerizations,see,e.g.Ref.1(e)].Oftensurfaceareaisimportantparticularlyifchromato-graphicusesareintended;insuchcircumstancesasmallvolumeofaporogenicsolventcanbeaddedtothemixture.InadditionalexperimentsinRef.29,forexample,themonomerandinitiatoraredis-solvedinamixtureofdioctylphthalateandn-decane(77:23v/v,4.5–7.5mL)beforebeingplacedinthereactionflask.Theresultantmaterialhasamuchgreatersurfacearea.Asanalternativetosuspensionpolymerization,emulsionpolymerizationoffersanumberofpotentialadvantages.Whilesuperficiallysimilar,thereare65 N.Aragragetal.twoimportantdifferences:(i)theinitiatoriswatersoluble,andsonotpresentinthemonomerphase;and(ii)theadditionofasurfactant(orsoap)stabilizesthemonomerphaseandpreventsagglomeration,thustheneedforglassypolymersiseliminated.*Theprocessisrathercomplex,butitisclearthatpolymerizationoccurslargelyinthemicellesgeneratedbythesoap.Becausethereislikelytobeonlyasingleradicalineachmicelle,bimoleculartermina-tionisunlikelyandextremelyhighmolecularweightsmaybeobtained(oftenachain-transferagentisaddedtomoderatethis).Thisprocessalsoservestogiverathernarrowpolydispersityandproduceseven-sizedsphericalparticles.Emulsionpolymerizationcanbeusedtogeneratepolystyrenemicrospheresofuptoabout1mindiameterinaconventionalsystem.Largeruniformparticlesarebestproducedinalow-gravityenvironment,thus,forexample,particleswith10mdiameterwereproducedonthemaidenflightoftheill-fatedspaceshuttleChallenger.30Protocol7.Emulsionpolymerizationofstyrene31Caution!Carryoutallproceduresinawell-ventilatedfume-hood,wearappro-priatedisposablegloves,alab-coat,andsafetyglasses.Allvacuum-lineworkshouldbeperformedwhilestandingbehindaprotectivePerspexscreen.Neveruseflat-bottomedflaskswithrotaryevaporators.Equipment●Dualmanifold(nitrogen/vacuum)●Resinkettle●Sourceofdrynitrogen●Condenser●Oil-bath●Hotplate●Apparatusforfiltrationunderreducedpressure:●MechanicalstirrerBuchnerflask,sintered-glassfunnel,andwateraspirator●NitrogeninletMaterials●Styrene,50mL,437mmolflammable,irritatingtoeyesandrespiratorysystem●Magnesiumsulfatedonotbreathdust,avoidcontactwithskinandeyes●Sodiumdodecylsulfate,1.0gharmfulifswallowedorinhaled,causesirritationtoskin,eyes,andrespiratorytract,maycauseallergicskinorrespiratoryreaction●Potassiumpersulfate,0.05g,0.2mmolirritant,harmful,avoidcontactwithskinandeyes,strongoxidizingagent●Aluminiumsulfatesolution,ca.100mL,5%w/vMethod1.Thestyreneisfreedofinhibitorsbyshakingwithsodiumhydroxideinasep-aratingfunnel.Itisthendriedwithmagnesiumsulfate.aDeionizedwaterispurgedwithinertgasforanhourpriortotheexperiment.*Famously,emulsionpolymerizationwasutilizedtoformstyrene–butadienesyntheticrubberduringtheSecondWorldWar[theMutualrecipeconsistsof(byweight)26%butadiene,ca.9%styrene,ca.63%water,ca.1.7%soap,0.17%dedecanethiol(addedasachain-transferagent)and0.1%potassiumpersulfateinitiator].66 2:Generalproceduresinchain-growthpolymerization2.Aresinkettleisequippedwithamechanicalstirrer,condenser,nitrogeninlet,andwater(100mL)isplacedintheflask.Thenstyrene(50mL,437mmol),potassiumpersulfate(0.05g,0.2mmol)areadded.Nitrogenisthenbubbledintothesolutionviaagasinlettube.3.Afterabout30min,thegasinletisremovedandthesystemplacedunderablanketofinertgasusingthedoublemanifoldandthesodiumdodecylsulfate(1.0g)isadded.Themechanicalstirreristhenstartedandvigorousstirringismaintained.Thesolutionisheatedto50Cfor2–4h.b4.Thepolymerlatexproducedisprecipitatedbyaddingasolutionofalu-miniumsulfateandboiling.Thepolystyreneisthenfiltered,washedwithwater,anddriedinthevacuumovenat55Cfor24h.aGiventhatthisexperimentisperformedinanaqueousenvironment,furtherdrying(by,e.g.distilla-tionfromcalciumhydride)isunnecessary.bSorensonrecommends70Cfor2hfollowedby95Cfor2h;SandlerandKarorecommend50Cfor2h.3.AnionicpolymerizationAlthoughthemechanismisachain-growthprocess,asforfree-radicalpoly-merizationabove,anionicpolymerizationexhibitsmarkeddifferencesintermsofcontrolofstructure,tacticity,andmolecularweight.Asthenameimplies,initiationandpropagation,proceedviaanionicintermediatesandconsequentlymonomerswhichbestundergosuchpolymerizationsarethosethatcanstabi-lizeanegativecharge.Monomersthatmaybepolymerizedthiswayinclude,styrene,methacrylate,acrylateesters,andbutadiene.Thecyanoacrylateesters,whichbyvirtueoftwopowerfulelectron-withdrawinggroupsareextremelyreactivetoveryweaknucleophiles,havefoundcommercialexploitationasadhesives.Whileanionicpolymerizationhasarelativelylonghistory32itistheworkofSzwarc,33whichisprobablythemostinfluentialinthisregard,inpar-ticularlyhisdevelopmentof‘livingpolymers’,whichmadethedevelopmentofmuchgreatercontrolofpolymerstructurespossible.Thisisofcoursebestillustratedbytheformationofblockcopolymers.Whenasolutionofstyreneispolymerizedwithbutyllithium(Protocol8)theorange-redcolourofthestyrylanionpersistsevenwhenallthemonomerisconsumed.Atthisstageasolutioncontaininganothermonomer,forexample,methylmethacrylate,canbeaddedandthepolymerizationwillresume.*Thus,apolymerwithwell-definedblocksofdifferentchemicalstructurescanbeformed.Suchblockcopolymershaveratherdifferentpropertiesfromtherandomcopolymersthatcanbeformedwiththefree-radicalmethodology(Protocol3).Oneofthemost*Itshouldbenotedthatsuchreactionscanonlyoccuriftheanionformedinthefirststageissuffi-cientlynucleophillictoinitiatepolymerizationofthesecondmonomer;forexample,subsequentadditionofstyrenetoamethacrylateterminatedanioncannotbeachieved.Forinstance,anequimolarmixtureofstyreneandmethylmethacrylateproducesalmostpurepoly(methylmethacrylate).34Infactitisgenerallythecasethatmethylmethacrylateandrelatedsystemscannotcopolymerizewithnon-polarmonomers.3567 N.Aragragetal.importantpropertiesofblockcopolymersisthetendencytophaseseparateatamolecularlevel;forexample,inastyrene–butadiene–styreneblockcopolymerthesoftbutadienesegmentsphaseseparatefromtherigidstyreneblocks.Suchmaterialbehaveslikeacross-linkedrubber.Onheating,thecross-linksareeffectivelyremovedwhenthestyreneblocksbecomefluid.Thermoplasticelastomershaveachievedconsiderablecommercialsuccess.Anionicpolymerizationishighlydemandingintermsofsolventpurityandparticularlywithrespecttotheneedforacompletelywater-freeenvironment.Inthisrespect,thebestresultsareconductedusingvacuum-linemethodology.Suchtechniquesmayinvolve,forexample,preparingreagentsonthevacuumlineinsitu;flame-sealingglasswareandtheuseofbreakseal-typeconnectors.Reference2providesadetailedaccountofhowsuchmethodologycanbeusedtoformanumberofcontrolledstructures.Itis,however,possibletoproducepolymerssuccessfullymakinguseoftheprocedurescommonlyemployedbyorganicchemistsforworkinginaninertatmosphere,thesetechniquesinclude,forexample,theuseofsyringesandseptatoaddair-sensitivereagents.Theprotocolsthatfollowfocuslargelyonthesetechniques.3.1ProvidinganinertenvironmentThefollowingproceduresallrelatetoanionicpolymerizations,whichmustbeperformedinaninertenvironment.Inmostcases,bothwaterandoxygenwillreactwiththeanionicpropagatingchainandmustthereforeberemoved.Although,asstatedabovesuchenvironmentsarebestprovidedusingvacuum-linetechniques,perfectlyacceptableresultsmaybeobtainedbyusingthetypesofproceduresfamiliartoallorganicchemistswhouseair-sensitivereagents,equipmentpre-driedandconnectedtothedoublemanifold,reagentstransferredusingsyringesintoflasksfittedwithsepta,etc.Thereareanumberofexcellentaccountsofsuchproceduresandalltheprotocolsusedinthissectionhavedrawnonthese.17,34–36Air-sensitivereagentsmaybesynthesizedinsituifrequired,butthemorecommonones,particularlythebutyllithiumsaresoldasstocksolutionsinasuitableinertsolventsuchashexane.Manychemicalcompaniesprovidesuchcompoundsinspeciallydesignedcontainerswhichmaketransferofthereagentrelativelystraightforward;IntheAldrichSure/Seal™system,34,35forexample,thereagentbottlehasacrowncapwithasmallholeinitlinedwithaTeflon®-backedelastomer;thisallowsasyringeneedletobeinsertedthroughtheliner.Onwithdrawingtheneedlethelinermayself-seal,butevenifitdoesnotthereisasimilarTeflon®elastomerlinerintheBakelitecap,whichprovidesanaddi-tionalseal.Suchmaterialscanhaveparticularlylongshelf-lives,particularlyiftheyarestoredat0C.*Inspiteofthis,lengthystorageofalkyllithium,forexample,isnotadvised,andthus,itmaybefalseeconomytopurchaselarger*AnimprovedsystemknownastheOxfordSure/SealValvecap,providedforusewithSure/Sealbot-tlesisreportedtogiveevengreatershelf-lifeforthereagent.68 2:Generalproceduresinchain-growthpolymerization(e.g.800mL)bottleswhenonlysmallquantitiesareusedtoinitiatepolymer-izationunlessthefrequencyofusagemeritsit.Disposaloflargequantitiesoforganometallicreagentisparticularlyproblematicandshouldonlybedonewithreferencetothetechnicalguidelines.*Thepossibilityofdecomposition,howeverslow,makesitimportantthattheactivityofthereagentisdeterminedbeforeuse.Thisisparticularlysointhecaseofanionicpolymerizationwherethemolecularweightisexpectedtobecloselydefinedbytheinitiatorconcen-trationbyasindicatedbyEqn(2),wherexnisthenumberaveragedegreeofpolymerizationand[M]and[I]relatetotheconcentrationsofmonomerandinitiator,respectively.Anumberofmethodsareavailablefordeterminingtheactivityoforganometallicsandinanearliervolumeinthisseries,Taylor37hasprovideddetailedexperimentalproceduresforthreesuchmethodsasfollows:1.Thedoubletitrationprocedure.38HerethetotalbaseconcentrationisdeterminedbyquenchingwithwaterandtitratingwithHCl.Second,thenon-organometallicbaseisdeterminedbydestroyingtheorganometallicwithanalkylhalide(generally1,2-dibromoethane)priortoquenchingandtitratingtodeterminetheconcentrationofbase.2.Charge-transfertitration.39Herethecolouredcharge-transfercomplexformedbetweenorganometallicsandcertainheterocycliccompoundsisusedasanindicatortodeterminetheend-pointofatitrationwithbutanol.3.Formationofcoloureddianions.402,5-Dimethoxybenzylalcohol,diphenylaceticacid,and1-pyreneaceticacid(3,Scheme10)areamongstanumberofcompoundsthatformcoloureddianionsonreactionwithorganolithiumcompounds.Theorganometallicreagentcanbetitrateddirectlyintoaflaskcontainingtheindicator,theend-pointbeingtheonsetofapermanentcolourduetotheinitialformationofthedianion.ApparentlythisprocedurewillalsoworkwithGrignardreagentsbuttheresultislessaccurate.37[M]xn(2)[I]O+OLi–CCOHOLi>1equivalentBuLi34Scheme10Reactionof1-pyreneaceticacidwithbutyllithiumtoformacoloureddianion.*Thepracticeofventingthebottlebyplacingasyringeneedlethroughthesealandleavinginthefumehoodisnotrecommendedexceptwithbottlesinwhichonlytracesofthereagentremain.69 N.Aragragetal.ThelatterofthethreeproceduresaboveisparticularlyconvenientandabriefdescriptionoftheexperimentalprocedureinvolvedisgiveninProtocol9.Polymerizationsthatuseorganometallicinitiatorsrequirecarefulprepara-tionandplanning,inparticulartoensurethatallglasswaresolventsandreagentsarecompletelydry.Glasswareisdriedinanovenfor24hpriortouseandtheapparatusissetupwhilehotandconnectedtoasourceofdrynitrogenorargon[usuallyviaadoublemanifoldsystem(seeearlier),butoccasionallyviaaballooncontaininginertgasconnectedtothetopoftheapparatus].Syringesandsyringeneedles,afterdryingintheoven,arecooledandstoredinadesiccatorunderinertgas,soastobereadywhenrequired.Solvents,monomers,andotherreagentsmustbedriedtothehighestpossiblespecificationsforthebestresults.Thisoftenmeansmultiplepurificationstepsandusingthesamemethodologyasusedforairandmoisturesensitivematerials.Ifpossiblethesereagentsshouldbedistilleddirectlyintothe(air-tight)polymerizationvesselafterthefinaldryingstage;ifthisisnotpossiblethenreagenttransfershouldbeperformedusingasyringeorcannularasdescribedbelow.Transferoftheorganometallicreagenttothereactionflaskisusuallyachievedviaaside-armfittedwithaseptumcapusingasyringe,orforlargerquantitiesofreagent(andinsomecasesformorereactivereagents),adouble-headedneedlewithoneendinthereagentbottle,andoneintheflask,inaprocessknownascannulation.Inthislattercase,transferisachievedusingapressureofinertgasappliedtothereagentbottle.Inthefor-mer,thereagentbottleispressurizedwithinertgasasshowninFigure2.3,ArgonornitrogenPlastictubingSyringewithneedle-lockLuerNeedleNeedleTostandSupportthebottleusingaringorclampFig.2.3Removalofanorganometallicreagentfromareagentbottleusingasyringe.70 2:Generalproceduresinchain-growthpolymerizationbeforethesyringeneedleisinsertedthroughthecap(thedrysyringeisflushedwithdrynitrogenimmediatelybeforeuse).Protocol8.Polymerizationofstyreneinitiatedbysec-butyllithium(Scheme11)Caution!Carryoutallproceduresinawell-ventilatedfume-hood,wearappro-priatedisposablegloves,alab-coat,andsafetyglasses.Allvacuum-lineworkshouldbeperformedwhilestandingbehindaprotectivePerspexscreen.Neveruseflat-bottomedflaskswithrotaryevaporators.BuLiTHFScheme11Polymerizationofstyreneinitiatedbysec-butyllithium.Equipment●Dualmanifold(nitrogen/vacuum)●Sourceofdrynitrogen●Two-neckedround-bottomedflask(250mL)●Syringe(1mL)●Nitrogengasinlet●Syringe(50mL)●Magneticstirrer●Rubberseptum●Teflon-coatedmagneticstirrerbar●Beaker(500mL)●Vacuumoven●Erlenmeyerflasks(250mL)●Apparatusforfiltrationunderreducedpressure:●RotaryevaporatorBuchnerflask,sintered-glassfunnel,and●Single-neckedround-bottomedflaskforusewateraspiratorwithrotaryevaporatorMaterials●Styrene,10mL,87mmolflammable,irritatingtoeyesandrespiratorysystem●sec-Butyllithium,1.3M,0.5mL,ca.0.65mmolhighlyflammable,reactsviolentlywithwater,spontaneouslyflammableinair,causesburns,harmfulbyinhalation●THF,50mLhighlyflammable,mayformperoxides,irritatingtoeyesandrespiratorysystem●Acetoneforcoolingbathhighlyflammable●SolidCO2forcoolingbathextremelycoldsolid,vapourcancauserapidsuffocation●Propan-2-ol,2mLhighlyflammable●Dichloromethane,ca.30mLharmfulbyinhalation,potentialcarcinogen●Methanol,ca.500mLhighlyflammable,toxicbyinhalationandifswallowedMethodPreparation:Dryallglasswareinanelectricovensetat125Cfor24hpriortoreaction.Distilasuitablequantity(50mL)ofTHFintoadryreceiverflaskfittedwithaseptum,distilstyrenefromcalciumhydrideunderreducedpressureintoadryreceiverflaskfittedwithaseptum.Butyllithiumistitratedwith1-pyreneaceticacid,toobtainanapproximatevalueforitsactivity.a71 N.Aragragetal.Protocol8.Continued1.Whiletheapparatusisstillhot,setupthetwo-neckedflaskwithaseptumcapandmagneticstirrerbar.Connecttothedoublemanifoldwithagasinletadapter,evacuatetheflaskandthenfillwithnitrogen.Allowtheflasktocooltoroomtemperature.b2.Flushasyringe(50mL)withnitrogen,byinsertingtheneedleintoaseptumcapfittedtoapieceoftubingconnectedtotheinertgassupply.WithdrawtheTHF(50mL)fromthereceivingflaskandtransferintothereactionvessel.Repeattheprocedureusingthestyrene(10mL,87mmol).Coolthereactionflasktoca.70Cusingadryice/acetonemixture.3.Adrysyringeneedleisconnectedtotheinertgassupplybymeansofsomeplastictubing,withagentleflowofgaspassingthroughtheneedle,insertthetipthroughthesealonthebottleofsec-butyllithium.Flushasyringe(1mL)withnitrogen,byinsertingthisintoaseptumcapfittedtoapieceoftubingconnectedtotheinertgassupply.Insertthesecondneedlethroughthesealonthebutyllithiumandwithdrawtherequiredamountofinitiator(0.5mL,0.65mmol)asshowninFigure2.3.4.Carefullyaddthebutyllithiumtothereactionflaskbyinsertingthesyringeneedlethroughtheseptumattachedtotheside-arm.Adarkredcolourationduetothepresenceofthestyrylanionwillbeproduced.Stirthepolymeriza-tionmixturefor4h.5.After4htheviscoussolutionshouldremainred,quenchthereactionbyaddingpropan-2-ol(2mL)viatheseptum(caution!).Thereactioncanbethenopenedtotheatmosphere.6.Thepolystyreneisisolatedbyremovingthesolventontherotaryevaporator,dissolvingthepolymerintheminimumvolumeofdichloromethane,andthenpouringthissolutionintoabeakercontainingaqueousmethanol(1:4,ca.10volume).Furtherpurificationisachievedbyrepeateddissolutionindichloromethane,followedbyre-precipitationintomethanol;finally,thewhitesolidisdriedinavacuumovenat60C.aAdrytwo-neckedround-bottomedflaskcontainingamagneticstirringbarischargedwithdry1-pyreneaceticacid(ca.100mg,0.38mmol),andfittedwitharubberseptumandanitrogeninlet.TheflaskisevacuatedthenflushedwithnitrogenusingthedoublemanifoldanddryTHF(10mL)isaddedandtheresultingsolutionstirred.Agraduatedsyringe(1mL)ischargedwiththeorganolithiumreagentandthisisaddeddrop-wisetothesolutionofpyreneaceticacidoverseveralminutesnotingthevolumeaddedwhentheredcolourofthedianionpersists.bAlternatively,thehotsystemcanbeevacuatedandthenflushedwithnitrogenseveraltimestoensurecompletereplacementoftheairwithdryinertgas.Althoughthepolymerizationwithbutyllithiumisaneffectivewayofgenerat-ingpolymer,bothinitiationandpropagationinionicpolymerizationsarerathercomplexprocessesandgovernedbyfactorssuchassolvationandbind-ingtocounterions.Forthepolymerizationofmethacrylates,aparticularproblemwithbutyllithiumisthereactivitytowardsthecarbonylgroup,for72 2:Generalproceduresinchain-growthpolymerizationthisreasonlessreactiveinitiatorssuchasdiphenylhexyllithium(Scheme12)havebeenusedwithsomesuccess.41Particularlyconvenientaresaltsbetweenlithiumandlargearomaticmoleculeswithacidichydrogens,oneofthemostcommonexamplesbeingfluorene.42Whilethiscompoundisaratherweakacid,itisofcourseconsiderablymoreacidicthanbutaneandconsequentlythesaltcanbeeasilypreparedbyreactionwithbutyllithium,thissaltcanbeusedtoinitiatethepolymerizationofmethylmethacrylateinarelativelysimpleprocedure.1(e),32Intheexamplebelowtheformationofalargelysyndiotacticpolymerisdescribed(Scheme13),thisstereochemicalcontrolisprovidedlargelybythesolventandhenceasimilarprocedureusingtolueneasthesolventwillproduceapredominantlyisotacticmaterial.BuLi–THFScheme12Reactionofbutyllithiumwith1,1-diphenylethenetoformdiphenylhexyllithium.Protocol9.Preparationofpredominantlysyndiotacticmethylmethacrylateusing9-fluorenyllithiumastheinitiator(Scheme13)Caution!Carryoutallproceduresinawell-ventilatedfume-hood,wearappro-priatedisposablegloves,alab-coat,andsafetyglasses.Allvacuum-lineworkshouldbeperformedwhilestandingbehindaprotectivePerspexscreen.MeOOBuLiMeMeO2CCH3CH3CO2Me–+LiScheme13Polymerizationofpolystyreneinitiatedwith9-fluorenyllithium.Equipment●Dualmanifold(nitrogen/vacuum)●Sourceofdrynitrogen●Two-neckedround-bottomedflask(250mL)●Syringe(1mL)●Nitrogengasinlet●Syringe(10mL)●Stirrer●Syringe(50mL)●Dryice/acetonebath●Vacuumoven73 N.Aragragetal.Protocol9.Continued●Teflon®-coatedmagneticstirrerbar●Rubberseptum●Apparatusforfiltrationunderreduced●Beaker(500mL)pressure:Buchnerflask,sintered-glass●Erlenmeyerflasks(250mL)funnel,andwateraspirator●CondenserMaterials●Fluorene,0.2g,1.2mmolavoidinhalationandcontactwithskinandeyes●Butyllithium,1.6M,0.3mL,0.5mmolhighlyflammable,reactsviolentlywithwater,spontaneouslyflammableinair,causesburns,harmfulbyinhalation●THF,50mLhighlyflammable,mayformperoxides,irritatingtoeyesandrespiratorysystem●Methylmethacrylate,10g,100mmolhighlyflammable,irritatingtorespiratorysystemandskin,maycausesensitizationbyskincontact●Acetoneforcoolingbathhighlyflammable●SolidCO2forcoolingbathextremelycoldsolid,vapourcancauserapidsuffocation●Methanol,ca.200mLhighlyflammable,toxicbyinhalationandifswallowed●Petroleumether,ca.1Lhighlyflammable●Dichloromethane,ca.30mLharmfulbyinhalation,potentialcarcinogenMethodPreparation:Drytheglasswareinanovenfor24hpriortoconstruction,allsol-ventsandmonomersshouldbedriedpriortouse(seeearlier).1.Atwo-neckedround-bottomedflask(250mL)isequippedwitharefluxcon-denser,septumcap,andmagneticstirrerbar,andconnectedtoasupplyofdryinertgasviathemanifoldsystem.Thesystemisthenevacuatedandheatedwithaflameorahotairguntoremoveanyresidualtraceofwaterandallowedtocoolundernitrogen.2.Fluorene(0.2g,1.2mmol)isthenaddedtotheflaskandtheflaskonceagainevacuatedthenpurgedwithnitrogen.DryTHFa(50mL)isthenaddedviatheseptum.Whenthefluorenehasdissolvedcompletely,n-butyllithium(0.3mL,0.5mmol)isthenaddedviatheseptum,andthemixturestirredfor1h,theorangecolourprovidinganindicationthatthereactioniscomplete.3.Thesolutionof9-fluorenyllithiumisthencooledtoca.70Cinadryice/acetonebathanddrymethylmethacrylate(10g,100mmol)bwhichhasbeenallowedtostandinthedryice/acetonebathforabout10minisaddedtothesolutionusingasyringe.Thepolymerizationisallowedtocontinueforabout5handthenthereactionisquenchedusingmethanol(10mL).4.Afterallowingtheviscoussolutiontowarmtoroomtemperature,thepolymerisprecipitatedbypouringslowlyinto500mLofpetroleumetherwithstirring.Thesolidpolymeristhencollectedanddissolvedindichloromethane,andre-precipitatedintopetrolasbefore.Theresultantpolymeristhencollectedatthepumpusingasintered-glassfunnelandwashedthoroughlywithmethanol.Finally,thepolymerisdriedfor24hinthevacuumovenat50C.ThetacticityofthepolymercanbegaugedfromNMRorIRspectroscopy.74 2:Generalproceduresinchain-growthpolymerizationaDriedwithCaHfor24handthendistilledfromsodiumwithbenzophenoneastheindicator(see2Table2.2).bMethylmethacrylateispassedthroughabasicaluminacolumndirectlyintoaround-bottomedflaskcontainingCaH2andstoredinthefridge.ThisshouldbedistilleddirectlyfromtheCaH2undervacuumpriortouse.Analternativemethodofinitiationisthroughtheuseoftheradicalanionproducedfromthereactionofsodium(orlithium)withnaphthalene.Suchradicalanionsreactwithstyrenebyelectrontransfertoformstyreneradicalanions;thesedimerizetoproduceadianion,whichinitiatespolymerizationasoutlinedinScheme14.Oneparticularfeatureofthismethodisthatpoly-merizationproceedsoutwardsfromthecentre.Subsequentreactionofthelivingchainsendswithanothersuitablemonomersystemproducesatriblockcopolymer.Thisistheprinciplebywhichstyrene–butadiene–styrenetriblockcopolymers(formedwhenbutadieneispolymerizedinthesameway,andstyreneisaddedassecondmonomer)areproducedcommercially.Thismate-rialbehavesasathermoplasticelastomer,sincetherigidstyreneblocksformcross-linksatroomtemperature;onheatingtheserigidstyreneportionssoften,allowingthematerialtoberemoulded.1(b)–Na––+–––2x––Scheme14Polymerizationofpolystyreneinitiatedwiththesodiumnaphthaleneanion.75 N.Aragragetal.Protocol10.PreparationofthesodiumnaphthaleneanionandpolymerizationofstyreneCaution!Carryoutallproceduresinawell-ventilatedfume-cupboard,wearappropriatedisposablegloves,alab-coat,andsafetyglasses.Allvacuum-lineworkshouldbeperformedwhilestandingbehindaprotectivePerspexscreen.Neveruseflat-bottomedflaskswithrotaryevaporators.Equipment●Dualmanifold(nitrogen/vacuum)●Three-neckedround-bottomedflask(250mL)●Sourceofdrynitrogen●Thermometer●Refluxcondensers●Gasbubbler●Syringe(50mL)●Mechanicaloverheadstirrer,stirrerrod,●Syringeneedleconnectedtoinertgassupplyandpaddle●Two-neckedround-bottomedflask(100mL)●Stirrer●Teflon®-coatedmagneticstirrerbar●Dryice/acetonebath●Teflon®-stirrerguider●Rubbersepta●Apparatusforfiltration,Buchnerfunnel,flask,●Vacuumovenandwaterpump●BeakersandErlenmeyerflasks(various)Materials●Naphthalene,12.8g,100mmolharmfulifswallowed,verytoxictoaquaticorganisms,maycauselong-termadverseeffectsinanaquaticenvironment●Sodiummetal,2.5g,108mmolreactsviolentlywithwaterliberatinghighlyflammablegases,causesburns●THF,100mLhighlyflammable,mayformperoxides,irritatingtoeyesandrespiratorysystem●Styrene,10mL,87mmolflammable,irritatingtoeyesandrespiratorysystem●Methanol,ca.500mLhighlyflammable,toxicbyinhalationandifswallowed●Dichloromethane,ca.30mLharmfulbyinhalation,potentialcarcinogen●Acetoneforcoolingbathhighlyflammable●SolidCO2forcoolingbathextremelycoldsolid,vapourcancauserapidsuffocation●Standardhydrochloricacidsolution(ca.0.1M)causesburns,irritatingtotherespiratorysystemMethodPreparation:Dryallglasswarebyleavinginanelectricovensetat125Cfor24hpriortoreaction.Distilasuitablequantity(50mL)ofTHFintoadryreceiverflaskfittedwithaseptum.Distilstyrenefromcalciumhydrideunderreducedpressureintoadryreceiverflaskfittedwithaseptum.Naphthaleneispurifiedbysublimationatreducedpressure.1.Whiletheapparatusisstillhot,aathree-neckedround-bottomedflask(250mL)isequippedwithanoverheadstirrer,arubberseptumthroughwhichaneedleconnectedtotheinertgassupplyisinsertedandacondensertowhichagasbubblercontainingsiliconefluidisattached.Theapparatusisthenlefttocoolwithagentlestreamofdrynitrogenflowingthroughthesystem.b2.Withthenitrogenflowingcondenserisremoved,naphthalene(12.8g,100mmol)isaddedtotheflaskandthecondenserquicklyreplaced.Thenusingadrysyringe,THF(100mL)istransferredtothereactionflask.76 2:Generalproceduresinchain-growthpolymerization3.Removeapieceofsodiumfromtheoilandcutpiecesfromthelump.Theseshouldbewashedinhexanecontainedinasmallbeaker,wipeddrywithapieceofcleanfilterpaper,weighed,andthenreplacedinthehexane.When2.5gofsodiumhasbeenobtainedthepiecesshouldbecuttoapproximatelythesizeofamatch-head(stillkeepingthesodiuminthehexaneasfaraspossible).Thepiecesofsodiumaredriedandquicklyaddedtotheflaskasinstep2.c4.Theflaskisstirredrapidlyandcooledbymeansofanice-bathsuchthatthetemperaturedoesnotexceedabout30C,thereactionmixtureisthenstirredfor2h.5.Asmallsample(3mL)isremovedfromtheflaskviatheseptumusingasyringe,anddroppedintomethanol(5mL)thissolutionisthenaddedtowater(10mL)andtitratedusingdilutehydrochloricacid(0.1M).d6.Thepre-driedtwo-neckedround-bottomedflask(100mL)isequippedwitharefluxcondenser,septumcap,andTeflon®-coatedmagneticstirrer,whilehota,bandconnectedtoasupplyofdryinertgasviathemanifoldsystem.Thesystemisthenevacuatedandflushedwithnitrogenseveraltimesandallowedtocoolundernitrogen.7.Usingasyringeneedle,dryTHF(50mL)isaddedtotheflask.Thenasmallquantityofthesodiumnaphthalenecatalystisaddeduntilthegreencolourpersists.eTherequiredamountofcatalystsolutionisthenadded(e.g.0.4mLseenoted)usingasyringe.Thesolutioniscooledtoca.78Cusingadryice/acetonebathandstirred.Styrene(10mL,87mmol)isthenaddedusingasyringe.Thesolutionturnsfromgreentoredincolour.8.Thepolymerizationisallowedtoproceedforca.2h,whereuponthereactioniswarmedtoroomtemperature.Thereactionisquenchedbytheadditionofmethanol(1mL),andthepolymerisisolatedbyprecipitationintomethanolasdetailedabove(Protocol8,Step6),anddriedinthevacuumovenat60C.aCare—wearheat-resistantgloves.bTheapparatusshouldbeusedimmediatelyonreachingroomtemperature;ifitisleftforanyperiodoftimeitcanbeflamed(infactahot-airgunisaconvenientheatsourceforthispurpose)underdrynitrogenandallowedtorecool.cThereactionbeginsalmostimmediatelyandadarkgreencolourduetothenaphthaleneradicalanionisobserved.dItisimportanttoobtainareasonableideaoftheinitiatorconcentrationsothatonecaneffectivelygaugetherelativequantitiesofstyreneandinitiatortoformthedesiredmolecularweightpolymerinthenextstage.eAfewdrops.Thiseffectivelytitratesthequantityofwaterpresentinthesolventandglassware.Blockcopolymershaveanumberofinterestingproperties,inparticular,whentheyaremadeupofincompatibleunits.Suchmaterialsshowextremelyinterestingmorphologies,42asitispossibletoobtainphaseseparation,witheachunitformingseparatedomains.Thepotentialforself-assemblyofsuchunitsisnowattractingconsiderableinterest,particularlyintheareaofpho-toniccrystals.43Asthefollowingproceduresshow,themethodsbywhich77 N.Aragragetal.blockcopolymerscanbeformedaresimilartothosedescribedabove,althoughfatigueprocessesmaybemoreimportantindeterminingthestruc-tureofthefinalpolymer,anditisrecommendedthatthepolymeristhor-oughlyanalysedby,forexample,gelpermeationchromatography(GPC)ateachstageofthepolymerizationprocess,inordertoestablishtheeffective-nessofthemethodology.Itshouldalsobenotedthatalthoughgoodqualitymaterialscanbepreparedusingthemethodsbelow,high-vacuumtechniquessuchasthosedescribedinRef.2giveoutstandingresultsintermsofmolecu-larweightdistribution,andfacilitatetheformationofquitecomplexpolymergeometries.Protocol11.Ablockcopolymerofstyreneandisoprene(Scheme15)Caution!Carryoutallproceduresinawell-ventilatedfume-cupboard,wearappropriatedisposablegloves,alab-coat,andsafetyglasses.Allvacuum-lineworkshouldbeperformedwhilestandingbehindaprotectivePerspexscreen.Neveruseflat-bottomedflaskswithrotaryevaporators.–BuBuLiTHFn–BuBunnm(andotherisomers)Scheme15Ablockcopolymerofstyreneandisoprene.Equipment●Dualmanifold(nitrogen/vacuum)●Teflon®-coatedmagneticstirrerbar●Sourceofdrynitrogen●Hotplatestirrer●Two-neckedround-bottomedflask(100mL)(2)●10cmlongnarrowboreneedle(2)●Gas-tightsyringe(10mL)●20cmlongnarrowboreneedle●Gas-tightsyringe(50mL)●Single-neckedround-bottomedflask(100mL)●Gas-tightsyringe(2mL)●BeakersandErlenmeyerflasks(various)●Two-neckedround-bottomedflask(250mL)●Rubbersepta●Dryice-bath●Dryice/acetonebath●Rotaryevaporator●Vacuumoven●Apparatusforfiltration,Buchnerfunnel,●Vacuumdesiccatorflask,andwaterpump78 2:Generalproceduresinchain-growthpolymerizationMaterials●Styrene,ca.5mL,44mmolflammable,harmfulbyinhalation●Isoprene,ca.5mL,50mmolextremelyflammableverytoxictoaquaticorganisms,maycauselong-termadverseeffectsinanaquaticenvironment●sec-Butyllithium1.3M,0.5mL,5.85mmolhighlyflammable,reactsviolentlywithwater,spontaneouslyflammableinair,causesburns,harmfulbyinhalation●THF,50mLhighlyflammable,mayformperoxides,irritatingtoeyesandrespiratorysystem●Acetoneforcoolingbathhighlyflammable●SolidCO2forcoolingbathextremelycoldsolid,vapourcancauserapidsuffocation●Methanol,ca.150mLtoxic,highlyflammable●Dichloromethane,ca.30mLharmfulbyinhalationpotentialcarcinogenMethodPreparation:Dryallglasswarebyleavinginanelectricovensetat125Cfor24hpriortoreaction.Distilasuitablequantity(50mL)ofTHFintoadryreceiverflaskfittedwithaseptum.Styrenemaybedistilledfromcalciumhydrideunderreducedpressureintoadryreceiverflaskfittedwithaseptumandthenpurgedwithinertgas.Isoprenemaybedistilledonagaslineovern-butyllithiumat0CbeforebeingdistilledintoadryreceiverflaskandpurgedwithinertgasasperRef.2.1.Whiletheapparatusisstillhot,atwo-neckedround-bottomedflask(250mL)aisequippedwithaTeflon-coatedmagneticstirrerbar,arubberseptumononeneckwhilstthesecondneckisconnectedtothedoublemanifold.2.Thepolymerizationflaskisthenevacuatedandthensubsequentlypurgedwithinertgas.3.Approximately50mLofdryTHFisthentransferredviasyringetotheflask.4.Therequiredvolumeofstyrene(e.g.5mL,44mmol)isthenaddedtotheTHFandthemixturestirred.bThemixtureisthencooleddowntoca.70Cwithadryice/acetonebath.5.Therequiredamountofinitiator(sec-butyllithium0.05mL,0.65mmol)isthenaddedtothepolymerizationtubewhilststirringvigorously.cThesolu-tionshouldturnredincolour.6.Allowthesolutiontowarmtoroomtemperature,andstirfor30min.Thencooldownthecontentoftheflasktoca.70C.d7.Oncetheflaskiscool,isoprene(5mL,50mmol)isaddedandthepolymer-izationmixtureisonceagainwarmedtoroomtemperatureandstirredforafurther30min.8.Thereactionisquenchedbyinjectingdrymethanol(1mL,caution!)andopeningthesystemtoair.9.Thesolutionisthentransferredtoasingle-neckedround-bottomedflask(100mL)andallthesolventisremovedusingarotaryevaporator.10.Thepolymerispurifiedbyredissolvingtheresidueinaminimumamountofdichloromethaneandprecipitationintoice-coldmethanol.Thesolutionisdecantedtoleaveawhiteprecipitateandtheremainingsolventremovedby79 N.Aragragetal.Protocol11.Continuedfiltrationatthewaterpump.Thisprocedureisthenrepeatedtwiceandthepolymerdriedusingavacuumdesiccatororvacuumoven.eaAsanalternative,atwo-neckedSchlenktubecanbeused(seeChapter3,Figure3.4).bAtthisstagethemixturecanbedegasedusingthefreeze–pump–thaw–purgemethod(outlinedinProtocol1).cCaremustbetakentoensurethattheinitiatorisinjecteddirectlyintothecold,stirringsolution.Initiatorthattouchesthesidesofthepolymerizationtubefirstmaybeliabletoreactwithstyreneresidue,thusnotinitiatingthesolutioneffectively.dAtthisstageanaliquotmayberemovedforanalysistocheckthepercentageconversionofmonomertopolymer.eThepreciseprocedureforpurificationwillbedeterminedbythecompositionofthecopolymer,ifthematerialissoftatroomtemperaturethenfiltrationwillnotbepossibleanddrainingthemajorityofthenon-solventoffwillbesufficient.Thismethodforthepreparationofpoly(styrene-b-tBuA)isbasedupontheproceduredescribedbyJerômeetal.44Teyssieandco-workers45,46demonstratedthattheadditionofLiClcanbeeffectiveinthelivinganionicpolymerizationoftheacrylicmonomers,becausea-typecomplex47isformedbetweenLiClandthegrowingsite.Thiscomplexpreventstheoccurrenceofside-reactionsatthepropagatingsite,thusmarkedlynarrowingthemolecularweightdistribution.Protocol12.Synthesisofpoly(styrene-b-tBuA)diblockcopolymerCaution!Carryoutallproceduresinawell-ventilatedfume-hood,wearappro-priatedisposablegloves,alab-coat,andsafetyglasses.Allvacuum-lineworkshouldbeperformedwhilestandingbehindaprotectivePerspexscreen.Neveruseflat-bottomedflaskswithrotaryevaporators.Equipment●Dualmanifold(nitrogen/vacuum)●Sourceofdrynitrogen●Two-neckedround-bottomedflask(100and50mL)●BeakersandErlenmeyerflasks(various)●Gas-tightsyringe(10mL)●Hotplatestirrer●Gas-tightsyringe(50mL)●Nitrogengasinlet●Gas-tightsyringe(2mL)●Syringeneedles(various)●Magneticstirrerbar●Rubbersepta●Dryice-bath●Apparatusforfiltration,Buchnerfunnel,●Rotaryevaporatorflask,andwaterpump●VacuumovenMaterials●Freshlydistilledstyrene,a6.6mL,58mmolflammable,harmfulbyinhalation●Freshlydistilledtert-butylacrylate,bhighlyflammable,irritatingtoeyesskinandrespiratory4.57mL,31mmolsystem.verytoxictoaquaticorganisms,maycauselong-termadverseeffectsinanaquaticenvironment●Lithiumchloride,0.02g,0.5mmolharmfulifswallowed,irritatingtoeyes,skin,andrespiratorysystem●-Methylstyrene,0.05mL,0.38mmolflammableirritant80 2:Generalproceduresinchain-growthpolymerization●sec-Butyllithium,1.3M,0.5mL,0.65mmolhighlyflammable,reactsviolentlywithwater,spontaneouslyflammableinair,causesburns,harmfulbyinhalation●THF50mLhighlyflammable,mayformperoxides,irritatingtoeyesandrespiratorysystem●Acetoneforcoolingbathhighlyflammable●SolidCO2forcoolingbathextremelycoldsolid,vapourcancauserapidsuffocation●Methanol,ca.150mLtoxic,highlyflammableMethodInitiatorpreparationThemonofunctionalinitiator[(-methylstyryl)-lithium(-MeStLi)]ispreparedbyreactingsec-BuLiwithaslightmolarexcessof-MeStatroomtemperatureindryTHF.1.Flushnitrogenthroughapre-driedtwo-neckedround-bottomedflask(50mL)equippedwithamagneticstirrerbarandsealedwithtwosepta.2.FreshlydistilledTHF(10mL)isaddeddirectlyviaagas-tightsyringethroughtheside-armoftheflask.3.sec-Butyllithium1.3M(0.5mL,0.65mmol)isthenaddedatroomtempera-turedirectlyviaagas-tightsyringethroughtheside-armoftheflask.4.-Methylstyrene(0.05mL,0.38mmol)isthenaddedtothestirredmixture,atroomtemperature,viaagas-tightsyringethroughtheside-armoftheflask.Thecolourofthesolutionshouldturnandstaydarkred.cPolymerizationreaction5.Intoadrytwo-necked,round-bottomedflask(100mL)equippedwithamag-neticstirrerbar,aseptumcap,andanitrogengasinletattachedtothedoublemanifold,addlithiumchloride(0.02g,0.5mmol)underaflowofnitrogen.FreshlydistilledTHF(50mL)isaddeddirectlyviaagas-tightsyringethroughtheside-armoftheflask.6.Theinitiatorsolutionistransferredintotheflaskbymeansofasyringe.7.Cooldownthemixturetoca.78Cusingadryice/acetonebathandaddfreshlydistilledstyrene(6.6mL,57mmol).Thesolutionshouldturnaredcolour.8.Allowthesolutiontowarmtoroomtemperatureandstirfor30min.Cooldownthecontentoftheflasktoca.78Candthenaddfreshlydistilledtert-butylacrylate,(4.57mL,31mmol).Stirthemixtureforafurther30minatroomtemperature.9.Methanol(5mL)isthenaddedtothepolymerizationflaskandthecontentsoftheflaskisstirredforafurther30min.10.Thesolutionisthentransferredtoasingle-neckedround-bottomedflask(250mL)andtheTHFremovedontherotaryevaporator.Thecrudemixtureisthendissolvedinaminimumamountofacetoneandthedissolvedmater-ialprecipitatedintoasolutionof7:3methanol:water.81 N.Aragragetal.Protocol12.Continued11.Theprecipitatedmaterialiscollected,dissolveditinacetoneandprecipi-tateditonceagain.Thedissolution/precipitationstepmustbedoneatleastthreetimestoensuretheeliminationofanytracesofunreactedinitiator.12.Theprecipitatedpolymer(whitesolid)isfilteredusingaBuchnerfilteranddriedundervacuum.aStyreneshouldbewashedwith10%NaOH(aq.),driedoverNaSOandthenfilteredinorderto24removeanystabilizer.Theresultantpre-driedstyreneshouldthenbedirectlydistilledcarefullyunderhighvacuumandusedimmediately.bMethacrylatemonomersshouldbepassedthroughabasicaluminacolumndirectlyintoaSchlenkflaskcontainingCaH2andstoredinthefridge.ThemonomershouldbedirectlydistilledcarefullyfromtheCaH2underhighvacuumandusedimmediately.cLossofcoloursuggeststhattracesofwaterarepresent,ifthecolourdisappearsrapidlythenthesys-temshouldbeinvestigatedforsourcesofadventitiouswater.Theseshouldberemovedandtheprocedurerepeated.Theblockcopolymerproducedintheaboveprotocolcanbehydrolysedtoproduceanacrylicacidcontainingsystem.Suchblockcopolymersarenotaccessibledirectlybyanionicpolymerizationduetothereactivityoftheacidichydrogentowardsbasicinitiators.Themethodforthepreparationofpoly(styrene-b-acrylicacid)givenbelowisbasedupontheproceduredescribedbyZangetal.48Protocol13.HydrolysisofPoly(styrene-b-tBuA)DiblockCopolymerCaution!Carryoutallproceduresinawell-ventilatedfume-hood,wearappro-priatedisposablegloves,alab-coat,andsafetyglasses.Allvacuum-lineworkshouldbeperformedwhilestandingbehindaprotectivePerspexscreen.Neveruseflat-bottomedflaskswithrotaryevaporators.Equipment●Dualmanifold(nitrogen/vacuum)●Sourceofdrynitrogen●Two-neckedround-bottomedflask(25mL)●Nitrogen-gasinlet●Single-neckedround-bottomedflask(100mL)●Condenser●Gas-tightsyringe(10mL)●Rubberseptum●Gas-tightsyringe(2mL)●10cmlongnarrowboreneedle(2)●Hotplatestirrerandtemperaturecontroller●Oil-bath●Vacuumoven●RotaryevaporatorMaterials●Hydrochloricacidcausesburns,irritant●1,4-Dioxane5mLhighlyflammable,irritatingtoeyesskinandrespiratorysystem,limitedevidenceofcarcinogeniceffects,repeatedexposuremaycauseskindrynessorcrackingMethod1.Intoadrytwo-necked,round-bottomedflask(25mL),equippedwithamag-neticstirrerbararubberseptumandacondenserfittedwithanitrogengas82 2:Generalproceduresinchain-growthpolymerizationinlet,isaddedtheblockcopolymerpoly(styrene-b-tBuA)(3g)and1,4-dioxane(5mL).Thegasinletisattachedtothedoublemanifoldsystemandtheflaskplacedunderanatmosphereofnitrogen(seeProtocol8).2.Theflaskisplacedintheoil-bathmountedonthehotplatestirrerandthethermostatsetto65C.Thepolymeristhenstirreduntilitdissolves.3.Anexcessofhydrochloricacid(theamountdependsonthenumberofacry-lateblockswithinthepolymer)isthenaddedslowlyviaagas-tightsyringethroughtheside-armoftheflask.4.Themixtureisthenstirredfor6h.Finally,thesolutionistransferredtoasingle-neckedround-bottomedflask(100mL)andthesolventremovedontherotaryevaporator.Thepolymerisdriedinthevacuumovenat40C.4.Ring-openingpolymerizationsinitiatedbyanionicreagentsThering-openingpolymerizationsofheterocycliccompoundsareimportant,notleastbecauseofthenumberofcommercialpolymersproducedinthisway.Thebest-knownexamplesincludeNylon6,whichisproducedfrom-caprolactamasshowninScheme16;poly(ethyleneoxide)producedbyring-openingpolymerizationofethyleneoxide(oroxirane),aroutetowhichisdescribedinProtocol14(Scheme17),andpoly(dimethylsiloxane)whichisformedfromacyclictetramerproducedonhydrolysisofdimethyl-silyldichlorideinawaysimilartothatdescribedinProtocol15.OONHAcidorbaseNHScheme16SynthesisofNylon6from-caprolactam.Thefinalproductsfromring-openingpolymerizationsoftenresemblepoly-mersthatmightbeproducedbystep-growthprocesses.However,amoredetailedconsiderationinmanycasesleadstotheconclusionthatsuchpolymer-izationsarechain-growthprocessesalthoughmoresubtlefactorsmayneedtobeconsidered,includingsomeexampleswherethering-openingstagemerelyservestogenerateadifunctionalmonomerwhichthenpolymerizesbystepgrowth.49Thefirstexample,namelythepolymerizationofethyleneoxide,illustrateshowever,thatsuchdetailsaside,manyofthetechniquesdescribedintheprevioussectionareappropriateforring-openingpolymerizations.Aswiththeanionicpolymerizations,boththepropagatingchain,andthecounterionmustbeconsideredifeffectivematerialsaretobeproduced.Thus,althoughnucleophilicattackisanimportantpartoftheprocess,coordinationofthe83 N.Aragragetal.resultingalkoxideanioncandeterminethesuccessofthepolymerization.Forexample,ethyleneoxideisnotpolymerizedbybutyllithium,althoughinitiationoccurs.Thisisaconsequenceoftightbindingbetweenthelithiumionandthealkoxideionproducedintheinitiationprocess.Morerecently,ithasbeenshownthatpolymerizationofethyleneoxidewithlithiumcounterionscanbeachievedinthepresenceofastrongLewisbase,whichactstodisruptthelithium/alkoxideinteractions.50,51Potassiumsaltsarelessproblematic,andthesituationisbetterstillifthemetalioniscomplexedwithacryptand,inthiscaseKryptofix®222.Thisisthecaseinthefollowingexample,whichisbasedonanexcellentaccountbyEisenbach52andBoileauetal.53*Protocol14.Ring-openingpolymerizationofethyleneoxideusingananionicinitiator(Scheme17)Caution!Carryoutallproceduresinawell-ventilatedfume-hood,wearappro-priatedisposablegloves,alab-coat,andsafetyglasses.Allvacuum-lineworkshouldbeperformedwhilestandingbehindaprotectivePerspexscreen.Neveruseflat-bottomedflaskswithrotaryevaporators.KCHCH+–22–2KTHFHCH2CHH+222NNH–+KOO–+–+NCH2CH2OKNCH2CH2OCH2CH2OKN–+KScheme17Anionicring-openingpolymerizationofethyleneoxide.Equipment●Dualmanifold(nitrogen/vacuum)●Sourceofdryargon●Two-neckedround-bottomedflask(50mL2)●Gas-tightsyringesandneedles(25,10,and1mL)●Round-bottomedflask(100mL)fitted●Gas-inlettubeswithside-armandtaps●Dewarcontainingliquidnitrogen●Polymerizationtubes●Lab-jack*Itshouldbenotedthatethyleneoxidecanalsobepolymerizedbycationicinitiatingsystemsandawiderangeofotheranionicinitiators.84 2:Generalproceduresinchain-growthpolymerization●Hotplatestirrerandtemperaturecontroller●Oil-bath®●Teflon-coatedmagneticstirrerbar●Rubbersepta●Thermostattedwater-bath❘●BeakersandErlenmeyerflasks(various)●Vacuumoven●Apparatusforfiltration,Buchnerfunnel,flask,●Dryice/acetonebathandwaterpumpMaterials●Ethyleneoxide,8mL,160mmolextremelyflammable,verytoxicbyinhalation,irritatingtoeyesskinandrespiratorysystem,maycausecancer,maycauseheritablegeneticdamage●THF,ca.50mLhighlyflammable,mayformperoxides,irritatingtoeyesandrespiratorysystem●1,1-Diphenylethene,0.6mL,3.8mmoltoxicityunknown●Potassiummetal,0.5g,13mmolreactsviolentlywithwater,contactwithwaterliberateshighlyflammablegases,causesburns●Sodiummetal,ca.0.2greactsviolentlywithwaterliberatinghighlyflammablegases,causesburns●Carbazole,0.1g,0.8mmolirritatingtoeyes,skin,andrespiratorysystem,verytoxictoaquaticsystems,maycauselong-termadverseeffectsintheaquaticenvironment●Hexaoxa-1,10-diazabicyclo[8,8,8]hexacosaneirritatingtoeyes,skin,andrespiratorysystem(Kryptofix®222),0.012g,0.03mmol●Liquidnitrogenforcooling.extremelycoldliquid,vapourcancauserapidsuffocation●Acetoneforcoolingbathhighlyflammable●SolidCO2forcoolingbathextremelycoldsolid,vapourcancauserapidsuffocation●Methanol,2mLhighlyflammable,toxicbyinhalationandifswallowed●Hexane,ca.2LHighlyflammable,harmfulbyinhalationandincontactwiththeskinMethodPreparation:Allglasswaremustbedriedintheovenpriortouse.1,1-Diphenyl-etheneisdistilledunderreducedpressure(b.p.113at2mmHg)54fromasmallamountofpotassiumintoatwo-neckedround-bottomedflaskfittedwithaseptumandconnectedtothedistillationapparatusviaaYoungs’tapsuchthatthecollect-ingflaskcanbefilledwithargonandremovedfromthedistillationapparatus.Carbazoleispurifiedbyrecrystallizationfromtoluene,followedbymethanol,andthensublimedinvacuum.4,7,13,16,21,24-Hexaoxa-1,10-diazabicyclo[8,8,8]hexacosane(Kryptofix®222)isdriedbyplacingtherequiredamountinaround-bottomedflaskandheatingat60Cfor24h.Initiatorpreparation1.Potassium(0.5g,13mmol)isplacedinatwo-neckedround-bottomedflask(50mL)fittedwitharubberseptumandconnectedtothedualmanifoldbyagas-inlettube.Apotassiummirroriscreatedbyevacuatingtheflaskandheat-ingthepotassium(caution!).TheflaskisthenplacedunderanatmosphereofargonanddryTHF(10mL,seeTable2.2)isaddedbysyringeandthemixtureiscooledinadryice/acetonemixture(78C).1,1-Diphenylethene(0.6mL,3.8mmol)isthenaddedbysyringe,whereuponadeepredcolourisformedindicatingtheimmediateformationof1,1,4,4-tetraphenyltetramethylenedipotassium.Thesolutionismaintainedat78Cforca.48htoensurecompletereaction.85 N.Aragragetal.Protocol14.Continued2.Underanatmosphereofargon,carbazole(0.1g,0.8mmol)isplacedintoatwo-neckedround-bottomedflask(50mL)connectedtotheinertgassupplyviathedoublemanifoldandfittedwithaseptumandaTeflon®-coatedmag-neticfollower.IntothisflaskisintroducedTHF(5mL)andthenusingasyringe,1,1,4,4-tetraphenyltetramethylenedipotassiumisaddedslowly,whilethesolutionisvigorouslystirred;afaintpinkcolourationindicatinganexcesshasbeenaddedandthattheadditionshouldbestopped.a3.Kryptofix®(0.012g,0.03mmol)isplacedinatwo-neckedround-bottomedflask(50mL)fittedwitharubberseptumandconnectedtothedoublemani-foldbyagas-inlettube.Theflaskisthenheatedto60Cforafurther2handthencooledtoroomtemperatureandimmediatelypriortopolymerization,theminimumvolumeofTHFisaddedtodissolvetheligand.Monomerpreparation4.IntoadrytubefittedwithaYoungs’tapandaQuickfitjoint(ofthetypeusedtopolymerizebutylacrylateinProtocol1)isplacedasmallpieceofsodium(aboutthesizeofamatch-head).Thetubeisconnectedtothemanifoldoravacuumline,evacuatedandasodiummirrorformed(asforpotassiumabove.)Thetubeisthencooled(78C,dryice/acetone)andethyleneoxide(ca.8mL)isaddedfromthecylinder.bThetubeisthenheldat10Cfor24h.Afterthistimetheliquidisonceagainconnectedtothegas-line,frozen(liquidnitrogen),andthetubeevacuated.Anidenticaltubecontainingasodiummirrorisalsopreparedonthesamelineandcooledto78C.Thefirsttubeisallowedtoreturntoroomtemperatureandethyleneoxideisthentransferredbyvirtueofitslowvapourpressure.Thesecondtubeisthenisolatedfromthesystemandonceagainallowedtostandundervacuumfor24h.Polymerization5.ThismaybeperformedinSchlenk-typeglassware55ofthetypeshowninFigure3.4,consistingofalongtubewithaside-armandtaps,bothatthisside-armandthetopoftheflask.However,around-bottomedflask(100mL)fittedwithsimilartapsisalsoeffective.Theside-armisfittedwitharubberseptumandthetapconnectingthistotheflaskisclosed.Underanatmosphereofargon,THF(ca.25mL)isdistilledintotheflaskandthestopperclosed.6.Thepolymerizationflaskisthenconnectedtoagas-line(orthedualmani-fold)andcooledunderliquidnitrogen.Theflaskisthenevacuatedand,withthepumpisolated,allowedtowarmto78C.Thetubecontainingtheethyl-eneoxideisalsoconnectedtothevacuumlineandtheseriesoftapscon-nectingthetwotubesopened.Asbefore,theethyleneoxidewilltransferunderitsownvapourpressure.7.Thetubeisdisconnectedfromthevacuumlineandcooledat78CwhilethesolutionofKryptofix®isaddedviatheside-armusingagas-tightsyringe,followedbytherequiredamountofthepotassiumcarbazole86 2:Generalproceduresinchain-growthpolymerization(0.25mL,0.025mmol).Thesolutionisthenallowedtowarmtoroomtemper-atureandthenplacedinathermostattedwater-bathat30Cfor1week(withintermittentagitation).8.After1weektheanionicchainendsareterminatedbytheadditionofmethanol(2mL)andthepolymerisprecipitatedintoanErlenmeyerflaskcontaininghexane(freshlydistilledca.1L).ThepolymeristhenredissolvedinTHFandre-precipitatedintohexaneasbefore,itisthenfilteredanddriedinthevacuumovenat40Cfor24h.aTheanionicspeciesshouldbetitratedtochecktheconcentrationofactivatedmaterialusingthedou-bletitrationproceduredescribedabove.38Althoughwithsufficientcaretheyieldsshouldbealmostquantitative,theconcentrationofinitiatorshouldbeadjustedinlinewiththesereadings.bEthyleneoxidecanbeconvenientlypreparedasinRef.52;bydropping2-chloroethanolintoasuspen-sionofcalciumoxideinwaterrefluxingunderaslightlyreducedpressure(adeviceknownasabaro-statcanbeusedforthis).Theethyleneoxidecanbecollectedinatrapat78C.Polysiloxanesformaclassofcommerciallyimportantinorganicpolymersusedforexampleinsealants,lubricants,greases,andelastomers.Poly(dimethylsiloxane)isthemostcommonlyfoundexample.Thepolymerispreparedbyaring-openingpolymerizationofoctamethylcyclotetrasiloxane,whichisitselfpreparedfromdimethyldichlorosilanebyhydrolysisasshowninScheme18.56Thefollowingprocedureisamodificationofthisapproachusingtetravinyltetramethylcyclotetrasiloxaneandservestoillustratethegen-eralapplicabilityofthemethod.SiOH2OOSiKOHClSiClSiOSiOSi2-propanolOScheme18Formationandring-openingpolymerizationofcyclicsiloxane.Protocol15.Formationandring-openingpolymerizationofoctavinylcyclotetrasiloxaneCaution!Carryoutallproceduresinawell-ventilatedfume-hood,wearappro-priatedisposablegloves,alab-coat,andsafetyglasses.Allvacuum-lineworkshouldbeperformedwhilestandingbehindaprotectivePerspexscreen.Neveruseflat-bottomedflaskswithrotaryevaporators.Equipment●Dualmanifold(nitrogen/vacuum)●Sourceofdrynitrogen●Three-neckedround-bottomedflask(250mL)●Rubberseptum87 N.Aragragetal.Protocol15.Continued●Soda-limeguardtube●Condenser●Droppingfunnels(100mL2)●Teflon®-coatedmagneticfollower●Erlenmeyerflask(250mL)andfunnel●Gasinletadapter●Separatingfunnel(500mL).●Single-neckedround-bottomedflasks●Syringe(50mL)●(250mL2)●Hotplatestirrer●Oil-bath●Dryingtube(CaCl2)●Two-neckedround-bottomedflask(100mL)●Apparatusfordistillationatreduced●Rotaryevaporatorpressure:foursingle-necked●Standarddistillationapparatus:thermometerround-bottomedflasks(50mL),condenser,still-head,condenser,receiver-adapter,thermometer,airbleed,‘pig-type’single-neckedround-bottomedflask(250mL)receiver-adapter,Claisenstill-head,andthermometerMaterials●Dichloromethylvinylsilane,27mL,0.21molhighlyflammable,reactsviolentlywithwater,causesburns,irritatingtorespiratorysystem●Potassiumhydroxide,0.20g,3.57mmolcausessevereburns●Hydrochloricacid(6M),10mLcausesburns,irritant●Diethylether,ca.100mLextremelyflammable,mayformperoxides●Magnesiumsulfate●THFhighlyflammable,mayformperoxides,irritatingtoeyesandrespiratorysystem●Drypropan-2-ol80mLhighlyflammable.irritatingtoeyes,vapourmaycausedrowsinessordizziness.MethodPreparation:Propan-2-olisdriedbyrefluxingfollowedbydistillationfromCaO.Thedistillateisthenallowedtostandovermolecularsieve(type5A)forseveraldaysfollowedbyfurtherfractionation.1.Athree-neckedround-bottomedflask(250mL)isequippedwithacondenser,twodroppingfunnels,andaTeflon®-coatedmagneticfollower.Tothisflaskisaddeddiethylether(25mL)andHCl(6M,10mL).Onedroppingfunnelischargedwithwater(60mL)andtheotherwithasolutionofdichloro-methylvinylsilane,(27mL,0.21mol)indiethylether(25mL)andthistubeisfittedwithasoda-limeguardtube.2.Thewaterandthedichloromethylvinylsilanesolutionarethenaddedslowlytotheflaskwithstirringtomaintaingentleboilingwithoutvigorousheating.3.Onceadditioniscomplete,afurtherportionofetherisaddedandthetwolayersareseparatedinaseparatingfunnel(500mL).Theaqueouslayeristhenextractedwithafurtherportionofether(50mL)andthecombinedorganiclay-ersaredriedwithMgSO4andfilteredundergravityusingaflutedfilterpaper.4.Theetherisremovedontherotaryevaporatorandtheproductisdistilledunderreducedpressure(60C,1mmHg)atoyieldacolourlessoil.b5.Potassiumhydroxide(0.20g3.57mmol)isplacedinasingle-neckedround-bottomedflask(250mL)equippedwithagas-inletadapter.Theflaskisattachedtothemanifold,evacuated(to0.01mmHg),andheatedto70Cfor19h.88 2:Generalproceduresinchain-growthpolymerization6.Theflaskisthenplacedunderanitrogenatmosphere,anddrypropan-2-ol(80mL)isaddedtotheflask,whichissetupfordistillationatatmosphericpressure.17andthevolumeofsolventisthenreducedbydistillationto30mL.Thisisthecatalystsolution.7.Thecatalystsolution(0.05mL)isaddedtoadrytwo-neckedround-bottomedflask(100mL),equippedwithagasinlet,underacontinuoussteamofnitro-gen.Theflaskisthenheatedto55C.Afterseveralminutes,awhitesolidisdepositedandnomoresolventisvisible.Atthisstagethesiloxane(1.00g)isadded,theflaskequippedwithadryingtube,andthenitrogeninletremovedandreplacedwithastopper.Theflaskisheatedrapidlyto160Ctoinitiatethepolymerizationprocessandthepolymerizationisallowedtoproceedfor3h,whereuponahighlyviscouspolymericoilisformed.cThepolymerissolubleinbenzeneandtoluene.daSeeProtocol1.bYield:4.66g,26%.cTracesofinorganicmaterialcanberemoved,ifrequired,bywashingasolutionofthepolymerwithaverydilutesolutionofhydrochloricacid(0.01M).d1HNMR(400MHz;CD;MeSi):5.90(1Hmvinyl-H),5.70(2H,m,vinyl-H),0.05(3H,s,methyl-H).H6644.1CationicpolymerizationTheabilityofamonomertoundergocationicpolymerizationisdependentonthestabilityofthecationproduceduringthepropagationstageofthereaction.Styreneundergoespolymerizationbycationic,anionic,andfree-radicalmechanismsowingtotheabilityofthephenylringtostabilizetheintermedi-ate.Vinylethersareparticularlysusceptible,duetothestabilizinginfluenceoftheoxygenlonepairs,andalthoughinsomecasesreactionmaybesomewhatvigorous,*ahighdegreeofcontrolisnowpossiblewithrelativelycomplexpolymersbeingmadewithquitenarrowpolydispersities.57Cationicpolymer-izationisgenerallyinitiatedbyprotonorLewisacids;andborontrifluorideetherateisquitecommonlyused,asisthecaseintheexamplegivenbelow.Protocol16.CationicpolymerizationofstyreneCaution!Carryoutallproceduresinawell-ventilatedfume-hood,wearappro-priatedisposablegloves,alab-coat,andsafetyglasses.Allvacuum-lineworkshouldbeperformedwhilestandingbehindaprotectivePerspexscreen.Neveruseflat-bottomedflaskswithrotaryevaporators.*Forexample,Sorenson1(e)describesthepolymerizationofvinylisobutyletherusingliquidpropanetomoderatetheheatofreaction;onpassingastreamofBF3throughthesolutionanextremelyrapidreac-tionoccurs,withconsiderablequantitiesofpropanebeingboiledoffintheprocess.89 N.Aragragetal.Protocol16.ContinuedEquipment●Dualmanifold(nitrogen/vacuum)●Sourceofdrynitrogen●Three-neckedround-bottomedflask(250mL)●Septum●Nitrogenbubbler●Thermometer●Disposablesyringeandneedle●Pasteurpipette●BeakersandErlenmeyerflasks(various)●Apparatusforfiltration,Buchnerfunnel,●Stirrerflask,andwaterpump●Teflon®-coatedmagneticstirrerbar●VacuumovenMaterials●Styrene,30mL,262mmolflammable,irritatingtoeyesandrespiratorysystem●Borontrifluorideetherate,0.1mL,0.79mmolcorrosive,moisturesensitive(distilled)●Toluene,75mLhighlyflammable,harmfulbyinhalation●THF,ca.10mLhighlyflammable,mayformperoxides,irritatingtoeyesandrespiratorysystem●Methanol,ca.1Lhighlyflammable,toxicbyinhalationandifswallowedMethod1.Setupthedrythree-neckedround-bottomedflask(250mL)withaTeflon®-coatedmagneticstirrerbaranitrogenbubbler,thermometer,andseptaandflushtheequipmentwithnitrogen.2.Addthestyrene(30mL,262mmol)andtoluene(75mL)tothethree-neckedflaskandstirthesolutiongently.3.Adddrop-wiseBF3Et2O(0.1mL,0.79mmol)viaadisposablesyringeandneedle.4.OnceadditionoftheBF3Et2Oiscomplete,separatetheneedle,syringebarrel,andplungerandtransferthemintoa50mLbeakerfilledwithmethanolinordertodestroyanyunreactedBF3.5.Maintainstirringfor5h,duringthistimetheviscosityofthesolutionwillincrease.6.AddthepolymerizationmixturedropwiseviaaPasteurpipetteto500mLofmethanolstirredinabeaker.Useaflatstirrerbarandadjustthestirringratesoastoinduceanon-contortedvortex.Afinewhiteprecipitatewillbepro-duced,ifthisisnotobservedthenadjustthestirringratetoproducethis.7.Re-dissolvethecrudepolymerinTHFandre-precipitatethepolymerinmethanolusingtheproceduredescribedinstep6.Filtertheproductanddryinavacuumovenat60C.5.CoordinationpolymersPolymerscienceisbroad-basedandrequiresanunderstandingofareastradi-tionallythoughtofasphysics,engineering,andmathematics,inadditiontotheorganicandphysicalchemistrymethodologiesdiscussedaboveandinthepreviouschapter.Untilnow,wehavemadelittlementionofanareaof90 2:Generalproceduresinchain-growthpolymerizationwhatmightbetraditionallythoughtofasinorganicchemistrybutwhichhastransformedpolymerscience,anditisfairtosaytheworldwelivein,throughthecommercializationoftheproducts;thisistheroleoftransitionmetalcompoundsintheformationofpolymers,thatis,coordinationcata-lysts.OftheseprobablythebestknownandtodatemostcommerciallysuccessfularetheZiegler–Nattacatalysts.58,59Thesecatalysts,namedafterthejointwinnersofthe1963NobelPrizeforChemistry,whopioneeredtheiruseanddevelopment,areusedtomanufactureawiderangeofcommercialpolymersincludinghigh-densitypolyethyleneandisotacticpolypropylene.Ingeneral,aZiegler–NattacatalystisconsideredtobeacombinationofatransitionmetalcompoundofanelementfromGroupsIVtoVIIIandanorganometalliccompoundfromGroupsItoIIIoftheperiodictable.However,themostcommonandsignificantmaterialswithinthisbroaddefi-nitionarethosebasedontitaniumandaluminiumcompounds;specificallytitaniumtri-andtetrahalidesandtrialkylaluminiumcompounds.Aluminiumalkylsareparticularlyhazardousandmustbehandledintheabsenceofoxygen.Becauseofthecommercialimportanceofthesepolymers,anenor-mousrangeofcatalystshasbeendevelopedandafulldiscussionisoutsidethescopeofthiswork,howeversomepracticalexamplescanbefoundintheexcellentbookbySorenson.1(e)CurrentlythemostcommonlyusedZiegler–NattatypesystemshavetitaniumtetrachlorideonasolidsupportparticularlyMgCl.60However,solublecatalystshavemuchhigherefficien-2cies,andmorerecentlytherehasbeenparticularinterestintheuseofsolublemetallocenecatalysts.Inparticular,thediscoverybyKaminskythatzirconocenes,whenusedinconjunctionwithmethylaluminoxane(MAO)(producedbypartialhydrolysisoftrimethylaluminium),isanextremelyactivecatalystforethenepolymerizationandhasleadtoasurgeofactivityinthisareaandtothedevelopmentofarangeofnewpolymericmaterialsnotpreviouslyavailable.61,62Theexamplebelow,describeshowbis(cyclopenta-dienyl)zirconiumdichlorideisusedinconjunctionwithMAOtopolymerize1-hexene,63asshowninScheme19.ClZrClAlOCH3Scheme19Polymerizationofhexeneusingmetallocene-basedcatalystsystem.91 N.Aragragetal.Protocol17.Polymerizationof1-hexeneusingametallocenecatalystCaution!Carryoutallproceduresinawell-ventilatedfume-hood(orwhereappro-priateinadry-box)wearappropriatedisposablegloves,alab-coat,andsafetyglasses.Allvacuum-lineworkshouldbeperformedwhilestandingbehindapro-tectivePerspexscreen.Neveruseflat-bottomedflaskswithrotaryevaporators.Equipment●Dualmanifold(argon/vacuum)●Sourceofdryargon●Two-neckedround-bottomedflask(100mL2)●Hotplatestirrer●Dry-box●Teflon®-coatedmagneticstirrerbar●Gas-tightsyringesandnarrowboreneedle●Apparatusforfiltration,Buchnerfunnel,flask,(2,10,and20mL)standardfunnelandwaterpump●Lab-jack●Single-neckedround-bottomedflask(25mL)●BeakersandErlenmeyerflasks(various)●Separatingfunnel●Dryice/acetonebath●Rubbersepta●Rotaryevaporator●VacuumovenMaterials●1-Hexene,2mL,16mmolhighlyflammable,harmful:maycauselungdamageifswallowed●Bis(cyclopentadienyl)zirconiumdichloride,irritatingtoeyes,skin,andrespiratorysystem0.0292g,0.1mmol●MAO(10%solutionintoluene),0.7mLreactsviolentlywithwater,spontaneously(12mmolwithrespecttoaluminium)flammableinair,toxicbyinhalation,incontactwithskin,andifswallowed,causesburns●Dichloromethane,ca.5mLharmfulbyinhalation,potentialcarcinogen●Toluene,5mLhighlyflammable,harmfulbyinhalation●Magnesiumsulfateanhydrous●Acetoneforcoolingbathhighlyflammable●SolidCO2forcoolingbathextremelycoldsolid,vapourcancauserapidsuffocation●Methanol,ca.200mLhighlyflammable,toxicbyinhalationandifswallowedMethodPreparation:Allglasswareisdriedinanelectricovenat125Cfor24hpriortouse;apparatusisconstructedwhilststillhotandallowedtocoolunderanatmosphereofinertgas.Tolueneisdistilledfromsodiumbenzophenoneandstoredunderargoninatwo-neckedflaskequippedwithatapandaseptumcap.1-Hexeneisdis-tilledfromCaH2andstoredunderargoninthesamewayasthetolueneabove.1.Ametallocenesolutionispreparedbyweighingoutbis(cyclopentadienyl)zir-coniumdichloride(0.0292g,0.1mmol)inaglove-boxunderanargonatmos-phereandplacinginadrysingle-neckedround-bottomedflask(25mL).Theflaskisthenfittedwithaappropriateseptumcapandremovedfromthedry-box.Withtheflaskconnectedtotheinertgassupplybymeansofasyringeneedleinsertedthroughtheseptum,drytoluene(5mL)isaddedbymeansofacleandrysyringe.2.Adrytwo-neckedround-bottomedflask(100mL)isequippedwithaTeflon®-coatedmagneticfollower,acondenser,andaseptumcap.Theflaskis92 2:Generalproceduresinchain-growthpolymerizationconnectedtothedualmanifoldbymeansofagas-inlettube,andisevacu-atedandthenmaintainedunderanatmosphereofargon.3.MAO(12.5mL,21mmolwithrespecttoaluminium)isaddedtothereactionflaskusingagas-tightsyringefollowedbythemetallocenesolution(0.2mL0.004mmol).Themixtureisplacedinadryice/acetonebathandallowedtostandat78Cfor1h.4.Themonomerispreparedforadditionbycoolingto78CinthepresenceofaportionofMAO.Atwo-neckedround-bottomedflask(100mL)fittedwitharubberseptumisattachedtothedoublemanifoldbymeansofagas-inlettubeandflushedwithargon.1-Hexene(2mL,16mmol)andMAO(0.7mL,12mmolwithrespecttoaluminium)areaddedusinggas-tightsyringesofappropriatesizes.Theflaskisthenplaceinadryice/acetonebathandallowedtostandat78Cfor30min.5.Themonomersolutionpreparedinstep4aboveisthenaddedtothemetal-locene/MAOsolutionusingasyringeasbefore.Thesolutionisthenstirredfor5daysat78C.6.After5days,thepolymerizationisterminatedbyadditionofice-water(50mL)andthetoluenelayerremoved.TheaqueouslayerisplacedinaseparatingfunnelandextractedwiththreeportionsofCH2Cl2(ca.325mL).Thecombinedorganicextractsarethendriedusinganhydrousmagnesiumsulfatefilteredandthesolventremovedontherotaryevaporator.7.Thecrudepolymerisdissolvedinasmallamountofdichloromethaneandprecipitatedbydroppingthissolutionintoacoldstirredsolutionofmethanol.Thisprocedureisrepeatedandthepolymercollectedbyfiltrationatthepumpanddriedinthevacuumovenat40Cfor24h.Adifferenttypeoforganometallicprocessthathasalsoseenmanyimport-antdevelopmentsinrecentyearsisthering-openingpolymerizationofcyclicalkenesinducedbyorganometalliccatalysts,alsoknownasring-openingmetathesispolymerization(ROMP).Forexample,cyclopenteneispolymer-izedbyaWCl/AliBucatalysttoproduceanacyclicpolymerasshownin63Scheme20.64Itisimpossibleheretodojusticetotheoutstandingworkthathasbeendoneinthisarea,65,66butasimpleexampleisgivenbelow;thisuti-lizesacatalystinventedbyProfessorR.Grubbs67topolymerizenorbornene(Scheme21).68Thiscatalystisparticularlyeasytouse;andsuchpolymeriza-tionsmay,forexample,beperformedinanundergraduatelaboratory.3WCl6iAlBu3Scheme20Ring-openingpolymerizationofcyclopentene.93 N.Aragragetal.Protocol18.Ring-openingpolymerizationofnorbornene(Scheme21)Caution!Carryoutallproceduresinawell-ventilatedfume-hood(orwhereappropriateinadry-box)wearappropriatedisposablegloves,alab-coat,andsafetyglasses.Allvacuum-lineworkshouldbeperformedwhilestandingbehindaprotectivePerspexscreen.P(CH)6113ClPhClP(C6H11)3Scheme21Ring-openingpolymerizationofnorbornene.Equipment●Dualmanifold(argon/vacuum)●Sourceofdryargon●Single-neckedround-bottomedflask(25mL)●Dry-box●Gas-tightsyringesandnarrowboreneedles●Apparatusforfiltration,Buchnerfunnel,flask,(1,5,and50mL)andwaterpump●Two-neckedround-bottomedflask(100mL)●Teflon®-coatedmagneticstirrerbar●Magneticstirrer●Rubbersepta●Condenser●Gas-inletadapter●BeakersandErlenmeyerflasks(various)●VacuumovenMaterials●Norbornene,1g,11mmolhighlyflammable●Benzylidene-bis(tricyclohexylphosphine)irritatingtoeyes,skin,andrespiratorysystemrutheniumdichloride,0.1g,0.1mmola●Dichloromethane,ca.45mLharmfulbyinhalation,potentialcarcinogen●Ethylvinylether,0.05mL,0.5mmolhighlyflammable,repeatedexposuremaycauseskindrynessorcracking,vapoursmaycausedrowsinessordizziness●Methanol,ca.200mLhighlyflammable,toxicbyinhalationandifswallowedMethodPreparation:Allglasswareisdriedinanelectricovenat125Cfor24hpriortouse;apparatusisconstructedwhilststillhot,andallowedtocoolunderanatmosphereofinertgas.Dichloromethaneispre-driedwithCaCl2followedbydistillationfromCaH2.1.Acatalystsolutionispreparedbyweighingoutbenzylidene-bis(tricyclo-hexylphosphine)rutheniumdichloride(0.1g,0.1mmol)inadry-boxunderan94 2:Generalproceduresinchain-growthpolymerizationargonatmosphereandplacinginadrysingle-neckedround-bottomedflask(25mL).Theflaskisthenfittedwithanappropriateseptumcapandremovedfromthedry-box.Withtheflaskconnectedtotheinertgassupplybymeansofasyringeneedleinsertedthroughtheseptum,drydichloromethane(3mL),isaddedbymeansofacleandrysyringe.b2.Adrytwo-neckedround-bottomedflask(100mL)isequippedwithaTeflon®-coatedmagneticfollower,acondenser,agas-inletadapter,andaseptumcap.Theflaskisthenchargedwithnorbornene(1g,11mmol).Theflaskisconnectedtothedualmanifoldbymeansofthegas-inletadapter,andisevacuatedcandthenmaintainedunderanatmosphereofargon.3.Bymeansofagas-tightsyringe,dichloromethane(40mL)isaddedthereac-tionflask,andthemixturestirreduntilthemonomerhasdissolved.Thepoly-merizationistheninitiatedbytheadditionof0.6mLofthecatalystsolutionviaagas-tightsyringe,andthesolutionstirredfor24h.4.Thepolymerizationisthenhaltedbytheadditionofethylvinylether(0.05mL,0.5mmol).dThepolymeristhenprecipitatedintomethanolandpurifiedbydissolvinginchloroformandre-precipitation.Thepolymeristhendriedinthevacuumovenat40C.aResearch-scalequantitiesofthiscatalystcanbeobtainedfromtheSigma-AldrichCorporation.bThisprocedurecanbeperformedusingaglovebag,butinsuchcircumstancesitisrecommendedthattheexactquantitiesrequiredforthepolymerization(step2)shouldbemeasured,toavoidanysub-sequentdecompositionofthecatalystsolution.cTheflaskmustbecooledatthisstagetopreventthemonomersubliming.dThisstageisnecessarytocleavethepolymerfromtheruthenium.6.ConclusionsTheexamplesdescribedinthischapteraredesignedtoprovideanindicationofsomeoftheproceduresthatareregularlyusedbypolymerchemiststopre-parematerials,particularlybychain-growthprocesses.Thereareofcoursemanyusefultechniquesandexamplesthathavenotbeenincludedandwehaveconcentratedon(forthemostpartatleast)relativelywell-establishedprocedures,whichhavestoodthetestoftime.Withincreasingdemandsonmaterialpropertiestheemphasisoncontrolledpolymerizationhasalsoincreased;ofcourseanionicpolymerizationandparticularlycoordinationpolymerizationtechniqueshavemuchtoofferinthisregard,butinrecentyearsothernewoptionshavebecomeavailabletothepolymerscientist.Someofthesearediscussedinthenextchapter.References1.Thereaderisreferredtoanumberofexcellenttextbooksonpolymerscience.Theseinclude:(a)Billmeyer,F.W.TextbookofPolymerScience,3rdedn;Wiley:NewYork;1984.(b)Stephens,M.P.PolymerChemistry:AnIntroduction,2nd95 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3Controlled/‘living’polymerizationmethodsWAYNEHAYESandSTEVERANNARD1.IntroductionChain-growthpolymerizationssuchasfree-radicalpolymerizationsarechar-acterizedbyfourkeyprocesses:(i)initiation,(ii)propagation,(iii)chaintransfer,and(iv)termination.1Ifitispossibletominimizethecontributionofchaintransferandterminationduringthepolymerization,itispossibletoachievealevelofcontrolovertheresultingpolymerandachieveapredeter-minednumberaveragemolecularweightandanarrowmolecularweightdis-tribution(polydispersity).Ifsuchanidealscenariocanbecreated,thenumberofpolymerchainsthatareproducedisequaltothenumberofiniti-atorgroups;thepolymerizationwillproceeduntilallofthemonomerhasbeenconsumedandthepolymerchainendswillremainactivesothatfurtheradditionofmonomerwillleadtocontinuedpolymerization.Thistypeofpolymerizationwastermeda‘living’polymerizationbySzwarc2in1956andrepresentsoneoftheultimategoalsofsyntheticpolymerchemists.Flory3determinedthatintheabsenceoftermination,thenumberofpropagatingpolymerchainsmustremainconstantandthattherateofpolymerizationforeachgrowingchainmustbeequal.Inthissituation,thenumberaveragedegreeofpolymerization(DPn)andhencethemolecularweightofthepoly-mercanbepredictedbysimpleconsiderationofthemonomertoinitiatorratio(seeeqns(1)and(2),respectively).[monomer]DPn(1)[initiator]Numberaveragemolecularweight(polymer)DPnmolecularweight(monomer)(2)Severalkeycriteriaareusedtoelucidatethe‘living’natureofapolymerization.4Forapolymerizationtobeconsidered‘living’,therateofinitiationmustexceedtherateofpropagation.Therefore,allthepropagatingpolymerchainsareformedsimultaneouslyandgrowatthesamerate.Ifthis W.HayesandS.Rannardsituationdidnotoccur,thefirstchainsformedwouldbelongerthanthoseinitiatedlaterandthemolecularweightdistributionofthepropagatingchainswouldbroaden.Inaddition,anideal‘living’or‘immortal’polymerizationmustnotexhibitanyterminationofthepropagatingpolymerchainsoverthelifetimeofthereaction.Consequently,‘living’polymerizationsarecharacterizedbyverynarrowmolecularweightdistributions(Mw/Mn1.2).TheabilityofthepropagatingspeciestoundergopolymerizationuntilfullmonomerconversionFunctionalgroupFunctionalgroupsPolymerXXPolymerXEnd-functionalizedpolymersBifunctional/telechelicpolymersABAABABblockcopolymersABAblockcopolymersPolymerAPolymerAPolymerBPolymerBGraft/brushpolymersLadder-typepolymersStarpolymersFig.3.1Thevarietyofpolymerandcopolymerarchitecturesthatcanbesynthesizedby‘living’polymerizationtechniques.100 3:Controlled/‘living’polymerizationmethodsandthentocontinuepolymerizinguponadditionofanothermonomerfeedisanotherkeyfeatureof‘living’polymerizations(i.e.theactivechainendsarestableenoughtoenablesynthesisofblockcopolymersviasequentialmonomeraddition).Ifallofthesecriteriahavebeensatisfied,polymersandblockcopolymersexhibitingPoisson-typemolecularweightdistributionswillbeproducedandalinearrelationshipexistsbetweenthenumberaveragemolecularweight(Mn)oftheresultantpolymerandmonomerconversion.Asaconsequenceofthedevelopmentof‘living’polymerizationmethodo-logies,syntheticpolymerchemistsarenowabletoconstruct,inapreciseman-ner,awidevarietyofpolymerarchitectures5(Figure3.1)thatwerepreviouslyinaccessibleusinguncontrolledchain-growthmethodssuchasfree-radicalpolymerizationsthatemployedinitiatorssuchasazobisisobutyronitrile(AIBN)orbenzoylperoxide.6Forexample,inlightofrecentdevelopmentsin‘living’anionicpolymerizationtechniques,ABAblockcopolymerssuchasstyrene–butadiene–styreneforuseinthermoplasticelastomerscanbepro-ducedinareliablefashiononanindustrialscale.5Theimplicationsof‘living’polymerizationmethodsuponmaterialsscienceareenormous,assyntheticpolymerchemistsnowhavearangeofpowerfulsynthetictoolsavailabletothemtofacilitatetheconstructionofwell-definedpolymersalmosttoorder.Inthisrespect,meaningfulstructure–propertyrelationships(analogoustothoseemployedindrugdiscoverybythepharmaceuticalindustry)canbecarriedoutforthefirsttime,enablingdetaileddevelopmentofhightechnologypolymericmaterials.2.Covalent‘living’polymerization:grouptransferpolymerizationSeveral‘living’polymerizationtechniqueshavebeenshowntoinitiateandpropagatebythereactionofanactivecovalentendgroupwithmonomers.OnesuchmethodistheGroupTransferPolymerization(GTP).Thispoly-merizationtechnique,firstdescribedbyWebsterandco-workers7fromtheresearchlaboratoriesofDuPont,employssilylketeneacetalsinthecovalent‘living’polymerizationofavarietyofalkylatedmethacrylates(Scheme1).InitiationinvolvesMichael-typeadditionofthemonomertothesilylketeneacetal.ThemonomeradductthusformedrapidlyaddsmoremonomerinarepetitiveMichael-typeadditionprocesstoaffordthedesiredpolymer.ThetermGTPwasadoptedtoindicatethatthesilylgroupofthesilylketeneacetalinitiatorsystemhasbeentransferredtotheterminalmoietyofthepropagatingpolymerandsubsequentlytothemonomerthatisundergoingaddition.Eachtransferofthesilylgrouptothemonomerregeneratesasilylketeneacetalgroupattheendofthepropagatingchain.Thepolymerizationmechanismhasreceivedextensiveinvestigationand,todate,adefinitivemechanismisyettoreceiveuniversalacceptance.Severalmechanismstorationalizethepolymerizationcharacteristicshavebeenproposed,including101 W.HayesandS.Rannardassociativeanddissociativeandpseudoanionicpathways.However,thefocusofthischapterdoesnotpermitanextensivediscussionofthevariousmecha-nisticproposalsandthereaderisreferredtotheliteratureformoredetails.7–12MeOOSiMe3OSiMe3++Nu–MeO2CROOORInitiatorCatalystnROOOSiMe3MeO2CORROOnMethacrylicpolymerScheme1GTPofmethacrylicmonomers.Silylketeneacetalsarerelativelystablespeciesandrequireactivationbyacatalystinordertoinitiatepolymerizationof,-unsaturatedmonomers.NumerouscatalystsforGTPpolymerizationshavebeenexamined7,13,14andthesestudieshaverevealedthatbifluoridesandbioxyanionssuchastris(dimethylamino)sulfoniumbifluoride(TASHF2)andtetra-n-butylammo-niumbibenzoate(TBABB),respectively,affordoptimumpolymerizationcharacteristics.(Note:Bifluoridebasedcatalystsarenotsolubleintetra-hydrofuran(THF)andthusacetonitrileisusedasthesolventinthesecases;ingeneralTBABBistheoptimumcatalystasitisreadilysolubleinTHFandaffordsbettercontrolofmolecularweight,conversion,andpolydispersity.)GTPhasbeenshowntoberobust(Mw/Mn1.1)andiscompatiblewithnumerous,-unsaturatedmonomersincludingacrylates,ketones,lactones,andpolyunsaturatedesterssuchasethylsorbate.Manyofthesepolymeriza-tionscanbecarriedoutatambienttemperatures,butthemethodcanalsobeperformedusingelevatedtemperatures.Inaddition,GTPissuitableforusewithawiderangeofreactionsolventsofvaryingpolarity(rangingfromn-heptanetoTHF,althoughnotethattheproticandelectrondonorsolventsarenotsuitableforGTP).AlthoughGTPdemonstratesthefundamentalcharacteristicsofa‘living’polymerization,namelynarrowmolecularweightdistribution,controlofmolecularweightderivedfromthemonomer/initiatorstoichiometry,andthe102 3:Controlled/‘living’polymerizationmethodsabilitytoconstructblockcopolymers,thetechniqueisnotfoolproofandisinhibitedbythepresenceofmoistureandinherentterminationreactionssuchasisomerizationandbackbiting.Protocol1.SynthesisoftheGTPcatalystTBABB(Scheme2)ThismethodforthepreparationofTBABBisbasedupontheproceduredescribedbyDickeretal.13,14–OCH2Cl2OO+–++(nBu)4NOH(nBu)4NHOHOOScheme2PreparationofTBABBcatalyst.Caution!Carryoutallproceduresinawell-ventilatedfume-cupboard,wearappropriatedisposablegloves,alab-coat,andsafetyglasses.Allvacuum-lineworkshouldbeperformedwhilestandingbehindaprotectivePerspexscreen.Neveruseflat-bottomedflaskswithrotaryevaporators.Equipment●Separatingfunnel(250mL)●Erlenmeyerflask(250mL)●Sintered-glassfilterfunnel(porosity2)●Single-neckedround-bottomedflask(500mL)Materials●Benzoicacid,20.0g,164mmolirritant,harmfulifswallowedandbyinhalation●Tetran-butylammoniumhydroxide,40%w/vaq.,causesburns,harmfulbyinhalation80mL●Dichloromethane,350mLcarcinogen,harmfulbyinhalation●Anhydrousmagnesiumsulfate,ca.15gharmfulbyinhalation●THFsolvent,250mLirritant,highlyflammablemayformexplosiveperoxides●Diethyletherforprecipitation,300mLirritant,highlyflammableMethod1.Toaseparatingfunnel(250mL),addbenzoicacid(10g,82mmol)andtetra-n-butylammoniumhydroxidesolution(40%w/vaq.,80mL)andvigorouslyshakethemixtureuntilalloftheacidhasdissolved.Venttheseparatingfun-nelatregularintervalstopreventthebuild-upofexcessivepressureintheseparatingfunnel.2.Extracttheaqueousphasewithdichloromethane(350mL)andcombinetheorganicextractsinanErlenmeyerflask(250mL).3.Addbenzoicacid(10g,82mmol)totheorganicextractsandstirwithaglassrodtoensurecompletedissolutionoftheacid.4.Drytheorganicphasewithanhydrousmagnesiumsulfate(ca.15g,30min).103 W.HayesandS.RannardProtocol1.Continued5.Filterthe‘dried’organicphaseatthepumpthroughasintered-glassfilterfunnel,transferthesolutiontoasingle-necked,round-bottomedflask(500mL)andconcentratethesolutioninvacuousingarotaryevaporator.6.DissolvetheresidualsolidinwarmTHF(ca.250mL)andconcentratethesolu-tionuntilhalfofthevolumeofsolventremainsusingarotaryevaporator.7.Tothisconcentratedsolution,slowlyadddiethylether(ca.250mL)untilafinewhitecrystallineproductisobserved.Filtertheorganicphaseatthepumpthroughasintered-glassfilterfunnelandwashtheproductwithdiethylether(ca.50mL).8.Transferthewhitecrystallineproducttoaclean,drysingle-necked,round-bottomedflask(100mL)anddryusingavacuumline.Yieldsca.90%aretypical.Protocol2.GTPofmethylmethacrylate(Scheme1)Caution!Carryoutallproceduresinawell-ventilatedfume-cupboard,wearappropriatedisposablegloves,alab-coat,andsafetyglasses.Allvacuum-lineworkshouldbeperformedwhilestandingbehindaprotectivePerspexscreen.Polymethylmethacrylate(PMMA)possessingadegreeofpolymerizationof190monomergroupsandMn19000hasbeentargetedinthefollowingprocedure.Equipment●Dualmanifold(nitrogen/vacuum)●Cannulaneedle●Vacuumsource●Three-necked,round-bottomedflask(250mL)●Sourceofdrynitrogen●Rubbersepta●Hotplatestirrer●Beaker(500mL)●Teflon-coatedmagneticstirrerbar●Buchnerfilter●Contactthermocouple●Buchnerfilterapparatus●20mLgas-tightsyringe20cmlong●Filterpaper(Whatmanno.1)narrowboreneedleMaterials●[(1-Methoxy-2-methyl-1-propenyl)oxy]trimethylsilane,airritant0.15ml,0.734mmol●Freshlydistilledmethylmethacrylate,bcausesburns,maycausesensitization15mL,140mmolbyinhalationandskincontact●TBABB,0.05g,0.103mmolirritant●FreshlydistilledTHF,c50mLirritant,highlyflammablemayformexplosiveperoxides●Methanolforprecipitation,ca.700mLtoxic,flammablecarcinogen,Chloroform,ca.20mLharmfulbyinhalationNote:SiliconegreaseshouldnotbeusedtosealreactionvesselsusedinGTPmethods.Employapiezontypegreasesorfineteflontapeinstead.104 3:Controlled/‘living’polymerizationmethodsMethod1.VacuumdistilTHF(50mL)directlyintoaclean,drythree-necked,round-bottomedflask(250mL)—thereactionflask.Purgetheflaskwithdrynitrogenandallowthesolventtowarmtoroomtemperature.Removeastopperandsealwithanappropriaterubberseptum.2.Cannulate[(1-methoxy-2-methyl-1-propenyl)oxy]trimethylsilane(0.15ml,0.734mmol)fromagraduated2mLSchlenkflaskusingatransferneedle(orcannula)(usingthistechniqueitispossibletoaddtheinitiatortoanaccuracyof0.05mL)byapplyingpressurefromthenitrogensupplyasshowninFigure3.2.3.Removetheseptumandaddtetran-butylammoniumbibenzoate(seeProtocol1)(0.05g,0.103mmol)tothesolutionwhilstmaintainingapositivenitrogenpressure.Oncetheadditioniscomplete,sealtheflaskwithanappropriaterubberseptum.4.Stirthesolutionforapproximately2minbeforeaddingfreshlydistilledmethylmethacrylate(15mL,140mmol)inadropwisefashionviaacannulaoragas-tightsyringetothereactorflaskatarateofapproximately1mL/min.5.Monitortheexothermusingacontactthermometer(attachthecontactthermometertothesideofthereactor)—typicaltemperaturesreachedvarybetween45and60C.6.Oncethereactionhascooledtoroomtemperature,addmethanol(ca.5mL)tothereactionmixtureinordertoterminatethepolymerization.7.Purifyandrecovertheresultantpolymerbyprecipitationusingdrop-wiseadditionoftheTHFsolutionintothevortexwallsofarapidlystirredten-foldexcessofcoldmethanol(ca.500mL).AbrilliantwhitefineprecipitateshouldN2N2OutletInletneedleRubberneedleseptaRubberseptumFreshlydistilledCannula[(1Methoxy-2-methyl-1-propenyl)needleContactoxy]trimethylsilanethermometerxx.x°CGraduatedStirrerReactionSchlenktubebarflaskFig.3.2Transferofinitiator/catalyst/solventtoreactionflask.105 W.HayesandS.RannardProtocol2.Continuedbeproduced.Filterthepolymeratthepumpthroughasintered-glassfilterfunnel,transferthesolidobtainedtoalargewatchglassanddryitinavacuumovenat50Cforatleast4h.Onceaconsistentweightisachieved,recordthecrudeyield.Yields95%aretypical.8.Transferthecrudepolymerintoa100mLbeakeranddissolveitinchloro-form(ca.10–20mL).Precipitatethepolymerinthesamemannerasdescribedinstep7bydrop-wiseadditionofthechloroformsolutiontoaten-foldexcessofcoldmethanol.Filterthepolymeratthepumpthroughasintered-glassfilterfunnel,transferthesolidobtainedtoalargewatchglassanddryitinavacuumovenat50Cforatleast8h.Onceaconstantweightisachieved,recordtheyieldofthebrilliantwhitepowder.9.Analysetheproductusinggelpermeationchromatography(GPC)calibratedwitharangeofPMMAnarrowstandardstodetermineMnandMw/Mn.aThegrouptransferinitiator[(1-methoxy-2-methyl-1-propenyl)oxy]trimethylsilaneiscommerciallyavailablealthoughitcanbesynthesizedfrommethylisobutyratebyfollowingtheprocedurefirstdescribedbyAinsworthetal.15andthemodificationdevelopedbyEastmondandGrigor.16Theiniti-ator,eithersynthesizedorpurchased,shouldbedistilledundervacuumintoa2mLgraduatedSchlenkflaskwith0.1mLgraduationsandstoredundernitrogen.bMethylmethacrylateshouldbepassedthroughabasicaluminacolumndirectlyintoaSchlenkflaskcontainingCaH2andstoredinthefridge.Methylmethacrylateshouldbedistilledwithcare,directlyfromtheCaH2underhighvacuumandusedimmediately.cTHFisdistilledasfollows:allowthesolventtostandoversodiumwireuntilnofurtherevolutionofgasisobserved.Transferthepre-driedTHFtoastillcontainingsodiumwire/benzophenoneandbringthesolventtorefluxunderastreamofdrynitrogenuntilthedeeppurplecolourofthesodiumbenzophe-noneketylpersists—thisindicatesthattheTHFisanhydrous.Underaflowofdrynitrogen,collectthedryTHFintoacleandryflaskthatcontainssodiumwireandthendistilltherequiredvolumedirectlyintothepolymerizationvesselundervacuumimmediatelypriortouse.Protocol3.BlockcopolymersynthesisusingGTP:synthesisofpoly(methylmethacrylate-b-n-butylmethacrylate)(Scheme3)Caution!Carryoutallproceduresinawell-ventilatedfume-hood,wearappropriatedisposablegloves,alab-coat,andsafetyglasses.Allvacuum-lineworkshouldbeperformedwhilestandingbehindaprotectivePerspexscreen.ThisprocedureiscarriedoutinexactlythesamewayasdescribedinProtocol2.However,inthisapproach,oncecompleteconversionoftheinitialmonomerfeedhasbeenattained(asdeterminedbyGPCanalysis)asecondmonomerisaddedtothereactorflask.Sincethepolymerizationexhibits‘living’character-istics,activepolymerchainendsstillexistinthemonomer‘starved’flaskandfurtheradditionofanothermonomerenablesthepolymerizationtocontinue,thereforeproducinganABblockcopolymer.106 3:Controlled/‘living’polymerizationmethodsnOSiMe3MeOCOSiMeOOOOMe2OMeMeO3++(nBu)NH4MeOOOOnInitiatorCatalystPoly(methylmethacrylate)mnOOBuOSiMe3MeOCn2OBuMeOOnBuOOnmPoly(methylmethacrylate-b-n-butylmethacrylate)Scheme3Synthesisofpoly(methylmethacrylateb-n-butylmethacrylate)usingGTP.Equipment●Dualmanifold(nitrogen/vacuum)●Cannulaneedle●Vacuumsource●Three-necked,round-bottomedflask(250mL)●Sourceofdrynitrogen●Rubbersepta●Hotplatestirrer●Beaker(500mL)●Teflon-coatedmagneticstirrerbar●Buchnerfilter●Contactthermocouple●Buchnerfilterapparatus●0.5mLgas-tightsyringe20cmlongnarrow●Filterpaper(Whatmanno.1)boreneedleMaterials●(1-Methoxy-2-methyl-1-propenyl)oxy]trimethylsilane,airritant0.15mL,0.734mmol●Freshlydistilledmethylmethacrylate,bcausesburns,maycausesensitization15mL,140mmolbyinhalationandskincontact●TBABB,0.05g,0.103mmolirritant●Freshlydistilledn-butylmethacrylate,bcausesburns,maycausesensitization22.5mL,140mmolbyinhalationandskincontact●FreshlydistilledTHF,c150mLirritant,flammable●Methanolforprecipitation,ca.700mLtoxic,highlyflammablemayformexplosiveperoxides●Chloroform,ca.20mLcarcinogen,harmfulbyinhalationMethod1.VacuumdistilTHF(50mL)directlyintoaclean,drythree-necked,round-bottomedflask(250mL)—thereactionflask.Purgetheflaskwithdrynitro-genandallowthesolventtowarmtoroomtemperature.Removeastopperandsealwithanappropriaterubberseptum.2.Cannulate[(1-methoxy-2-methyl-1-propenyl)oxy]trimethylsilane(0.15mL,0.734mmol)fromagraduated2mLSchlenkflaskusingatransferneedle(orcannula)(usingthistechniqueitispossibletoaddtheinitiatortoanaccuracyof0.05mL)byapplyingpressurefromthenitrogensupplyasshowninFigure3.2.107 W.HayesandS.RannardProtocol3.Continued3.RemovetheseptumandaddTBABB(seeProtocol1)(0.05g,0.103mmol)tothesolutionwhilstmaintainingapositivenitrogenpressure.Oncetheaddi-tioniscomplete,sealtheflaskwithanappropriaterubberseptum.4.Stirthesolutionforapproximately2minbeforeaddingfreshlydistilledmethylmethacrylate(15mL,140mmol)inadrop-wisefashionviaacannulaoragas-tightsyringetothereactorflaskatarateofapproximately1mL/min.5.Monitortheexothermusingacontactthermometer(attachthecontactthermometertothesideofthereactor)—typicaltemperaturesreachedvarybetween45and60C.6.Oncethereactionhascooledtoroomtemperature,removeanaliquotofthereactionmixtureandaddittoasmallamountofmethanoltoterminatethepolymerizationofthealiquot.AnalysethealiquotbyGPCtodeterminethesuccessoftheinitialpolymerization.7.Addfreshlydistilledn-butylmethacrylate(22.5mL,140mmol)inadrop-wisefashionviaacannulatothereactorflask.8.Determinesuccessfulreinitiationbymonitoringtheexothermofthesecondpolymerization.Whenthereactionmixturehasreturnedtoroomtemperatureaddmethanol(ca.5mL)inordertoterminatethepolymerization.9.Purifyandrecovertheresultantpolymerbyprecipitationusingdrop-wiseadditionoftheTHFsolutionintothevortexwallsofarapidlystirredten-foldexcessofcoldmethanol(ca.500mL).Abrilliantwhitefineprecipitateshouldbeproduced.Filterthepolymeratthepumpthroughasintered-glassfilterfunnel,transferthesolidobtainedtoalargewatchglassanddryitinavacuumovenat50Cforatleast4h.Onceaconsistentweightisachieved,recordthecrudeyield.Yields95%aretypical.10.Transferthecrudepolymerintoa100mLbeakeranddissolveitinchloro-form(ca.10–20mL).Precipitatethepolymerinthesamemannerasdescribedinstep9bydrop-wiseadditionofthechloroformsolutiontoaten-foldexcessofcoldmethanol.Filterthepolymeratthepumpthroughasintered-glassfilterfunnel,transferthesolidobtainedtoalargewatchglassanddryitinavacuumovenat50Cforatleast8h.Onceaconstantweightisachieved,recordtheyieldofthebrilliantwhitepowder.11.AnalysetheproductusingGPCcalibratedwitharangeofPMMAnarrowstandardstodetermineMnandMw/MnandalsocomparetheproductMntothehomopolymeraliquotremovedafterthefirstpolymerization.aSeeProtocol2.bMethacrylatemonomersshouldbepassedthroughabasicaluminacolumndirectlyintoaSchlenkflaskcontainingCaH2andstoredinthefridge.ThemonomershouldbedirectlydistilledcarefullyfromtheCaH2underhighvacuumandusedimmediately.cSeeProtocol2.108 3:Controlled/‘living’polymerizationmethods3.Controlledfree-radicalpolymerizationsmediatedbynitroxidesThenatureoffree-radicalpolymerizationhastraditionallyhinderedattemptstoproduceanideal‘living’freeradicalpolymerizationtechnique.Itisverydifficulttopreventchaintransferandterminationreactionsinfree-radicalpolymerizationsandalthoughseveralmethodshaveaffordedpolymerswithverylowpolydispersities(Mw/Mn1.1),theseapproachesareoftenreferredtoas‘controlled’polymerizationsratherthan‘living’intheliterature.Intheearly1980s,Moadetal.17initiallyattemptedtocontrolfree-radicalpolymerizationusingstablefreeradicalssuchasnitroxides.Followingdevel-opmentalworkbyGeorgesetal.atXerox,18theapproachhasledtothereal-izationofadiverserangeofpolymerarchitectures19–21thatwerepreviouslyunobtainableusingtraditionalanionicorcationicpolymerizationtechniques.Polymerizationsofthistypeinvolveinteractionsbetweentwotypesofradicalspecies:(i)transientand(ii)stable(orpersistent).Thestableradicalscancombinewithhighlyreactivetransientradicalstoformtheso-called‘dormant’adductsaspartofadynamicequilibrium.Inthisdormantstate,bothradicalspeciesareeffectivelyinactiveandcannotparticipateinreactionswithotherreactiveradicals.Thedormantspecies,however,maybecontrollablydissociatedtoyieldthetransientandstablespecies.Afterdisso-ciation,thetransientradicalattheendofthegrowingpolymerchainreactsrapidlywithvinylmonomerstoformpolymerchains.Iftheconcentrationofthestableradicalspeciesishighenough,thetransientradicalattheendofthegrowingchainreactswiththefreestableradicalto‘cap’thegrowingendofthepolymerchainandreformthedormantspecies.Thecontinuedformationandcappingofthetransientspeciesduringpolymerization,minimizesitsconcentrationand,therefore,reducestheoccurrenceofterminationreactionsandproduces‘living’conditions.IncontrasttotheGTPpolymerizationmethodsdescribedabove,con-trolledfree-radicalpolymerizationsinvolvingnitroxidestypicallyemployaunimolecularinitiator22,23(asshowninScheme4)withthemonomerwith-outtheneedforacatalyst.Theunimolecularinitiatorincorporatesalatentnitroxidefreeradicalthatismorestablethanthepropagatingpolymerrad-ical.TheC–Obondbetweenthenitroxideunitandthe‘masked’initiatingcarboncentreisthermallylabile(dissociationoccursatapproximately125C).Therefore,polymerizationsofthistypearesimplycarriedoutbydis-solvingtheinitiatorinthebulkmonomerandheatingthemixturetotempera-tures125C.Thehighlyreactivevinylicradicalliberatedcanthusparticipateinpropagationwiththemonomerandthestablefreenitroxideradical‘mediates’thepolymerizationbyrepetitiverecombinationanddisso-ciationwiththegrowingpolymerchain.Consequently,adegreeofcontrolofthefree-radicalpolymerizationisachievedwithdefinedmolecularweightandnarrowpolydispersities(Mw/Mn1.1)ofthepolymersbeingobtained.109 W.HayesandS.RannardOO>125°COONONitroxide+ONstablefreeradicalDissociationActivestyryl-typeradicalPolymerizationandend-cappingOONOnScheme4Polymerizationofstyreneusinganitroxide-basedunimolecularinitiator.Alternativebimolecularmethodshavebeenreported17thatinvolvemixingappropriateratiosofmonomerwithfree-radicalinitiators(suchasbenzoylperoxide)andanexcessofthenitroxidestablefree-radicalmoiety.Suchbimolecularmethodsdonotaffordthesamedegreeofcontrolofmolecularweightandpolydispersitysincethestoichiometryofthemediatingsystemcannotbeaccuratelydefined,whichisacrucialfactorinthesecontrolledpolymerizationsystems.Awidevarietyofunimolecularnitroxidebasedinitiatorsystemshavebeendescribedintheliteraturewiththosebaseduponthe2,2,6,6-tetramethylpiperidinyl-1-oxy(TEMPO)groupprovingtobethemostcommonlyused.Whilepossessingmanyofthekeyadvantagesofcontrolled/‘living’poly-merizationmethods,nitroxide-mediatedfree-radicalpolymerizationsdoexhibitseverallimitations.Therangeofmonomersthathavebeenpolymer-izedusingnitroxide-mediatedtechniquesincludestyrenics,acrylamidesand(meth)acrylatesbutthesehavepredominantlybeenreportedinbulkpolymer-izations(i.e.withoutsolvent)andareconductedatelevatedtemperatureforlongtimeperiods.Inaddition,synthesisoftheunimolecularinitiatorcanprovetroublesome(dependentuponthetyperequired)andoftenrequiresextensivepurificationinordertoattainsufficientpuritylevelstoallowmolecu-larweightcontrol.Protocol4.Synthesisofnitroxideunimolecularinitiatorusingbenzoylperoxide(Scheme5)ThismethodforthepreparationofaTEMPO-basedunimolecularinitiatingsystemisbasedupontheproceduredescribedbyHawkerandco-workers.22110 3:Controlled/‘living’polymerizationmethodsCaution!Carryoutallproceduresinawell-ventilatedfume-hood,wearappro-priatedisposablegloves,alab-coat,andsafetyglasses.Allvacuum-lineworkshouldbeperformedwhilestandingbehindaprotectivePerspexscreen.ONOO~125°CONO++O2Scheme5Synthesisofnitroxideunimolecularinitiatorusingbenzoylperoxide.Equipment●Dualmanifold(nitrogen/vacuum)●Contactthermocouple●Sourceofdrynitrogen●25mLgas-tightsyringe20cmlongnarrowboreneedle●Three-necked,round-bottomedflask(100mL)●Single-neckedround-bottomedflask(2250mL)●Rubbersepta●Chromatographiccolumn(ca.30cmlong,ca.50mmi.d.)●Teflon-coatedmagneticstirrerbar●Scintillationvials(5020mL)●Hotplatestirrer●Oil-bathMaterials●Benzoylperoxide,1.14g,4.25mmolriskofexplosionbyshock,friction,fire,orotherignitionsources,maycausefire,irritatingtoeyes,maycausesensitizationbyskincontact●TEMPO,1.48g,9.5mmolcausesburns,harmfulbyinhalation●Freshlydistilledstyrene,a50mL,flammable,harmfulbyinhalation,0.436molirritatingtoeyesandskin●Dichloromethane,ca.500mLcarcinogen,harmfulbyinhalation●Hexane,ca.250mLhighlyflammable,irritatingtotheskin,vapoursmaycausedrowsinessanddizziness,harmfultolungs,possibleriskofimpairedfertility,toxic●Silica,ca.150gharmfulbyinhalation,irritatingtorespiratorysystemMethod1.Intoadrythree-necked,round-bottomedflask(100mL)thatisequippedwithacondenseraddfreshlydistilledstyrenea(50mL,0.436mol)directlyviaagas-tightsyringethroughtheside-armoftheflaskandthenflushtheflaskwithnitrogen.2.Whilemaintainingthereactionflaskunderapositivepressureofnitrogen,addTEMPO(1.48g,9.5mmol)tothestyrene.3.Note:Carerequiredinthisstep!Whilemaintainingthereactionflaskunderapositivepressureofnitrogen,addbenzoylperoxide(1.14g,4.25mmol)tothestyrenicsolution.Oncetheadditioniscomplete,sealtheflaskwithanappropriaterubberseptum.111 W.HayesandS.RannardProtocol4.Continued4.Placethereactionflaskinanoil-baththatismaintainedatatemperatureof90Candheatthemixtureunderasteadyflowofnitrogenforaperiodofca.20h.Useacontactthermometertomaintainthetemperaturesetting.5.Allowthereactionmixturetocooltoroomtemperature.6.Transferthereactionmixtureintoasingle-neckedround-bottomedflask(250mL).7.Vacuumdistilthereactionmixturetoremovetheexcessstyrene.8.Dissolvethecrudemixtureintheminimumvolumeof1:1hexane/dichloromethane.9.Applytheconcentratedsolutiontotheheadofapackedchromatographiccolumnb(packedwithsilicagel)usingaPasteurpipette.10.Initiallyelutethecolumnwith1:1hexane/dichloromethane,oncethestyrenehaseluted,graduallyincreasethepolarityofthemobilephasetodichloromethane.11.Combinethefractionscorrespondingtothedesirednitroxideunimolecularinitiatorandtransferthesolutionintoasingle-neckedround-bottomedflask(250mL).12.Usingarotaryevaporator,concentratethesolutionuntilaclearoil(oftenyellowishinappearance)isproduced.Yieldsca.40%aretypical.aStyreneshouldbewashedwith10%NaOH(aq.),driedoverNaSOandthenfilteredatthepumpin24ordertoremoveanystabilizer.Theresultantpre-driedstyreneshouldthenbedirectlydistilledcarefullyunderhighvacuumandusedimmediately.bGuidelinestocolumnchromatography:priortopurifyingthecrudeproduct,alwaysoptimizethechro-matographicconditionsusingthinlayerchromatography(TLC).Calculatehowmuchofthestationaryphase(aluminaorsilica)isrequiredbyassessingtheoptimumTLCseparation.MeasurethedifferenceinRfbetweentherequiredproductandtheby-products.Ageneralguide:iftheRfdifferenceisapproximately0.2,40gofsilica/aluminapergramofcrudeproductisrequired;iftheRfdifferenceis0.4,20gofalumina/silicapergramofcrudeproductisrequired.Weighouttherequiredamountofalumina/silica(inafume-hood)andtoitaddthesolventtobeusedastheinitialeluentinordertoprepareaslurry.Thisprocesswillgenerateheatandbeforetheslurrysoproducedcanbepackedintotheemptycolumnitmustbeallowedtocool.Gentlystirtheslurrytoremovethegasbubbles.Intothebaseofthecleanemptychromatographiccolumn,placeaplugofcottonwool(nottootightlypacked)andpourontoasmallamountofsand.Thecottonwoolplugisusedtopreventthesta-tionaryphasepouringoutofthecolumn.Tapthecolumncarefullysothatthesandislevel.Somecolumnshaveaporousglassfritlocatedatthebottomofthecolumnpriorthetap,inthesecases,itisnotnecessarytopourinsandoruseacottonwoolplug.Slowlypourtheslurryintothecolumn,ensuringthataminimumnumberofairbubblesarecreated.Openthetapofthecolumnandallowthesolventintheslurrytosteadilyrunintoasuitablysizedcol-lectionvessel(beaker/conicalflask).Gentlytapthesidesofthecolumnwithapieceofthickrubbertub-ingtofreeanyairbubblesthatpersistinthepackedcolumnandtoensurethatthestationaryphaseiscompactedintoauniformpackedbed.Itmaybenecessarytorepeattheaboveprocedureinordertopackallofthestationaryphasethatisrequiredforthedesiredseparation.Ifthisisthecase,allowthesolventintheslurrytoruntoapproximately1cmabovethelevelofthesettlingstationaryphase.Turnthetapofthecolumntostoptheflowofthesolvent.Gentlypourinthesecondbatchofslurryandreopenthetap.Repeattheaboveprocessuntilallthestationaryphaseisloadedintothecolumn.Note:Ifanyofthestationaryphasepoursintothecollectionvessel,thenthecolumnwillneedtobedismantledandreconstructed.112 3:Controlled/‘living’polymerizationmethodsOnceallthestationaryphasehasbeenloadedintothecolumnandhassettledsuchthatthebediscompact,level,andstable(markthesideofthecolumnwithamarkerpentorecordthelevelofthesta-tionaryphaseasitsettles),pourasmallamountofsandcarefullyontotheheadofthestationaryphase.Thisisusedtopreventdisruptionofthetopfewcentimetresofthestationaryphasewhenfreshmobilephasesolventsareaddedtothecolumn.Thecolumncannowbeusedtopurifythecrudeproduct.Allowthesolventlevelinthecolumntodroptojustabove(ca.1mm)thelevelofthestationaryphase.Applythecrudemixtureasaconcen-tratedsolutioninasolventsystemthatislesspolarthanthesolventsystemtobeusedastheinitialcol-umnmobilephase.Allowthelevelofthecrudeproductsolutiontodroptothetopofthestationaryphase,butdonotallowthecolumntobecomedry.Carefullypourinthefirstaliquotofmobilephaseandallowthattorunatasteadyratethroughthecolumn.Oncetheflowofsolventhasstartedthroughthecolumn,theseparationmustnotbestoppedSolventflowCompressedcontrollergasGroundglass/Quick-fitjointSolventreservoirSolventSandSampleSilica/aluminagelSandCottonwool/glassfritConicalflask/testtubeFig.3.3Experimentalset-upforflashcolumnchromatography.113 W.HayesandS.RannardProtocol4.Continueduntilalloftherequiredproductshavebeeneluted.Neverallowthecolumntorundry.Collectregular-sizedfractions(usescintillationvialsca.20mL)anduseTLCanalysistomonitorthecomponentselut-ingfromthecolumn.ForFlashcolumnchromatography,thecolumnpreparationisanalogoustothatdescribedabove,however,thestationaryphasematerialisoffinergradeandrequirespressureinordertoforcethesolventthroughthecolumn(Figure3.3).Protocol5.BulkpolymerizationofstyreneusingaTEMPO-basedunimolecularinitiator(Scheme4)Caution!Carryoutallproceduresinawell-ventilatedfume-hood,wearappropriatedisposablegloves,alab-coat,andsafetyglasses.Allvacuum-lineworkshouldbeperformedwhilestandingbehindaprotectivePerspexscreen.Polystyrenepossessingadegreeofpolymerizationof192monomerunitsandMn20300hasbeentargetedinthefollowingproceduredescribedbyHawkerandco-workers.22Equipment●Dualmanifold(nitrogen/vacuum)●Schlenkflask(10mL)●Vacuumsource●Three-waytap,gas-tightandequippedwithground-glassjoint●Sourceofdrynitrogen●Rubbersepta●Hotplatestirrer●Beaker(1500mL)●Teflon-coatedmagneticstirrerbar●Buchnerfilter●Contactthermocouple●Buchnerfilterapparatus●0.5mLgas-tightsyringe20cmlongnarrow●Filterpaper(Whatmanno.1)boreneedle●Oil-bathMaterials●Freshlydistilledstyrene,a5.21g,50mmolflammable,harmfulbyinhalation,irritatingtoeyesandskin●TEMPO-basedunimolecularinitiator,0.099g,0.26mmoltreatastoxic●THFforprecipitation,ca.20mLirritant,highlyflammablemayformexplosiveperoxides●Methanolforprecipitation,2ca.500mLirritant,flammableMethod1.Toaclean,drySchlenkflask(10mL)thatismaintainedunderpositivenitro-genpressureviatheside-arm(thatisequippedwithanappropriaterubberseptum)(Figure3.4),addtheTEMPO-basedunimolecularinitiator(0.099g,0.26mmol).2.SealtheSchlenkflaskbyattachingthethree-waytapthatisequippedwithaground-glassjoint.Useeitherhigh-qualityvacuumgreaseorpreferably,Teflontapetocreateavapour-tightsealontheflask.Redirectthenitrogen114 3:Controlled/‘living’polymerizationmethodsN2Three-waytapRubberseptumVacuumMonomer+Contactinitiatingsystemthermometer~110°CStirrerSchlenktubebarHeatsourceFig.3.4ExperimentalapparatusforbulkpolymerizationofstyreneusingTEMPO-basedunimolecularinitiators.purgebyconnectingthenitrogeninlettothethree-waytapandopeningtheventontheside-armoftheSchlenktube.3.Totheabovemixture,addfreshlydistilledstyrene(5.21g,50mmol)directlyviaagas-tightsyringethroughtheside-armoftheSchlenktube.Oncetheadditioniscomplete,sealtheflaskbyclosingtheside-armtap.4.Degasthemixturebyusingrepetitivefreeze–pump–thawcyclesb(repeatthecycleatleastthreetimes).5.Sealthetubeunderanitrogenatmosphereandthenplaceitinanoil-baththatismaintainedatatemperatureof123C.Uponimmersioninthehotoil-bath,thepolymerizationmixturewillbecomehomogeneousandwilldevelopayellowish-redcolour.6.Thepolymerizationmixturewilleventuallysolidifyandatthispoint(typic-ally24h)theSchlenkflaskshouldberemovedfromthehotoil-bathandallowedtocooltoroomtemperature.7.DissolvethesolidintheminimumvolumeofTHF(
10mL).8.PrecipitatethepolystyrenebydroppingtheconcentratedTHFsolutionusingPasteurpipetteintothevortexwallsofarapidlystirredten-foldexcessofcoldmethanol(ca.500mL).Containthemethanolinalargebeaker(1500mL)tocarryoutthisoperation.Afinewhiteprecipitateshouldresult.c115 W.HayesandS.RannardProtocol5.Continued9.Filterthesuspensionanddrythewhitepowderobtainedinavacuumoven(setto50C).Followingdrying,recordthemassofpolystyreneobtained.10.DissolvethepolystyreneobtainedinTHFsoastoobtainaviscoussolutionandthenrepeatsteps8and9.11.AnalysetheproductusingGPCcalibratedwitharangeofpolystyrenenar-rowstandardstodetermineMnandMw/Mn.aSeeProtocol4.bFreeze–pump–thawdegassingiscarriedoutasfollows:(i)EnsurethattheSchlenkflaskhasbeenthor-oughlypurgedwithnitrogen.(ii)FreezethesolutionbyimmersingtheSchlenkflaskinabathofliquidnitrogen(carerequiredwhenhandlingliquefiedgases)thatiscontainedinanitrogenDewar.(iii)Oncethesolutioniscompletelyfrozen,keeptheflasksubmergedintheliquidnitrogenandthenapplyhighvacuumtoitbyrotatingthethree-waytaptotheappropriateposition.Afterashortperiod(typically1min),sealtheSchlenkflaskbyagainrotatingthethree-waytaptotheappropriateposition.(iv)Removetheflaskfromtheliquidnitrogenbath.Allowthecontentsoftheflasktowarmuptoroomtemperatureandthesolutionwillmelt(asthisoccurs,smallgasbubbleswillappearanddissipateintothevoidabovethesurfaceofthesolution).(v)Increasethenitrogengaspressure(soastoavoidsuckback)andthenbackfilltheSchlenktubewithnitrogenbyslowlyrotatingthethree-waytaptotheappropriateposition.Repeatsteps2–5atleastthreetimes.cIfanopaquewhitesolutionisobtained,thecrudepolystyrenesolutionistoodilute.RemovemoreTHFfromthissolutionusingrotaryevaporationandthenre-continuetheprecipitation.Alternatively,ifwhite‘string-like’materialresultsfromtheinitialadditionofthepolymersolutiontothemethanol,thenthecrudepolystyrenesolutionistooconcentratedandwillrequiredilutionbytheadditionofTHF.Attheendoftheadditionofthecrudepolymersolutiontothemethanol,ifafinewhitedispersionthatcanbereadilyfilteredhasnotbeenobtained,thensimplyremoveallofthesolventbyrotaryevapora-tionandrepeattheprocess,inthiscaseadjustingtheconcentrationofthecrudepolymersolutionandthevolumeofmethanolused.4.Controlledfree-radicalpolymerizations:atomtransferfree-radicalpolymerizations(ATRP)andaqueousATRPAtomtransferfree-radicalpolymerization24(ATRP)proceedsbyatransient/stableradicalmechanismanalagoustonitroxide-mediatedfree-radicalpolymerizations(seeSection3).Thiscontrolledpolymerizationconceptwasfirstdescribed25,26independentlybytworesearchgroupsin1995,andexhibitsahighdegreeofcontroloverthemolecularweightofthedesiredpolymerandmoreremarkably,theabilitytorealizeverynarrowmolecularweightdistributions(Mw/Mn1.05).ATRPmethodologiesinvolve(seeScheme6)theone-electronoxidationofatransitionmetal(‘MLn’where‘L’isaligand)withconcomitantabstractionofahalideatomfromastableorganichalide(thedormantspecies‘RX’)toleadtothegenerationofahighlyreactiveorganicradical(thetransientspecies‘R•’).Thisorganicrad-icalcanfreelypropagateinthepresenceofmonomer.Subsequentreductiveabstractionofthehalidefromthemetalbythetransient(propagating)radical‘P•’leadstothegenerationofadormantpolymer‘PX’.mxmx116 3:Controlled/‘living’polymerizationmethodsDormantTransientRX++MLnRXMLnMonomerPmX++MLnPmXMLnMonomerPm+1X++MLnPm+1XMLnx(Monomer)Propagationcontinuesuntil[monomer]~0Pm+xX++MLnPm+xXMLnScheme6SimplifiedgeneralmechanismforATRP.Awidevarietyoftransitionmetalshavebeenstudiedand,inaddition,numerousligandsystemshavealsobeeninvestigated.24Ofthosestudied,thecopper(I)/copper(II)redoxcouplehasprovedtobethemostpopulartrans-itionmetalincombinationwitheither2,2
-bipyridineor2-pyridinecarbalde-hydeimine27ligandsystems.ATRPhasbeenshowntobeaveryversatilecontrolledpolymerizationsystemandcompatiblewithadiversesetofmonomers(styrene,methylmethacrylate,acrylatesetc).Themethodologyhasrecentlybeenadaptedtoallowthecontrolledroomtemperaturepolymer-izationofhydrophilicmonomersinaqueoussolvent,28–31thusbecomingthefirst‘living’polymerizationtotoleratelargeamountsofwaterandallowawiderangeofwater-solubleblockcopolymersyntheses.Inaddition,ATRPhasalsoenabledthesynthesisofawiderangeofhydrophilicandhydro-phobicpolymerarchitecturesthatcouldnotberealizedviamoreconventionalpolymerizationtechniques.32,33117 W.HayesandS.RannardProtocol6.BulkpolymerizationofstyreneusingATRPCaution!Carryoutallproceduresinawell-ventilatedfume-hood,wearappro-priatedisposablegloves,alab-coat,andsafetyglasses.Allvacuum-lineworkshouldbeperformedwhilestandingbehindaprotectivePerspexscreen.Polystyrenepossessingadegreeofpolymerizationof95monomerunitsandMn10000hasbeentargetedinthefollowingbulkpolymerizationprocedurereportedbyMatyjaszewskiandco-workers24,26(Scheme7).BrBrNCu(I)Br++n2N110°CnScheme7PolymerizationofstyreneusingATRP.Equipment●Dualmanifold(nitrogen/vacuum)●0.5mLgas-tightsyringe20cmlongnarrowboreneedle●Vacuumsource●Shortchromatographiccolumn(ca.15cmlong,ca.20mmi.d.)●Sourceofdrynitrogen●Scintillationvials(5020mL)●Hotplatestirrer●Beaker(21500mL)●Contactthermocouple●Single-neckedround-bottomedflask(250mL)●Teflon-coatedmagneticstirrerbar●Buchnerfilter●Schlenkflask(10mL)equipped●Buchnerfilterapparatuswithside-armandgas-tighttap●Three-waytap,gas-tightandequipped●Filterpaper(Whatmanno.1)withground-glassjoint●Smallrubbersepta●Oil-bathNote:Usethesameexperimentalset-upasdescribedinProtocol5.Materials●Freshlydistilledstyrene,a6.01g,57.7mmolflammable,harmfulbyinhalation,irritatingtoeyesandskin●Copper(I)bromide,0.088g,0.61mmolirritatingtoeyes,respiratorysystem,andskin●Benzylbromide,0.103g,0.60mmolirritatingtoeyes,respiratorysystem,andskin●2,2
-Bipyridine,0.196g,1.26mmoltoxicbyinhalation,incontactwithskin,andifswallowed,irritatingtoeyes,respiratorysystem,andskin●THFforprecipitationandaluminacolumn,irritant,highlyflammablemayformca.250mLexplosiveperoxides●Neutralalumina,ca.15gharmfulbyinhalation,irritatingtorespiratorysystem●Methanolforprecipitation,2ca.500mLirritant,flammableMethod1.Toaclean,drySchlenkflask(10mL)thatismaintainedunderpositivenitro-genpressureviatheside-arm,addcopper(I)bromide(0.088g,0.734mmol),118 3:Controlled/‘living’polymerizationmethods2,2
-bipyridine(0.196g,0.734mmol)andbenzylbromide(0.103g,0.734mmol).2.SealtheSchlenkflaskbyattachingthethree-waytapthatisequippedwithaground-glassjoint.Useeitherhigh-qualityvacuumgreaseorpreferably,Teflontapetocreateavapour-tightsealontheflask.Redirectthenitrogenpurgebyconnectingthenitrogeninlettothethree-waytapandopeningtheventontheside-armoftheSchlenktube.3.Totheabovemixture,addfreshlydistilledstyrene(6.01g,57.7mmol)directlyviaagas-tightsyringethroughtheside-armoftheSchlenktube.Oncetheadditioniscomplete,sealtheflaskbyclosingtheside-armtapandequipitwithanappropriaterubberseptum.4.Degasthemixturebyusingrepetitivefreeze–pump–thawcyclesb(repeatthecycleatleastthreetimes).5.Sealthetubeunderanitrogenatmosphereandthenplaceitinanoil-baththatismaintainedatatemperatureof110C.Uponimmersioninthehotoil-bath,thepolymerizationmixturewillbecomehomogeneousandwilldevelopadeepred/browncolour.6.Thepolymerizationmixturewilleventuallysolidifyandatthispoint(typ-ically18–24h)theSchlenkflaskshouldberemovedfromthehotoil-bathandallowedtocooltoroomtemperature.7.DissolvethesolidintheminimumvolumeofTHF(ca.3–5mL)andapplythisconcentratedsolutiontoashortaluminacolumnc(ca.15cmlong,
20mmi.d.containingapproximately10galuminapackedinTHF).PassTHFthroughthecolumnandcollectanappropriatenumberoffractions(ca.5mLfractions)untilallofthepolystyrenehaseluted(usingashortglasscapillary,placeapproximately1LofeachfractionontoasmallsilicaTLCplateandvisualizetheplateunderaUVlamp—ifpolystyreneispresent,adarkbluespotwillbeapparent).8.TransferalloftheTHFfractionsthatcontainthepolystyreneintoasingle-neckedround-bottomedflask(ca.100mL)andconcentratethesolutionusingarotaryevaporatoruntiltheviscosityofthesolutionincreases(thevolumeofthesolutionwillbeca.10mL).9.PrecipitatethepolystyrenebydroppingtheconcentratedTHFsolutionusingPasteurpipetteintothevortexwallsofarapidlystirredten-foldexcessofcoldmethanol(ca.500mL).Containthemethanolinalargebeaker(1500mL)tocarryoutthisoperation.Afinewhiteprecipitateshouldresult.d10.Filterthesuspensionanddrythewhitepowderobtainedinavacuumoven(setto50C).Followingdrying,recordthemassofpolystyreneobtained.11.DissolvethepolystyreneobtainedinTHFsoastoobtainaviscoussolutionandthenrepeatsteps9and10.12.Onceaconstantweightisachieved,recordtheyieldofthebrilliantwhitepowder.119 W.HayesandS.RannardProtocol6.Continued13.AnalysetheproductusingGPCcalibratedwitharangeofpolystyrenenar-rowstandardstodetermineMnandMw/Mn.aSeeProtocol4.bSeeProtocol5.cSeeProtocol4.dSeeProtocol5.Protocol7.Synthesisofthe2-bromoisobutyrateesterofpoly(ethyleneoxide)(PEG-Br):anaqueousATRPinitiatorThismethodforthepreparationofthePEG-Brinitiatorisbasedupontheproced-uredescribedbyWangandArmes34(Scheme8).OBrOOPhMe/Et3NOMeOOH+MeOOnnBrBrScheme8PreparationofthePEG-Br.Caution!Carryoutallproceduresinawell-ventilatedfume-cupboard,wearappropriatedisposablegloves,alab-coat,andsafetyglasses.Allvacuum-lineworkshouldbeperformedwhilestandingbehindaprotectivePerspexscreen.Neveruseflat-bottomedflaskswithrotaryevaporators.Equipment●Dean–Starkapparatus●Glassstoppers●Vacuumsource●Beaker(500mL)●Three-neckedround-bottomedflask(500mL)●5mLgas-tightsyringe10cmnarrowboreneedle●Hotplatestirrer●Filterpaper(Whatmanno.1)●Teflon-coatedmagneticstirrerbar●Buchnerfilterapparatus●Pressure-equalizingadditionfunnel(10mL)●Buchnerfunnel●Drynitrogensource●Watercondensor●Rubbersepta●Oil-bathMaterials●Monomethoxy-cappedpoly(ethyleneglycol)irritant,harmfulifswallowedandbyinhalationMn1100,20.0g,18.3mmol●Triethylamine,4.7mL,36.7mmolflammable,irritant,harmfulbyinhalation●2-Bromoisobutyrylbromidecorrosive,irritant,harmfulbyinhalation●Toluene,250mLirritant,flammable●Diethyletherforprecipitation,2250mLirritant,highlyflammableMethod1.Addmonomethoxy-cappedpoly(ethyleneglycol)(Mn1100,20.0g,18.3mmol)toaclean,drythree-neckedflask(500mL)underapositivepressureofdry120 3:Controlled/‘living’polymerizationmethodsnitrogen.Transfertoluene(250mL)totheflaskandaddthestirrerbar.FittheDeanandStarkapparatusandcondensertotheflaskandstoppertheremainingnecks.Heatthemixturegentlyuntilahomogeneoussolutionhasbeenformed.2.Increasethetemperatureoftheoil-bathuntilthesolutionbeginstoreflux.CollecttheinitialfractionintheDean–Starkapparatus.Thisisthewater/tolueneazeotropeandremovalofthisfractionwillensureadrytoluenesolutionofpoly(ethyleneglycol).Allowthesolutiontocool.3.Whilstmaintainingapositivepressureofdrynitrogen,removetheDean–Starkapparatusandrefitthecondenserandnitrogensupplytotheflask.Replaceonestopperwitharubberseptumandfitapressure-equalizingaddi-tionfunnel(10mL)totheotherneckoftheflask.4.Usingagas-tightsyringe(5mL),addtriethylamine(4.7mL,36.7mmol)totheroomtemperaturesolutionandstir.Add2-bromoisobutyrylbromide(4.54mL,36.7mmol)totheadditionfunnel.Addthe2-bromisobutyrylbrom-idetothereactiondropwise,over15min,sothatanyexothermiscontrolled.Stirthereactionatroomtemperatureforafurther48hwhilstmaintainingapositivepressureofdrynitrogen.5.FilterthewhiteprecipitateusingaBuchnerfiltrationapparatusanddiscardtheprecipitate.Concentratetheremainingclearsolutiontoapproximately50mLusingarotaryevaporator.Precipitatetheproductfromtheconcentratebydrop-wiseadditionintothevortexwallsofrapidlystirredcolddiethylether(250mL).FilterthewhiteprecipitatefromthesolventusingaBuchnerfiltrationapparatus.Dissolvetheprecipitateintoluene(50mL)andrepeattheprecipitationprocess.Filterthewhiteprecipitateagainanddryundervacuumtoremovealltracesofsolvent.Thefinalproductshouldbestoredunderdrynitrogeninthedark.Yields90%areusual.6.AnalysethePEG-Brproductusing1HNMR,13CNMR,andFT-IRspectro-scopiesandMALDI-TOFmassspectrometry.35Protocol8.Polymerizationofoligo(ethyleneglycol)methacrylateusingaqueousATRPThismethodforaqueousATRPisbasedupontheproceduredescribedbyWangandArmes34(Scheme9).Caution!Carryoutallproceduresinawell-ventilatedfume-cupboard,wearappropriatedisposablegloves,alab-coat,andsafetyglasses.Allvacuum-lineworkshouldbeperformedwhilestandingbehindaprotectivePerspexscreen.Poly(oligoethyleneglycolmethacrylate)possessingadegreeofpolymeriza-tionof20repeatunitsandamolecularweightMn9000hasbeentargetedinthefollowingpolymerizationprocedure.121 W.HayesandS.RannardProtocol8.ContinuedMeMeRBr/Cu(I)ClBipy/H2OOOOOOnmMeOmMeOEGMApoly(OEGMA)Scheme9Polymerizationofoligo(ethyleneglycol)methacrylateusingaqueousATRP(RBrPEG-Br).Equipment●Two-neckedround-bottomedflask(100mL)●Sintered-glassfilterfunnel(porosity2)●Hotplatestirrer●Teflon-coatedmagneticstirrerbar●Drynitrogensource●Rubbersepta●10cmnarrowboreneedle●2cmnarrowboreneedle●Buchnerfilterapparatus●5mLsamplevial●Glassstopper●VacuumsourceMaterials●Oligo(ethyleneglycol)methacrylate[averageharmful,irritatingtoeyesandskin,degreeofpolymerization7],10g,23.8mmolpossiblesensitizer●PEG-Br,a0.5g,1.20mmoltreatastoxic●Copper(I)Bromide,0.172g,1.20mmolirritatingtoeyes,respiratorysystem,andskin●2,2
-bipyridine,0.375g,2.40mmolharmful,irritatingtoeyesandskin,harmful●Deionizedwater,5mLnon-toxic●SilicairritatingtotherespiratorysystemMethod1.Adddeionizedwater(5mL),PEG-Brinitiatora(0.5g,1.20mmol),oligo(ethyl-eneglycol)methacrylate(10g,23.8mmol)andmagneticstirrerbartoa100mLtwo-neckedround-bottomedflask.Fitarubberseptumtoeachneck.Placethesmallneedleintooneseptumtoactasavent.2.Attachthe10cmneedletotheendofarubbertubejoinedtoadrynitrogensource.Placetheneedleintothesecondseptumandbubbledrynitrogenthroughthesolutionfor30mintoremovealloxygen.3.Afterdegassingthesolution,removetheneedlefromthesolutionbutdonotremovefromtheseptum.Removethesmallventneedlefromthefirstseptum.4.Fillasamplevial(5mL)withdrynitrogenandreplacethecap.WeightheCu(I)Br(0.172g,1.20mmol)and2,2
-bipyridine(0.375g,2.40mmol)intothenitrogen-filledsamplevialandreplacecap.5.Removethefirstseptumfromthereactionflaskwhilemaintainingapositivepressureofdrynitrogenthroughthesecondseptum.Emptythecontentsofthesamplevial(Cu(I)Br/2,2
-bipyridine)intotheflask,stoppertheopenneck122 3:Controlled/‘living’polymerizationmethodswithaglassstopper,andstiratroomtemperaturefor1hunderthedrynitrogenpressure.6.ThereactionmixturewillbecomedarkbrownindicatingthepredominantpresenceoftheCu(I)species.Anexotherm(5–10C)maybenoted.(Kineticdatahaveshownthat99%conversionofmonomerisachievedwithin25min.)7.Addthesintered-glassfunneltotheBuchnerfiltersystemandattachthevacuumsource.Fillthefunneltoadepthof2cmusinganhydroussilica.Filtertheaqueouspolymersolutionthroughthesilica.Abluecolourwillappear,indicatingtheCu(II)speciesthatisformedinthepresenceofoxygen.Thesolutionofpolymermustbefreeze-driedovernighttoremoveallwaterandleaveawhitesolidpolymerproduct.Yields90%aretypical.8.AnalysethepolymerusingGPC(THFusingPMMAstandards),1HNMR,13CNMR,andIRspectroscopies.aSeeProtocol7.Thecontrolledpolymerizationtechniquesthathavebeendescribedabovedonot,ingeneral(withtheexceptionofGTP),requireexhaustiveexclusionofmoistureandpurificationofmonomersandreagents.Severalofthe‘liv-ing’polymerizationmethodsreportedsofardosuffertheseexperimentalrestrictionsand,thus,uptakeofthesetechniquesbythepolymercommunityhasbeenlimited.Thereareseveralnotableexamplesof‘living’polymeriza-tionsthatmeritrecognition,includinganionicmethods,36cationicpolymer-izations,37‘immortal’polymerizationsmediatedbymetalloporphyrinreagents,38reversibleadditionfragmentationchaintransfer(RAFT)39tech-niquesandring-openingmetathesispolymerizations(ROMP).40Eachofthese‘living’polymerizationmethodshasitsownbeneficialattributesandmonomercompatibilitycharacteristicsand,therefore,carefulconsiderationmustbetakenwhenselectinga‘living’polymerizationprocess.References1.Foranexcellentdescriptionofthemechanismofchain-growthpolymerization,see:Odian,G.InPrinciplesofPolymerization,3rdedn.,Wiley-Interscience:NewYork;1991,Ch.3.2.(a)Szwarc,M.;Levy,M.;Milkovich,R.J.Am.Chem.Soc.1956,78,2656.(b)Szwarc,M.J.Polym.Sci.,PartA:Polym.Chem.1998,36,ix.3.Flory,P.J.PrinciplesofPolymerChemistry;CornellUniversityPress:NewYork;1953.4.Quirk,R.P.;Lee,B.Polym.Int.1992,27,359.5.Webster,O.W.Science1991,251,887.6.Sorenson,W.R.;Campbell,T.W.PreparativeMethodsofPolymerChemistry,2ndedn.,Wiley-Interscience:NewYork;1968,Ch.4.123 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4Step-growthpolymerization—basicsanddevelopmentofnewmaterialsZHIQUNHE,ERICA.WHALE,andFREDJ.DAVIS1.IntroductionStep-growthpolymerizationisoftenreferredtoascondensationpolymer-ization,sinceoften—butbynomeansalways—smallmoleculessuchaswaterarereleasedduringtheformationofthepolymerchains.Thereareanumberofdifferencesinthewaypolymerizationoccursinstep-growthpolymerizationcomparedtochain-growthprocesses,andthesehavemarkedpracticalimplications.Themostobviousdifferenceisthat,asthenameimplies,thepolymerchaingrowsinastep-wisefashion;theinitialstageofthereactioninvolvestheconversionofmonomerstodimersandfromtheseotherlowermolecularweightoligomers.1Itisonlyasthereac-tionnearscompletionthatsignificantquantitiesofhighermolecularweightmaterialcanbeformed.Thus,inordertoobtaineffectivemolecularweights,thereactionmustproceedalmosttocompletion,indeedthemolecu-larweight(intermsofthenumberaveragedegreeofpolymerizationxn)ofthepolymercanbelinkedtotheextentofreaction(p)usingeqn(1).Thus,inthesimplestcaseofadifunctional(AB)monomer,when50%oftheavailablegroupshavereacted,thenumberaveragedegreeofpolymeriza-tionisonly2.1xn(1)1pTheconsequenceofeqn(1)isthathighmolecularweightsinstep-growthpolymerizationsareassociatedwithhighlyefficientreactionsthatdonothaveside-reactions.Notwithstandingthis,thetypesofmolecularweightsassociatedwithchain-growthprocessesarenotencounteredintheseprocesses(exceptinthecaseofmonomerswithmorethantworeactivegroupswhere 4:Step-growthpolymerizationhyper-branchedorevencross-linkedpolymersarepossible).Thereisanadditionalcomplication,namelytheroleofcyclization.Kricheldorf2hasrecentlyshownthatunderperfectconditionscyclizationistheultimatefateofanypolymerizationreaction.Thus,underextremelyhighconversionsthepredictiongivenbyeqn(1)wouldoverestimatetheactualmolecularweightsproduced.Moleculesthatundergostep-growthpolymerizationmusthaveatleasttworeactivefunctionalgroups.Ifthefunctionalityisgreaterthanthis,forexample,trifunctional,thenhyperbranchedpolymersorevencross-linkedsystemscanbeformed.3,4Commonly,thisinvolvesthereactionoftwodifferentreactivedifunctionalmonomers.SuchasystemisoftenclassifiedasanAABBsystemandiswellknowntochemistrystudentsintheformoftheformationofNylon6,6viathecondensationofadipoylchloridewith1,6-diaminohexane,inaninterfacialpolymerization,oftenreferredtoastheNylonropetrick.*Asimilarprocedurecanbeusedtoformanester,andanexampleisgivenlater.Asanalternativetousingratherreactivedi-acidchlorides,wherethepossibilitythataproportionofthematerialcanbecomedeactivatedby,forexample,hydrolysis,carboxylicacidsmaybeactivatedinsitu;aparticularlypopularexampleofthisbeingthephosphorylationreaction.5Thisapproachhasanumberofadvantages,oneofwhichisoffer-ingthepossibilityofpolymerizingbyfunctionalmonomerssuchas4-aminobenzoicacid,6therebycircumventingtheneedforstoichiometricbalance.7Inotherinstances,thereactionisforcedbyremovingvolatileby-productsfromthereaction,andlessreactivematerialsmaygivequitereasonablemolecularweightpolymersinthisway.2.ThesynthesisofanaromaticpolyamideTherangeofchemicalreactionsthatcanbeusedtoformstep-growthtypepolymersistoolargetodescribeadequatelyhere.Asaconsequence,thischapterfocusesonsomeoftheproblemsassociatedwithformingaromaticpolymers.SuchsystemshaveattractedconsiderableinterestinviewofthesuccessofKevlarandthearamidfibres.Theyofferparticularsyntheticchallenges,oneofwhichbeingthatalevelofintractabilitygenerallyaccom-paniestheincreaseinmechanicalstrengthassociatedwithrigidrodsystems.Thisfirstexampleisrepresentativeofaprocedurefrequentlyusedfor*Approximately3gofhexane-1,6-diamineisdissolvedinaqueoussodiumhydroxide(0.5M,50mL)andplacedinabeaker(100mL).Asolutionofadipoylchloride(care!lachrymator)inhexane(1gin50mL)isaddedtothisbeakerandtwolayerswillbeseen.Attheinterfacebetweentheaqueousandthenon-aqueousphase,athinfilmwillform.ThisfilmcanbepulledusingapairoftweezerstoformalongstrandofNylon6,6.127 Z.Heetal.thesynthesisofpolyamides;thepolymerispreparedinsolutionusingthephosphorylationproceduredescribedabove.8Protocol1.Anaromaticpolyamideformedbetween1,4-diaminobenzeneandisophthalicacid(Scheme1)Caution!Carryoutallproceduresinawell-ventilatedfume-cupboard,wearappropriatedisposablegloves,alab-coat,andsafetyglasses.OOHOOHH2NNH2+12(PhO)3P/NMPNLiClOONHHNNH3Scheme1Formationofpolyamideusingphosphorylationreaction.Equipment●Two-neckedround-bottomedflask(250mL)●Erlenmeyerflasks(various)●ApparatusforSoxhletextraction,single-necked●Apparatusforfiltration,Buchnerfunnelround-bottomedflask,Soxhletextractorandflask,waterpumpthimbleandcondenser●Condenser●Hotplate/magneticstirrerandoil-bath●Teflon®-coatedmagneticfollower●Thermometerandground-glassadapter●Vacuumdesiccator●VacuumovenMaterials●p-phenylenediamine,2.16g,20mmoltoxicbyskincontact,inhalationandifswallowed,maycausesensitizationbyskincontact128 4:Step-growthpolymerization●Sodiumdithionate,3.5gmaycausefire,harmfulifswallowed,contactwithacids,liberatestoxicgas●Decolourizingcarbon,approximately3–5g●Isophthalicacid,3.32g,0.02molirritant●Phosphorouspentoxidecausessevereburns●N-methylpyrrolidone(NMP),60mLirritatingtoskin,eyes,andrespiratorysystem●Pyridine,40mLhighlyflammable,harmfulbyskincontact,inhalationandifswallowed●Dimethylacetamide,ca.50mLharmfulbyskincontactandinhalation,eyeirritant●Methanol,ca.500mLtoxicbyinhalationandifswallowed,highlyflammable●Triphenylphosphate,10.5mL,0.04molirritatingtoskin,eyes,andrespiratorysystem,prolongedcontactmaycauseskinsensitization●Lithiumchloride,ca.3gharmful,irritatingtoskin,eyes,andrespiratorysystem,potentialteratogenMethodPreparation:InanErlenmeyerflask(1L)p-phenylenediamine(100g)isdis-solvedinhotwater(300mL)containingsodiumdithionate(3.5g)andthesolu-tionisthenfilteredandcooledinanice-bathtocrystallize.Thewhitecrystalsformedarecollectedbyfiltrationatthewaterpump,driedinairandtheninavacuumdesiccatoroverphosphorouspentoxide.aIsophthalicacidispurifiedbyrecrystallizationfromhotmethanol;thehotsolutionisfilteredandthencooledinanice–salt-bath,thewhitecrystalsformedarecollectedbyfiltrationatthewaterpumpanddriedinavacuumoven.1.Inatwo-neckedround-bottomedflask(250mL),equippedwithathermo-meter,condenser,andamagneticstirrerisplacedp-phenylenediamine(2.16g,20mmol)andisophthalicacid(3.32g,20mmol).TothismixtureNMP,60mLandpyridine(40mL)containinglithiumchloride(1.4g,4%byweight)areaddedandthentriphenylphosphite(10.5mL,40mmol)isaddedandthemixtureisstirredtogiveadark-colouredsolution.2.Thetemperatureisraisedto85–95Candthemixtureismaintainedatthistemperaturefor6–7h.Thereactionisthencooledtoroomtemperatureandmethanolisaddedtoprecipitatethepolymer.3.ThecrudepolymerispurifiedbydissolvingindimethylacetamidecontainingLiCl(3%byweight)andprecipitatingusingmethanol.Thisprocedureisrepeatedtwice.4ThepolymeristhenpurifiedbySoxhletextractionusingmethanolfor6–8h.Finally,thepolymerisdriedinavacuumovenat40Cfor24h.baYield83g(83%);thecolourchangesgraduallyfromwhitetopurpleonstorage.bTypicalyield99%,M8.7103,M19.1103(GPCinDMFcontaining1%lithiumbromidenwusingpolyethyleneoxideandpolyethyleneglycolasstandards).129 Z.Heetal.3.Preparationofamain-chainliquidcrystallinepoly(esterether)withaflexibleside-chain(Scheme2)OOOCH3CH3OOOO+OOHHOOCH3CH254OOO–CHCOHOOO32OOCH3CH26Scheme2Preparationofamainchainliquidcrystallinepoly(esterether)withaflexibleside-chain.OOCH3CH2COClCH3CH2CH2CH3HOOHOO7(1)AlCl83(2)HCl(3)NaS2O4OOCH3CH3HOOHOOCH3COClOOCH3CH2CH3CH289Scheme3Formationofanaromaticdi-esterwithaflexibleside-chain.Acommonmethodforpolyesterformationisviatrans-esterification.TheproceduredescribedbelowusesaprocedurethatismodifiedfromthatdescribedinSorenson.9Inthiscase,aromaticdi-acid5anddi-ester4monomersarereactedtogetherinthemelt.Duringthepolymerization,themolecularweightgrowswhilevolatileside-productiscontinuouslyremovedfromthereactionvesselbymeansofavacuumpump.Scheme2describestheformationofamain-chainliquidcrystallinepoly(esterether)containing130 4:Step-growthpolymerizationflexibleside-chainunits.Suchunitscandramaticallyimprovetheprocess-abilityofsuchpolymersalbeitattheexpenseofsomeotherproperties,10andmaybeintroducedintohydroquinonesusingtheFriesrearrangement(Scheme3)asoutlinedbelow.Thethreearomaticringspresentinthepolymerdescribedhereforma‘hardrod’topromoteliquidcrystallinephaseformation,andbecauseofthepresenceoftheside-groupthephaseisformedatarelativelylowtemperature,namely125–230C.Asaconsequenceofthisenhancedprocessi-bility,thepolymercanbealigneduniaxiallyinthenematicphaseusingamag-neticfield(B0.6T)andtheorientationcanbepreservedbyarapidcooling.Protocol2.Preparationofanaromaticdi-esterwithaflexibleside-chain4foruseinatrans-esterificationpolymerizationCaution!Carryoutallproceduresinawell-ventilatedfume-cupboard,wearappropriatedisposablegloves,alab-coat,andsafetyglasses.Equipment●2Three-neckedround-bottomedflasks(1L)●Condensers●Thermometer●Droppingfunnelandstopper●Hotplatestirrer/water-bathandoil-bath●TLCplates(withfluorescentindicator)●Nitrogeninlet●Gasbubbler●Apparatusforfiltration,Buchnerfunnel●Erlenmeyerflasksandflask,waterpump●Ice-bath●Single-neckedround-bottomedflask(500mL)●Dryingtube(CaCl2)●Teflon®-coatedmagneticfollower●Rotaryevaporator●Vacuumoven●PowderfunnelMaterials●Hydroquinone,30g,0.27molharmfulbyinhalationandifswallowed●Tetrahydrofuran,400mLhighlyflammable,irritatingtoeyesandrespiratorysystem,mayformexplosiveperoxides●Pyridine,60mLhighlyflammable,harmfulbyskincontact,inhalationandifswallowed●Propionoylchloride,61mL,0.60molhighlyflammable,causesburns,reactsviolentlywithwater●Aluminiumchloride,112g,0.84molcausesburns●Hydrochloricacid(concentrated)causesburns,irritatingtorespiratorysystem●Saturatedsodiumbicarbonatesolutionpotentiallyirritatingtoeyes,skin,andrespiratorysystem●Dichloromethaneharmfulbyinhalation,potentialcarcinogen●Sulfuricacidsolution(ca.5M),50mLextremelycorrosive,causesseriousburns,harmfulbyingestion,inhalation,andskincontact,chronicexposuremayresultinlungdamageandpossiblycancer●Sodiumdithionite,90g,517mmolmaycausefire,harmfulifswallowed,contactwithacidsliberatestoxicgas●Sodiumhydroxidesolution(1.5M),600mLcausesburns●Acetylchloride,170mL,2.16molhighlyflammable,reactsviolentlywithwater,causesburns131 Z.Heetal.Protocol2.Continued●Magnesium,0.05g,2mmolhighlyflammable,contactwithwaterliberatesextremelyflammablegas●Diethylether,ca.200mLextremelyflammable,mayformexplosiveperoxides●Aluminiumoxideforchromatographyirritatingtorespiratorysystem●Ethanolhighlyflammable●Petroleumetherhighlyflammable●EthylacetatehighlyflammableMethodStep1:Formationofthediester1.Hydroquinone(30g,270mmol)isaddedtoathree-neckedflask(1L)equippedwithacondenser,adroppingfunnel,athermometer,andaTeflon-coatedmagneticfollower,followedbytetrahydrofuran(400mL).Whentheentiresolidisdissolved,pyridine(60mL)isadded.Thesolutionisthencooledtobelow10Cbymeansofanice-bath.2.Fromthedroppingfunnel,propionoylchloride(61mL,0.600mmol)isaddedwithstirringtothehydroquinonesolutionwhilstensuringthetemperaturedoesnotexceed10C.Anorangeprecipitateisobservedimmediately.Onceadditioniscomplete,thereactionmixtureisstirredovernight(whereupontheorangeprecipitatebecomeswhite).Atthisstagethinlayerchromatogra-phy(TLC)shouldconfirmtheformationofthediester.a3.Oncompletionofthereaction,thesolventisremovedontherotaryevapor-ator,andtheproductdissolvedindichloromethane,andwashedtwicewithsulfuricacidsolution(approximately5M,50mL).Thepaleyellowsolutioniswashedrepeatedlywithwater,andfinallywithsaturatedsodiumbicarbonatesolutiontillthepHis7.Finally,thesolventisremovedandthewhitesolidisrecrystallizedfromaqueousethanol(1500mL,50%)anddriedinavacuumovenat50C.Step2:Friesrearrangement11ofhydroquinonedipropionate4.Athree-neckedflaskisequippedwithanitrogeninlet,andacondenserwithagasbubblerattached.5.Dryhydroquinonedipropionate(55g,0.28mol)andaluminiumchloride(112g,0.84mol)arefinelygroundandmixedusingamortarandpestle,andthenintroducedintothereactionflaskviatheunusedneckbymeansofapowderfunnel,andthestopperisplacedontheneck.6.Thetemperatureisincreasedslowlyto110–120Cbymeansofanoil-bath;atabout110Chydrogenchloridewillbeevolvedfromthereaction.Thetem-peratureismaintainedforabout1handthemixtureisthenheatedfurtherto160C(slowlyover1h)andthistemperatureismaintainedforafurther5h.Afterthistime,theinitialyellowcolourationofthereactantsistransformedtoadarkbrownorevenblackcolour.132 4:Step-growthpolymerization7.Aftercooling,thealuminiumchlorideisdecomposedbytheadditionofcrushedicetothereactionmixturefollowedbyhydrochloricacid(concen-trated28mL).Theproductisthenextractedfromaqueoussolutionusingdiethylether.8.Asolutioncontainingsodiumdithionite(150gperlitre)insodiumhydrox-idesolution(1.5M)isprepared.Thecrudeproductfromstep7aboveisplacedinaflaskandpartiallydissolvedindiethylether.Thismixtureisthenpouredintoaseparatingfunnelandthealkalinesodiumdithionitesolutionisadded(600mL).bThefunnelisthenshakenvigorously,thewaterphasecollectedandtheetherphasewashedwithfurtherportionsofthesodiumdithionatesolutionuntiltheaqueousphasebecomeslighter.9.Theaqueousmaterialfromstep8iscollectedandacidifiedwithconcen-tratedhydrochloricacid;ayellowprecipitateoftherequiredproductisformedatca.pH7.Thisproductiscollectedbyfiltrationatthepumpandpurifiedbyrecrystallizationusingamixtureofethanolandpetroleumether(1:9,500mL).cStep3:Esterificationof2,5-dihydroxypropiophenone10.Asingle-neckedround-bottomedflask(500mL)isfittedwithacondenserandadryingtube,and2,5-dihydroxypropiophenone(17g,0.1mol),acetylchloride(170mL),andmagnesium(0.05g)areadded.Thereactionmixtureisheatedtorefluxinawater-bathsetatatemperatureof55–60C.Aftertwodaystheexcessacetylchlorideisremovedunderreducedpressure(rotaryevaporator).11.Thecrudeproductfromstep10aboveispurifiedbydrycolumnflashchromatography12,dandthenbyrecrystallizationfromamixedsolventofpetroleumetherandethylacetate(1:1)toyieldcolourlesscrystals(m.p.57–60C).aIfTLCrevealsanunexpectedspot,thenitmaybepossibletocompletetheconversionbyaddingafur-therportionofpropionoylchlorideasinsteps1and2.bHydroquinonesareparticularlysusceptibletoaerialoxidation,butthequinonesproducedarereadilyreduced.cTheproductobtainedbycrystallizationcontainedatracecontaminantasrevealedbyTLC;neverthe-less,thiswasconsideredsufficientlypuretocarryontothenextstagewherepurificationiseasier.Theproductcanbepurifiedbycolumnchromatographyonsilica,usingamixedsolventsystemcomposedofpetroleumetherandethylacetate;thematerialisratherpolarandhasonlylimitedsolubilityinthiseluantmixturemakingthisprocesstooinefficienttobedoneonalargescale.dActivatedAlO(neutral)isusedasthestationaryphase.Thisisplacedinasintered-glassfunnel23(100mL),placedonacleanBuchnerflaskandconnectedtothewateraspirator,andallowedtosettle.Thecrudeproductisplacedontopofthestationaryphaseasasolution,andtheelutingsolventpassedthroughwiththeaidofthewatervacuum.Inthiscase,amixedsolventofethylacetateandpetroleumetherissuitable,andthepolarityofthesolventisincreasedfrom5%to60%ethylacetatein5%stepsusinga100mLofsolventateachelution.Someexcellentaccountsofthisprocedurearegivenelsewhere.13,14133 Z.Heetal.Protocol3.Preparationofamain-chainliquidcrystallinepoly(esterether)withaflexibleside-chainCaution!Carryoutallproceduresinawell-ventilatedfume-cupboard,wearappropriatedisposablegloves,alab-coat,andsafetyglasses.Equipment●Dualmanifold(nitrogen/vacuum)●Sourceofdrynitrogen●Glasstubewithaground-glasstop●Bunsenburnerandside-arm●Glassmortarandpestle●Screwtopthermometeradapter●Wood’smetalbath●Gasbubbler●Apparatusforfiltration,Buchnerfunnel●Finecapillary(madefromanordinarypipette)andflask,waterpump●Anelectromagnet(B
0.6T)equippedwith●Vacuumovenathinhot-stageandatemperaturecontroller●Kaptonsheetof25mthicknessMaterials●Monomer4,0.97g,4mmoltreatasharmful●Monomer5,1.5g,4mmoltreatasharmful●Zincacetatedihydrate,0.5mg,2106molharmfulbyinhalationandifswallowed,irritant●Antimony(lll)oxide,0.7mg,2106moltoxicbyskincontact,inhalation,andifswallowed,potentialcarcinogen●Methanoltoxicbyinhalationandifswallowed,highlyflammable●p-chlorophenolharmfulbyskincontact,inhalation,andifswallowed●Wood’smetalharmfulbyinhalation,incontactwiththeskin,andifswallowedMethodPreparation:Monomer4issynthesizedasabove;monomer5ispreparedusingaprocedureanalogoustothatdescribedinProtocol5below.a1.Anequalmolaramountofmonomer4(0.97g,4mmol)andmonomer5(1.5g,4mmol)aregroundtoafinepowderinaglassmortar.Themixtureisthentransferredtoaglasstubeequippedwithaside-armandaground-glassjoint.TothesemonomersisthenaddedthecatalystmixtureconsistingofZn(CHCO)2HO(0.5mg,2106mol)andSbO(0.7mg,2106mol).322232.Anitrogeninletisconstructedusingafinecapillarybheldthroughascrew-topQuickfitthermometeradapter,placedontopoftheglasstube.Thesystemisadjustedsuchthatthecapillaryreachesthebottomoftheglasstube.Theside-armisconnectedtoagasbubbler.TheglasstubeisthenplacedinaWood’smetalbath,whichisheatedbymeansofaBunsenburner(care!).3.AflowofnitrogengasisallowedtopassthroughthereactionmixtureandisheatedbymeansoftheWood’smetalbath.Whenthemixturebecomesmolten,thetemperatureismaintained.Thepressureinsidetheglasstubeisreduced,firstusingthewateraspiratortoremovemostoftheaceticacidpro-ducedinthereaction,andthenusingastandardrotarypumpforabout3h.c134 4:Step-growthpolymerization4.Whenthereactionisjudgedtobecomplete,thereactionmixtureiscooledandremovedfromtheWood’smetalbath.Thepolymeriscollectedbybreak-ingtheglasstube.5.Thecrudepolymerispurifiedbydissolvinginp-chlorophenolat80Cfol-lowedbyprecipitationbytheadditionofcoldmethanoltothesolution.Thepurifiedpolymeriswashedwithmethanolthreetimesandthendriedinavacuumovenat50Cfor12–18h.6.Apolymerfilmof1–2cmdiameterand0.5–1.0mmthicknessispreparedbymeltingonahotplateinbetweentwosheetsofKapton.Aftercooling,thetopsheetispeeledoff.7.Toalignthesamplemagnetically,thefilmpreparedinstep6isplacedonahot-stageinbetweenthetwopolesofanelectromagnet.Thehot-stageispoweredbyatemperaturecontrollerandthetemperatureprobedwithathermocouple(Chrome–alumel—type3).Themagneticfielddirectionmustbemarkedcarefullyonthesample.Thehot-stageisconnectedtoasupplyofnitrogenandthesampleismaintainedunderanitrogenatmosphereforthedurationoftheexperiment.(Thispreventsthermallyinitiatedoxidationofthesample.)Thesampleisthenheatedto190C,andwhenthetemperatureisstabilizedthemagneticfieldisswitchedon.8.Themagneticfieldismaintainedfor2h,andthesampleiscooledrapidlyonacoldmetalsurfaceorwithliquidnitrogenassoonasthepowersupplyofthemagnetisturnedoff.ThefilmisthenplacedinthesampleholderofasuitableX-raydiffractometer(withaxisverticallyaligned)andthediffractionpatternisrecordedwithaflat-platecamera.aMethyl-p-hydroxybenzoate(33.6g,220mmol)andpotassiumcarbonate(30.4g,220mmol)aredis-solvedinDMF(180mL).Thesolutionisheatedto70–80Cwithstirring,anddibromooctane(25g,90mmol)isaddedtothesolution,whichisheatedovernight.Monomer5isisolatedbyprecipitationintowaterfollowedbyrecrystallization.Thedi-ester(30g,70mmol)ishydrolysedwithpotassiumhydroxide(24.3g,435mmol).bAfineglasscapillarycanbepreparedfromastandardPasteurpipette,byheatingtheglassendofthepipetteinahotflamewhilstholdingthepipettefirmlyinbothhands.Whentheglasssoftensandbeginstodeform,thepipetteisquicklyremovedfromtheheatsourceandtheendspulledapart.cThehighviscosityofthepolymermeltmaycauseproblems.Inacondensationpolymerization,viscosityofthepolymermeltwillgraduallyincreaseasthereactionprogresses.However,theincreaseofthemolecularweightmayalsobelimitedbythehighviscosity,asthemonomerdiffusionrateisdrasticallyreduced.Althoughitislikelythatlittleaceticacidisobservedcondensingatthevacuumoutlet,itisimportanttokeepthereactiongoinginordertoimprovethemolecularweightatthisstage.4.Non-periodiccrystallizationfromaside-chainbearingcopolyesterInhighlyaromaticpolymers,processibilityisamajorproblem.Onepossiblesolutiontothismightbetopreparecopolymers,sincethedisruptionofregularsequencesshouldrestrictcrystallization.15Unfortunately,itisfound135 Z.Heetal.thatshortsequencesinthepolymerchainlocallymatchtoformcrystals,sotheimprovementinprocessibilityislessthanwhatmightbehoped.16Inthisexample,bothabiphenylandaphenylunitareincludedinacopolymer,withthephenylringsystemfurthersubstitutedwithanaliphaticside-chain,inordertopromoteadditionaldisruptiontoanysolid-stateordering.17Themodificationofpolymerrepeatunitsaltersthepropertiesofthefinalpoly-mersdramatically.Thepolymersproducedexhibitcomplexcrystallizationbehaviour.18Thepolymerdescribedhereispreparedthroughinterfacialpolymerization9usingavariationofthewell-knownSchotten–Baumannreaction.Thereac-tionisshowninScheme4.Toworkeffectively,thearomaticOHgroupsmustbedeprotonatedbytreatmentwithbase,andthephenolateionsproducedfromthemonomers10and11thenreactwithsebacoylchloride12.Infact,intheexamplechosen,thepolymerformedwasfoundtohavearatherlowmolecularweight.Protocol4.Formationofacopolyesterbyaninterfacialpolymerization(Scheme4)Caution!Carryoutallproceduresinawell-ventilatedfume-cupboard,wearappropriatedisposablegloves,alab-coat,andsafetyglasses.mHOOHOOOBuO+n+m(CH)28ClCl1012nHOOH11OOOO(CH2)8(CH2)8OOOOOOnOm13BuOScheme4Interfacialpolymerizationtoformanaromaticpolyester.136 4:Step-growthpolymerizationEquipment●Highspeedblender●Dryingtube●Burette●Erlenmeyerflask(250mL)●Single-neckedround-bottomedflask(250mL)●Condenser●Soxhletextractorandthimble●Hotplatestirrerandoil-bath●Apparatusforfiltration,Buchnerfunnel●Differentialscanningcalorimeter(DSC),andflask,waterpumpaluminiumcontainerforDSC●Glassbeaker(1L)●Teflon®-coatedmagneticstirrerbar●ColumnMaterials●Monomer10,0.83g,5mmoltreatasharmful●Biphenol11,0.93g,5mmoltreatasharmful●Sebacoylchloride12,2.3mL,10mmolreactsviolentlywithwaterliberatingtoxicgas,harmfulbyskincontact,inhalation,andifswallowed●Sodiumhydroxide,3.98g,100molcausesburns●Molecularsieve(type4A)dustmaycauseirritationifinhaled●Alumina,typeUG,200meshirritant●Benzoicacidforstandardizationirritant,harmfulifswallowedandbyinhalation●Sodalimefortrapcausesburns●Distilledwater●Tetrabutylammoniumhydrogensulfate,irritant0.18g,0.05mmol●Methanoltoxicbyinhalationandifswallowed,highlyflammable●Chloroformharmfulbyinhalationandifswallowed,potentialcarcinogenMethodPreparation:Monomer10ispreparedbyesterificationof2,5-dihydroxybenzoicacid.aSebacoylchlorideisdistilledunderreducedpressure(b.p.124–125Cat0.7mmHg).1.Carbondioxideandoxygen-freewater19,20isobtainedbyrefluxingdistilledwaterinaround-bottomedflaskwithasodalime-filleddryingtubeontopofthecondenserfor3–4h.Theflaskisthenpurgedwithnitrogenandstoppered.2.Sodiumhydroxidepellets(3.98g,100mmol)aredissolvedinCO2/O2-freewater(300mL)andstoredundernitrogen.TheNaOHsolutionistitratedwithbenzoicacidasastandardusingphenolphthaleinastheindicator.3.Ethanol-freechloroform19isobtainedbypassingethanolthroughacolumnofaluminiumoxide(typeUG,200mesh).Itisthenstoredovermolecularsieve(type4A).4.Biphenol(0.93g,5mmol)andmonomer10(0.83g,5mmol)aredissolvedintheCO2/O2-freesodiumhydroxidesolutionpreparedinstep2above.Thesolutionisthenplacedintoahouseholdblenderbtoformtheaqueousphaseoftheinterfacialpolymerization.Then,tetrabutylammoniumhydrogensulfate(0.18g,0.05mmol)isaddedasphasetransfercatalyst.5.Sebacoylchloride(2.3mL,10mmol)isdissolvedinethanol-freechloroformtoformtheorganicphase.6.Theorganicphasefromstep5ispouredintotheblenderandstirredathighspeedforabout5min,moreCO2/O2-freewatercanbeaddedifnecessary.137 Z.Heetal.Protocol4.Continued7.Theproductisthenputintoabeakerandthechloroformisevaporatedoff.cTheresultingpolymerisfilteredatthewateraspiratorandwashedwithmethanol.ItisthenplacedinaSoxhletthimbleandextractedinaSoxhletapparatususingmethanol.Thisremovesunreactedmonomerandanyotherlowmolecularweightmaterial.Thefinalpolymerwillbeanoff-whitepowder.8.ThecrystallizationbehaviourofthematerialisprobedbyDSC.Asampleofthepolymer(0.01g)isaccuratelyweighedandencapsulatedinanaluminiumcontainerforDSC.ThesampleisplacedintheDSCchamber(seeChapter1)andthenheatedto250Candthetemperatureheldfor5min.Thesampleisthencooledat20C/mintoroomtemperature.Thesamesampleisthenscannedat20Cmin1fromroomtemperatureto250Cinordertorecordthemeltingtransitioncurve.Toobservenon-periodicphenomena,thesampleisfirstheatedupto250Cat20Cmin1andheldatthistemperaturefor5min.Thesampleisthenrapidlycooledto160Candheldatthistemperaturefor12h;itisthenrapidlycooledto120Candheldfor12h,thencooledandheldat90C.dThesampleisthencooledat20Cmin1toroomtemperature.Recordingaheatingscanwillrevealmultipletransitionpeaks.a2,5-Dihydroxybenzoicacid(18.8g,120mmol),butanol(23mL,250mmol),andHSO(3–4mL,conc.)24arerefluxedintoluenepreviouslydriedoversodium(25mL)inaflaskequippedwithaTeflon-coatedmagneticstirrerandaDean–Starktrapfor9h.Oncompletionofthereaction(asrevealedbyTLC),theproductispouredintowaterandextractedwithether.Washingwithsodiumhydrogencarbonatesolutionandthenwaterfollowedbyrecrystallizingfrompetroleumether(60–80fractions)givestheproductasawhitesolid.bItisveryimportanttostirthereactionathighspeedduringthepolymerizationstage.Astandardhouseholdblenderisaconvenientmethodofmixingforinterfacialpolymerization,butshouldnotbeusedwithflammablesolvents.cCare!Significantquantitiesofchloroformshould,ofcourse,beremovedbyusing,forexample,arotaryevaporatorinthenormalway.dThemeltingtemperatureofthepolymerwillbeaffectedbythemolecularweightandcopolymercom-position.Hence,themeltingtemperatureofthefinalcopolymermaybeslightlydifferent.Thetemper-aturesgivenaboverelatetoapolymerwithameltingpointof150C.Ifthetemperatureishigherthanthis,thentheinitialheatingshouldberepeatedandthetemperaturesincreasedaccordingly.5.Acomparisonofmeltpolymerizationofanaromaticdi-acidcontaininganethyleneglycolspacerwithpolymerizationinasolventanddispersioninaninorganicmediumIntheproceduresbelow,methodologyisdescribedtofacilitatemediumscale(ca.100g)synthesisofamain-chainthermotropicliquidcrystallinepolymercontainingethyleneglycolunitsasaflexiblespacerbetweentherigidaromaticunits.Twomethodsaredescribed;meltpolymerization,andpolymerizationinaheat-transfersolventwithaninorganicmedium(Claytone).21Formeltpoly-merization,thematerialisobtainedasanextremelyrigidsolid,whileinthe138 4:Step-growthpolymerizationinorganicmediumthepolymerremainsdispersedevenwhenthereactionisnearcompletion.Inbothcases,highconversionscanbeachieved,butitisnoticeablethatforthemeltpolymersomedecompositionoccursatthelaterstagesofthereaction.Notonlyisthepolymerdiscoloured,buthydroquinoneisevolved.Polymerizationusingaheat-transfersolventappearstobethemosteffectiveintermsofproducinghighmolecularweight;thereislittlediscoloura-tionandnohydroquinoneevolved,suggestinglowlevelsofdecomposition.Althoughthematerialiscontaminatedwiththeinorganicdispersingmedium,thisispresentinrelativelylowconcentrationsand,ascanbeseenfromthepro-tocolsbelow,thepolymericmaterialproducedisrelativelyeasytohandle.Protocol5.Reactionofethyl4-hydroxybenzoatewith1,2-bis(2-chloroethoxy)ethaneandhydrolysistoformthecorrespondingdi-acid18(Scheme5)OOOOOOEtOHHOOEtOO14(1)NaOHK2CO3,KI+(2)HClDMFClOOOOClOO15OOOEtOH1617Scheme5Synthesisofapolymerizablearomaticdi-acidwithaflexiblecouplingchain.Equipment●Three-neckedround-bottomedflask(1L)●Condensers●Thermometer●Droppingfunnelandstopper●Hotplatestirrerandoil-bath●Dean–Starktrap●Single-neckedround-bottomedflask●TLCplate(withfluorescentindicator)●Apparatusforfiltration,Buchnerfunnel●Erlenmeyerflasks(various)andflask,waterpump●Teflon-coatedmagneticfollowerMaterials●Ethyl-4-hydroxybenzoate,182.6g,1.1molirritatingtoeyes,skin,andrespiratorysystem●Potassiumcarbonate,151g,1.1molirritatingtoeyes,skin,andrespiratorysystem●Potassiumiodide,0.5g,3mmolirritant●Dimethylformamide(DMF),500mLpotentiallyteratogenic,harmfulincontactwithskin,irritatingtoeyes●1,2-Bis(2-chloroethoxy)ethane,93.5g,0.5moltoxicbyskincontact,harmfulifswallowed,riskofeyedamage,irritatingtoeyes,skinandrespiratorysystem,mayformexplosiveperoxides●Petroleumether/ethylacetatemixture(3:2forTLC)highlyflammable●Ethanolhighlyflammable●Hydrochloricacid(concentrated)causesburns,irritatingtorespiratorysystem139 Z.Heetal.Protocol5.ContinuedMethod1.DMF(500mL)isplacedinadrythree-neckedflask(1L)equippedwithacondenser,athermometer,andadroppingfunnel.Ethyl-4-hydroxybenzoatea(182.6g,1.1mol),potassiumcarbonate(151g,1.1mol)andpotassiumiodide(0.5g,3mmol)areaddedtotheDMF.Arelativelylargeamountofsolidmaterialremainsundissolved.b2.Themixtureisthenheatedto80Cand1,2-bis(2-chloroethoxy)ethane(93.5g,0.5mol)isaddedoverabout3h.HeatingoftheresultantmixtureisthencontinuedwithoccasionalstirringuntilTLCsuggeststhatthereactionisessentiallycomplete.c,dInthiscase,afteraboutninedaysTLCshowsthatthemajorityofthematerialispresentaseitherethyl4-hydroxybenzoate(which,ofcourse,ispresentinslightexcess)orasthedi-aromaticetherwithonlyafaintspotduetothemono-aromaticcompound.3.Theflaskisthenallowedtocooltoroomtemperatureandtippedinto3Lofwater,whereuponanoilisformed,whichrapidlysolidifiestogiveawhiteproduct.Thissolidisfiltered,andrecrystallizedfromethanoluntilthesolu-tionisnolongeryellowandTLCshowsonlythepresenceofthedi-ester.Typicalyield85g(38%).e4.Asingle-neckedround-bottomedflaskisequippedwithaDean–Starktrap,fcondenser,andTeflon®-coatedmagneticfollower.Thedi-ester(68.5g)isaddedtotheflask.Thenpotassiumhydroxide(56g,1mol)dissolvedinwater(500mL)isaddedtogetherwithethanol(200mL).5.Thesolutionisthenheatedtoboiling.Afterca.1–2hallthematerialwilldissolve,andthesolventisremovedfromtheside-arm,untiltherateofcollectionslowssubstantially(afterca.200mLhasbeenremoved).aAlthoughthismaybesimplymisfortuneonthepartoftheworker,onebatchofthisstartingcompoundwasseverelycontaminatedwiththedimethylester.Botharefineindependently,butthemixtureisnot,sincethecrudeproductcannotbereadilypurifiedbycrystallization.bAsaconsequenceofthissolidmaterial,magneticstirringofthesolutionisnotpossible.Inviewofthelongperiodrequiredforreaction,mechanicalstirringwasdeemedunsuitable;asaconsequencenostirringwasusedinthisprocedure.cSolventpetroleumether/ethylacetate(3:2)—3spots:topspot,R0.46,duetoethyl4-hydroxybenzoate,fnextspot,Rf0.33,duetomono-ether,andlowestspot,Rf0.20,duetodi-ether.dAsmallsampleistakenfromthereactionflaskanddilutedwithasmallamountofwater,thiscausestheorganicmaterialtoprecipitateandallowssomeofthesolventtoberemovedwithapipette.Thenacetoneisaddedtodissolvetheprecipitate.ThisprocedurereducestheamountofDMFpresent,whichcaused‘smearing’ofthespots.eImprovedyieldscanbeobtainedbyincreasingtheamountofKIto1%andincreasingthetemperatureto~100C(intheliquid).However,sincecaremustbetakentoavoidoverheatingasthesolidmaterialintheflaskresultsinaninhomogeneoustemperaturedistribution,thisisprobablynotsuitedtothequantitieshere.Undertheseforcingconditions,theintermediatespot(whichispresumedtobeduetomonosubstitutedmaterials)islostin48h.fThereis,ofcourse,noelementofphaseseparationhere.Thisset-upsimplyprovidesaneasywaytomaintainthesolutionatconstantrefluxand,subsequently,removethevolatilecomponentwithoutchangingfromarefluxtoadistillationarrangement.Infact,theset-upshowninChapter9,thatis,that140 4:Step-growthpolymerization6.ThesolutionisthenallowedtocoolandacidifiedwithHCl.Thesolidisthencollectedbyfiltrationgwashedwithwater,transferredtoanErlenmeyerflask(3L),heatedinwater(
1L),andfiltered.Thisprocedureisthenrepeatedusingmethanolasthesolvent.Afterallowingthemethanoltocool,thesuspensionisfilteredanddriedatthevacuumpump.gThesolidisthendriedinanovenat110Cforatleasttwodays(toaconstantweight);yieldafterdrying48g.hdesignedforremovingwaterfromsolventsofhigherdensity,isbettersincethevolatilecomponentisconstantlycycledthroughtheside-armduringtherefluxingstage.gWithsomedifficulty,thematerialwasfoundtobeveryfineandtendstoblocksinteredfunnels.Consequently,theprocedureforfilteringthismaterialwastoallowmostofthesampletopassthroughundergravity,andtousethepumptoremovethefinalresidues.hTLCshowedonespotandNMRrevealednootherorganiccontaminants.Protocol6.Meltpolymerizationofanaromaticdi-acidcontaininganethyleneglycolspacerEquipment●Single-neckedround-bottomedflask(500mL)●Dualmanifold(nitrogen/vacuum)●Wood’smetalbath●Vacuumsource●Bunsenburner●Sourceofdrynitrogen●Gasoutlettubes(2)●Buchnerfunnelwithground-glassjointMaterials●Di-acid,47.9g,123mmoltreatasharmful●Hydroquinonediacetate,23.8g,123mmolirritatingtoeyes,respiratorysystem,andskin●Antimony(III)oxide,22mg,7.5105moltoxicbyskincontact,inhalationandifswallowed,potentialcarcinogen●Zincacetatedihydrate,16mg,7.3105molharmfulbyinhalationandifswallowed,irritant●Wood’smetalharmfulbyinhalation,incontactwiththeskin,andifswallowed●EthanolhighlyflammableMethodPreparation:Thetetraethyleneglycol-linkeddi-acidmonomerisdriedunderhighvacuumfor2hpriortouse.Hydroquinonediacetateisrecrystallizedfromethanolanddriedundervacuumtoconstantweight.Allglasswareisdriedintheovenat125Cpriortouse.1.Thedrydi-acid(47.9g,0.123mol)andhydroquinonediacetate(23.8g,0.123mol)aregroundusingamortarandpestletoensurethoroughmixing,andantimony(III)oxide(22mg,7.5105mol)andzincacetatedihydrate(16mg,7.3105mol)areadded.Themixtureisthenplacedinapre-weighedsingle-neckedround-bottomedflask(500mL)andweighed.2.Theround-bottomedflaskcontainingthemixtureisfittedwithanoutlettubeattachedtoacollectingflask(aBuchnerflaskwithaground-glassjoint),andthencetothedual-manifoldsystem.Thesystemisthenevacuatedandflushedwithargonseveraltimes.141 Z.Heetal.Protocol6.Continued3.Theround-bottomedflaskisplacedinawarmWood’smetalbathandthebathheateduntilthematerialmelts,awhereuponvigorousbubblingwillstartandaceticacidwillbeliberated.Theflaskismaintainedatthistemperatureuntilnofurtheraceticacidisdistilledover.4.Atthispoint,theflaskisevacuatedviathemanifold(wateraspirator)andafurtherquantityofaceticacidisdistilled.Finally,thepressureisfurtherreducedusingarotarypumptogiveavacuumofca.1mmHgandafurtherquantityofaceticacidisremoved,andheatingisallowedtocontinueforabout30minatthispressure.b5.Theflaskcontainingthepolymerisbrokenandthesolidmaterialremoved.Thispolymeristransferredtoapolyethenebagandtreatedwithahammertoproducesmallparticles.Yield54g(95%).aAtabathtemperatureof260C.bAfterca.1hatlowpressure,theliquidwilldarkenslightlyandsomewhitecrystalswillbeobservedroundtheneckoftheflask—thesehavebeenidentifiedbymassspectrometryashydroquinoneandsuggeststhatthepolymerisdecomposingundertheseconditions.Protocol7.Polymerizationofanaromaticdi-acidcontaininganethyleneglycolspacerbypolymerizationinasolventanddispersioninaninorganicmediumEquipment●Three-neckedround-bottomedflask(500mL)●Dualmanifold(nitrogen/vacuum)●Heatingmantle●Vacuumsource●BeakersandErlenmeyerflasks(various)●Sourceofdrynitrogen●Mechanicalstirrer,polishedglassstirrerrod,●Apparatusforfiltration,Buchnerfunnelpaddle,andTeflonstirrerguideandflask,waterpump●Gasoutlettubes(2)●Thermometer●Mortarandpestle●Buchnerfunnelwithground-glassjointMaterials●Di-acid,50.9,131mmoltreatasharmful●Hydroquinonediacetate,25.3g,131mmolirritatingtoeyes,respiratorysystem,andskin●Antimony(III)oxide,23mg,7.9105moltoxicbyskincontact,inhalation,andifswallowed,potentialcarcinogen●Zincacetatedihydrate,17mg,7.8105molharmfulbyinhalationandifswallowed,irritant●Wood’smetalharmfulbyinhalation,incontactwiththeskin,andifswallowed●Claytone,0.7girritatingtoeyes,respiratorysystem,andskin,carcinogenpotential(inhalation)●High-boilingheat-transferfluidtreatasharmful(Dowtherm),200mL●Ethanolhighlyflammable●Acetonehighlyflammable142 4:Step-growthpolymerizationMethodPreparation:Thetetraethyleneglycol-linkeddiacidmonomerisdriedunderhighvacuumfor2hpriortouse.Hydroquinonediacetateisrecrystallizedfromethanolanddriedundervacuumtoconstantweight.Allglasswareisdriedintheovenat125Cpriortouse.1.Thedrydi-acid(50.9g,0.131mol)andhydroquinonediacetate(25.3g,0.131mol)aregroundusingamortarandpestleandantimony(III)oxide(23mg)andzincacetatedihydrate(17mg)areadded.2.Thismixtureisthenplacedinathree-neckedround-bottomedflaskequippedwithathermometer(0–300C),anoverheadstirrer,andanoutlettubecon-nectedby(thick-walled)tubingtoaBuchnerflaskfittedwithaQuickfit(female)joint.Theconicalflaskis,inturn,attachedtothedual-manifoldsys-temusingasimilaroutlettube.3.Aninorganicclay(Claytone,0.7g)isaddedtogetherwithahigh-boilingheat-transferfluid(Dowtherm,200mL).Themixtureisheatedto250Candstirredvigorously,whereuponliquid(largelyaceticacid)iscollectedintheconicalflask.4.Aftertheinitialboilingoftheliquidsubsides(ca.2h),avacuum(wateraspir-ator)isappliedtoremovefurtheraceticacid.Aftertreatingundervacuum,argonisreadmittedtotheflaskandthesystemleftforafurther10min.Thiscycleofevacuationandheatingunderargoniscontinuedforabout2huntilnomoreliquidiscollected.5.Themixtureisthenallowedtocool,whereuponthepolymerseparatesoutfromthesolvent(andbecomescloudy)atca.200C.Thispolymeristhentrans-ferredintoabeaker(mostlywhilestillliquid,althoughthesolidcouldeasilyberemovedfromtheflask).Acetoneisthenaddedtothewaxysolidobtainedandthematerialgroundunderacetoneusingamortarandpestle.Theproductisthenfiltered,washedfurtherwithacetoneandfinallywashedbyheatinginacetone.Thematerialisdriedinanovenat140C.Yield57g(93%).References1.Flory,P.J.PrinciplesofPolymerChemistry;CornellUniversityPress:Ithaca,NY;1953.2.Kricheldorf,H.R.;Rabenstein,M.;Maskos,M.;Schmidt,M.Macromolecules2001,34,713–722.3.Stockmayer,W.H.J.Chem.Phys.1944,12,125.4.Feast,W.J.;Stainton,N.M.J.Mater.Chem.1994,4,1159–1165.5.(a)Higashi,F.;Ogata,S.;Aoki,Y.J.Polym.Sci.,Polym.Chem.Ed.1982,20,2081.(b)Yamazaki,N.;Matsumoto,M.;Higashi,F.J.Polym.Sci.,Polym.Chem.Ed.1975,13,1373.6.Idemura,S.;Preston,J.J.Polym.Sci.,PartA.:Polym.Chem.Ed.2003,41,1014–1026.143 Z.Heetal.7.Stevens,M.P.PolymerChemistry,AnIntroduction,2ndedn;OUP:Oxford;1990.8.He,Z.;Davis,F.J.;Mitchell,G.R.Polymer1994,35,2218–2221.9.Sorenson,W.R.;Campbell,T.W.PreparativeMethodsofPolymerChemistry,2ndedn;JohnWiley&Sons:NewYork;1968.10.He,Z.;Davis,F.J.;Mitchell,G.R.Eur.Polym.J.1996,32,735–746.11.Fries,K.;Finck,G.Ber.1908,41,2447.12.Harwood,L.M.AldrichimicaActa1985,18,25.13.Harwood,L.M.;Moody,C.J.;Percy,J.M.ExperimentalOrganicChemistry,StandardandMicroscale,2ndedn;Blackwells:Oxford;2000.14.Casey,M.;Leonard,J.;Lygo,B.;Proctor,G.AdvancedPracticalOrganicChemistry;Blackie:Glasgow;1990.15.(a)Flory,P.J.J.Chem.Phys.1947,15,684.(b)Flory,P.J.J.Chem.Phys.1949,17,223.(c)Flory,P.J.Trans.FaradaySoc.1955,51,848.16.Windle,A.H.;Viney,C.;Golombok,R.;Donald,A.M.;Mitchell,G.R.FaradayDiscuss.1985,79,55.17.Zhou,Q.-F.;Lenz,R.W.J.Polym.Sci.,Polym.Chem.Ed.1983,21,3313–3320.18.He,Z.;Davis,F.J.;Olley,R.H.;Mitchell,G.R.Polymer2001,42,5351–5363.19.Perrin,D.D.;Armarego,W.L.F.PurificationofLaboratoryChemicals,3rdedn;PergamonPress:NewYork;1988.20.Furniss,B.S.;Hannaford,A.J.;Smith,P.W.G.;Tachell,A.R.VOGEL’sTextbookofPracticalOrganicChemistry,5thedn;LongmanScientific:Essex,UK;1988.21.Bunn,A.;Griffin,B.P.;Macdonald,W.A.;Rance,D.G.Polymer1992,33,3066–3072.144 5Theformationofcyclicoligomersduringstep-growthpolymerizationABDERRAZAKBENHAIDA,PHILIPHODGE,andHOWARDM.COLQUHOUN1.IntroductionStep-growthpolymerizationiscontrolledbothbytheefficiencyofthesyn-theticrouteschosen(asindicatedinChapter4)andbystatisticalconsidera-tions.Inparticular,theformationofthedesiredpolymerisalmostalwaysaccompaniedbyacyclicoligomerfraction.1,2Asthedilutionincreases,3thechancesofcyclizationalsoincrease,sincepolymerizationisasecond-orderprocessinvolvingthereactionbetweenlinearspecies,whereascyclization,involvingthe(intramolecular)reactionbetweenthetwoendsofalinearmole-cule,isinherentlyafirst-orderprocess.Cyclizationisaparticularfeatureoftheearlystagesofastep-growthpolymerization(uptoextentsofreactionof98–99%),whereaproportionoftheendgroupsthatreactareonthesamemolecule.Hence,cyclicsform.Sincethechancesofmeetingoftheendgroupsdecreaserapidlyasthedistancebetweenthemincreases,thecyclicsareofrelativelylowmolecularweight,thatis,theyareoligomers.Furtherreactionleadsmainlytolinearmolecules,althoughatextremelyhighconver-sionsthenumberofendgroupsisquitesmallandintramolecularreactionsessentiallyterminatetheprocess,suchthatitmightbeexpectedthatallchainsultimatelycyclize.4,5Practicallythough,thelevelsofconversionnecessarytoobtaintheseverylargeringsareextremelyhighanddifficulttoobtain(eitherbyvirtueofsidereactions,monomerimperfections,orsimplythelevelofviscosityofhighmolecularweightpolymersolutions).Whatisusuallyobtained,therefore,isamixtureofcyclicsandlinearmolecules.However,sincecyclicoligomersoftendifferconsiderablyin,forexample,solubilitycomparedtotheirhighmolarmasslinearhomologues,separationisoftenrelativelystraightforward.6Thecommercialimportanceofpolymersproducedbystep-growthpoly-merizationgivesaparticularsignificancetounderstandingthenatureofsuch A.B.Haidaetal.materials.Thepresenceofcyclicoligomerscanbedetrimentaltothepolymerpropertiessincetheirpresencecouldcauseproblemsduringprocessing.Forinstance,cyclicoligomersofpolyethyleneterephthalate(PET)tendtomigratetothesurfaceofspunfibresand,undercertainconditions,theycrystallizetoproduceasurface‘bloom’whichinterfereswithsubsequentdyeing.Morerecently,itisthereverseofcyclization,namelyring-openingpolymerization,whichhasbeenaparticularfocusofattention.Suchring-openingpolymeriza-tionsofferanattractiveroutetohighperformancepolymers,7particularlyinviewofthelowviscosityoftheoligomericprecursors,theabsenceofvolatileby-productsandthefactthatfornon-strainedringsthepolymerizationisentropicallydrivenandessentiallythermallyneutral.Arangeofsophisticatedtechniqueshasbeenusedtosynthesizecyclicsystems,8inparticular,withregardtosupermolecularchemistry.9However,astatisticalapproachbasedonhighdilutionhastheadvantageofsimplicity,thismakesthisapproachparticularlyattractiveforcommercialprocesses,wherelarge-scaleproductionmayberequired.Unfortunately,verydilutesolutionsallowthesynthesisofonlysmallamountsofproducts,andthusformostsyntheticworkaninfluxionprocedureisusuallymorepractical.Inthepseudo-high-dilutionmethod,thereactantsarebroughttogetherataratethatislowerthantherateofthereaction,andaresubjectedtorapiddispersioninadiluent.Typically,controlledslowadditionisachievedusingaprecisiondroppingfunnelorasyringepump.Thereactivechainconcentrationismaintainedataverylowlevel,sothatthereactiveendgroupswillreactintramolecularly(cyclization),ratherthanundergoingintermolecularcon-densation(chainextension).Apseudo-high-dilutionreactionrequiresthatreactiveintermediatesarerapidlydilutedastheyareintroduced,favouringtheformationofcyclics,andifthelinkingreactionsarenotreversiblethefinalconcentrationsofproductscanbehigh.Therateofthecondensationreactionmustbehighrelativetotherateofreactantaddition,sothatreactantconcentrationsdonotbuildupduringthereaction.Providedthattheringssoformeddonotreactfurther,highfinalconcentrationofcyclicmaterials(upto1.0M)canbeobtained.ThisprocedurecorrespondstotheRuggli/Zieglerhigh-dilutiontechnique.Inthefollowingaccount,theproductionofcyclicsystemsinseveralstep-growthpolymerizationsisdescribed,withparticularemphasisonwaysinwhichtheamountofcyclicmaterialcanbemaximized.2.Synthesisandextractionofcyclicoligomersofpoly(etherketone)Poly(etherketone)(PEK)1isacrystallinehigh-performancearomaticpolymer.Itcanbepreparedinsolution10fromthecondensationof4,4
-dihydroxybenzophenonewith4,4
-difluorobenzophenone,inthepres-enceofanhydrouspotassiumcarbonate,usingdiphenylsulfoneassolventat146 5:Cyclicoligomersbystep-growthpolymerizationhightemperature(310C),asshowninScheme1.Thereactionmustbeperformedathightemperaturetopreventprematurecrystallizationofthepolymeratonlylowmolecularweight.Afterpolymerization,thediphenylsul-fonecanberemovedfromtheproductbyextractionwithhotmethanol.Materialproducedinthiswaystillcontainsmorethan10%ofcyclicsystems,whichmaybeextractedwithchloroform,since,asisoftenfoundforcyclicoligomers,6theydiffersubstantiallyinsolubilityfromtheparentpolymer.Protocol1.SynthesisofPEKandisolationofcyclicoligomers(Scheme1)Caution!Carryoutallproceduresinawell-ventilatedfume-hood,wearappro-priatedisposablegloves,alab-coat,andsafetyglasses.Neveruseflat-bottomedflasksonrotaryevaporators.OOFFOOn13K2CO3OPh2SO2,310°COHOOHO2n4Scheme1SynthesisofPEKbyreactionof4,4
-dihydroxybenzophenoneand4,4
-difluorobenzophenone.Equipment●Dualmanifold(nitrogen/vacuum)●Sourceofdrynitrogen●Three-neckedround-bottomedflask●Condenser(100mL)●Erlenmeyerflask●Hot-platestirrerandoil-bath●ApparatusforSoxhletextraction,●Apparatusforfiltrationundersingle-neckedround-bottomedreducedpressure:Buchnerfunnel,flask,Soxhletextractorthimbleandflask,andwateraspiratorcondenser●Teflon-coatedmagneticfollower●Thermometer●Nitrogeninlet147 A.B.Haidaetal.Protocol1.Continued●Aluminiumsheet●Mechanicalstirrer,polishedglassstirrerrod,●Heatingmantleandsand-bathpaddle,andTeflonstirrerguideMaterials●4,4
-dihydroxybenzophenone,irritatingtoeyes,skin,and2.0g,9.3mmolrespiratorysystem●Anhydrouspotassiumcarbonate,irritatingtoeyes,skin,and1.70g,12.3mmolrespiratorysystem●Diphenylsulfone,13.30gharmfulifswallowed,irritatingtoeyes,skin,andrespiratorysystem●4,4
-Difluorobenzophenone,Irritatingtoeyes,skin,and2.04g,9.3mmolrespiratorysystem●Chloroform,ca.100mLharmfulbyinhalation,andifswallowed,potentialcarcinogen●Methanol,ca.300mLtoxicbyinhalationandifswallowed,highlyflammableMethod1.A100mLthree-neckedround-bottomedflaskisequippedwithacondenser,fittedwithanitrogeninlet,amechanicalstirrer,andathermometer.Tothisflaskisaddedamixtureof4,4
-dihydroxybenzophenone(2.0g,9.3mmol)andanhydrouspotassiumcarbonate(1.70g,12.3mmol)indiphenylsulfone(13.30g).a2.Theflaskisplacedinasand-bathcontainedinaheatingmantleandthereac-tionmixtureisvigorouslystirredat200Cunderanitrogenatmospherefor1h.Then4,4
-difluorobenzophenone(2.04g,9.3mmol)isaddedrapidlyandthetemperatureisgraduallyraisedto310Candheldatthistemperaturefor3h.3.Whenthepolymerizationiscomplete,thehotviscousmixtureispouredontoacleanaluminiumsheetandallowedtocool.Atoffee-likesolidisformed.Thisiscollectedandmilledtoapowder.Thepowderisthenextractedwithrefluxingmethanol(2150mLportions)inordertoremovethediphenyl-sulfone.Thefinepowderthatremainsiswashedwithwaterandthenmethanol,anddriedtogivethecrudeproduct(3.41g,93%).4.Toisolatethecyclicmaterial,thecrudeproductisextractedwithchloroform.Asampleofthecrudeproduct(1.50g)isplacedinaSoxhletthimble,andextractedwithchloroformfor24h.Thechloroformisremovedontherotaryevaporatortogivecyclicoligomers.b,caThismaterialactsasasolventatthetemperatureofthepolymerization(m.p.127–129C,b.p.379C).bThesampleobtainedhad
0.65dL/g(HSO);T152CandT370C.Themolecularinh24gmweightcanbeestimatedbypartialreductionofasmallportionofpolymer3withtriethylsilaneandtrifluoroaceticacidtogiveasampleinwhich68%ofthecarbonylshavebeenreduced(by1HNMR).Thismaterialissolubleindimethylacetamide(thesamplehadMn8400andMw13900byGPC).c13%w/woftotalproduct;GPCshowsthisfractiontoconsistofcyclicsfromthetrimeruptotheoctamer.148 5:Cyclicoligomersbystep-growthpolymerizationThepreparationofPEKinsolutionmakestheformationofringsmorelikelythan,forexample,inmeltpolymerizations,suchasthosedescribedinChapter4.Inprinciple,theproportioncanbeincreasedsubstan-tially,however,byusingconditionsthatkeeptheconcentrationofreactivechainendslow.Asnotedabove,lowconcentrationsare,atbest,inconvenientonalaboratoryscale,andcertainlywouldnotbeamenabletoscale-upforcommercialproduction.However,ifthemonomerisintroducedslowly,suchthatitreactsmorerapidlythantherateofaddition,thenintramolecularreac-tionisfavoured.Thesituationiscomplicatedbythepossibilityofareversiblefluoride-inducedcleavageoftheoxygen–phenylbond,sothatifthefluorideionstaysinsolutionthereisapossibilitythattheopen-chainformandthecyclicformmayequilibrate.11Nevertheless,thefollowingprocedureshowshowthisapproachmaybeusedtoisolatecyclicoligomersofPEK.12Thereactioninvolvestheintramolecularreactionof4-fluoro-4
-hydroxybenzophenone5(itselfproducedfrom4,4
-difluorobenzophenone1asshowninScheme2)inamixtureofNMPandtolueneinthepresenceofsodiumcarbonate(Scheme3).Theprocessgivesahighyieldofcyclicmaterial.Suchringsmaythenbepolymerizedbyreactionwiththepotassiumsaltof4-hydroxybenzophenoneat385C.12OOK2CO3FFDMSOHOF1KCO523NMP/TolueneOOn4Scheme2SynthesisofPEKwithahighconcentrationofmacrocycles.149 A.B.Haidaetal.OOOOOOOOOOOOOOOOOOOOOOOO4a4b4cScheme3Cyclicoligomerssynthesizedfrom4-fluro-4
-hydroxybenzophenone.Protocol2.SynthesisofcyclicoligomersofPEKunderpseudo-high-dilutionconditionsCaution!Carryoutallproceduresinawell-ventilatedfume-hood,wearappropri-atedisposablegloves,alab-coat,andsafetyglasses.Neveruseflat-bottomedflaskswithrotaryevaporators.Equipment●Dualmanifold(nitrogen/vacuum)●Sourceofdrynitrogen●Nitrogeninlet●Condensers●Hot-platestirrerandoil-bath●TLCplate(withfluorescentindicator)●Apparatusforfiltration,Buchner●ApparatusforSoxhletextraction,funnelandflask,wateraspiratorsingle-neckedround-bottomed●Three-neckedround-bottomedflaskflask,Soxhletextractorthimbleand(500mL)condenser●Teflon-coatedmagneticfollower●Single-neckedround-bottomedflask●Dean–Starktrap(500mL)●Thermometer●Separatingfunnel(500mL)●Erlenmeyerflasks(varioussizes)●Syringepump●Vacuumoven●ChromatographiccolumnMaterials●4,4
-Difluorobenzophenone,15.0g,68mmolirritatingtoeyes,skin,andrespiratorysystem●4-fluoro-4
-hydroxybenzophenone,5.00g,23mmolirritatingtoeyes,skin,andrespiratorysystem●Sodiumhydroxide,5.44g,136mmolcausesburns●DMSO,150mLharmfuliftakeninternally,irritatingtoeyes●Hydrochloricacid,150mLof20%causesburns,irritatingtorespiratorysystem●Anhydrouspotassiumcarbonate,2.00g,irritatingtoeyes,skin,14.7mmolandrespiratorysystem●Dichloromethane,ca.100mLharmfulbyinhalation,potentialcarcinogen●Toluene(forreactionandrecrystallization)highlyflammable,harmfulbyinhalation150 5:Cyclicoligomersbystep-growthpolymerization●Silica(particlesizeof0.040–0.063nm)harmfulbyinhalation,irritatingtorespiratorysystem●N-Methyl-2-pyrrolidone(NMP),300mLharmful,possiblereproductivetoxin●Methanol,600mLtoxicbyinhalationandifswallowed,highlyflammable●Chloroformforextractionandharmfulbyinhalation,andifchromatographyswallowed,potentialcarcinogen●EthylacetateforchromatographyhighlyflammableMethod1.Toasingle-neckedround-bottomedflaskequippedwithacondenser,aTeflon-coatedmagneticfollowerandinlettothedoublemanifoldisaddedamixtureof4,4
-difluorobenzophenone(15.0g,68mmol),sodiumhydroxide(5.44g,136mmol),water(35mL),andDMSO(150mL).2.Theflaskisevacuated,placedunderanitrogenatmosphere,andstirredvigorouslyat60Cfor2h.Thetemperatureisthenraisedto70Candstirringcontinuedforafurther20h.3.Themixtureiscooledtoroomtemperatureandthenadded,withvigorousstirring,toanErlenmeyerflaskcontainingcoldwater(300mL).Inaseparat-ingfunnel(500mL),thesolutioniswashedwithdichloromethane(275ml).Theaqueouslayeriscollectedandacidifiedwithhydrochloricacid(150mLof20%).Thewhiteprecipitateiscollectedbyfiltrationatthewateraspirator,washedwithwateranddriedat60C.Theproductispurifiedbyrecrystalliza-tionfromtoluene.a4.A500mLthree-neckedround-bottomedflaskisequippedwithaDean–Starktrap,acondenser,athermometer,andanitrogeninlet.Tothisflaskisaddedanhydrouspotassiumcarbonate(2.00g,14.7mmol),NMPa(250mL),andtoluene(45mL).Thesolutionispurgedwithnitrogen,stirredvigorously,andthetemperatureisraisedto145–150C.5.Asolutionof4-fluoro-4
-hydroxybenzophenone(5.00g,23mmol)inNMP(45mL)isaddedovera24hperiodusingasyringepump.bWhenadditioniscomplete,thereactionisstirredforafurtherhourat145–150Candthencooledtoroomtemperature.6.Thereactionmixtureisaddedslowlytocoldmethanol(300mL).Awhitepre-cipitateforms.Theprecipitateiscollectedbyfiltrationatthewateraspirator,washedwithwater(300mL)andthenmethanol(300mL).Finally,theprod-uctisdriedinavacuumovenat70C.7.Aportionofthecrudeproductfromstep3aboveisthenplacedinaSoxhletthimbleandextractedwithchloroformfor24h.Thechloroformisremovedontherotaryevaporatortogiveaproductconsistingessentiallyofcyclicoligomers.c8.Individualcyclicoligomersareisolatedfromthecrudeproductfromstep7byextractingwithdichloromethaneandsubjectingthisextracttocolumnchromatographyonsilicageldusinggradientelution;amixtureofchloroformandethylacetatecanbeusedstartingwithalowproportionofthemorepolarethylacetate(0.5%)andfinishingwithaslightlylarger151 A.B.Haidaetal.Protocol2.Continuedquantity(2%).Thisprocedureyieldsthetrimer,tetramer,andpentamer(structuresshowninScheme3).eaYield12.60g(86%),m.p.168C,NMPisfreshlydistilledfromcalciumhydride.bThisallowstheadditionofreagentsataslowratesuchthattheconcentrationiskeptlowatalltimes;atthesametimetheDean–Starktrapfacilitatestheremovalofwateranddrivesthereactiontowardsoligomerformation.cTypicalyieldofcyclicmaterial79%;GPCindicatestrimer12%,tetramer33%,pentamer9%,hexamer9%,heptamer7%,octamer7%,andnonamer1%.dMercksilicagel60ofparticlesizeof0.040–0.063nm.eTheoligomersareobtainedinvaryingquantitiesfrom50to200mg.Forthetrimerandtetramer,crys-talssuitableforX-rayanalysismaybegrown.3.Synthesisofsomesulfone-linkedparacyclophanesfrommacrocyclicthioethersPoly(1,4-phenylenesulfone)hasanexceptionallyhighmeltingpoint,believedtobeinexcessof500C.13Clearly,processingsuchmaterialrepres-entsanenormouschallenge.Consequently,thepolymerrepresentsanattractivetargetforaprecursorroutebasedonthering-openingpolymeriza-tionofcyclicoligomers.Thus,thedevelopmentofcyclicprecursorstosuchmaterialsisatopicofgreatinterest.Inthissection,aroutetosuchasystemisdescribed.14,15Itinvolvesthreesteps:thefirstisthesynthesisof4,4
-thiobis(benzenethiol)8,bychlorosulfonationofdiphenylsulfidefollowedbyreductionasoutlinedinScheme4,thesecondisthenucleophiliccondensationpolymerizationofthisdithiolwithand4,4
-dichlorodiphenylsulfone9underconditionsofhighdilution;finally,theresultingmacrocyclesareoxidizedtosulfone-linkedparacyclophanes.Inthisway,cyclicsystemscontaining4,8,12,16,and20benzeneringscanbeproduced.*Protocol3.Preparationof4,4
-thiobis(benzenethiol)(Scheme4)andpolymerizationwith4,4
-dichlorodiphenylsulfoneunderconditionsofhighdilution(Scheme5)Caution!Carryoutallproceduresinawell-ventilatedfume-hood,wearappro-priatedisposablegloves,alab-coat,andsafetyglasses.*Inprinciple,cyclicsystemswithsixunitscannotbeformeddirectlyinthisreaction,however,inarelatedreactioninwhichtheoxidizedformof8,thatis4,4
-sufonylbis(benzenethiol)isreactedwith4,4
-dichlorodiphenylsulfone,thecyclicsystemcontainingsixaromaticringshasbeenfoundtopredomi-nate.Thisarisesbyintramoleculardisplacementofabridgingthioethergroupratherthanaterminalhalide.14152 5:Cyclicoligomersbystep-growthpolymerizationSO2ClSHSSSSO2ClSH687Scheme4Synthesisof4,4
-thiobis(benzenethiol).SOOHSSHSS8OOSSSnClCl109OOOOSSSSOOOOn11Scheme5Synthesisofmacrocyclicthioethersulfonesandtheiroxidationtosulfone-linkedparacyclophanes.Equipment●Three-,two-,andsingle-necked●Condenserround-bottomedflasks(500mL,1L,100mL,respectively)●Hot-platestirrerandoil-bath●Gasinletandgasoutlet●Droppingfunnel(pressure-equalizing)●Apparatusforfiltration,Buchnerfunneland●Erlenmeyerflasksflask,wateraspirator(varioussizes)●Dean–Starktrap●Thermometer●Chromatographycolumn●Vacuumoven●Teflon-coatedmagneticfollower153 A.B.Haidaetal.Protocol3.ContinuedMaterials●Diphenylsulfide,15.0g,80.0mmolharmfulifinhaled,irritant●Chlorosulfonicacid,30mLoxidizer,corrosive,causessevereeye,nose,andthroatburns,toxicbyinhalation●Silicagelforchromatographyharmfulbyinhalation,irritatingtorespiratorysystem●THFhighlyflammable,mayformperoxides,irritatingtoeyesandrespiratorysystem●Stannouschloridedihydrate,irritant,maycauseburns,harmfulbyinhalation,100g,450mmolskinabsorption,andifswallowed●Glacialaceticacid,ca.500mLflammable,causessevereburns●Anhydroushydrogenchloridecausessevereburns,irritatingtorespiratorysystem●Hydrochloricacid(concentrated),150mLcausessevereburns,irritatingtorespiratorysystem●NaOH(5%),200mLcausesburns●Anhydrouspotassiumcarbonate,2.40g,irritatingtoeyes,skin,and17.2mmolrespiratorysystem●Dimethylacetamide,200mLharmfulbyinhalationandincontactwiththeskin,irritatingtoeyes●Toluene,45mLhighlyflammable,harmfulbyinhalation●4,4
-Dichlorodiphenylsulfone,2.47g,8.63mmoltreatasharmful●Trifluoroaceticacid,12mLharmfulbyinhalation,causessevereburns●Hydrogenperoxide(30%aqueoussolution),10mLoxidant,causesburns●Chloroformforextractionandchromatographyharmfulbyinhalation,andifswallowed,potentialcarcinogen●EthylacetateforchromatographyhighlyflammableMethod1.Toasingle-neckedround-bottomedflaskequippedwithamagneticstirrerandagasoutlettubewhichisconnectedtoawatertrapaisaddeddiphenylsulfide(15.0g,80.0mmol)andchlorosulfonicacid(30mL).Themixtureisstirredatroomtemperaturefor8h.2.Thesolutionisthencautiouslyquenchedinicewater,whereuponawhiteprecipitateisobtained.Thisprecipitateisquicklyfilteredoffandwashedwithchilledwateruntilneutral.3.Thewhitecrudeproductisdriedinavacuumovenat60C,andthenpurifiedbycolumnchromatographyoversilicagelusingTHFastheeluenttogive4,4
-thiobis(benzenesulfonylchloride).b4.Atwo-neckedround-bottomedflaskisequippedwithamagneticstirrer,acondenser,agasinlettube,andagasoutlettube;thegasinlettubeiscon-nectedtoasourceofanhydrousHClcandtheoutlettubeasinnotea.5.Stannouschloridedihydrate(100g,0.45mol)andglacialaceticacid(400mL)areaddedtotheflaskandthemixtureisheatedto50Candstirredwhileanhydroushydrogenchlorideisbubbledintotheflask,untilthemix-tureissaturated.d6.Whenallthestannouschloridehasdissolved,4,4
-thiobis(benzenesul-fonylchloride)7(10g,0.026mol)isaddedquicklytothestirredsolutionunderaflowofanhydroushydrogenchloride.Thesolutionisthenheatedat80Cfor24h,andrefluxedfor3h.154 5:Cyclicoligomersbystep-growthpolymerization7.Uponcoolingtoroomtemperature,brightyellowcrystalsprecipitatefromthesolution.Thisprecipitateisdissolvedin5%NaOH(200mL),andthesolutionfilteredthroughasintered-glassfunnelintohydrochloricacid(con-centrated,150mL).Thecollectedsolidisthendriedandrecrystallizedfromglacialaceticacidtogiveyellowcrystalsof4,4
-thiobis(benzenethiol)8.e8.A500mLthree-neckedround-bottomedflaskisequippedwithamagneticfollower,athermometer,adroppingfunnel(pressure-equalizing),aDean–Starktrap,condenser,andnitrogeninlet.Tothisflaskisaddedanhyd-rouspotassiumcarbonate(2.40g,17.2mmol),dimethylacetamide(200mL),andtoluene(45mL).Thesolutionispurgedwithnitrogen,thesuspensionofpotassiumcarbonateisstirredvigorously,andtheflaskisheatedintheoil-bathsuchthatthetolueneisrefluxing.9.Amixtureof4,4
-dichlorophenylsulfone9(2.47g,8.63mmol)and4,4
-thiobis(benzenethiol)8(2.16g,8.63mmol)dissolvedindimethyl-acetamide(100mL)isaddeddrop-wiseover5htothestirredrefluxingsus-pension.Oncompletionoftheaddition,thetolueneisremoved(thiscanbedoneusingtheDean–Starktrap)andthetemperatureofthereactionisraisedto155Candmaintainedatthistemperatureforafurther15h.10.Themixtureisallowedtocool,filteredtoremovetheprecipitatedsalts,andthefiltrateconcentratedtoabout60mL.f11.Theresultingprecipitateisthencollectedbyfiltrationatthewateraspirator,washedwithwateruntilalltheacidisremoved(i.e.thewashingisneutralwhentestedwithpHpaper),andthensuspendedinmethanolinasingle-neckedround-bottomedflaskequippedwithacondenserandamagneticfollower.Themixtureisthenstirredat60Cfor30min.Thesolidiscollectedbyfiltrationatthewateraspirator,andthendriedinavacuumovenat70Cfor12–15h.12.Theproductfromstep11containsamixtureofcyclicoligomers.Thesecanbeseparatedbycolumnchromatographyonsilicausingmixturesofethylacetateandchloroform(graduallyincreasingtheethylacetateconcentration).g13.Theisolatedcyclicoligomer(0.25g)issuspendedintrifluoroaceticacid(12mL)inasingle-neckedround-bottomedflaskequippedwithacondenserandamagneticfollower.Thesuspensionisheatedto60Cwithstirringandasolutionof30%aqueoushydrogenperoxide(10mL)isaddedoveraperiodof15min.14.Thetemperatureofthereactionisthenraisedto80Candheatingcontinuedfor3hat80C.Themixtureisthencooledandtheproductcollectedbyfiltrationatthewateraspirator.Finally,therecoveredsolidiswashedwithwaterandmethanol,anddriedinthevacuumovenat100C.aLargequantitiesofhydrogenchlorideshouldnotbeventeddirectlyintothefume-cupboard;usuallytheacidcanbescrubbedbypassingintowater.Itisvitalthatthewaterattheoutletcannotenterthereactionflask.Aninvertedfunnelplacedinabeakerofwatersuchthatitdipsjustbelowthesurfaceissuitablehere.bYield24.5g,80%,m.p.156C.155 A.B.Haidaetal.Protocol3.ContinuedcAnhydroushydrogenchloridegascanbegeneratedbyaddingdrop-wiseconcentratedsulfuricacid(80mL)toNaCl(100g).dThewell-knownprocedureusingzincdustandacidgivesonlyverypooryields.eYield5.20g,80%,m.p.110C(byDSC).fForexample,bydistillationunderreducedpressure.gYieldsofcycliccompounds10:n1,0.25%(m.p.362C);n2,9%(m.p.374C),n3,4.5%(m.p.158C),n4,1%(Tg134C),n5,0.6%(Tg128C).4.SummaryCyclicsystemsareinherentlyproducedinstep-growthpolymerizations.Oligomericmaterialscanbeproducedusingpseudo-high-dilutioncondi-tions;thatis,byslowadditionofreactingmonomertothepolymerizationreaction.Thisprovidesapowerfultoolfordramaticallyincreasingtheyieldsofcyclics(providedequilibrationprocessesdonotcomeintoplay).Thecyclicsystemsproducedhaveconsiderablepotentialasfeedstocksforentropically-drivenring-openingpolymerizations.16References1.Semlyn,J.A.,ed.,CyclicPolymers;Elsevier:NewYork;1986.2.(a)Maravigna,P.;Montaudo,G.InComprehensivePolymerScience;Allen,G.;Bevington,J.C.,eds,Pergamon:Oxford;1989,Vol.5,pp.63–90.(b)Suter,U.R.InComprehensivePolymerScience;Allen,G.;Bevington,J.C.,eds,Pergamon:Oxford;1989,Vol.5,pp.91–96.3.Fawcett,A.H.;Mee,R.A.W.;McBride,F.W.Macromolecules1995,28,1481.4.Kricheldorf,H.R.;Rabenstein,M.;Maskos,M.;Schmidt,M.Macromolecules2001,34,713–722.5.Kricheldorf,H.R.Macromolecules2003,36,2302–2308.6.(a)Bryant,J.J.L.;Semlyen,A.J.Polymer1997,38,191.(b)Bryant,J.J.L.;Semlyen,A.J.Polymer1997,38,4531.7.Hodge,P.;Colquhoun,H.M.;Williams,D.J.Chem.Ind.(London)1998,162.8.Parker,D.,ed.,MacrocycleSynthesis:APracticalApproach;OxfordUniversityPress:Oxford;1996.9.Steed,J.W.;Atwood,J.L.SupramolecularChemistry;Wiley:Chichester;2000.10.Staniland,P.A.InComprehensivePolymerScience;Allen,G.;Bevington,J.C.,eds,Pergamon:Oxford;1989,Vol.5,p.492.11.Colquhoun,H.M.;Lewis,D.F.;Hodge,P.;Ben-Haida,A.;Williams,D.J.;Baxter,I.Macromolecules2002,35,6875–6882.12.Ben-Haida,A.;Colquhoun,H.M.;Hodge,P.;Williams,D.J.J.Mater.Chem.2000,10,2011–2016.13.Robello,D.R.;Ulman,A.;Urankar,E.J.Macromolecules1993,26,6718–6721.14.Baxter,I.;Ben-Haida,A.;Colquhoun,H.M.;Hodge,P.;Kohnke,F.H.;Williams,D.J.Chem.Eur.J.2000,6,4285–4296.15.Baxter,I.;Colquhoun,H.M.;Hodge,P.;Kohnke,F.H.;Williams,D.J.;Chem.Commun.1998,283–284.156 5:Cyclicoligomersbystep-growthpolymerization16.(a)Brunnelle,D.J.;Shannon,T.G.Macromolecules1991,24,3035.(b)Miyatake,K.;Yokoi,Y.;Yamamoto,K.;Tsuchida,E.;Hay,A.S.Macromolecules1997,30,4502.(c)Chen,M.;Gibson,H.W.Macromolecules1996,29,5502.(d)Colquhoun,H.M.;Lewis,D.F.;Fairman,R.A.;Baxter,I.;Williams,D.J.J.Mater.Chem.1997,7,1.157 6ThesynthesisofconductingpolymersbasedonheterocycliccompoundsDAVIDJ.WALTON,FREDJ.DAVIS,andPHILIPJ.LANGLEY1.IntroductionPolymersarebestknownfortheireffectivenessaselectricalinsulators,indeedelectricalwiringthroughouttheworldisnowsheathedinplastic.However,itwasrecognizedearlyonthatpolymerswithanappropriatestruc-tureoughttobeabletoconductelectricity.Unfortunately,thesamefeaturesthatmightallowthisphenomenonalsointroduceintractabilityandprocess-ingdifficulties.Asaconsequence,itwasnotuntilthemid-1970sthatthepotentialofthesematerialswasexploredandbetter-definedmaterialsstartedtobemade.Therearenownumerouspolymerswithsubstantialelectricalconductivitiesandthetopicofelectricallyconductingpolymersstillcontin-uestoexcitewithmanyhundredsofnewpublicationsprintedeachyear.ThebackbonestructuresofsomeofconjugatedpolymersaregiveninTable6.1.Inthischapterweshalldealwithelectrochemicalandchemicalsynthesesofsomerelativelysimpleexamples.Forelectricalconductivity,itisnecessarytotransferchargealongaconjug-atedchain,betweenchains,andalsoalonggrainboundariesorbetweenparticles.Themostenergeticallydifficultprocesswillcontroltherateofchargetransportandthiswillvarywithnatureofthepolymer,itsphysicalform,andotherparameters,butinallcasesconjugationalongthechainisnecessaryalthoughitisnotsufficientforcarbonaceouspolymerstosimplypossessaconjugatedchain.Topromoteconductivity-overlapalongtheentirepolymerchainlengthisrequiredtogiveahalf-filledbandofdelocalized-electrons.Inrealsystems,distortionsofthebondsdisrupttheconjugation,andthematerialsaregenerallysemiconductors.Thehighermetallicconduc-tioncanbeachievedbyaprocessknownasdopinginwhichelectronsareaddedormoregenerallyremovedfromtheconjugatedsystem(althoughthisisnotsameasthedopingprocessfoundinsemiconductortechnology)Thesimplestconjugatedpolymerchainisapolyacetylenechain.Suchmaterialscanbepreparedbycoordinationpolymerization,1orusinga 6:ConductingpolymersfromheterocyclesTable6.1Somepolymerbackbonestructuresformingthebasisforconductingmaterials*12Polyacetylene(trans)Polyacetylene(cis)SNHnn34PolythiophenePolypyrroleNHnn56PolyanilinePoly(phenylenevinylene)*Intheconductingformthesearegenerallypolycationic,chargecompensatedbyanionsthatorigi-natefromtheoxidisingmedium.sophisticatedrouteinvolvingthedegradationofasolubleprecursorpolymer.2Thereareparticularissuessuchaslong-termstabilitythathavetodatemiti-gatedagainstthecommercializationofpolyacetylene,althoughtherelatedpolymerpoly(phenylenevinylene)(PPV)hasattractedattentionbecauseofitsphotophysicalproperties,particularlyasthebasisofapolymerlight-emittingdiode(LED),inwhichanelectricalsignalisconvertedintotheemissionoflight.3Arangeofotherorganicpolymerscanalsobeprepared,inparticularthroughtheoxidationofelectron-richaromaticheterocyclessuchaspyrrole.Polypyrrole(andrelatedheteroaromaticmaterialssuchaspolyanilineandpolythiophene)canbereadilypreparedinthepolycationicformthrougheitherchemical4orelectrochemical5oxidationoftheappropriatemonomertogiveflexible,free-standingfilmsthatarestableinair.Someoftheseproceduresareextremelysimple,andanumberofexamplesaregivenbelow.First,however,abriefintroductiontotheprinciplesofelectrochemicalsynthesisisincluded.2.ElectrochemicalsynthesisThepreparationofpolypyrrole,polythiophene,polyaniline,andrelatedconductingpolymersdemonstratesprinciplesofelectrochemicalsynthesisthataremorewidelyapplicable,anditisinstructivetoexaminetheseindetail.159 D.J.Waltonetal.Anelectrochemicalcellispartofthecompleteelectricalcircuitofthesystemandthuselectronsmusttravelthroughitjustlikeanyotherelectricalcomponent.Ithasaresistance,andunderalteringorvariablecurrentandvoltageconditionsitwillhaveacapacitance.Totransversethecell,electronsmustleavethecath-odeleavingareduced(electron-richspecies)inthecell,whilesimultaneouslyelectronsmustpassintotheanodefromaspeciesinthecellthatbecomesoxidized(electron-poor).Tocompletethecircuitionsmustcrossthecell(cationstowardsthecathodecompetingwithanionstowardstheanode).Clearly,theenergynecessarytopasselectronsrightacrossthecellinvolvestheinherentenergeticsofelectrontransfersatbothelectrodes(‘electrodepoten-tials’oftheprocessesinvolved)andacomponentrelatingtomasstransport,whichinvolvesthediffusionofspeciestoandfromtheelectrodeaswellasthemobilityofionscrossingthecentreofthecell.Highlyoxidizedandreducedspeciesaresimultaneouslyformed,howeverwemayonlybeinterestedinoneofthese,andbecausetheycouldreacttogetherunfavourablyifallowedtomeet,wemaykeepthemapartbyasemi-permeablemembranebetweenthecellcompart-ments.Thiswillincreasetheoverallcellresistancetosomeextentandwillaffectthecellvoltagerequiredtomaintainelectrolysis.Nowifthereweretwohighlyreactivespecies(fortheoxidationandreduc-tionprocess),itwouldrequireonlyalowvoltagetodrivethetwoelectrodereactions.*Infactabatteryisadevicethatcontainsspeciesthataresuffi-cientlyreactivesothatinsteadofneedinganyexternallysuppliedvoltagetomoveelectrons,theelectronsaredrivenexternallyundertheenergyofreac-tion.Alternatively,twounreactivespecies(orevenjustone,ifsufficientlyunreactive)willrequireahighervoltageforelectrolysis.Theupshotisthatthemeasuredvoltagenecessarytodriveacellwiththeminimumtwoelectrodesisacomplexmixtureofpotentialsatbothelec-trodestogetherwithvariousvoltagelossesinthesystem,andwedonotknow,iftherequiredvoltageshouldsuddenlybeseentoriseafteraperiodofelectrolysis,whetherthisisduetosometime-dependenteffectattheanode,thecathodeorelsewhereinthesystem.Sincethemeasuredvoltageintheabovearrangementisambiguous,itiscommontorunatwo-electrodecellatconstantcurrent,sothatthenumberofelectronsbeingtransferredinunittimeisknown,andthechargepassedduringelectrolysis,whichisanimportantfigureofmerittobemonitored,issimplytheproductoftheconstantcurrentandthetimeofpassing.Thisisprocedu-rallysimple,requiringonlyastraightforwardpowersourceasapparatus,buttheremaybecomplexitiesininterpretationofresults.Theelectrolysismix-turecontainsasolvent,anelectrolytesalt,andtheelectroactivespeciesofinterest;andalthoughinitiallythiselectroactivespecieswillnecessarilybechosentobethemostreactive,astimegoesbyandthespeciesbecomes*Thevoltagebetweenthetwoelectrodesinasimplecellofthistypeishighlydependentuponanum-beroffactorsandmoreusuallyathree-electrodecellcontainingachemicalstandardisused(seetext).160 6:Conductingpolymersfromheterocyclesdepleted,inordertomaintainconstantcurrentthepowersourcewillincreaseitsappliedvoltagesothatanotherspecieswillstarttoreact.Thiscouldbethesolvent,forinstance,formingdisadvantageousby-products.Onewaytospotthishappeningistonotetheriseincellvoltageifthepowersourcehasaread-outtodisplaythevoltageitisdeliveringtomaintaincurrent(orelsetheopera-torshouldmakesurethereisavoltmeterinparallelacrossthecell).However,avoltagerisecouldindicatedepletionatthecounter-electrode,partialfoulingofacellmembraneorsomeothereffectthatdoesnotcompromisethereactionofinterestattheworkingelectrode.Furthermore,itmaybethattheoperatorhasselectedtoohighacurrentdensity(currentperunitareaofelectrode)per-hapsevenfromthestartofelectrolysis,suchthattheconcentrationanddiffu-sionpropertiesofthedesiredelectroactivespeciescannotmaintainthiscurrentvalue.Inthiscaseotherprocesseswillinterfere.Now,thisisnotusuallyaproblemforproducingpolypyrroleandrelatedpoly-mers,sinceatypicalfilmontheelectrodeweighsonlysometensofmilligrams,andanelectrolytecontaining,forexample,0.01Mpyrrolecansupportitsforma-tionwithoutappreciabledepletionofthemonomer.Constant-currentelectroly-sisisthereforeoftenusedforthesepolymers;althoughitshouldbenotedthattheexactpropertiesofthefilmcanvarywithpreparationconditions,andwiththismethodologytheexactelectrodepotentialisnotknown.Thereisafurtherconsiderationforthetwo-electrodeorconstant-current(gal-vanostatic)situation,inthatanunusualelectrodematerialsuchasconductiveindium–tinoxide,someothersemiconductororevenanotherconductingorganiccompound,whichitmaybedesiredtocoatintheconductingpolymer,maynotbeabletooperateattoohighacurrentdensity(suchthatelectrochemi-caldamagetotheelectrodeoccursinsteadofthedesiredreaction).Iftheelec-trodemetalisitselfreactivesuchasaluminium,copper,andiron,(andthiscanbeaparticularproblemforoxidations)thentransformationoftheelectrodematerialcancompetewiththedesiredreaction.Thisisrarelyaproblemforahighlyconductingnoblemetalelectrodesuchasplatinum,whichcantoleratehighcurrentdensities.Onebenefitoftheconstant-currentmethodology,however,isthatthetotalchargeQpassed(animportantparameterwhenthereareknownamountsofelectroactivespecies)canbequantifiedsimplybyknowingthetimetforwhichconstantcurrentihaspassedsince(Qit).Theproblemswiththetwo-electrodemethodologydescribedabovecanbeovercomebycarefulcontroloftheelectrodepotentialattheworkingelectrode.Thisis,afterall,themostimportantparameterinanelectrolysis,andifallelec-tronsaretransferredatthesameenergy,thenonlythereactionofchoicewilltakeplace.Todothisrequiresanadditionalelectrode,whichisareferenceelec-trodeagainstwhichpotentialscanbemeasured.Thethree-electrodeconfigura-tionrequiresmorecomplexelectrochemicalapparatuscalledapotentiostat.Theprincipleisanalogoustothesituationinathermalreactioninwhichaheatingmantleissimplyturnedtoaparticularsettingandtheapparatus161 D.J.Waltonetal.allowedtoheatup.Amoreaccuratemeansofcontrolistoemployadigitalthermometerthatgivesfeedbacktotheheatersothat,if,forexample,atemperatureof60Cisdesiredinsidethereactionflask,thencontinuouscomparisonoftheheatedsolutionwiththecalibratedreferencetemperaturedeviceallowsthisvaluetobemaintained.Thisistheequivalentofathree-electrodeelectrolysis,inwhichthereiscontinuouscomparisonbetweenathermodynamicallyreversiblestandardreferencepotentialandthepotentialoftheworkingelectrodetomaintainasetvalue.Atypicalreferencecoupleisthenormalhydrogenelectrode(NHE)inwhichthereactionisHe1_Hatacatalyticsurfacesuchasplatinum22black.However,thisinvolvesthecumbersomeprocedureofbubblinghydrogengas(usuallyfromagascylinderwithimportantsafetyconsequences)intotheelectrolysiscell,somorecommonlyusedreferenceelectrodesaresaturatedcalomel[Hg(I)/Hg(0)](standardcalomelelectrodeorSCE)orsilversilverchloride[Ag(I)/Ag(0)],whichareconvenientlyfabricatedinglasstubesthatmaybecappedbyaglassfritorasaltbridge.Thedifferentstandardreactionshavedifferentchemicalpotentialsandsoitisalwaysimportanttostatewhichreferenceelectrodeisusedwhenquotingvoltages.Strictly,thereferenceelec-trodeshouldbeinfinitelyclosetotheworkingelectrode,butnottouchingit.Inpracticalterms,theelectronicmake-upofapotentiostatallowsveryhighresistanceinthereferenceelectrodecircuit,sothateffectivelyonlyaminus-culecurrentflows(thisisnecessarytokeepthereferencecouplewithintheconditionsofexactthermodynamicreversibility)andsothetipoftherefer-enceelectrodeneednotbeinsuchcloseproximitytotheworkingelectrodesurfaceafterall,especiallyinaconductivesolutionsuchasanaqueousonewherethereisnotsogreataresistancedropacrossthedistancebetweenthetwoelectrodesasthereiselsewhereinthereferenceelectrodecircuit.Theworkingandreferenceelectrodesarethuspoisedatasetpotential,whichwillbebetween3V,sincealmostthewholeoforganicelectrochem-istryoccurswithinthis6-Vrange.(Thesearetruethermodynamicelectrodepotentialsand3Vcorrespondsroughlytotheoxidationofbenzene,while3Vcorrespondsroughlytothereductionofbenzene.)Pyrroleelectro-oxi-dationtypicallytakesplaceabove0.8V(versusSCEreference).However,thepotentialbetweentheworkingandcounter-electrodeswillbehigherthanthesetelectrodepotentialbetweenthereferenceelectrodeandtheworkingeletrode,reflectingthecounter-electrodereactionandotherprocessesrequiringelectricalenergy.Theimportantpointisnowthatastheelectroactivereagentbecomesdepletedwithtimethecellcurrentwilldieaway,eventuallytonothing,withoutanyhigher-energyprocessoccurring,andifforinstancedegradationofanindium–tinoxideelectrodecouldbesuchaprocessthenitwillnotoccur.However,sinceinpotentiostaticelectrolysisthecurrentisnolongeratafixedvalue,toquantifythechargepassedeitheranintegratingdevicesuchasacoulometer(coulombmeter)mustbeputinserieswiththecellorelseacurrent–timeplotmustberecordedandtheareaunderneathitcalculated.162 6:ConductingpolymersfromheterocyclesPotentiostaticelectrolysisisamoresophisticatedtool,necessarywhentherearecompetingprocesseswithsimilarelectrodepotentials(onlythelowestpotentialonecanbeachieveddistinctfromanyothers),andisessentialwhenadynamicmethodisrequired,forexamplerampingavoltagefromonevaluetoanotherandbackagain.Thisisamethodusedintheproductionofconductingpolymers,particularlypolyaniline,wherebetterqualitypolymerfilmsareobtainedbythismethod.Therangeofelectrochemicalapproachesavailableprovidesexcellentflexibilityfortuningthenatureoftheproducts,theirdopinglevelsandeventheirmorphology.Thewiderangeofheteroatomicsystemsavailableinthiswayisdemonstratedbythegeneralformula7.1/m⊕R'R''R
,R,RareforexamplealkylgroupsXise.g.N,OYYise.g.CH2,NHXmisanintegerAisacounterion(R''')NmA73.SynthesisofpolypyrroleThisiswithoutdoubttheeasiestconductingpolymertoprepareelectrochemi-cally.Pyrrolewillformapolymeronawidevarietyofelectrodematerials,withoutgreatcareoverchoiceofpotentialifpotentiostatic,orofcurrentdens-ityifgalvanostatic,inawidevarietyofsolventsincludingwater,withagreatrangeofelectrolytesaltspresent(Scheme1).Electrolysismaybeterminated(a)NNNNNHHHHH–89X–Xe–(b)NNNNHHHH10Scheme1(a)Electrochemicalpreparationofpoly(pyrrole)and(b)separateredoxbetweenchargedandunchargedforms.163 D.J.Waltonetal.togiveanadherentelectrodecoating,orelsecontinueduntilthefilmformedisthickenoughtobepeeledfromtheelectrode.Protocol1.ElectrochemicalpolymerizationofpyrroleCaution!Carryoutallproceduresinawell-ventilatedfume-cupboard,wearappropriatedisposablegloves,alab-coat,andsafetyglasses.Equipment●Potentiostat●Volumetricflask(100mL)●Electochemicalcellwithsuitable●Sourceofdrynitrogenelectrodes,carbonrod,conducting●Deionizedwaterglasselectrode,SCEMaterials●Pyrrole,0.67g,10mmolflammable,harmfulbyinhalation,toxicifswallowed,riskofseriousdamagetoeyes●Sodiump-toluenesulfonate,1.94g,10mmolirritatingtoeyesandrespiratorysystem●Calciumhydridecontactwithwaterliberateshighlyflammablegases●DeionizedwaterMethodPreparation:pyrroleisdistilledslowlyfromcalciumhydrideunderreducedpressurepriortouseandstoredinthefridgeinabrownbottleat4C.1.Pyrrole(0.67g,10mmol)andsodiump-toluenesulfonate(1.94g,0.01mol)aareaddedtoavolumetricflask(100mL),andwaterisaddedtouptothegraduation.2.Thesolutionispouredintotheelectrochemicalcell.Thiscellisflatbottomedandcylindricalinconstructionandhasagasinletandtwoside-armswithfemaleQuickfitjointsintowhichareinsertedtwomalejointsterminatedwithsintered-glassfrits.Theconducting-glasselectrodebisthenattachedtoacrocodileclipwithalongwirecontact,whichisclippedsothatthecrocodileclipisabovethesurfaceoftheliquid.ThegraphiterodandSCEarethenplacedintheside-armsprovided(separatedfromthesolutionbyasintered-glassfrit).3.Withthepotentiostatonstandbytheelectrodesareconnecteduptothecorrectoutputsandtheprogrammeselected,forexample,apotentialof1.0V(versusSCE)isappropriate.4.Thepotentiostatisswitchedonandablackfilmisseentoformontheelec-trode.Electrolysisisthencontinuedforabout30mins.Theblackfilmisthenwashedandpeeledfromtheelectrodeforsubsequentanalysis.aPolarsolventsarenormallyused;alternativestowaterinclude,acetonitrile,propylenecarbonate,methanol,andtetrahydrofuran.Dimethylformamideisnotsogoodbuthasbeenuseddespitesome164 6:Conductingpolymersfromheterocyclesearlyclaims.6Insomecircumstances,ratherlesspolarsolventsincludingdichloromethanemightbeused.Formostorganicsolventsatetraalkylammoniumsaltisusuallyusedinplaceofthesodiumorpotassiumsalt;awidevarietyofbothtetraethylandtetrabutylammoniumsaltsareavailablefromSigma-Aldrichandothersuppliers.Thebackgroundelectrolyteassistsinthecarryingofcharge,andsoitisimportantthatanionicsaltisincluded.Inaddition,sincethepolymerwilltakeuptheanionsfromthissalt,itsnatureisimportant.Sodiump-toluenesulfonateproducesgoodqualityfilms,whichmayhaveadegreeofanisotropyintheiramorphousstructure.7,8bConductingglass,platinumoranyotherinertmaterialisrecommended.However,theprocedureissosimplethatpolypyrrolep-toluenesulfonatecanbepreparedasalecturedemonstrationinadrinkingglassusingsteelnailsaselectrodespoweredbyabattery.cForgalvanostaticoperation,acurrentdensity(i.e.currentperunitelectrodearea)upto10mAcm2(butgenerallylower)isconvenient.Betterqualityfilms(certainlyintermsofanisotropy)canbeobtainedbyscanningthevoltagebetween0and1.0Vorbetterstillbyapplyingasquare-wavepotential.7Polypyrroleproducedelectrochemicallymayexhibitsomestructuralorganization,whichcanbeprobedbyX-rayscattering,butadditionallybyneutronscattering.8Thislattertechniquerequirestheuseofadeuterium-basedpolymer,tominimizeinelasticscattering.Theelectrochemicalpoly-merizationislargelyperformedasabove(withsomemodificationstoallowtheuseofD2O),andthemonomeranddopantmoleculescanbesynthesizedatrelativelylowcostasoutlinedbelow.Pyrrole-d5isobtainedbyhydrogen–deuteriumexchangeinacidicD2O,whilethesulfonatesaltispreparedbyastandardpreparation9inwhichtheprotonatedcompoundsareexchangedforthedeuteratedones.Protocol2.Electrochemicalpolymerizationofpyrrole-d5dopedwithsodiump-toluenesulfonate-d8.Caution!Carryoutallproceduresinawell-ventilatedfume-cupboard;wearappropriatedisposablegloves,alab-coat,andsafetyglasses.Equipment●Dualmanifoldnitrogen/vacuum●Sourceofdrynitrogen●Potentiostat●Volumetricflask(100mL)●Electochemicalcellwithsuitableelectrodes,●Apparatusforfiltrationunderreducedpressure:carbonrod,conductingglasselectrode,SCEBuchnerfunnel,flask,andwateraspirator●Three-neckedround-bottomedflask●Small-scalevacuumdistillationapparatus●Deionizedwater●Erlenmeyerflask(varioussizes)●Gas-inletadapter●Condenser●Overheadstirrer,stirrerrod,gland,●Glovebag(AldrichAtmosbag)andpaddle●Vacuumoven●Hotplateandoil-bathMaterials●Pyrrole,30mL,440mmolflammable,harmfulbyinhalation,toxicifswallowed,riskofseriousdamagetoeyes●Calciumhydridecontactwithwaterliberateshighlyflammablegases165 D.J.Waltonetal.Protocol2.Continued●Toluene-d8,25g,250mmolhighlyflammable,harmfulbyinhalation●NaCl●D2O,50mLhighconcentrationsinthebodycanaffectbiochemicalprocesses●DCl(conc.inD2O),0.5mLcausessevereburns●D2SO4,25g,245mmolcausessevereburns●CaCl2irritatingtoeyes●SodiumcarbonateirritatingtoeyesMethodPreparation:Pyrroleisdistilledslowlyfromcalciumhydrideunderreducedpressurepriortouseandstoredinthefridgeinabrownbottleat4C.1.Underablanketofnitrogenaasingle-neckedround-bottomedflaskequippedwithaTeflon®-coatedmagneticfollowerischargedwithpyrrole(30mL,440mmol),D2O(50mL),andDCl(concentrated,0.5mL),themixtureisconnectedtothenitrogensupplyusingagas-inletadapter,andstirredvigor-ouslyfor24h.2.Thepyrroleisseparatedusingaseparatingfunnelandpouredintoanotherround-bottomedflaskandstep1isrepeated.Thisprocedureisthenrepeatedfivetimeswhereuponpyrroleshouldcontainabout98%deuterium.bThesubstitutionlevelischeckedbyinfrared(IR)spectroscopy.cFinally,thepyr-roleisdriedwithCaCl2andthendistilledatreducedpressurefromCaH2(inasmall-scalevacuumdistillationapparatus).3.Adrythree-neckedround-bottomedflask(250mL)isequippedwithanover-headstirrer,acondenser,andagas-inletadapterandunderablanketofnitrogentoluene-d8(25g,250mmol)isaddedtogetherwithD2SO4(25g,245mmol).d4.Thereactionmixtureisheatedinanoil-bathmaintainedat120C.Afterabout1h,thetoluenelayeriscooledtoroomtemperatureandpouredintocoldwater(100mL).e5.Theacidisneutralizedbythecarefuladditionofsodiumcarbonateandthesolutionisheatedtoboilingandthensaturatedwithsodiumchloride.6.Thehotsolutionfromstep5isthenfilteredundergravity,toremoveanyundissolvedsodiumchloride,andcooledinice.Thewhitecrystalsofthedeuteratedsodiump-toluenesulphonatesodiumsaltarecollectedbyfiltra-tionusingaBuchnerfunnelandtheproductisrecrystallizedfromhotwateranddriedinavacuumovenat100C7.Pyrrole-d5(0.72g,0.01mol)andsodiump-toluenesulfonate-d8(2.02g,0.01mol)areaddedtoadryvolumetricflask(100mL).Underablanketofnitro-gen,D2Oisaddedsuchthattheflaskisfilledtothelineandtheflaskstoppered.8.AnelectrochemicalcellisarrangedasinProtocol1(step2),exceptthatthecellisplacedinaglovebagtogetherwiththeflaskcontainingthemonomerandelectrolyte.Theglovebagissealedandtheelectrochemicaloxidationproceeds166 6:ConductingpolymersfromheterocyclesinanidenticalfashiontoProtocol1.Thefinalpolymermustberemovedfromtheelectrodeinadryenvironmentandprotectedfrommoisture.aAnupturnedglassfunnelattachedtoasupplyofdrynitrogenisplacedabovetheflask.bAtthisstagethepyrroleandaqueoussolutionaresubstantiallycontaminatedwithblackpolymericmaterial.cThepeakat3400cm1duetotheN–Hisshiftedtoca.2500cm1(N–D);thepeakat3100cm1(C–H)isshiftedtoca.2300cm1(C–D).dTheuseofDSOistopreventanysubstitutionofprotonswithdeuteriumduringthereaction.24eDOisnotnecessaryatthisstage.2Chemicaloxidationofpyrrolecanbeachievedwithanumberofoxid-ants,buttheapproachbelowusingferricchlorideseemstobeoneofthemostpopular.Asimpleapproachistomakeuseoftheslightsolubilityofpyrroleinwater,*althoughforless-solublepyrrolesaninterfacialmethodcanbeused,withthepyrrolederivativedissolvedinforexampletoluene.Intheexamplebelowthereactivityofpyrroleisdemonstratedbythesynthesisofpolymericmaterialfrom2,4-dimethylpyrrole;10herethemethylgroupisblockingoneofthemorereactive2-(or-)positions.Thus,although2,4-dimethylpyrroleshouldnotgivethetypical-linkedpyrrole,polymericmaterialisstillformed.Inthiscase,theremaybe-couplingandalsothemethylgroupsmaybesomewhatreactive,andtheremaybesomelinkagesviaCH2,itshouldalsobenotedthatadetailedanalysisoftheproductproduced(seebelow)suggeststhatoxygenmaybeincorporated.However,despitethecom-plexnatureofthereaction,aconductingpowderisobtained.Protocol3.Chemicaloxidationof2,4-dimethylpyrroleusingferricchlorideCaution!Carryoutallproceduresinawell-ventilatedfume-cupboard,wearappropriatedisposablegloves,alab-coat,andsafetyglasses.Equipment●Teflon®-coatedmagneticstirrerbar●Single-neckedround-bottomedflask(250mL)●Magneticstirrer●Apparatusforfiltration,Buchnerflaskandfunnel,andwateraspirator●Condenser●VacuumovenMaterials●2,4-Dimethylpyrrole,0.371mL,3.6mmolirritatingtoeyes,skin,andrespiratorysystem●Calciumhydridecontactwithwaterliberateshighlyflammablegases*PyrroleinacetonitrilereactswithFeCl3verywelltogiveapowder,butcangethotifyoumixeverythingtooquickly.167 D.J.Waltonetal.Protocol3.Continued●Anhydrousferricchloride,1.17g,7.2mmolcausesburns●Toluene,20mLhighlyflammable,harmfulbyinhalationMethodPreparation:2,4-Dimethylpyrroleisdistilledslowlyfromcalciumhydrideunderreducedpressurepriortouseandstoredinthefridgeat4C.1.2,4-Dimethylpyrrole(0.371mL,3.6mmol)isdissolvedintoluene(20mL)ainaround-bottomedflaskequippedwithacondenserandamagneticfollower.Tothisisaddedasolutionofiron(III)chloride(1.17g,7.2mmol)inwater(7.2mLtomakea0.1Msolution).2.Aftershakingthesolutionisstirredfor24hatroomtemperature,afterwhichtimethereactionmixturecontainsaconsiderablequantityofsolidresidue.3.Theresiduefromstep2aboveiscollectedbyfiltrationatthewaterpumpwashedwithwateranddriedinavacuumovenat40C.Thematerialhasanumberaveragedegreeofpolymerizationofabout7byMALDI-TOFspectrometrybandNMR(seeChapter1).aPyrrolemaybeoxidizeddirectlyinwaterasfollows:freshlydistilledpyrrole(0.67g,10mmol)isaddedtowaterinanErlenmeyerflask(250mL),equippedwithaTeflon®-coatedmagneticstirrerbar.Thesolutionisstirredvigorouslyandaqueousferricchloridesolution(4.055ganhydrousferricchloridein50mLwater)isadded.Ablackprecipitateisimmediatelyformed;after20min,thisprecipitateiscollectedbyfiltration,washedwithcopiousamountsofwater,anddriedundervacuum.ThepropertiesdependonthemolarratiosofFe(III)andpyrrole.11bThemassspectrumalsoshowspeaksatM17showingfurtheroxidationpresumablybyreactionofthecationicintermediatewithwater.Moresophisticatedderivativesofpyrrolehavebeendevelopedforavarietyofreasons,forexample,3-alkylpyrrolessuchas3-octylpyrrolehavebeenpreparedtoimproveprocessibility.Particularinteresthasbeenshowninthedevelopmentofmaterialsthatexhibitliquidcrystallineproperties.Inthefollowingexample,12a3-substitutedpyrrolewithmeso-genicpropertiesissynthesizedusingtherouteshowninScheme2.Apar-ticularfeatureofthisistheformationofN-(p-toluenesulfonyl)pyrroletocontrolsubstitutionatthe3-positionratherthanthe2-position,whichisotherwisemorereactive.Mesogenicmaterialsofferparticularadvantagesintermsofprocessibilityandmoreimportantly,inprovidingconductingpoly-merfilmswithalignmentpredeterminedpriortopolymerization.Thismonomerispolymerizedinanumberofwaysmostnotablyasapartiallyalignedfilm.Thelatterprocessrequirescustom-builtapparatus,anddifferentlaboratoriesmayhavedifferentapproaches,13butitservestoillustratetheprinciple.168 6:ConductingpolymersfromheterocyclesOBrOBrCH(CH)C(1)K(metal)N224ClNOSOOSONH(2)CH3SO2Cl8(ii)(i)CHCH331112OOAlkalineBrHOCNOCNhydrolysis(iii)N(iv)NHH1413NaBH4/propan-2-olOCNreflux24h(v)NH15Scheme2Preparationofa3-substitutedpyrrolewithamesogenicunitintheside-chain.Protocol4.PreparationofpotassiumpyrroleandsubsequentformationofN-(p-toluenesulfonyl)pyrrole[Scheme2(i)]Caution!Carryoutallproceduresinawell-ventilatedfume-cupboard,wearappropriatedisposablegloves,alab-coat,andsafetyglasses.Neveruseflat-bottomedflaskswithrotaryevaporators.Potassiumpresentsanextremefireriskandappropriateprecautionsshouldbetakenatalltimes.Equipment●Three-neckedround-bottomedflask●Pressure-equalizingdroppingfunnel●Refluxcondenser●Buchnerflask(1L)●Heatsource,namelyhotplate,oil-bath,and●Apparatusfordistillationunderreducedthermometerpressure●Watchglass●Sintered-glassfunnel(porosity3)●Overheadstirrer●Penknifeorscalpel●Apparatusforrecrystallization,Erlenmeyer●Stirrergland,rod,andTeflonstirrerpaddleflask,Buchnerflask,funnel,andwater●Beaker(500mL)aspiratorMaterials●Potassium,10.1g,256mmolreactsviolentlywithwater,contactwithwaterliberateshighlyflammablegases,causesburns●Pyrrole,20mL,289mmolflammable,harmfulbyinhalation,toxicifswallowed,riskofseriousdamagetoeyes●p-Toluenesulfonylchloride,40.6g,213mmolharmfuloncontactwiththeskinorifswallowed169 D.J.Waltonetal.Protocol4.Continued●DryTHF,500mLhighlyflammable,mayformperoxides,irritatingtoeyesandrespiratorysystem●Calciumhydridecontactwithwaterliberateshighlyflammablegases●Methanolhighlyflammable,toxicbyinhalationandifswallowed●Petroleumether(40–60)highlyflammable●Xylene(anhydrous)flammable,harmfulbyinhalation●Drynitrogenasphyxiationhazard●Celiteirritatingtoeyesandrespiratorysystem,possiblecarcino-genMethodPreparation:Allglassequipmentisdriedinanovenat150C,assembledwhilehot(useheat-resistantgloves),andallowedtocoolunderanatmosphereofdrynitrogen.Pyrroleisdriedbydistillingunderreducedpressure(wateraspirator)fromcalciumhydrideimmediatelybeforeuse.ap-Toluenesulfonylchlorideisrecrystallizedfrompetroleumether(60–80Cfraction).b1.Athree-neckedround-bottomedflask(1L)isequippedwithagasinlet,apressure-equalizingdroppingfunnel,andacondenserattachedtoasourceoftheinertgassupply(usingthemanifoldsystemdescribedinChapter2).2.Thesystemispurgedwithinertgas(argonornitrogen)anddryTHF(200mL)isplacedintheflask.3.Apieceoffreshpotassiummetalc(10.0g,256mmol)isplacedinabeakercontaininganhydrousxyleneunderablanketofinertgasandsmallpieces,arecutunderthexylene(Cared)andslowlyadded,withvigorousstirringtotheTHF.Thesuspensionisthenheatedtorefluxwhilemaintainingstirring,whereuponsmallbeadsofmoltenpotassiumareformed.4.Pyrrole(20ml,289mmolin100mLofdryTHF)isaddeddrop-wisetothesuspensionofmoltenpotassiumandheatingiscontinueduntilthepotassiumhasbeencompletelyconsumed.Themixtureofpotassiumpyrroleiscooledandmaybestoredoruseddirectly.Tostorethepotassiumpyrrole,thesolidmustbefilteredquicklyatthepumpunderablanketofnitrogen,washedwellwithdryTHFanddriedinavacuumdesiccatoroverP2O5.Thedrysolid(whichisyellowincolour)canthenbestoredundernitrogen.FordirectconversiontoN-(p-toluenesulfonyl)pyrrole,thenproceedasinstep5below.5.ThemixtureofpotassiumpyrroleisdilutedwithafurtherquantityofTHF(100mL)tofacilitatepartialdissolutionofthewhitesolidandasolutionofrecrystallizedp-toluenesulfonylchloride(40.6g,213mmol)indryTHF(200mL)isaddeddrop-wise.(Care!Thisrectionisexothermicandadditionshouldbecontrolledsothatonlyslightwarmingoccurs.)Themixtureisthenallowedtostirfor24h.6.ThesolutionisthenfilteredthroughaNo.3sinteredfunnelcontainingCelite®asafilteraidandtheTHFisremovedusingtherotaryevaporatortogiveawhiteresidue.170 6:Conductingpolymersfromheterocycles7.Recrystallizationfrommethanolanddryingat50CgivesN-tosylpyrroleasawhitecrystallinesolid(meltingpoint103C,eyield37.0g,78.5%).faPyrrolepurifiedinthiswaymaybekeptinbrownbottlesandstoredundernitrogeninthefreezerforseveralmonthswithoutbecomingcoloured,however,itisrecommendedthatfreshlypurifiedmaterialbeusedinthiscase.bTheuseoffreshlypurchasedmaterialisadvocated,materialwhichhasbeenlefttostandforalongperiodcontainssubstantialamountsofp-toluenesulfonicacidandthereforeareducedmeltingpoint.Thismaybepurified14bydissolvingintheminimumamountofCHClandfilteringthenfurtherdiluting3(fivetimes)withpetroleumether(30–40C)andfilteringoncemore.Thesolutionisthenconcentratedtoasmallvolumetogivepurep-toluenesulfonylchloride(m.p.68–69C).cPotassiummetalshouldbecarefullyinspectedpriortousetoensuretherearenotracesofperoxideonthesurface,itisneveradvisabletousepotassiumfromcontainersstoredforlongperiods.dInordertoavoiddropletsofcondensationfromthefume-hoodfallingintothebeakercontainingthepotassiumandthuscausingafire,thebeakershouldbecoveredwithawatchglass.Anyexcesspotas-siummustbedisposedofcarefullybyreactionwithtert-butanol(Notethanoloriso-propanol,bothofwhichigniteoncontactwithpotassium).eWeobtained103C,literaturevalue15104.5C.fAnidenticalprocedurecanbeusedfortheformationofN-benzenesulfonylpyrrole.Typicalquantitieswhichmaybeusedarepotassiummetal(10g,256mmol),pyrrole(25mL,19.3g,288mmol)andN-benzenesulfonylchloride(45.1g,255mmol).Thematerialisobtainedasapalebrownsolid,whichispurifiedbyrecrystallizationwithoutfiltrationfollowedbydryinginvacuoat45Ctogivepalebrowncrystals[yield30.5g,57.6%,m.p.:87–89C(lit.value1589–89.5C)].Protocol5.PreparationofN-benzenesulfonyl-3(6-bromohexanoyl)pyrroleaandhydrolysisto3-(6-bromohexanoyl)pyrrole[Scheme2(ii)and(iii)]Caution!Carryoutallproceduresinawell-ventilatedfume-cupboard,wearappropriatedisposablegloves,alab-coat,andsafetyglasses.Neveruseflat-bottomedflaskswithrotaryevaporators.Equipment●Dualmanifoldnitrogen/vacuum●Sourceofdrynitrogen(gasmanifold)●Two-neckedround-bottomedflask(1L)●Pressure-equalizingdroppingfunnel●Refluxcondenser●Buchnerflask(1L)●Magneticstirrer●Ice-bathforcooling●Single-neckedround-bottomedflask(1L)●Separatingfunnel(500mL)●Apparatusforrecrystallization,Erlenmeyer●Round-bottomedflask(500mL)forusewithflask,Buchnerflask,funnelandwateraspiratorrotaryevaporator●RotaryevaporatorMaterials●N-benzenesulfonylpyrrole,11.3g,54.5mmoltreatasharmful●Anhydrousaluminiumchloride,10.8g,81mmolcausesburns●6-bromohexanoylchloride,15g,70mmolreactsviolentlywithwater,causesburns,irritatingtoeyes,skin,andrespiratorysystem●Dichloromethane,ca.500mLharmfulbyinhalation,potentialcarcinogen●Anhydrousmagnesiumsulfate●Brine●Dioxane,300mL.highlyflammable,mayformperoxides,harmfulbyinhalation171 D.J.Waltonetal.Protocol5.Continued●Sodiumhydroxidesolution(5M),300mLcausesburns●Methanolhighlyflammable,toxicbyinhalationandifswallowed●Diethyletherforpurificationextremelyflammable,mayformperoxides●Petroleumether(60–80)forpurificationhighlyflammable●Alumina(neutral)forchromatographyirritatingtorespiratorysystemMethod1.Atwo-neckedround-bottomedflask(1L)isequippedwitharefluxcon-denser,apressure-equalizingdroppingfunnel,aTeflon®-coatedmagneticstirrerbarandanitrogeninlet.b2.Drydichloromethane(200mL—seeChapter2)isaddedtotheflasktogetherwithanhydrousaluminiumchloride(10.8g,81mmol)andthemixtureisstirredunderanitrogenatmosphere.3.6-Bromohexanoylchloride(15g,70.3mmol)indichloromethane(150mL)isplacedinthedroppingfunnel.Thisisthenaddeddrop-wisetotheflaskat20Candthemixtureallowedtostirfor20min.4.N-Benzenesulfonylpyrrole(11.3g,54mmol)inCH2Cl2(150mL)isthenaddeddrop-wisewhilemaintainingthetemperaturebelow5Cbycoolingwithice.Thereactionislefttostirforca.20h.c5.Thereactionmixtureiscarefullyhydrolysedwithice-waterandtheorganicphasecollected.TheaqueouslayeristhenextractedwithCH2Cl2(threeportions).Thecombinedorganicsarethenwashedwithbrineanddriedoveranhydrousmagnesiumsulfate;filtrationfollowedbyevapora-tionofthesolventtoyieldadarkbrownoil,whichcrystallizesuponstand-ing.Thebrownsolidisrecrystallizedfrommethanol(m.p.53–54.5,yield17.3g,83%).6.Inaround-bottomedflask(1L)equippedwithacondenserN-benzenesulfonyl-3(6-bromohexanoyl)pyrrole(12.0g,31.3mmol)isaddedtogetherwithamixtureof1,4-dioxane(300mL)andNaOHsolution(5M,300mL).Thereactionmixtureisstirredatroomtemperaturefor48–72huntilthinlayerchromato-graphy(TLC)indicatestheabsenceofstartingmaterial.d7.Thedioxaneisremovedontherotaryevaporatorandthepaleyellowsolidobtainedisdissolvedindichloromethaneandtheaqueouslayerisextractedwithtwofurtherportionsofdichloromethane.Theorganicsarethencom-bined,washedwithsaturatedNaClsolution,anddriedwithanhydrousmag-nesiumsulfate.Thesolutionisthenfilteredandthesolventremovedtoyieldapaleyellowoil,whichcrystallizesoncooling.8.Thesolidispurifiedusingcolumnchromatographyonneutralaluminaeusingdiethyletherandpetroleumether(1:1)toelutetheproduct.Thesolidprod-uct(crudeyield8.0g,100%)isrecrystallizedfromdiethylether/petroleumether(60–80fraction)togivewhitecrystals(m.p.73.5–76C).172 6:ConductingpolymersfromheterocyclesaTheN-tosylpyrrolederivativewasalsopreparedinthesameway.bConnectedviathecondensertoadoublemanifold(seeChapter2).cArangeofconditionshavebeeninvestigatedforasimilaralkylationanditwouldseemthattheregiospecificityisindependentoftheconcentrationofthesulfonylpyrrole,andthereactiontemperature,butthattheformationofthe3-productisfavouredbyperformingthereactionindilutehomogeneoussolution;amoreconcentratedsolutionofthecomplexwasfoundtofavour2-substitution.12dTLCindicatedonemajorandoneminorproduct.eWashedwithwater(10%w/v).Protocol6.Preparationof3-[6-(4
-cyanobiphenyl-4-yloxy)hexanoyl]pyrroleandreductionto3-[6-(4
-cyanobiphenyl-4-yloxy)hexyl]pyrrole[Scheme2(iv)and(v)]Caution!Carryoutallproceduresinawell-ventilatedfume-cupboard,wearappropriatedisposablegloves,alab-coat,andsafetyglasses.Neveruseflat-bottomedflaskswithrotaryevaporators.Equipment●Single-neckedround-bottomedflask(500mL)●Apparatusforrecrystallization,Erlenmeyerflask,Buchnerflask,funnel,andwateraspirator●Refluxcondenser●Vacuumoven●Hotplatemagneticstirrer●Teflon-coatedmagneticstirrerbar●RotaryevaporatorMaterials●3-(6-Bromohexanoyl)pyrrole,8.00g,32.8mmoltreatasharmful●Anhydrouspotassiumcarbonate,13.83g,100mmolharmfulifswallowed,irritatingtoeyes,skin,andrespiratorysystem●Potassiumiodide(trace)irritant●4-Cyano-4
-hydroxybiphenyl,6.39g,32.7mmol●Dimethylformamide,165mLpotentiallyteratogenic,harmfulincontactwithskin,irritatingtoeyes●Propan-2-olhighlyflammable●Phosphorouspentoxidecausessevereburns●Sodiumborohydride,5.29g,139.8mmolharmfulifswallowed,irritatingtoeyesandrespiratorysystem●Ethylacetatehighlyflammable●Petroleumether(60–80fraction)highlyflammable●Dichloromethaneharmfulbyinhalation,potentialcarcinogen●Silicaharmfulbyinhalation,irritatingtorespiratorysystemMethod1.Asingle-neckedround-bottomedflask(500mL)isequippedwitharefluxcondenserandaTeflon®-coatedmagneticstirrerbar.aTothisisadded3-(6-bromohexanoyl)pyrrole(8.00g,32.8mmol),anhydrouspota-ssiumcarbonate(13.83g,100mmol),4-cyano-4
-hydroxybiphenyl(6.39g,32.7mmol),Potassiumiodide(trace)b,anddimethylformamide(165mL).Themixtureiswarmedto90–100Cfor1h.173 D.J.Waltonetal.Protocol6.Continued2.Theproductisprecipitatedfromsolutionbyadditionofalargeexcessofdemineralizedwaterandfilteredatthepump,washingwithcopiousamountsofwater.3.Thecream-colouredsolidisdriedatthepump,andthenplacedinavacuumovenoverP2O5at65Covernight.Theproductisthenrecrystallizedfromamixtureofpropan-2-olandwater(10.1g,86%,m.p.131C).4.Toasingle-neckedround-bottomedflask(500mL)fittedwitharefluxcondenser,isaddedpropan-2-ol(150mL),then3-[6-(4
-cyanobiphenyl-4-yloxy)hexanoyl]pyrrole(4.64g,13.0mmol)andNaBH4(5.29g,139.8mmol)areaddedandthemixturerefluxedfor48h.5.Thereactioniscarefullyhydrolysedwithwaterandthesolventremovedontherotaryevaporator.Ethylacetateisaddedtothecruderesiduetodissolveorganicmaterial;thisprocedureisrepeatedthreetimeswithfurtheradditionofethylacetate.Removalofthesolventyieldsacream-colouredsolid,whichisdissolvedindichloromethaneandpassedthroughabedofsilicatoremovepolymericresidues.Thiscleanerproductisrecrystallizedfromamixtureofethylacetateandpetroleumether(60–80fraction)toyieldwhitecrystals[2.5g,56%,m.p.:C,86.0;C96.6;N(72.4–72.0)I]c,whichcanbedriedina12vacuumdesiccator.aThisaidsinitialmixingofthereagentsbutoncethereissubstantialsolidintheflask,willnotbeeffective,additionalmeasurestostirthemixturedonotappeartobenecessary.bThiscatalysestheS2reaction.NcThemonomerexhibitscomplexphasebehaviour,inparticular,amonotropicliquidcrystallinephase,whichisonlyapparentoncooling,suchmaterialscanonlybeproperlycharacterizedbyusingdifferen-tialscanningcalorimetry(DSC)inconjuctionwithopticalmicroscopyandalsobyX-rayscattering(seeChapter1).Protocol7.Polymerizationof3-[6-(4
-cyanobiphenyl-4-yloxy)hexyl]pyrroleunderanaerobicconditionsaCaution!Carryoutallproceduresinawell-ventilatedfume-cupboard,wearappropriatedisposablegloves,alab-coat,andsafetyglasses.Equipment●Dualmanifoldsystemvacuum/nitrogen●Sourceofdrynitrogen●Three-neckedround-bottomedflask(250mL)●Two-neckedround-bottomedflask(250mL)●Filterstick●Vacuumpump●Hotplatemagneticstirrer●Magneticstirrerbar●Two-waytapwithQuickfitadapter●Cannula●Syringeandneedles●Rubbersepta●Single-neckedround-bottomedflasks(250mL3)174 6:ConductingpolymersfromheterocyclesMaterials●3-[6-(4
-cyanobiphenyl-4-yloxy)hexyl]pyrrole,0.19g,0.5mmoltreatasharmful●Anhydrousferricchloride,0.27gcausesburns●Deionizedwater●Acetonitrilehighlyflammable,toxicbyinhalation,incontactwithskin,andifswallowed●NitrogengasasphyxiationhazardMethodPreparation:Allsolutions,solvents,andreagentsmustbethoroughlydegassedpriortouseasfollows:acetonitrileisplacedinasingle-neckedround-bottomedflaskandplacedinanultrasonic-bathfor30min.Theflaskisthenfittedwitharubberseptumandanoutletneedleandaneedleconnectedbytubingtoasourceofdrynitrogenareinsertedthroughtheseptum.Nitrogenisthenbub-bledthroughthesolutionfor60–90min.Thereafter,theacetonitrileiskeptundernitrogenatalltimesb.Asolutionof3-[6-(4
-cyanobiphenyl-4-yloxy)hexyl]pyr-role(0.19g,0.5mmol)inacetonitrile(20mL)isdegassedinanidenticalfashion,asisdeionizedwaterforwashing.1.Athree-neckedround-bottomedflaskisequippedwithamagneticfollower,arubberseptum(S1),atwo-waytapandafilterstick(aglassinlettubewithasintered-glassfritatoneend),whichisalsosealedatitsopenendwithasuit-ablerubberseptum(S2).2.Toflaskisaddedanhydrousferricchloride(0.27g)andtheflaskisthenevacu-atedrepeatedly(fivetimes)underhighvacuumandrefilledwithnitrogen,usingadouble-manifoldsystemconnectedtothetwo-waytap.3.Degassedacetonitrile[Highperformanceliquidchromatography(HPLC)grade,20mL]isthenaddedviatherubberseptum(S1)usingacleandrysyringe.Thedegassedmonomersolution(seeabove)isaddedtotheflaskbysyringeandstirred.Ablackprecipitateisformedwithinminutesbutthesolu-tionisstirredforafurther17–18h.4.Aclean,dry,degassedtwo-neckedround-bottomedflaskisequippedwitharubberseptumandagas-inlettube.Thegas-inlettubeisinturnconnectedtothepump.Adouble-headedneedle(cannula—seee.g.Chapter3)isinsertedintheseptuminthisflaskandthenthroughtheseptumattachedtothefilterstick(S2).Thereactionsolventisthenremovedbymeansofthevacuumthroughthiscannula,5.Thepolymericsolidsremainingintheflaskarewashedwithdegassedwater(threeportions)followedbydegassedacetonitrile(twoportions),andfilteredasinstep4above.Thewashedpolymersaredriedundervacuumfor2–3h.aAsanalternative3-[6-(4
-cyanobiphenyl-4-yloxy)hexyl]pyrrolecanbeoxidizedwithcopper(II)perchlorate(Care!Contactwithcombustiblematerialmaycausefire,irritant)asfollows:3-[6-(4
-cyanobiphenyl-4-yloxy)hexyl]pyrrole(0.34g,1mmol)isdissolvedinacetonitrile(8–10mL)andaddedtotwo-neckedround-bottomedflaskfittedwithanitrogenbubblerandanitrogengasinlet(e.g.aneedleconnectedtotheinertgassupplyinsertedthrougharubberseptum).Thesolutionismaintained175 D.J.Waltonetal.Protocol7.Continuedunderacontinuousstreamofnitrogenandheldat201Cinathermostattedwater-bath.Copper(II)perchloratehexahydrate,Cu(ClO4)26H2O(0.74g,2mmol)isdissolvedinacetonitrile(8–10mL)andaddeddrop-wisetothemonomersolution.Ablackprecipitateisformedimmediatelyintheclearsolu-tion.Themixtureisstirredforaminimumof90minandthenfiltered.Thesolidpolymeristhenwashedunderfiltrationwithcopiousamountsofwaterfollowedbyacetonitrile,inordertoremoveunreactedmonomerandoxidant.Finally,thepolymeriswashedwithhotacetonitrileusingaSoxhletextractor,forupto6–8h.Dryinginvacuoforafurther6–8hyieldspoly3-[6-(4
-cyanobiphenyl-4-yloxy)hexyl]pyrroleasanamorphousblacksolid.bSubsequentmanipulationsofsolventsareperformedwithnitrogen-purgedsyringesand/oracannula,throughdegassed,flasksfittedwithsepta(seetext).Thepresenceofthemesogenicside-chainsallowsforthedevelopmentoforientationinfilmspriortopolymerization.Ifthemonomeristhenpoly-merizedinthisalignedstate,itwouldbeexpectedthattheorientationimpartedonthepyrroleunitsbyassociationwiththemesogenswouldbecomeincorporatedintothepolymer.Highlevelsofanisotropymaylead,forexample,tonewapplicationsthatcanexploitthedifferentconductingmechanismsalongandorthogonaltothepolymerchains.16Theapparatusforpolymerizingthesubstitutedpyrrolesasanalignedfilmconsistsofareactioncellthroughwhichbrominevapour(theoxidant)canbepassed.Thisapparatusisdesignedtofitwithinthecavityofapolarizingmicroscope,andcontainsanapertureforviewingthesampletoensuretherequiredphase/alignmentstate.Protocol8.Polymerizationof3-[6-(4
-cyanobiphenyl-4-yloxy)hexyl]pyrroleasanalignedfilmEquipment●TypeKChromel–Aluminelthermocouple●Vacuumoven●Temperaturecontroller●Glassslide●Glassreactioncellwithinletandoutletfor●Aluminiumheatingblockdesignedforusenitrogenandoxidantvapourwiththereactioncell●Opticalmicroscope●Powersupply●Sourceofdrynitrogen●2DreschelbottlesMaterials●3-[6-(4
-cyanobiphenyl-4-yloxy)hexyl]pyrrole,treatasharmfulca.50mg,1.3mmol●Acetonitrilehighlyflammable,toxicbyinhalation,incontactwithskin,andifswallowed●Nitrogengasasphyxiationhazard●Dimethylformamidepotentiallyteratogenic,harmfulincontactwithskin,irritatingtoeyes176 6:Conductingpolymersfromheterocycles●Bromineverytoxicbyinhalation,causessevereburns●Probimide®32irritatingtoeyes,skin,andrespiratorysystem●Sodiumthiosulfatesolution(saturated)Method1.Aglassslide(ca.1cm1cm)isspin-coatedwithasolutionofProbimide®32indimethylformamide.aThecoatedslideisannealedathightemperatures(ca.200C),followedbyunidirectionalrubbingwithasoftcloth,toyieldahard,inert,rubbedpolymerfilm,suitableforenticinghomogeneousalignmentofamesophase.2.Thesampletobepolymerized(15,ca.50mg)isdepositedontheglassslideandplacedinareactioncellcavity.bThereactioncellisconnectedononesidetoareservoirofbromineinaglasstubefittedwithbothgasinletandoutletvalves(suchthatnitrogencanbepassedthroughthetube,butwithoutbubblingthroughthebromine).Betweenthebrominereservoirandthecellisathree-waytap,whichisconnectedtoaseparatenitrogeninletandallowsthepassageofbrominefree-nitrogenthroughthecellasrequired.Ontheoppositeside,thecellisconnectedtotwoDreschelbottlesarrangedinseriescontainingasaturatedsolutionofsodiumthiosulfatetodestroytheeffluentbrominevapour.c3.Thecellisplacedinanaluminiumheatingblockshapedouttocontainthecellandfittedwithfourheatingelements,connectedtoa10-Apowersupply,andplacedinthecavityofapolarizingmicroscope.dThecellisthenpurgedwithacontinuousstreamofnitrogenandheatedtotheapproximaterequiredtemperatureeforpolymerizationintheliquidcrystallineregion;thisinvolvesheatingtoca.80Csuchthatthesamplebecomesisotropicandthencoolingfairlyrapidlyto60Coruntilanopticaltexturetypicalofaliquidcrystallinephaseisobserved.f4.Withthesampleintherequiredphase,thenitrogenispassedoverthetubecontainingbromineandthistubewarmedwithabeakercontaininghotwatertospeedupevaporationofbromine.Brominevapouristhenallowedtopassoverthesamplecontinuouslyuntilpolymerizationappearscomplete.Thecellisthenre-purgedwithfreshnitrogenalone,cooled,andtheglassslidecontainingthepolymericdepositremoved.Thesamplesarewashed(stillattachedtotheglassslide)bystandinginacetonitrilefor24handdriedundervacuumfor3–4h.gaThispolyimideprecursorformsapolymercoatingontheglasssurface,ontowhichalignmentmaybeintroducedbyrubbing,beforethecoatinghashardened;suchrubbedfilmsinduceorientationinliquidcrystallinematerials.bThereactioncellconsistsofasmallglassvesselequippedwithaninletandoutlet,topermitthethroughputofoxidantvapourandnitrogen(asacarriergas).c2SO2Br→SO22Br.23246dBothhalvesoftheheatingblockcontainasmallaperture,orthogonaltotheplaneof,andpositionedaboveandbelow,thecellcentre.Thispermitsthepassageoflightthroughthecelltotheeyepiecelens.177 D.J.Waltonetal.Protocol8.ContinuedeThetemperatureofthecellisregulatedwithatemperaturecontroller,connectedtothecellviaatypeKChromel–Aluminelthermocouple,whichisinsertedintoasmallaperturewithintheheatingblock.fThisprocedureisrequiredbecausethepyrrolederivativeformsamonotropicliquidcrystallinephase;thatis,itisonlyobservedoncoolingfromtheisotropic,andiskineticallyfavouredbutthermo-dynamicallyunfavoured;notwithstandingthisthephaseissufficientlystableinthiscasetoallowpolymerization.gTheprocedureappearstomuchmoreefficientintheisotropicphasethaninthenematicphase.Inthenematicphasepolymerizationmaybeconfinedlargelytothesurfaceforthickerfilms;intheisotropicphase,polymerizationismuchmoreuniform.4.SynthesisofpolyanilinePolyaniline(Scheme3),isnotstrictlyaheteroaromaticmonomer,buthasanumberofsimilaritiestopolypyrrole.Therearedifferences,however,oneofwhichisthatarethreeredoxlevelseachofwhichmaybeprotonatedordeprotonated.Ofthese,thepH-drivenswitchbetweentheemeraldine(17)saltandemeraldinebase(18)isattractinginterest.17⊕–2.5e,–2HNH2NHNHNHNH⊕⊕1617AA⊕HOHNHNHNN18NHNHNN1922⊕NHNNHNH⊕⊕2123Scheme3Oxidationofanilineandpossibleoxidationlevelsandprotonationlevelsofthepolyanilineproduced.Polyanilineislesstolerantofpreparationconditionsthanpolypyrrole,andthelistofaniondopantsusedinthepreparationismorelimited.However,subsequentreplacementoftheanionusedinpreparationbyadodecylben-zenesulfonatemakespolyanilinebecomesolubleinsolventssuchasN-methylpyrrolidone(NMP),orm-cresol,anditcanbespin-coatedorother-wisesolution-processed.Inasimilarwayderivativesofaniline,suchas178 6:Conductingpolymersfromheterocycles2-methoxyaniline18whenoxidizedinasimilarfashiontothatgiveninProtocol9belowgiveaconductingpolymerthatissolubleinsolventssuchaschloroform,dichloromethane,andacetonitrile.Protocol9.ElectrochemicalpolymerizationofanilineCaution!Carryoutallproceduresinawell-ventilatedfume-cupboard,wearappropriatedisposablegloves,alab-coat,andsafetyglasses.Equipment●Potentiostat●Volumetricflask●Electochemicalcellwithsuitableelectrodes,●Deionizedwatercarbonrod,platinumfoilelectrode,SCEMaterials●Aniline,0.93g,10mmoltoxicbyinhalation,incontactwithskin,andifswallowed,dangerofcumulativeeffects●Hydrochloricacid,1M,100mLcausesburns,irritatingtorespiratorysystem●DeionisedwaterMethodPreparation:Anilineisdistilledfromcalciumhydrideunderreducedpressurepriortouseandstoredundernitrogeninthefridgeat4C.1.Avolumetricflask(100mL)ischargedwithaniline(0.93g,10mmol)andmadeuptothemarkwithhydrochloricacid(1M).Thesolutionisthenpurgedwithnitrogenforapproximatelyanhourpriortouse.2.Thesolutionispouredintotheelectrochemicalcell.ThisisarrangedasdescribedinProtocol1,butheretheworkingelectrodeisapieceofplatinumfoilathathaspreviouslybeencleanedwithnitricacid(concentrated)followedbywashingwithwateranddryinginanovenat120C.3.Withthepotentiostatonstandby,theelectrodesareconnecteduptothecorrectoutputsandthepotentialselected;typically,thiswillbe1.2V(versusSCE).Nitrogengasisthenslowlybubbledthroughtheelectrolyte.4.Thepotentiostatisswitchedontoapplythepotentialacrosstheelectrodesandablue-blackfilmisseentoformontheelectrode.Electrolysisisthencontinueduntilsufficientmaterialisformed.bThefilmisthenwashedwithwateranddriedinthevacuumovenat40C.aOtherelectrodessuchasgoldcanbeused,butfilmsformedonplatiniumgenerallyhavegoodadhesionqualities.bTypically,thisisdeterminedbythetotalchargedelivered.179 D.J.Waltonetal.Protocol10.ChemicalOxidationofAnilineCaution!Carryoutallproceduresinawell-ventilatedfume-cupboard,wearappropriatedisposablegloves,alab-coatandsafetyglasses.ThefollowingprocedureisbasedononedescribedbyAlanJ.Heeger19whojointlysharedthe2000NobelprizeforchemistrywithHidekiShirakawaandAlanG.MacDiarmidfortheirworkonconductingpolymers.Equipment●Mechanicalstirrer,stirrerrod,●Ice-bathforcoolingpaddle,andstirrergland●Three-neckedround-bottomedflask(1L)●Apparatusforfiltration,Buchnerflask,andfunnel●Thermometer●DroppingfunnelMaterials●Aniline,20mL,20.43g,220mmoltoxicbyinhalation,incontactwithskin,andifswallowed,dangerofcumulativeeffects●Ammoniumpersulfate,contactwithcombustiblematerialmaycausefire,irritatingto23.0g,110mmoleyes,skin,andrespiratorysystem,harmfulifswallowed,maycausesensitizationbyinhalationandskincontact●hydrochloricacid,1.5M,500mLcausesburns,irritatingtorespiratorysystem●Methanolhighlyflammable,toxicbyinhalationandifswallowed●Diethyletherextremelyflammable,mayformperoxidesMethod1.Athree-neckedround-bottomedflask(1L)isequippedwithathermometer,amechanical(overhead)stirrer,aandadroppingfunnel.AqueousHCl(1.5M,250mL)isaddedfollowedbyaniline(20.43g,220mmol).Thesolutioniscoolediniceto0C.2.Asolutioncontainingammoniumpersulfate(23.0g,110mmol)inaqueousHCl(1.5M,250mL)isplacedinthedroppingfunnelandthenveryslowlybaddedtotheanilinesolutionwhilstmaintainingthetemperaturecloseto0C.3.Aftertheadditioniscomplete,thereactionmixtureisthenleftstirringforafurtherhour.4.Thesolidpolyanilineiscollectedfromthereactionmixturebyfiltrationandwashedthoroughlywithwater.Thesolidisthenwashedwithseveralportionsofmethanolandfinallywithdiethylether.cThesolidisthendriedundervacuumfor48horuntilaconstantmassisreached.daAmagneticstirrerwillnotcopewiththequantitiesofsolidmaterialproducedinthisreaction,particularcareisneededtoensurethattherodisexactlyverticalandthepaddlerotatesfreely,andofcourse,isnotobstructedbythethermometer.bHeegerrecommendsanadditionperiodof3h.cThiswashingisbestundertakenbyremovingthesolidfromthefiltrationapparatusandplacingitinabeaker.Thesolidcanthenbemixedthoroughlywiththeorganicsolventandrefiltered.dThepolyanilinecanbeconvertedtothebaseformbystirringwithasolutionofaqueousammonia(3%)for3hfollowedbywashingasinstep3.180 6:Conductingpolymersfromheterocycles5.SynthesisofpolythiopheneThiophenediffersfrompyrroleandanilineinthatitisinsolubleinwaterandlesselectron-richthaneitherofthesetwomoleculeswithaconsequencethatitisoxidizedatahigherpotential,sufficientlyhighthatoxidationofwatermayinter-fereintheprocess.Bothconsiderationsmeanthatthematerialmustbepolymer-izedinanon-aqueousmedium,andacetonitrileornitrobenzeneareoftenchosen.20,21Thefollowingexampleisbroadlyapplicabletomostsubstitutedthiophenesandhasbeenusedfortheoxidationofarangeoflong-chainalkylthiophenes.223-Hexylthiopheneandarangeofother3-substitutedmaterialsareavailablecommercially,andcanbepolymerizedelectrochemically.Chemicalpolymerizationisusuallyperformedusingorganometalliccouplingreactions,23asimpleexamplebeingtheoneshowninScheme4,24inthisexample,thearyliodideandthestannylthiophenearereactedinequimolarquantitiesindrydimethylformamideinthepresenceof[Pd(PPh)]25(10mol%)at80–90C.34Itmustbenoted,however,thatthepolymerproducedisbothinitsneutralnon-conductingform,andhasrandomregiochemistry;nowadays,particulareffortisbeingputintothedevelopmentofsubstitutedthiopheneswithregularregiochemistryusingorganometalliccouplingreactions.26,27Someregioregularpolythiophenesandtheirprecursorsareavailablecommercially.C6H11C6H11Pd(PPh3)4+IIMe3SnSSnMe3SSDMF90°CSScheme4Preparationofaregio-randompoly(thiophene)derivativebyapalladium-catalysedpolycondensation.Protocol11.Electrochemicalpolymerizationof3-hexylthiophene(Scheme5)Caution!Carryoutallproceduresinawell-ventilatedfume-cupboard,wearappropriatedisposablegloves,alab-coat,andsafetyglasses.+SSSSS–XScheme5Electrochemicalpreparationofpoly(3-hexylthiophene).181 D.J.Waltonetal.Protocol11.ContinuedEquipment●Potentiostat●Volumetricflask●Electrochemicalcellwithsuitableelectrodes,●Vacuumdesiccatorconductingglass,platinumgauzeelectrode,SCE●SourceofdrynitrogenMaterials●3-Hexylthiophene,1.68g,10mmolflammable,treatastoxic●Nitrogengasasphyxiationhazard●Nitrobenzene,100mLhighlyflammable,toxicbyinhalationincontactwithskinandifswallowed●Tetrabutylammoniumhexafluorophosphate,corrosive,harmfulbyinhalation0.69g,2.5mmol●Hexane,forwashinghighlyflammable,harmfulbyinhalationandincontactwiththeskinMethodPreparation:Nitrobenzeneisdriedovercalciumchlorideandthendistilledfrombariumoxide,3-hexylthiopheneisdistilledunderreducedpressure.1.Avolumetricflask(100mL)ischargedwith3-hexylthiophenea(1.68g10mmol)andtetraethylammoniumhexafluorophosphate(0.69g,2.5mmol)andmadeuptothemarkwithnitrobenzene.bThesolutionisthenpurgedwithnitrogenforapproximatelyanhourpriortouse.2.Thesolutionispouredintotheelectrochemicalcell.ThisisarrangedasdescribedinProtocol1,withtheworkingelectrode(anode)beingapieceofconductingindium–tinoxideglass(1.5cm1.5cm)andthecounter-electrodeaplatinumgauzeusinganSCEasthereference.Theelectrochemicalcellisthenplacedinawater-bathmaintainedat10C.c3.Withthepotentiostatonstandby,theelectrodesareconnecteduptothecorrectoutputs.Drynitrogengasisthenslowlybubbledthroughtheelectrolyte.4.Thepotentiostatisswitchedontoapplythepotentialacrosstheelectrodesandacolouredfilmisseentoform.dElectrolysisisthencontinueduntilsuffi-cientmaterialisformed.Thefilmisthenwashedwithhexaneanddriedinavacuumdesiccator.a3-Hexylthiopheneisavailablecommerciallyoritcanbeobtainedbythenickel-catalysedcouplingofhexylmagnesiumbromidewith3-bromothiophene.28bAcetonitrileorpropylenecarbonatearepreferredsolventsforelectrochemicalreactions,butthesolu-bilityofmanyalkylthiophenederivativesispoor.cAnalternativearrangementusesawater-jacketedelectrochemicalcellwithwaterfromthecoolant-bathcontinuouslypassedthroughthesystem.dElectrochemicaloxidationisusuallyperformedinconstantcurrentmode;anoptimumcurrentdensityisupto10mAcm2(usuallyahighercurrentdensityisusedthanfor,say,theoxidationofpyrrole).182 6:ConductingpolymersfromheterocyclesWhileelectrochemicalpolymerizationrepresentsarelativelystraightforwardmethodofproducingpolythiophenesandforexample,offersparticularpotentialforgeneratingcontrolledstructuresonelectrodesurfaces29thereareclearlysomerandomfactorsinthepolymerization,whichinvolvestheformationofcationradicals;defectsincludecouplinginthe3-position(calculationshaveshownthatthiophenehassignificantreactivityatthe3-position,unlikepyr-role,wherethe-positionisfavoured)30andfor3-alkylthiophenesanon-regioregularstructure(i.e.head-to-tailandhead-to-headpolymerization).Organometalliccouplingreactionshaveprovedparticularlysuccessfulatcoun-teringthisproblem.TheprocedurebelowisbasedononedesignedbyMcCullough.31Protocol12.Regiospecificformationofpoly(3-hexylthiophene)byanickel-catalysedcross-coupling(Scheme6)Br/CHCOHLDA/THF232BrLiBrSSSMgBr2.OEt2Ni(dppp)Cl2SBrMgBrLiBrSSSScheme6Caution!Carryoutallproceduresinawell-ventilatedfume-cupboard,wearappropriatedisposablegloves,alab-coat,andsafetyglasses.Neveruseflat-bottomedflaskswithrotaryevaporators.Equipment●Three-neckedround-bottomedflask(250mL)●Pressure-equalizingdroppingfunnel●Gasinlet●Condenser●Teflon®-coatedmagneticstirrerbar●Gasoutlet●Funnel●Water-bath183 D.J.Waltonetal.Protocol12.Continued●Solid-additiontube●Apparatusfordistillationatreducedpressure:●Separatingfunnel(250mL)foursingle-neckedround-bottomedflasks●Septumcap(50mL),condenser,thermometer,airbleed,●Drytwo-neckedflask(250mL)‘pig-type’receiver-adapter,Claisenstill-head,andthermometerMaterials●3-Hexylthiophene,10g,60mmolflammable,treatastoxic●Argonasphyxiationhazard●Bromine,3.1mL,0.06mmolverytoxicbyinhalation,causessevereburns●Sodiummetabisulfite,ca.1g.harmfulbyinhalation,incontactwithskin,andifswallowed●Sodiumhydroxidesolution(1M)causessevereburns●Aceticacid,25mLflammable,causessevereburns●Magnesiumbromideetherate,2.58g,10mmolhighlyflammable●Dichloro[1,3-bis(diphenylphosphino)propane]cancersuspectagentnickel(II),0.026g,0.05mmol●Di-isopropylamine,1.4mL,10mmolhighlyflammable●Butyllithium,4.0mL,10mmolhighlyflammable,reactsviolentlywithwater,spontaneouslyflam-mableinair,causesburns,harmfulbyinhalation●Ethanol(forcoolant)highlyflammable●Acetone(forcoolant)highlyflammable●Methanolhighlyflammable,toxicbyinhalationandifswallowed●SolidCO2(dryice)extremecold,maycauseburns,asphyxiationhazard●THF,50mLhighlyflammable,mayformperoxides,irritatingtoeyesandrespiratorysystemMethodPreparation:Allglassequipmentisdriedinanovenat150C,assembledwhilehot(useheat-resistantgloves),andallowedtocoolunderanatmos-phereofdrynitrogen.THFisdriedbysodiumbenzophenoneasoutlinedinChapter2.1.Athree-neckedround-bottomedflask(250mL)isequippedwithagas-inlettube,aapressure-equalizingdroppingfunnel,acondenser,andaTeflon®-coatedmagneticstirrerbar.Totheendofthecondenserisattachedagasout-letconnectedtoatraptoremoveanyHBrevolved.b2.Theflaskischargedwith3-hexylthiophenec(10g,60mmol),aceticacid(70mL),andpurgedwithArgon,andcooledinawater-bathatabout10C.3.Bromineinaceticacid(3.1mL,0.06mmol,in25mL)isthenaddedfromthedroppingfunneldrop-wiseoveraperiodofabout1hinordertoensurethetemperatureremainsatabout10–15C.4.Thematerialisstirredforafurther30mininanice-bath,andthemixtureisthenpouredontoamixtureofwaterandcrushedice(approximately100mL)containingsodiummetabisulfite(ca.1g).Thecrudeproductisthenisolatedbyextractionwithdiethyletherinaseparatingfunnel,andtheetherlayeristhenwashedwiththreeportionsofsodiumhydroxidesolution(1M)toremovetheaceticacid.Theproductisfinallypurifiedunderreducedpressuretogive2-bromo-3-hexylthiophene.184 6:Conductingpolymersfromheterocycles5.Adrythree-neckedflask(250mL)isequippedwithacondenser,aseptumcap,asolidsampleadditiontube,dandaTeflon®-coatedmagneticstirrer.Theadditiontubeisthenchargedwithmagnesiumbromideetherate(2.58g,10mmol).Thecondenseristhenconnectedtothedoublemani-foldviaagasadapterandtheflaskisevacuatedandthenpurgedwithargon.6.UsingdrysyringesasoutlinedintheprocedurefortheuseofbutyllithiuminChapter2,eaddtothisflaskdrydi-isopropylaminef(1.4mL,10mmol),anddryTHF(50mL).Thenatroomtemperatureaddbutyllithium(4.0mL,2.5M,10mmol).Themixtureisthencooledinadryice/ethanol-bath(40C)andstirredfor40min.7.Themixtureisthencooledto78Cusingadryice/acetone-bathandmag-nesiumbromideetherate(2.58g,10mmol)isaddedfromthesolid-additionadapter,andthereactionstirredat78Cfor30min.Thereactionmixtureisthenwarmedto40C(dryice/ethanol)andstirredforafurther15min.8.Thereactionisthenslowlywarmedto5C(ice–saltwater-bath),andanupturnedfunnelconnectedtotheinertgassupplyisplacedjustabovethesolidadditionadapter,agentleflowofargonispassedthroughthisandtheadapterquicklyremovedwhileNi(dppp)Cl2(0.026g,0.05mmol)isadded(Caution!).gTheadapteristhenquicklyreplacedandtheinertgassupplyremoved.9.Themixtureisallowedtowarmtoroomtemperatureovernightandthepoly-merprecipitatedbydroppingintocoldmethanol,thesolidisfilteredatthewateraspirator,washedwithmethanol,waterandmethanol,anddriedinthevacuumovenat30C.haThisshouldallownitrogenfromthemanifoldtopassthroughthesolution,anall-in-onepieceispreferabletoascrewthreadarrangementthroughwhichaglasspipetteispassedbutinthiscasethecompleteexclusionofoxygenandwaterisnotrequired.bAnupturnedfunnelimmersedinwatershouldsufficehere.cSeeProtocol11.dThisconsistsofabenttubewithamaleQuickfitjoint.Thepowderisplacedinthetubebeforethereactionthetubeisthenattachedtooneofthenecksoftheflask(notthecentralverticalone).Thetubeisthenswivelledaroundwhenthesolidisrequired.Thisarrangementallowsthesolidtobeaddedinacompletelyair-freeenvironment.32OncetheGrignardreagentisformed,thesolidadditionmaybeperformeddirectlyfromoneofthenecksunderablanketofnitrogen.eThesyringeandneedlearedriedintheovenandallowedtocoolinadesiccator,thesyringeisthenflushedwithargon.AsecondneedleattachedtotheinertgassupplyispassedthroughthesealontheSure-Sealbottleandthesyringeneedleispassedthroughthebottleseal.fDi-isopropylaminemaybedriedovercalciumhydrideanddistilledundernitrogenpriortouse,butthecompoundisavailablefromAldrichpackagedinaSure-Sealcontainer.gSuchcouplingsaregenerallyexothermic,forexample,theadditionofthisnickelcatalysttoamixtureofvinylchloride,and4-chlorophenylmagnesiumbromideinetherat0Cleadsafterashortinductionperiodtoaviolentuncontrollablereaction.33Thescaleandconditionsusedhere,however,aresufficienttomoderatethereaction.hMcCulloughrecommendstheremovalofoligomersbySoxhletextractionwithmethanol,followedbyhexane.31185 D.J.Waltonetal.6.ConclusionsThischapterhasprovidedsomeexamplesofthewaysinwhichconjugatedpolymerscanbeprepared.Whiletheaccountisnotofcourseexhaustive,andindeedmanyextremelyimportantsyntheticrouteshavenotbeenincluded,suchastheformationofpolyacetylenebythe‘Durham’route,34itdoesservetoillustratethattherangeofsynthetictechniquesvaryfromthesimpletotheextremelysophisticated.Electrochemicalsynthesisislargelyintheformerclassification,however,itdoeshaveconsiderablepotentialinthedesignofmaterialsformolecularelectronicssinceitwillallowpatternstobeformedontheelectrodesurface.Withthecontinuingdemandfornewmaterialsbothforelectronicandpowerdistributionneeds,itistobeexpectedthatthisareawillcontinuetodevelopintheforeseeablefuture.References1.Shirakawa,H.;Ikeda,S.Polym.J.1971,2,231.2.(a)Feast,W.J.Chem.Ind.1985,263.(b)Edwards,J.H.;Feast,W.J.;Bott,D.C.Polymer1984,25,395–398.3.Friend,R.H.;Gymer,R.W.;Holmes,A.B.;Burroughes,J.H.;MarksR.N.;Taliani,C.;Bradley,D.D.C.;DosSantos,D.A.;Bredas,J.L.;Logdlund,M.;Salaneck,W.R.Nature1999,397(6715),121–128.4.Bocchi,V.;Gardini,G.P.J.Chem.Soc.,Chem.Commun.1986,148.5.Diaz,A.F.;Kanazawa,K.K.;Gardini,G.P.J.Chem.Soc.,Chem.Commun.1979,635.6.Otero,T.F.;Arevalo,A.H.Synth.Met.1994,66,25–32.7.Kiani,M.S.;Bhat,N.V.;Davis,F.J.;Mitchell,G.R.Polymer1992,33,4113–4120.8.Mitchell,G.R.;Davis,F.J.;Cywinski,R.;Howells,W.S.J.Phys.C:SolidStatePhys.1988,21,L411–L413.9.Furniss,B.S.;Hannaford,A.J.;Smith,P.W.G.;Tachell,A.R.Vogels’sTextbookofPracticalOrganicChemistry,5thedn;LongmonScientific:Essex,UK;1988.10.Cross,M.G.;Walton,D.;Morse,N.J.;Mortimer,R.J.;Rosseinsky,R.;Simmonds,D.J.J.Electroanal.Chem.1985,189,389.11.Armes,S.P.Synth.Met.1987,20,365–371.12.(a)Langley,P.J.;Davis,F.J.;Mitchell,G.R.J.Chem.Soc.,PerkinTrans.2,1997,2229.(b)Langley,P.J.;Davis,F.J.;Mitchell,G.R.Mol.Cryst.Liq.Cryst.1993,236,225.13.Jego,C.;Agricole,B.;Vicentini,F.;Barrouillet,J.;Mauzac,M.;Mingotaud,C.J.Phys.Chem.1994,98,13408.14.Perin,D.D.;Armarego,W.L.F.PurificationofLaboratoryChemicals,3rdedn;Pergamon:Oxford;1988.15.Papadopoulos,E.P.;Haider,N.F.TetrahedronLett.1968,14,1721.16.Chen,Y.;Imrie,C.T.;Ryder,K.S.J.Mater.Chem.2001,11(4),990–995.17.Higgins,R.W.T.;Zaidi,N.A.;Monkman,A.P.Adv.Funct.Mater.2001,11(6),407–412.18.Macinnes,D.,Jr.;Funt,B.L.Synth.Met.1988,25,235–242.186 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7SomeexamplesofdendrimersynthesisDONALDA.TOMALIA1.IntroductionDendrimersarehighlybranchedmacromoleculeswithuniquestructuralproperties.Theymaybethoughtofascore–shelltypemacromoleculeswhereintheyamplifytheirmassandterminalgroupsasafunctionofgrowthstages.Thesegrowthstagesarereferredtoasgenerations(i.e.G0,1,2,...).Theypossessthreekeyarchitecturalfeatures:(i)acoreregion;(ii)interiorshellzonescontainingcascadingtiersofbranchcells(generations)withradialconnectivitytotheinitiatorcore;and(iii)anexteriororsurfaceregionofterminalmoietiesattachedtotheoutermostgeneration.Withthisarchitecture,acarefulchoiceofbuildingblocksandfunctionalgroupscanprovidecontrolovershape,dimensions,density,polarity,reactivity,andsolubility.1Oneoftheearlierdendrimersmade,usingadivergentstrategy,istheStarburst®poly(amidoamine)(PAMAM)dendrimerfamily(Scheme1).2Thismethodinvolvedassemblingrepeatunitstointroducebranchcellsaroundtheinitiatorcorethroughsuccessivechemicalreactionsattheperi-pheryofthegrowingmacromolecule.ThefirststepofPAMAMsynthesisinvolvesMichaeladditionoffourmolesofmethylacrylatetothenucle-ophilicethylenediaminecore.Thisleadstoanelectrophiliccarbomethoxysurface,whichisthenallowedtoreactwithanexcessof1,2-diaminoethanetogiveanucleophilicsurfaceatgenerationzero.Reiterationofthesetwostepsnowinvolvesadditionof8molofmethylacrylatetogiveG0.5(elec-trophilic,carbomethoxysurface).ThisisfollowedbyamidationtoreturntoanucleophilicsurfaceatG1.0.Asaresultofthisreiterativebranchcellassembly,itisapparentthattheseconstructionsfollowsystematicdendriticbranchingrules,withradialsymmetrygivingawell-definedthree-dimensionalgeometrytothefinaldendriticproduct.3Editor’sNote:ProfessorTomaliaisoneofthepioneersofdendrimerchemistry,theimportanceoftheworkdescribedhereisreflectedinthehugeinterestcurrentlysurroundingthistopic.4–12 7:SomeexamplesofdendrimersynthesisOOOMeOMeMeOONNH2NH2N1.2equiv.perNH2OMe40°CMeOOMeOHOMeOH(30%)NH2(70%)8°C,48hH2N16equiv.EDAperesterNH2H2NOONHHNNNNHHNOONH2H2NG=0PAMAMstar-branched(NH2)4012312243611InitiatorcoreNc=3(Ammoniacore)Scheme1Ingeneral,theplacementofreactivefunctionalitiesontheexteriorsurfaceofthedendrimersallowsintroductionofawidevarietyofterminalmoieties.Inalternatesyntheticapproaches,spacergroupshavebeendeliberatelyintro-ducedtorelievethesterichindranceinordertofacilitateconstructionofthenextgeneration.Thismayprovidethepossibilityofenhancinginteriorcargospacesfor‘guest–host’typechemistry.13189 D.A.Tomalia2.ExcessreagentmethodProtocol1.Caution!Carryoutallproceduresinawell-ventilatedhood,weardisposablevinylorlatexgloves,andchemical-resistantsafetygoggles.Equipment●Dualmanifold(nitrogen/vacuum)●Sourceofdrynitrogen●Two-necked,round-bottomedflask(200mL3)●Additionfunnel(150mL)●Nitrogeninlet●Ice-bath●Rotaryevaporator●Apparatusforazeotropicdistillation:single-neckedround-bottomedflasks,condenser,distillationhead,thermometer,andadapterMaterials●Methanol(HPLCgrade),300mLhighlyflammable,toxicbyinhalationandifswallowed●1,2-Diaminoethane,200mLflammable,harmfulincontactwithskinandifswallowed,causesburns,maycausesensitizationbyskincontact●Methylacrylate,100mLhighlyflammable,harmfulbyinhalation,incontactwithskin,andifswallowed,irritatingtoeyes,skin,andrespiratorysystem,maycausesensitizationbyskincontact●Toluenehighlyflammable,harmfulbyinhalationMethodPreparation:1,2-Diaminoethaneandmethylacrylatearefreshlydistilledpriortouse.Note:Thefollowingreactionmixturesmustbecooledto~0Cbeforeaddingtogether.Allreactionmixturesmustbekeptunderablanketofnitrogenatalltimes.Synthesisofstar-branchedester-terminatedprecursor:(core:1,2-diaminoethane;G
0);[dendri-PAMAM(CO2Me)4]1.Prepareasolutionofmethylacrylate(35g,37mL,0.407mol)inmethanol(10mL)andtransferittothetwo-neckedround-bottomedflaskinanice-bath.2.Prepareasolutionof1,2-diaminoethane(5g,5.5mL,0.083mol)inmethanol(10mL)andtransferittotheadditionfunnel.Addthesolutionslowlyoveraperiodof2h,andmonitortherateofadditionperiodicallytoensurethatapproximately1.25mLofthissolutionisaddedevery10min.Thefinalmixturemustbestirredfor30minat0Candthenallowedtowarmtoroomtemperaturefollowedbystirringforafurther24h.3.Removetheexcesssolventunderreducedpressureat40C,re-dissolvein(20mL)methanolandevacuateasbefore,followedbydryingtheresultingcolourlessoilundervacuum(101mmHg,40C)overnight.190 7:Someexamplesofdendrimersynthesis4.ObtainNMR(1H,13C),massspectra,andsizeexclusionchromatography(SEC)ofthisproducttoassureproductidentityandqualityforuseinthenextgrowthstep.SynthesisofPAMAMstar-branchedamine-terminatedprecursor:(core:1,2-diaminoethane;G
0);[dendri-PAMAM(NH2)4]Efficientbranchingamplificationrequiresreactionswithaveryhighdegreeofselectivitytominimizeanystructuraldefects.Thetetradirectionalamineterminated(G0)star-branchedcompoundcore(1,2-diaminoethane)isakeyintermediateinthesynthesisofhighlypuredendrimericmacromolecules.ThisgenerationzeroPAMAMintermediateismadebythecontrolledadditionoftheesterterminatedprecursortoa100-foldexcessof1,2-diaminoethane.Formationoftheamidelinkageishighlyexothermicanditisabsolutelyessentialtokeepthereactionbelow40C.Controlofthereactionisobtainedbyaddingtheesterterminateddendrimerat5C.Dendrimeramidationversusbridgingamidationarekineticallysimilar.Topreventbothintradendrimericcyclizationaswellasinterdendrimerbridgings,alargeexcessof1,2-diamino-ethaneisused.Theexcesscanberemovedtoanundetectablelevelbyazeotropictechniques.5.Prepareasolutionofethylenediamine(37.56g,43mL,0.625mol)inmethanol(50mL)andtransferittoatwo-neckedround-bottomedflaskinanice-bath.6.PrepareasolutionofPAMAM(G0)(5g,0.0125mol)inmethanol(20mL)andtransferittotheadditionfunnel.Addthesolutionslowlyoveraperiodof10minandkeepthetemperaturebelow0C.Stirthefinalmixturefor96hatroomtemperature.7.WhenestergroupsarenolongerdetectablebyNMRspectroscopy,removethesolventsunderreducedpressuremaintainingthetemperaturenohigherthan40C.Removetheexcess1,2-diaminoethanebyusinganazeotropicmixtureoftolueneandmethanol.Theremainingtoluenecanberemovedbyazeotropicdistillationusingmethanol.Finally,removetheremainingmethanolundervacuum(101mmHg,40C,48h).8.Drytheresultingcolourlessoilundervacuum(101mmHg,40C)overnight.9.ObtainNMR(1H,13C),massspectra,andSECasthisproductwillbeusedinthenextstep.SynthesisofPAMAMdendrimeresterterminated:(core:1,2-diaminoethane;G
1.0);[dendri-PAMAM(CO2Me)8]10.Prepareasolutionofmethylacrylate(12.9g,13.5mL,0.15mol)inmethanol(20mL)andtransferittoatwo-neckedround-bottomedflaskinanice-bath.191 Dendri-(polyamidoamine)Gen.Reagents/reactionconditionsGenerationalshellsandsub-shellsMeacrylate,MeOHPAMAM-(COMe)4(a)↑264(2.4eq./–NH2);40°C/24hPAMAM-(NH)3(a)↑EDA,MeOH;5°C/8days232(808moles/ester)Meacrylate,MeOHPAMAM-(COMe)3(a)↑232(2.4eq./–NH2;40°C/24hPAMAM-(NH2)162(b)·EDA,MeOH;5°C/7days3(b)(404moles/ester)Meacrylate,MeOH(a)PAMAM-(COMe)2(a)·216(2.4eq./–NH2);40°C/24hEDA,MeOH;5°C/6days2(b)(–COMe)PAMAM-(NH2)81(b)·(202moles/ester)2(–COMe)Meacrylate,MeOH(a)2PAMAM-(COMe)1(a)↑28(2.4eq./–NH2);40°C/24h(–CO2Me)EDA,MeOH;5°C/5days1(b)(–CO2Me)PAMAM-(NH)0(b)↑24(101moles/ester)(–COMe)2(a)PAMAM-(COMe)Meacrylate,MeOH(–COMe)240(a)·(1.2eq./NH22);40°C/24h(b)(–CO2Me)0(–COMe)·2(a)(–COMe)(–NH)(–COMe)222CoreGeneration:(–COMe)(–NH)(–COMe)222(a)(–COMe)(–NH)(–COMe)222HH(–CO2Me)(–NH2)(–CO2Me)NCHCHN(–CO2Me)(–NH2)(–CO2Me)(–NH2)(–CO2Me)22HH(–CO2Me)(–NH2)(–CO2Me)(–NH2)(–CO2Me)(–COMe)(–NH)(–COMe)(–NH)(–COMe)(–NH)(–COMe)2222222(–COMe)(–NH)(–COMe)(–NH)(–COMe)(–NH)(–COMe)(–NH)(–COMe)2222222224Fig.7.1CoreShellSequencing®forthesynthesisofPAMAM-dendrimers. 7:Someexamplesofdendrimersynthesis11.PrepareasolutionofPAMAM(G0,amineterminated)(8g,0.015mol)inmethanol(20mL)andtransferittotheadditionfunnel.Addthesolutionslowlyoveraperiodof1handkeepthetemperaturebelow0C.Stirthefinalmixturefor24hatroomtemperature.12.Removetheexcesssolventunderreducedpressureat50Canddrytheresultingcolourlessoilundervacuum(101mmHg,40C)overnight.13.ObtainNMR(1H,13C),massspectra,andSECasthisproductwillbeusedinthenextstep.SynthesisofPAMAMdendrimeramineterminated:(core:1,2-diaminoethane;G
1.0);[dendri-PAMAM(NH2)8)]14.Prepareasolutionofethylenediamine(60g,65mL,0.994mol)inmethanol(100mL)andtransferittoatwo-neckedround-bottomedflaskinanice-bath.15.PrepareasolutionofPAMAM(G1.0,esterterminated)(5g,0.004mol)inmethanol(20mL)andtransferittotheadditionfunnel.Addthesolutionslowlyoveraperiodof10minandkeepthetemperaturebelow0C.Stirthefinalmixturefor96hatroomtemperature.16.WhenestergroupsarenolongerdetectablebyNMRspectroscopy,removethesolventsunderreducedpressuremaintainingthetemperaturenohigherthan40C.Removetheexcess1,2-diaminoethanebyusinganazeotropicmixtureoftolueneandmethanol.Theremainingtoluenecanberemovedbyazeotropicdistillationusingmethanol.Finally,removetheremainingmethanolundervacuum(101mmHg,40C,48h).17.Drytheresultingcolourlessoilundervacuum(101mmHg,40C)overnight.18.ObtainNMR(1H,13C),massspectra,andSEC.SeeFigure7.1forthesynthe-sisofPAMAM-dendrimers.3.Protection–deprotectionmethodAmorecompactStarburst®dendrimercanbedesignedwhicheliminatestheneedforexcessreagent,byusing‘protect–deprotect’schemes.Inthissyntheticapproach,thereactivebranchcellreagentcontainsmultiplefunctionalitiesthataremaskedinacyclicstructure.Forexample,abicyclicorthoesterstructuremaybeusedtomaskthreehydroxylgroupsofpentaery-thritolwhichleavesoneunprotectedhydroxylgroupforcoupling.14Animportantrequirementforthissynthesisistheefficientformationofetherlinkages.ThesyntheticamplicationisinitiatedfromatetrabromidePE-Br4core.Branchcellreiterationisafour-stepprocessinvolving:(a)nucleophilicdisplacementofbromideionsbyalkoxidefunctionality;(b)mildacidhydro-lysisofthebicyclicorthoestergrouptodeprotectedthreehydroxylgroups/orthoestermoiety;(c)tosylationofthehydroxylgroups;andfinally193 D.A.Tomalia(d)bromideiondisplacementofthetosylategroupstocontinuethesequencetothenextgenerationlevel(Scheme2).Thechronologicalsequencingandamplificationpatternsforthepoly(ether)dendrimersareillustratedinFigure7.2.OOOOBrBrHOONaHOOOO+ODMFBrBrOOOOOOOMHTBOOOStar-branchedPE(MBO)4HOOHHOOHcat.HClHOOOOHEtOHHOOOOHHOOHHOOHG1-PE(OH)12HOHOOHOHHOOHHOOHHOOHHOOHOOHOOOOHHOOHOOOOHOOHOOHOOOOHOOHOOHHOOOOHHOOHHOHOOHOHHOOHOHOHHOOHG1-PE(OH)36(Four-armbranched)Scheme2194 Dendri-Gen.Reagents/reactionconditionsGenerationalshellsandsub-shellsPoly(ether)*PE-(MBO)122(a)·MHTBO,DMF,NaH,24hPE-(Br)361(d)·NaBr,(DMAc),150°C/1hPE-(Tos)361(c)↑TosCl,(pyridine),7daysPE-(OH)361(b)↑HCl,(MeOH)PE-(MBO)121(a)↑MHTBO,DMF,NaH,24hPE-(Br)120(d)↑NaBr,(DMAc),150°C/1hPE-(Tos)120(c)↑TosCl,(pyridine),5daysPE-(OH)120(b)↑HCl,(MeOH)PE-(MBO)40(a)↑MHTBO,DMF,NaH,24h–0.5(b)↑NaBr,(diethyleneglycol)–0.5(a)↑TosCl,(pyridine)·CoreGeneration:0(a)(b)1(a)(b)(c)(d)2(a)(b)(c)(d)3(a)CH2O(OH),(Tos),(Br)CH2OCH2CCH2OMe(OH),(Tos),(Br)OCH2CCH2OMeCH2O(OH),(Tos),(Br)CH2OCH2OHCH2O(OH),(Tos),(Br)OCH2O(OH),(Tos),(Br)CH2OHOCH2CCH2OH(Tos),(Br)OCH2CCH2OMe(OH),(Tos),(Br)OCH2CCH2OMe(OH),(Tos),(Br)OCH2CCH2OMeCH2OHCH2O(OH),(Tos),(Br)OCH2O(OH),(Tos),(Br)CH2O(Core)CH2O(OH),(Tos),(Br)CH2OCH2CCH2OMe(OH),(Tos),(Br)OCH2CCH2OMeCH2O(OH),(Tos),(Br)CH2O4Fig.7.2CoreShellSequencing®forthesynthesisofPE-dendrimers. D.A.TomaliaProtocol2.Caution!Carryoutallproceduresinawell-ventilatedhood,andweardispos-ablevinylorlatexgloves,andchemical-resistantsafetygoggles.Equipment●Dualmanifold(nitrogen/vacuum)●Sourceofdrynitrogen●Single-necked,round-bottomedflasks●Gas-inletadapter(2)(500and199mL)●Mechanicalstirrer●Additionfunnel(150mL)●Condenser●Dean–Starktrap●Septa●Dewarcondenser●Magneticstirrerbar●HotplateStirrer/oil-bath●Apparatusforfiltration,Erlenmeyerflasks,Buchnerflasks,funnel,fastflowfilterpaper,andwateraspirator.●Vacuumoven●Powderadditionfunnel●Two-neckedround-bottomedflasks●Erlenmeyerflasks(varioussizes)(500and250mL)●Pressure-equalizingdroppingfunnel●Three-neckedround-bottomedflask(500mL)Materials●p-Toluenesulfonylchloride,18.7g,9.8mmollacrymator,harmfuloncontactwiththeskinorifswallowed●1methyl-4-hydroxymethyl-2,6,7-trioxabicyclo-avoidskincontact[2,2,2]-octane(MHTBO),50g●Dimethylformamide(DMF),ca.250mLpotentiallyteratogenic,harmfulincontactwithskin,irritatingtoeyes●Hexane,400mLhighlyflammable,harmfulbyinhalationandincontactwiththeskin●Toluene,250mLhighlyflammable,harmfulbyinhalation●Sodiumhydride(NaH),8.3g,348mmol(13.7gofcontactwithwaterreleasesflammablea60%dispersioninmineraloil)gases,causesburns●Dioctylphthalate,200mLmayimpairfertility,potentiallyteratogenic●Pyridinep-toluenesulfonate(PPTS),1g,4mmolirritatingincontactwithskin,eyes,andrespiratorysystem●Pentaerythritol,27.2g,200mmolavoidskincontact●Triethylorthoacetate,32.44g,36.6mL,200mmolflammable,irritatingtoeyesandrespiratorysystem●Pentaerythrityltetrabromide,20g,51.6mmol,avoidskincontact(206mmolbromide)●Pyridine,140mLhighlyflammable,harmfulbyinhalation,incontactwiththeskin,andifswallowed●N,N-Dimethylacetamide,40mLpotentialteratogen,harmfulbyinhalationandincontactwiththeskin●Sodiumbromide,8g,78mmol●Sodiumchloride,75g●HCl(conc.),1.2mLcausessevereburns●Methanolhighlyflammable,toxicbyinhalationandifswallowed●Chloroformharmfulbyinhalation,potentialcarcinogen●Ethylacetatehighlyflammable196 7:SomeexamplesofdendrimersynthesisSynthesisofthereactivebranchcellReagent:1-methyl-4-hydroxymethyl-2,6,7-trioxabicyclo-[2,2,2]-octane(MHTBO)1.Toaround-bottomedflask(500mL)equippedwithaDean–Starktrapfittedwitharefluxcondenserandamagneticstirrerbar,addpentaerythritol(27.2g,200mmol),triethylorthoacetate(32.44g,36.6mL,200mmol),PPTS(1g,4mmol),and200mLofdioctylphthalate.2.Attachthecondensertothedualmanifoldusingagas-inletadapter,andplacethesystemunderanitrogenatmosphere.aHeatthereactionmixtureonanoil-bath,withstirringat140Cfor2–3hundernitrogenuntilquantitativerecoveryofethanol(32mLtheoretical)isobtained.Replacethenitrogenlinewithanaspiratorvacuum(25mmHg)toremovetheresidualethanol.3.ReplacethetrapwithalargeDewarcondensercontainingice-waterandevacuatethemixtureat0.1mmHg.4.Raisethebathtemperatureto160Ctoremoveanyresidueproduct.5.Dissolvethecrudeproductin250mLofrefluxingtoluene,filterhot,andallowtocooltoroomtemperaturefor3h.Leavethismixtureinthefreezer(10C)for18h.FilterthemixtureinaBuchnerfunnelcontainingfastflowfilterpaper.6.Allowthewhitesolidtodryinairfor15minandthenvacuumdryat25Covernight.b7.ObtainNMR(1H,13C),andmassspectra,asthisproductwillbeusedinthenextstep.Synthesisofpoly(ether)dendrimersfromapentaerythritolcorePE(MBO)48.Toatwo-necked500mLround-bottomedflaskequippedwithamechanicalstirrer,apowderadditionfunnel,candarubberseptum,addsodiumhydride(7.3g,304mmol,12gofa60%dispersioninmineraloil)and100mLofhexane.Stirthemixturefor5minthenallowthereactantstosettletogiveaclearmixtureanddecantintoabeakerofcontainingmethanol.Repeatthisprocedurethreetimesdandthenremovethemechanicalstirrerandconnectthesystemtothedualmanifoldusingagasinlet.Evacuatethegreyish-whiteslurryathighvacuumtoaconstantweightofsodiumhydride(6.5g,270mmol).Then,withtheflaskunderanatmosphereofnitrogen,addanhydrousDMF(150mL)viaacannula.9.AddMHTBO(39.2g,245mmol)totheadditionfunnelandplaceunderaninertatmosphereusingthemanifoldsystem.ThenaddtheMHTBOover
30min.Aftermostofthegasevolutionhasceased,heatat60Cfor1.5huntilgasevolutionhasceasedcompletely.10.Addpentaerythrityltetrabromide(20g,51.6mmol,206mmolbromide)totheabovemixture.11.Heatthemixtureat75Cfor22hundernitrogen.Coolthemixtureto25Candadddrop-wisetoaflaskcontaining1Lofawell-stirredice-water.197 D.A.TomaliaProtocol2.Continued12.FilterthismixtureinalargeBuchnerfunnelcontainingfastflowfilterpaper.Washthewhitesolidwithdeionizedwater(4100mL)anddrythesolidat40Cunderhighvacuumovernight.13.ObtainNMR(1H,13C),massspectra,andSEC,asthisproductwillbeusedinthenextstep.Synthesisofpoly(ether):[dendri-PE(OH)12]14.AddPE(MBO)4(8g,11.4mmol)tomethanol(130mL)inatwo-neckedround-bottomedflask(250mL)equippedwithacondenserandadroppingfunnel.15.Add1.2mLofconcentratedHCltothelatterreactionmixture.Gentlyrefluxfor1h.16.AddaDean–Starktraptothesystem(betweentheflaskandcondenser),dis-tilmethanolandmethylacetateuntilonlyaboutone-thirdofthesolventremains.Coolthismixtureto10C.17.Filtertheprecipitateandwashitwithmethanol.Drythefinalproductunderhighvacuumovernightat25C.18.ObtainNMR(1H,13C),massspectra,andSEC,asthisproductwillbeusedinthenextstep.Synthesisofpoly(ether):[dendri-PE(Tos)12]19.Adddendri-PE(OH)12(2g,3.29mmol)toaflame-dried500mLthree-neckedflaskequippedwithastirrerbar,apressure-equalizingdroppingfunnelfit-tedwitharubberseptum,acondenser,andathermometer,andattachedviathecondensertothedualmanifold.20.Add40mLanhydrouspyridineviaacannula.Coolthemixtureto0C.21.Inaflame-driedflaskprepareasolutionofp-toluenesulfonylchloride(18.7g,9.8mmol,30equiv.perdendri-PE-(OH)12)in100mLanhydrouspyridine.eCannulatransferthismixturetothedroppingfunnel.AddthissolutionfromthedroppingfunneltothePE-(OH)12solutionmaintainingthetemperatureat0–5C.Maintainthetemperatureat0Candstirfor1h.22.Sealtheflaskandleavethemixtureatroomtemperaturefor4days.23.Pourthismixtureinto500mLice-wateranddecantthesolventaftertheprecipitatehasagglomeratedatthebottomofthebeaker.24.Drythecrudeproductat40Cunderhighvacuumovernight.Dissolvethissolidin100mLofchloroformandfiltertheprecipitate.Drythefinalproductunderhighvacuumovernightat25C.25.ObtainNMR(1H,13C),massspectra,andSEC,asthisproductwillbeusedinthenextstep.Synthesisofpoly(ether);[dendri-PE(Br)12]26.Adddendri-PE(Tos)12(6.35g,2.58mol,31mmolTos),40mLofanhydrousN,N-dimethylacetamideandsodiumbromide(8g,78mmol,30equiv.per198 7:SomeexamplesofdendrimersynthesisPE(Tos)12)toa100mLone-neckedround-bottomedflaskcontainingastirbar.27.Connecttheflasktothemanifoldandheatthemixtureat150Cfor1.5hwithstirringunderN2,thencoolto25Candpourintoice-water.28.Filtertheprecipitate,washitwithdeionizedwater,anddrythefinalproductunderhighvacuumovernight.29.Recrystallizefromboilingethylacetateandvacuumdrythefinalproduct.30.ObtainNMR(1H,13C)andmassspectraasthisproductwillbeusedinthenextstep.Synthesisofpoly(ether):[dendri-PE(MBO)12]31.WeighNaH(1.7g,ofa60%dispersioninmineraloil,1.0gNaH,43.5mmol)andwashtwicewith50mLofhexanes,thenvacuumdryat30–40C.32.Atwo-neckedround-bottomedflask(250mL)containingastirrerbarisequippedwitharubberseptumandarefluxcondenser,andconnectedtothenitrogensupply(dualmanifold)withagas-inletadapter.Addsodiumhydride(1.0g,43.5mmol)totheflaskandthenanhydrousDMF(100mL)viaacannula.AddMHTBO(5.8g,36.3mmol,2equiv.perbromide)andheatthemixtureat60Cfor1.5h.Theevaluationofhydrogenwillceasewithinonehourandthemixturebecomeshomogeneousandclear.33.Adddendri-PE(Br)12(2.0g,1.5mol,18mmolbromide)tothemixtureandheatat140CunderN2witharefluxcondenserattachedfor22h.34.Coolthemixtureto25Candpourinto800mLoficewatercontaining75gofNaCl.35.Filtertheprecipitateandwashitwithdeionizedwater(350mL)anddrythefinalproductunderhighvacuumat70Cfor5hthen25Cfor12h.36.ObtainNMR(1H,13C),massspectra,andSEC.aThemanifoldenablesthistobedonebyevacuatingtheflaskandthenallowingnitrogenintothesystem(seeChapter2).bTheproductmaybedried,forexample,usingavacuumovenoravacuumdesiccator.cForexample,Aldrichsupplyfunnelswhicharedesignedtodeliverfree-flowinggranularmaterialtoreactionsundervacuumconditionsdThisprocedureremovesthemineraloil.eUsingatwo-neckedround-bottomedflaskattachedtothemanifoldusingagasinlettubeandfittedwithaseptum,see,forexample,Chapter2,Protocol14.References1.Tomaila,D.A.;Baker,H.;Dewald,J.;Hall,M.;Kallos,G.;Martin,S.;Roeck,J.;Ryder,J.;Smith,P.Polym.J.(Tokyo)1985,17,117–132.2.Tomalia,D.A.;Baker,H.;Dewald,J.;Hall,M.;Kallos,G.;Martin,S.;Roeck,J.;Ryder,J.;Smith,P.Macromolecules1986,2466–2468.3.Smith,P.B.;Martin,S.J.;Hall,M.J.;Tomalia,D.A.InAppliedPolymerAnalysis,andCharacterization;Mitchell,J.Jr.,ed.,HanserPublishers:Munich;1987,pp.357–385.199 D.A.Tomalia4.Zeng,F.;Zimmermann,F.C.Chem.Rev.1997,97(5),1681–1712.5.Romagnoli,B.;Hayes,W.J.Mater.Chem.2002,12,767–799.6.Fréchet,J.M.J.;Hawker,C.J.ComprehensivePolymerScience;2ndSuppl.,Aggaraval,S.L.;Russo,S.,eds,Pergamon:Oxford;1996.7.Voit,B.I.ActaPolym.1995,46,87–99.8.Gitting,P.J.;Twyman,L.J.Supramol.Chem.2003,15,5–23.9.Grayson,S.K.;FrechetJ.M.J.Chem.Rev.2001,101(12),3819–3867.10.Fischer,M.;Vogtle,F.Angew.Chem.,Int.Ed.Engl.1999,38(7),885–905.11.Inoue,K.Prog.Polym.Sci.2000,25(4),453–571.12.Aulenta,F.;Hayes,W.;Rannard,S.Eur.Polym.J.2003,39(9),1741–1771.13.Tomalia,D.A.;Naylor,A.M.;Goddard,W.A.III.Angew.Chem.1990,102(2),119–157,(Angew.Chem.,Int.Ed.Engl.1990,29(2),138–175).14.Padias,A.B.;Hall,H.K.,Jr.;Tomalia,D.A.;McConnell,J.R.J.Org.Chem.1987,52,5305–5312.200 8NewmethodologiesinthepreparationofimprintedpolymersCAMERONALEXANDER,NICOLEKIRSCH,andMICHAELWHITCOMBE1.IntroductionMolecularimprintingisarapidlyemergingmethodforthecreationofrecognitionsitesinsyntheticpolymers,1–5andtheresultantmaterialsoffercon-siderablepromiseasselectiveadsorbentsinanumberofapplications.6–16Thetechniqueexploitstheprincipleofusingelementsofatargetmoleculetocreateitsownrecognitionsite.Thisisachievedbytheformationofahighlycross-linkedpolymericmatrixaroundatemplate,whichcanbethetargetmoleculeitselforaclosestructuralanalogue.Thekeytothisprocedureistoensurethat,duringthepolymerization,functionalgroupsofthetemplatemoleculearefullyengagedininteractionswith‘complementaryfunctional-ity’ofpolymer-formingcomponents.Theseinteractionsarethen‘lockedin’bytheincorporationofthewholeassemblyintothepolymerstructure.Subsequentremovalofthetemplaterevealsthenewlycreatedbindingsitescontainingfunctionalgroupsintheprecisestereochemicalarrangementtoensurerecognitionofthetargetinahighlyselectivemanner(Scheme1).aRemovetemplateTemplateAssemblyPolymerizecTemplateTemplate(Binding)Re-bindtemplateb1234Scheme1Generalizeddepictionofthemolecularimprintingtechnique:1—monomersa,b,andcformanattachmenttocomplementarysitesonthetemplate.2—Thepre-assembledtemplate–monomercomplexispolymerizedwithalargeexcessofcross-linker.3—Therigidpolymerformedinthisprocessretainsanarrangementoffunctionalelementscomplementarybothinshapeandspatialorientationtothetemplate.4—Removalofthetemplaterevealsabindingpocketorcavity,whichcanbeusedtorecapturethetemplatespecies. (a)EGDM,OporogenOOOpolymerizeOO1aHydrolyseBindHHReleaseOOOH1b(b)(1)DVB,porogen,NpolymerizeNSiHHO(2)HydrolyseOO2a2bScheme2Thepreparationofpolymersbythe‘sacrificialspacer’approachimprintedagainst:(a)cholesteroland(b)pyridine. 8:NewmethodologiesforimprintedpolymersThefirstreportsofmolecularimprintinginorganicpolymers17involvedthetemplatingofprotectedsugars,intheformofesterswithapolymerizableboronicacid(however,seeRef.18foranearlierexampleoftheimprintingconcept)intoacross-linkedpolymer‘scaffold’,andvariationsofthebasictechniquehavenowbeenadoptedbymanyresearchgroupsaroundtheworld.19Ingeneral,molecularlyimprintedpolymers(MIPs)arepreparedbythermalorphotochemicalfree-radicalroutes,employingacrylicorvinylicmonomersinasolventchosentoensurethatthefinalmatrixismicroporous.Thenumbersandtypesofmoleculeswhichhavenowbeenimprintedisverylarge,butakeyfactorinthepreparationofMIPmaterialswiththedesiredrecognitionpropertiesisstillthechemicalnatureofthelinkbetweenthetemplateandthepolymerbackbone.Consequently,strategiesbywhichthetemplatecanbesecurelyfixedinspaceasthegrowingmatrixformsaroundit,yetbereadilyremovedtogeneratetherecognitionsiteafterpolymersynthesisiscomplete,areofparticularinterest.Amethodinwhichthesedemandsmaybeachievedisbycovalentlylinkingthetemplatetoapolymer-izablemonomerbyareadilycleavablespacergroup,whichisdesignedinsuchawaythatbreakageofthetemplate–polymerlinkyieldsfunctionalitywhichcanre-bindthetemplatebynon-covalentbonds.Thisistermedthesacrificialspacerapproach,andtwoexamplesaregivenforthepreparationofmonomers(1a,2a)andpolymers(1b,2b)designedtorecognizeasteroid,cholesterol,20andasimpleheterocycle,pyridine,21asshowninScheme2.2.SacrificialspacerapproachProtocol1a.Preparationofcholesteryl4-vinylphenylcarbonate1a(Scheme3)Caution!Carryoutallproceduresinawell-ventilatedfume-cupboard,wearappropriateprotectivegloves,alab-coat,andsafetyglasses.Allvacuum-lineworkshouldbeperformedwhilebehindaprotectiveblast-proofscreen.Checkallglasswareforstarcracksbeforeusingundervacuumandneveruseflat-bottomedflaskswithrotaryevaporators.OCH3(1)KOH(aq)OOH(2)CO2Scheme3Preparationof4-vinylphenol.Equipment●Laboratorymagneticstirrer●Three-neckedreactionflaskwithadditionfunnel,thermometer,andguardtubes●Ice-bath●Separatingfunnel203 C.Alexanderetal.Protocol1a.Continued●Tefloncoatedmagneticfollower●Icesaltbath●Conicalflasks(250mL)●Tefloncoatedmagneticfollower●Buchnerflask,Buchnerfunnel,andfilterpaperMaterials●4-Acetoxystyrene10g,62mmolharmfulbyinhalation,incontactwithskinand,ifswallowed●Cholesterylchloroformate7.5g,17mmolcorrosive,causesburns●Potassiumhydroxide8.6g,153mmolcorrosive,harmfulifswallowed,causessevereburns●CO2cylinderandtrapordryicetoextremelycold,maycauseburnsgenerateCO2gas●Tetrahydrofuran(THF),anhydroushighlyflammable,irritant,mayformexplosiveperoxides,irritatingtoeyesandrespiratorysystem●Triethylamine,anhydrous2.9g,4mL,29mmolhighlyflammable,corrosive,harmfulbyinhalation,incontactwithskin,andifswallowed,causessevereburns●Dichloromethanecarcinogen,harmfulbyinhalation●Magnesiumsulfate,dried●2-Propanol(isopropanol)highlyflammable,irritatingtoeyes,vapoursmaycausedrowsinessanddizziness●Hexanehighlyflammable,irritatingtoskin,harmful,dangerofseriousdamagetohealthbyprolongedexposureduetoinhalationMethodPreparationof4-vinylphenol:Thismethod20wasbasedonthatoriginallypub-lishedbyCorsonetal.221.Dissolve8.6gofpotassiumhydroxide(8.6g,153mol)indistilledwater(85mL)ina250mLconicalflask,cooltoroomtemperature.2.AddTHF(1mL)and4-acetoxystyrene(10g,62mmol).Vigorouslystirthereactionmixtureatroomtemperatureuntiltheoilylayerhascompletelydis-solvedintheaqueouspart(approximately1h).3.Filterthesolutionintoaclean250mLflaskandstandinanice-bath.4.ConnectaPasteurpipetteorlengthofglasstubetoasourceofCO2gasviaflexibletubing.Ifusingacylinder,includeaDreschelbottleorothertraptopreventliquidsucking-backintothecylinderhead.BubbleCO2intothecooledmixture,withstirring,toprecipitatethephenol.5.Onceprecipitationiscomplete,filteroffthecrystalsofthephenol,washwithwateranddryundervacuum,alternativelythedampfiltratecanbetakenupOHOTHF,EtNO3ClOOO1aScheme4Preparationofcholesteryl(4-vinyl)phenylcarbonate.204 8:Newmethodologiesforimprintedpolymersindiethylether,thesolutiondriedwithmagnesiumsulfate,filteredandevapo-ratedbeforerecrystallizationfromhexane.(Thislatterprocedureisrecom-mendedformaterialusedinProtocol2a.)Storethe4-vinylphenolinthefreezer.Preparationofcholesteryl(4-vinyl)phenylcarbonate1a20(Scheme4)1.Ina250mLthree-neckedflaskfittedwithathermometeranddroppingfunnel,dissolve4-vinylphenol(2.0g,17mmol)inamixtureofTHF(60mL)andtri-ethylamine(4mL).Closetheflaskwithacalciumchlorideorsilicagel-filledguardtube(dryingtube)andcoolthesolutionto10Cinanice–salt-bath.2.Dissolvecholesterylchloroformate(7.5g,17mmol)in40mLofTHFandaddthissolutiontothedroppingfunnel.Closethedroppingfunnelwithasecondguardtube(alternativelyuseastopperedpressure-equalizingdroppingfunnel).3.Addthesolutionofchloroformatedrop-wisetothestirredsolutionofphenolsuchthatthetemperatureofthereactionmixturedoesnotriseabove0C.Awhiteprecipitateoftriethylaminehydrochloridewillformasthereactionproceeds.Whentheadditioniscomplete,removetheice-bathandallowtheflasktowarmtoroomtemperature.4.Afterstirringforafurther3h,orovernightifpreferred,transferthecontentsoftheflasktoasingle-neckedflaskandremovethesolventbyrotaryevaporation,keepingthetemperaturebelow40C.5.Dissolvethesolidresiduein100mLofdichloromethaneandtransfertoaseparatingfunnel.Washthelowerorganiclayertwicewith50mLofwaterandoncewiththesamevolumeofbrine.Drythedichloromethanesolutionwithmagnesiumsulfate,filterandevaporate.6.Recrystallizeonceortwicefromisopropanoloraqueousacetone.Theproductwillberecoveredascolourlesscrystals,m.pt146–147C.Protocol1b.Preparationofcholesterol-imprintedpolymer201bEquipment●Vacuumline●Quickfittesttubeandvacuumstopcockadapter●Thermostaticallycontrolledwater-bath●Grindingequipment●Sievesforparticlesizing,ifrequired●Sintered-glassfunnelandfilterflask●Soxhletextractor,paperthimble,flask,andheatingmantle●Single-neckedround-bottomedflask(50mL)●RefluxcondenserMaterials●Ethyleneglycoldimethacrylateirritant(EGDMA)inhibitor-freea8.34mL,8.76g,44.2mmol●Toluenebhighlyflammable,harmfulbyinhalation205 C.Alexanderetal.Protocol1b.Continued●Hexaneb,chighlyflammable,irritatingtoskin,harmful:dangerofseriousdamagetohealthbyprolongedexposurethroughinhalation●Azo-bis-isobutyronitrile(AIBN)explosive,harmful,riskofexplosionbyshock,(0.149g,0.9mmol)friction,fire,orothersourcesofignition,highlyflammable,harmfulbyinhalationandifswallowed●Methanolhighlyflammable,toxicbyinhalation,incontactwithskin,andifswallowed●Sodiumhydroxidecorrosive,causessevereburns●Hydrochloricacidcorrosive,causesburns,irritatingtorespiratorysystemMethodPreparationofimprintedpolymerincorporatingcholesteryl(4-vinyl)phenylcarbonate201bd1.Forthepreparationof10gofpolymer:placecholesteryl(4-vinyl)phenylcarbonate(1.24g,2.33mmol),EGDMA(8.34mL,8.76g,44.2mmol),AIBN(149mg,1mol%),toluene(2mL),andhexane(18mL)inaQuickfittesttubeofacapacitysuchthatthetubeisnomorethanathirdfull.Agitatetodissolvethecontents.2.Lightlylubricatetheglassjointwithvacuumgreasetopreventpolymerfromformingbetweentheglasssurfaces,closethetubewithavacuumstopcockandattachtoavacuumline.3.Freezethetubecontentswithliquidnitrogen.4.Openthevacuuminletandevacuatetheheadspaceinthetube.5.Closethestopcock,removetheliquidnitrogenDewarandallowthetubecontentstothaw.Dissolvedairwilloutgasasthepolymerizationmixturemelts.Thawingcanbeassistedbytheapplicationofabeakercontainingwarmwater.6.Oncethawed,nitrogengascanbeadmittedtothetubetoequalizethepressure.7.Repeatsteps3–6fortwomorecycles,exceptonthelastcycledonotadmitnitrogen,butleavethecontentsofthetubeatreducedpressure.8.Removethesealedtubefromthevacuumlineandsubmergeittojustabovethelevelofthecontentsinathermostattedwater-bathat65C.Ensurethatthetubecontentsareahomogeneoussolutionbyagitationifnecessary.Thecontentsofthetubeshouldbegintosolidifywithinthefirst5–10minofheatingbutthepolymerizationshouldbecontinuedforaround24h.Maintainthewaterlevelinthebathduringthistime.9.Removethetubecontainingthewhiteblockofpolymerfromthebathandallowtocool.10.Openthetubeafterreleasingthevacuumandcleananyvacuumgreasefromtheground-glassjointwithatissuemoistenedwithethylacetate.11.Holdthebaseofthetubeinaclothincaseofbreakageandchipthepolymerintomanageablepieceswiththeendofaspatulaandcollectthechunksofpolymerinafilterfunnel.Smallpiecesofmaterialcanbewashedfromthe206 8:Newmethodologiesforimprintedpolymerstubeusingmethanol.Itisnotnormallynecessarytobreaktheglassinordertorecoverthepolymer.12.Washthepolymerparticleswellwithmethanolandallowtoair-dryonthefilterfunnel.13.Transferthepolymertoamillandgrindtoapowder.14.CollectthepolymerpowderandplaceitinaSoxhletthimble.Caution!Donotinhalethedust.15.ExtractthepolymerwithmethanolinaSoxhletapparatusfor12htoremoveinitiatorfragmentsandunreactedmonomers.16.Drythepolymerinavacuumovenorvacuumdesiccator.Templateremoval:201.Weigh2.5gofthepolymerand1gofsodiumhydroxideina50mLround-bottomedflaskandadd25mLofmethanol.2.Fitarefluxcondensertotheflaskandlowerintoanoil-bathat90C.Stirthemixturewhileheatingunderrefluxforupto6h.3.Cooltheflaskandpourthecontentsintoabeakercontaining250mLofwaterand12mLofconcentratedhydrochloricacid.Stirthemixturefor20min.4.Filter-offthepolymerandwashcarefullyonthefilterwithwater,50:50water/methanolandmethanol.aTheinhibitorcanberemovedbywashingtheEGDMAwithdilutesodiumhydroxidesolution(approx.0.1M)inaseparatingfunnel,followedbywashingwithwater,thenwithsaturatedbrine,anddryingtheorganiclayerovercalciumchloride.Asthedensityofthismonomerisclosetothatofwater,sep-arationofthelayerscanbetroublesome.Abetterseparationcanbeachievedbytheadditionofsomebrinetothehydroxidesolutionandtothewater-washuntilthelayersareclearlydefined(organiclayeruppermost).Alternatively,themonomercanbetreatedwithbaseandwashedasasolutionindiethyletherandtheexcesssolventremovedbyrotaryevaporationusingacoolwater-bathafterthedryingstep.Thisprocedurecanbecarriedoutinadvanceandthede-inhibitedmonomerstoredinarefriger-atorforuptoaweekbeforeuse.Afinal‘polish’canbeappliedtothemonomerbyfiltrationthroughashortcolumnofactivatedneutralaluminabeforeuse.bTolueneandhexanewerebothdistilledfromcalciumhydridebeforeuse.cIsohexane(MerckorFisherScientific)canbeusedasalesstoxicalternativeton-hexane.dEssentially,thesamebasicprotocolcanbeadaptedforthepreparationofnon-covalentlyimprintedpolymers.Inthiscase,thecholesteroltemplatemonomerisreplacedbythetemplatetobeimprintedandadditionalfunctionalmonomer(ormonomers)isincludedinthepolymerizationmixture,atapre-determinedmolarratiowithrespecttothetemplate.Typicalfunctionalmonomersmightbechosenfromamongst:methacrylicacid,itaconicacid,vinylpyridine,dimethylaminoethylmethacrylate,acryl-amide,hydroxyethylmethacylate,andmanymore.Typicalsolventsfornon-covalentimprintingincludechloroform,THF,andacetonitrile.Templatesareremovedfromnon-covalentlyimprintedpolymersbyexhaustivewashingwithasuitablesolvent.Protocol2a.Preparationof(4-vinylphenyoxy)dimethylphenylsilane212a(Scheme5)Caution!Thisprocedureshouldbecarriedoutinawell-ventilatedfume-cupboard,wearappropriateprotectivegloves,alab-coat,andsafetyglasses.All207 C.Alexanderetal.Protocol2a.Continuedvacuum-lineworkshouldbeperformedwhilebehindaprotectiveblast-proofscreen.Checkallglasswareforstarcracksbeforeusingundervacuumandneveruseflat-bottomedflaskswithrotaryevaporators.SiClEt2O,pyridineOHSiO2aScheme5Preparationof4-vinylphenyoxydimethylphenylsilane.Equipment●Laboratorymagneticstirrer●50mLTwo-neckedround-bottomedflaskequippedwithseptaandstopcock●2mLand10mLgas-tightsyringes●Sourceofdrynitrogengas●Rotaryevaporator●Minidistillationkit●VacuumlineMaterials●4-Vinylphenol3g,24mmolcorrosive,treatasharmful●Pyridine,anhydrous2mLhighlyflammable,harmfulbyinhalation,incontactwithskin,andifswallowed●Diethylether,driedoversodiumextremelyflammable,mayformexplosiveperoxides,harmfulandfreshlydistilledbeforeuse20mLifswallowed,vapoursmaycausedrowsinessand●Chlorodimethylphenylsilane4.27gdizzinesscorrosive,causesburns,irritating(4.2mL),25mmoltorespiratorysystem●2,6-Di-tert-butyl-4-methylphenol(BHT)traceca.5mgirritantMethodPreparationof4-vinylphenyoxydimethylphenylsilane2a1.Weigh4-vinylphenol(3.0g,24mmol)intoa50mLtwo-neckedflask.2.Purgetheflaskwithdrynitrogenandsealwithatight-fittingrubberseptum.3.Usinggas-tightsyringes,chargetheflaskwithdiethylether(20mL)andpyridine(2mL)andstirtomixthoroughly.4.Addchlorodimethylphenylsilane(4.2mL,4.27g,25mmol)drop-wisetothereactionmixtureviasyringe.Awhiteprecipitateofpyridinehydrochloridewillformasthereactionproceeds.5.Stirthecontentsoftheflaskfor2h,removetheprecipitatebyfiltrationandwashthesolidobtainedwithdrydiethylether.6.CombinetheetherfractionsandaddafewcrystalsofBHT,as4-vinylpheny-oxydimethylphenylsilanereadilypolymerizesonstanding.7.Evaporatethesolventanddistilltheresidueunderreducedpressuretoobtainacolourlessliquid,b.p.104–106C/0.2mbar.208 8:NewmethodologiesforimprintedpolymersProtocol2b.Preparationof4-vinylphenoxydimethylsilane-imprintedpolymer212bEquipment●Vacuumline●Quickfittesttubeandvacuumstopcockadapter●Thermostaticallycontrolledwater-bath●Grindingequipment●Sintered-glassfunnelandfilterflask●Soxhletextractor,paperthimble,flask,andheatingmantleMaterials●Divinylbenzene(DVB),irritantinhibitor-freea2.70mL,2.47g,19mmol●Hexaneb5mLhighlyflammable,irritatingtoskin,harmful:dangerofseriousdamagetohealthbyprolongedexposurethroughinhalation●AIBN64mg,0.4mmolexplosive,harmful,riskofexplosionbyshock,friction,fire,orothersourcesofignition,highlyflammable,harmfulbyinhalationandifswallowed●Methanolhighlyflammable,irritatingtoskin,harmful:dangerofseriousdamagetohealthbyprolongedexposurethroughinhalation●Hydrochloricacid20mL,corrosive,causesburns,irritatingtorespiratorysystem(5Minmethanol)●Tetrahydrofuranhighlyflammable,irritant,mayformexplosiveperoxides,irritatingtoeyesandrespiratorysystemMethodPreparationofpolymerincorporating4-vinylphenoxydimethylsilane211.Forthepreparationof2.5gofpolymer:place4-vinylphenoxydimethylsilane(254mg,1mmol),DVB(2.70mL,2.47g,19mmol),AIBN(64mg,1mol%),andhexane(5mL)ina25mLQuickfittesttube.Agitatetodissolvethecontents.2.Lightlylubricatetheglassjointwithvacuumgreasetopreventpolymerfromformingbetweentheglasssurfaces,closethetubewithavacuumstopcockandattachtoavacuumline.3.Freezethetubecontentswithliquidnitrogen,anddegasthesolutionasdescribedinProtocol1b.4.Removethesealedtubefromthevacuumlineandheatinthermostattedwaterbathat65Cfor24h.Theonsetofpolymerizationmaynotbeeasytodetect,butgelationshouldoccurwithinafewhours.5.Attheendofthereactiontime,removethetubefromthewater-bathandallowtocool.6.Carefullyadmitairtothetubeandremoveanyvacuumgreasefromtheground-glassjoint.7.RecoverthepolymerfromthetubeassetoutinProtocol1b:itshouldbenotedthatdivinylbenzene-basedpolymerscanbeverybrittleandsoitisnecessarytobecarefultoavoidglasswarebreakageandriskofinjury.209 C.Alexanderetal.Protocol2b.Continued8.Washtheobtainedpolymerwithmethanolandallowtoair-dryonthefilterfunnel.9.Transferthepolymerparticlesintoamill(e.g.FritschPulverisette‘O’grindingmill)andgrindtoafinepowder.10.CollectthepolymerpowderandplaceitinaSoxhletthimble(avoidinhala-tionofdust).11.ExtractthepolymerwithmethanolinaSoxhletapparatusfor12h,thendrythepolymerat80Cundervacuum.Templateremoval1.Weigh1.0gofthepolymerina50mLround-bottomedflaskandadd20mLofHCl,dilutedto5Mwithmethanol.2.Fitarefluxcondensertotheflaskandlowerintoanoil-bathat80C.Stirthemixturewhileheatingunderrefluxforupto6h.3.Cooltheflaskandfilterthepolymer.4.Washthepolymercarefullyonthefilterwithmethanol/water,methanol,andTHFandallowtoair-dry.5.Extractthepolymerwithdiethyletherandthendryundervacuumat80C.aTheinhibitorcanberemovedbyextractionwithbaseusingaproceduresimilartothatforEGDMA,seefootnotea,Protocol1b,above.bSeefootnotec,Protocol1b,above.3.Preparationofbacteria-imprintedpolymersThecomponentstypicallyusedtoprepareMIPsincludeacrylicacid,ethylene-glycoldimethacrylate,ordivinylbenzeneinsolventssuchaschloroformortoluene,andpolymerspreparedinthiswayaregenerallyintheformofabulkmonolith,withahighlycross-linkedmicroporousstructure.Inordertoexposebindingsitesdeepwithinthematrix,thepolymersarethengroundtoafinepowder.Asaresult,mostinvestigationsofthemolecularimprintingtechniquehavebeenlimitedtosmallorganicmoleculesasthetemplatestoovercomethedifficultiesofdiffusionintothepolymermatrix.However,toimprintlargerspecies,suchasmacromolecularaggregates,orevenwholecells,adifferentmethodologyisrequiredsuchthattherecogni-tionsitescanbegeneratedineasilyaccessiblesurfaces.Theprotocolinvolvespolymersynthesisatanaqueous/organicinterfaceundercondi-tionswherelossofcellstructureandviabilityarekepttoaminimum.Inordertoimprintbacteriasuchas,forexample,ListeriamonocytogenesorSalmonellaenteritidisfullmicrobiologicalsafetyprecautionsshouldbeused,inadditiontoconventionaltechniquesforhandlingreactiveandcorrosivechemicals.210 8:NewmethodologiesforimprintedpolymersProtocol3.Preparationofbacteria-imprintedpolymerbeads23Caution!Thisprocedureshouldbecarriedoutinawell-ventilatedfume-cupboardwithaUVshieldinalaboratoryequippedtoCategory2MicroorganismHandlingStandards.UVprotectiveglasses,disposablegloves,andfulllengthlaboratorycoatshouldbewornthroughout.Equipment●Shaker/Incubator●Centrifuge●IKA-MINI-MRstirrer●Beaker(500mL,tallform)●Glasscrystallizingdish●Droppingfunnel(50mL)●Sourceofnitrogen●Blak-RayB-100AUVlamp●Zeissconfocallaserscanningmicroscope(LSM1D),488nmargonionlaser●NikonF301cameraMaterials●Poly(allylamine)(PAA),Mw100000irritant●(3-N-morpholino)propylsulphonicacid(MOPS)irritant●Acridineorange1mL(10mgmL1)possiblemutagen●FITC-ConcanavalinAirritant,harmful●1,6-Hexanedioldiacrylate14.5g,14.4mL,64mmolharmful,flammable●Adipoylchloride1.5g,1.2mL,8.2mmolharmful,corrosive,lachrymator●AIBN300mg,1.8mmolkeepcold,maydecomposeexplosively●1-Ethyl-3-(3-dimethylaminopropyl)carbodiimide(EDC)5mg,0.025mmolharmful●Dibutylether(DBE)14.4mLharmful,flammable●1,1,2-Trichlorotrifluoroethane270mLharmful●FOMBLIN™Diisocyanate1.5girritant●Sodiumacetate●Manganesechloride●Calciumchloride●Sodiumchloride●Methanoltoxic,flammable●Ethanolflammable●Nutrientbroth●Coryneformbroth●MethanolicHCI6N,150mLtoxicflammable,causesburnsMethodGrowthandstainingofmicroorganisms1.Obtainsuspensionsofmicroorganismsbyovernightgrowthat37Cofstockculturesinnutrientbroth(S.enteritidis)orcoryneformbroth(L.monocytogenes).2.Centrifuge6mLsuspensionsofcells(8000rpm,10min),removesupernatantandresuspendinMOPSbuffer(pH7.8,0.6M,10mL).3.Addacridineorangesolution(10mgmL1,1mL)andincubatefor3h.211 C.Alexanderetal.Protocol3.Continued4.Centrifugethestainedcells(5min,3000rpm),removethesupernatant,andre-suspendbacterialpelletsinMOPSbuffer(pH7.8,0.6N,10mL)byvortexmixing(30s).Preparationofpolymericbeadsinthepresenceofmicroorganisms(seeFigure8.1):1.StirasolutionofMOPSbuffer(pH7.8,0.6N,250mL)inareactionvessel(500mLtall-formbeaker)equippedwithamagneticbaratsetting5overaIKA-MINI-MRstirrerplatewhilstpassingasteadystreamofnitrogenviaaPasteurpipettefor10min.2.Prepareasolutionofadipoylchloride(1.2mL,1.5g,8.2mmol)inamixedorganicphasecontainingdibutylether(14.4mL),1,6-hexanedioldiacrylate(14.4mL,14.5g,64mmol),andAIBN(300mg,1.8mmol),andaddtotheMOPSbuffer.3.RemovethePasteurpipetteandcoverthebeakerwithglasscrystallizingdish.4.Increasethestirrerspeedtosetting6for2mintodispersetheorganicdroplets.5.RemovethecoveringdishandaddrapidlyasuspensionofL.monocyto-genes(acridineorangestained,200Lof1010cfumL1)inMOPSbuffer(50mL)andcontinuestirringfor3min.6.AddthePAAsolution(0.2Meq.in0.6MMOPS,pH7.8,45mL)drop-wisewithMOPS(30mLof0.6M).7.AssesscapsulesforbacterialattachmentbyConfocalLaserScanningMicroscopy(CLSM).8.Re-coverthebeakerwithcrystallizingdishandirradiatecontentsofthebeakerwithUV(Blak-RayB-100Alamp)withstirringfor12h.9.Filtertheresultantpolymerbeads,washwithwater(3100mL)andmethanol(3100mL)andallowtodryinair.Surfacemodificationofpolymerbeadswithattachedmicroorganisms1.Stirrapidlythepolymerbeads(1.0g)in1,1,2-trichlorotrifluoroethane(250mL)whilstaddingdrop-wiseasolutionofFOMBLINdiisocyanate(1.5g,perfluoropolyether,diisocyanatoterminated)in1,1,2-trifluorotrichloroethane(20mL)viaafunnelequippedwithadryingtube.2.Continuestirringfor3hbeforeaddingthesuspensiontomethanol(250mL).Filterthesuspensionandwashthebeadswithfurthermethanol(5100mL).Removalofmicroorganismsfrompolymersurfaces1.Refluxasuspensionofpolymerbeadswithattachedmicroorganisms(250mg)in6MHCl/methanol(150mL)for36h,withregularmonitoringoftheextentofcellremovalbyscanningelectronmicroscopy.2.Filterthebeadsandwashrepeatedlyinmethanol(5250mL)anddryinair.212 Organicsolvent+di-acidchloride+diacrylate(a)(b)(c)BacteriaOrganicPolyamidePoly(acrylate)Poly(allylamine)phaseshellcoreInterfacialPhotochemicalcondensationcross-linkingReactsurfaceNH2withdiisocyanatoperfluoropolyether(f)(e)(d)ExposedNH2groupsLigandinsiteFluoropolymerLigand-CO2HRemovebacteriaEDCbyacidhydrolysisFig.8.1Diagramshowingthestagesintheformationofbacteria-imprintedpolymerbeads. C.Alexanderetal.Protocol3.ContinuedFluorescent-labellingofimprintedsitesatpolymersurface1.Prepareabuffersolution(sodiumacetate50mM,5mMMnCl2,5mMCaCl2,5mL),addethanol(500L)andasuspensionofbeads(100mg),andstirgentlywhilstaddingFITC-ConcanavalinA(1mg,~0.0001mmol).2.AdjustthepHofthesolutionto4.75andthenaddEDC(5mg,0.025mmol)inacetatebuffer(1mL).3.Continuethereactionovernightwithgentleshaking.4.Washthebeadswithwater(510mL)andMeOH(510mL).References1.Wulff,G.Angew.Chem.Int.Ed.Engl.1995,34,1812.2.Shea,K.J.TrendsPolym.Sci.1994,2,166.3.Haupt,K.Chem.Commun.2003,171.4.Whitcombe,M.J.;Vulfson,E.N.Adv.Mater.2001,13,467.5.Sellergren,B.,ed.MolecularlyImprintedPolymers:Man-MadeMimicsofAntibodiesandtheirApplicationsinAnalyticalChemistry;Elsevier:Amsterdam;2001.6.Whitcombe,M.J.;Alexander,C.;Vulfson,E.N.Synlett2000,911.7.Alexander,C.;Davidson,L.;Hayes,W.Tet.2003,59,2025.8.Wulff,G.Chem.Rev.2002,102,1.9.Takeuchi,T.;Haginaka,J.J.Chromatogr.B1999,728,1.10.Stevenson,D.TrendsAnal.Chem.1999,18,154.11.Sellergren,B.;Andersson,L.I.Meth.—ACompanionMeth.Enzymol.2000,22,92.12.Schweitz,L.;Spégel,P.;Nilsson,S.Electrophoresis2001,22,4053.13.Remcho,V.T.;Tan,Z.J.Anal.Chem.1999,71,A248.14.Ramström,O.;Skudar,K.;Haines,J.;Patel,P.;Brüggemann,O.J.Agric.FoodChem.2001,49,2105.15.Piletsky,S.A.;Turner,A.P.F.Electroanalysis2002,14,317.16.Ramström,O.;Ye,L.;Krook,M.;Mosbach,K.Chromatographia1998,47,465.17.Wulff,G.;Sarhan,A.Angew.Chem.Int.Ed.Engl.1972,11,341.18.Theconceptofimprinting(insilicagel)issometimescreditedtoF.H.Dickey,forthepreparationofspecificadsorbents:Dickey,F.H.Proc.Natl.Acad.Sci.USA1949,35,227.19.SeetheSocietyofMolecularImprintingwebsiteavailableatwww.smi.tuberlin.de.20.Whitcombe,M.J.;Rodriguez,M.E.;Villar,P.;Vulfson,E.N.J.Am.Chem.Soc.1995,117,7105.21.Kirsch,N.;Alexander,C.;Lübke,M.;Whitcombe,M.J.;Vulfson,E.N.Polymer2000,41,5583.22.Corson,B.B.;Heintzelman,W.J.;Schwartzman,L.H.;Tiefenthal,H.E.;Lokken,R.J.;Nichels,J.E.;Atwood,G.R.;Pavlik,F.J.J.Org.Chem.1958,23,544.23.Aherne,A.;Alexander,C.;Payne,M.J.;Pérez,N.;Vulfson,E.N.J.Am.Chem.Soc.1996,118,8771.214 9LiquidcrystallinepolymersSANGDILI.PATEL,FREDJ.DAVIS,PHILIPM.S.ROBERTS,CRAIGD.HASSON,DAVIDLACEY,ALANW.HALL,ANDREASGREVE,andHEINOFINKELMANN1.IntroductionTheideaofcombiningtheanisotropicbehaviourofliquidcrystallinemateri-alswiththepropertiesofmacromolecularsystemswasfirstsuggestedbyOnsanger1andsubsequentlyFlory.2Theactualrealizationthatsuchsystemscouldexistcamefromstudiesofnaturalpolymerssuchasthetobaccomosaicvirus.3Interestinthesesystemsintensifiedwiththedevelopmentofhigh-strengthsystems,basedonrigid-rodsystems,notablythearamidfibres,4however,liquidcrystallinityinsuchsystemsoccursonlyathightemperat-ures,usuallyclosetothedecompositionpointofthepolymer.5Itwasonlyinthelate1970sthatthedesigncriteriaforliquidcrystallinepolymersbecameapparent,thesecretbeinglargelyinthedecouplingoftherigidaromaticgroupswhichgiverisetotheanisotropicbehaviour.Asaresultoftheseideastwoclassificationsofliquidcrystallinematerialsweredescribed(Figure9.1).6Main-chainliquidcrystallinepolymers,arethoseinwhichrigidaromaticmoleculesformpartofthepolymerbackbone,eitherasacontinuouschainorFig.9.1Schematicrepresentationofthetwomainclassesofliquidcrystallinepolymers:(a)main-chainliquidcrystallinepolymer;(b)side-chainliquidcrystallinepolymer. S.I.Pateletal.separatedbyaseriesofmethylenegroupsinordertolowertemperatureatwhichliquidcrystallinephasebehaviourisobserved.Side-chainsystemsresemblethecomb-likesystemsstudiedbyShibaevandPlate,7andhavetherigidaromaticgroupsattachedasaside-chain.Ingeneral,themonomersystemsrequiredformain-chainliquidcrystallinepolymersarerelativelysimple;syntheticallythesesystemsarepreparedbystep-growthmethodsandthemainchallengeisoftenmaintainingsufficientsolubilitytoallowsuitablechain-lengthstobegrown(anexampleofhowsuchproblemsmightbeovercomeisgiveninChapter4).Side-chainsystemstendtobeproducedfrommorecomplexstructuralsub-units,andmaybepro-ducedeitherbypolymerizationoftheappropriatemonomerorbyfunctional-izationofapreformedpolymerbackbone.8Examplesofbothapproachesaregiveninthischapter.Fromapracticalviewpoint,theadvantageofside-chainsystemsisthattheytendtobemuchmoresolubleincommonorganicsolventsandalsothatthermalphasetransitionsoccuratreasonabletemperat-ures(reasonablebeingwellbelowthetemperatureatwhichthepolymerdecomposes).Afurtheradvantageofsuchside-chainsystemsisthatthephasebehaviourcanbeeffectivelytunedthroughthechemicalmodificationsofthethreecomponents,namelytheside-group,theflexiblecouplingchainandthepolymerbackbone.6Theformertwounitsaregenerallyusedtocontroltheupperphasetransitiontemperature,thelatterthelowerlimitofthemesophase,since,forthemostpart,side-chainsystemsareatacticandthelowerlimitiscontrolledbythepolymerglasstransition,ratherthanbycrystallization,asisthecaseforlowmolecularweightliquidcrystals.Thisisclearlyseeninthecaseofthetwomostcommonlypreparedclassesofside-chainliquidcrystallinepolymersinthatsiloxanesaredesignedtohavearela-tivelylowglasstransitionandthusexhibitliquidcrystallinephasesatroomtemperature;incontrast,9acrylatesgenerallyhaveratherhigherglasstransi-tions,whichnecessitateheatingtoaccessthemesophase,8althoughherethestructuremaybelockedinthroughrapidcoolingtoroomtemperature.9Althoughliquidcrystallinepolymershavesomedisadvantagesintermsofthedisplayapplicationsfamiliarinconventionalliquidcrystallinematerials,notleastbecausetheirintrinsichighviscosityprecludesrapidresponses,theirpolymericnaturemakesothernovelapplicationspossible.10Oneareathathasattractedparticularinterestbothfromatheoretical11andapractical12pointofviewistheideaofcross-linkingmaterialstoproduceliquidcrystallineelastomers.Suchmaterialsprovideanadditionalchallengetothesyntheticchemistsincetheirformationrequiresnotonlythepreparationofmonomersandpolymers,butalsothedevelopmentofsuitablecross-linkingprocedures.Furthermore,thepropertiesofsuchmaterialsdependheavilyonthestateofthematerialatthetimeofcross-linkingandparticularlywherethisinvolvesforminganetworkfromapreformedpolymer,thisfinalchemicaltransformationmaybethemostcomplexofall.Inthischapterwehaveincludedexamplestocoverthemostcommonprocessesinvolvedinthesynthesisof216 9:LiquidCrystallinepolymersliquidcrystallinematerials.Thus,wehaveprovideddetailsofthesynthesisofaliquidcrystallineacrylate,itscopolymerizationwith2-hydroxyethylacrylate,andsubsequentcross-linkingundercontrolledconditionstoprepareanelastomer.Inadditionweincludedetailsofthepreparationofsomesilox-anebasedsystemswherethemesogenicunitisaddedtoapreformedsiloxanesystem;theuseofaningeniousmethodofcross-linkingtoprovideelastomersformedunderanappliedstressisdescribed.2.Synthesisofanacrylate-basedliquidcrystalpolymerThesynthesisofacrylatematerialsisrelativelystraightforward,andcanbeperformedwithouttherecoursetocomplexreagentsandequipment,but,becauseofthepolymerizationstepmayrequireparticularcaretoensurethepurityofthefinalmaterial.Thisisparticularlysointhefollowingexample,whereacyanobenzoateesterisusedtoprovidetheanisotropicphasestruc-ture,sincetheelectron-withdrawinggroupmakesthisesterparticularlysus-ceptibletohydrolysis.Thefirststepintheproductionofamesogenicmonomerinvolvestheacetylationof6-chlorohexanolusingastandardpreparativeprocedure,13followedbyetherificationandsubsequenthydroly-sisasshowninScheme1.Protocol1.Synthesisof4-(6-hydroxyhexyloxy)benzoicacid(Scheme1)Caution!Carryoutallproceduresinawell-ventilatedfume-cupboard,wearappropriatedisposablegloves,alab-coat,andsafetyglasses.AcOAcHO(CH2)6ClAcO(CH2)6ClPyridineAcO(CH2)nClK2CO3/DMFHOCO2MeAcO(CH2)6OCO2MeKI(trace)12KOH/H2O/EtOHHO(CH2)6OCO2H3Scheme1217 S.I.Pateletal.Protocol1.ContinuedEquipment●Two-neckedround-bottomedflask(1L)●Powderfunnel●Refluxcondenser●TLCplates(silicagel)●Thermometer●Glassstirringrod●Teflon-coatedmagneticstirrerbar●Erlenmeyerflask(varioussizes)●Hotplatestirrer●Round-bottomedflask(1L)●Erlenmeyerflask(3L)●BuchnerFlask(3L)●Three-neckedround-bottomedflask(1L)●Sintered-glassfunnel(porosity2)●Droppingfunnel(250mL)Materials●6-Chlorohexanol,100g,0.73molirritant,harmful●Pyridine,58g,0.73molhighlyflammable,harmfulbyinhalation,incontactwithskin,andifswallowed●Aceticanhydride,306g,3molflammable,corrosive●Water●Magnesiumsulfate,anhydrous,ca.15g●Dimethylformamide,300mLpotentiallyteratogenic,harmfulincontactwithskin,irritatingtoeyes●Ethanol,250mLhighlyflammable●Potassiumcarbonate,69.1g,0.5molirritatingtoeyes,skin,andrespiratorysystem●Methylp-hydroxybenzoate,60g,0.40molirritatingtoeyes,skin,andrespiratorysystem●Potassiumiodide(catalyticamount)Irritant●Petroleumether(b.p.40–60C),ca.6mLhighlyflammable●Ethylacetate,ca.4mLhighlyflammable●Potassiumhydroxide,64.7g,1.16molharmfulifswallowed,causessevereburns●Hydrochloricacid,12N,100mLcorrosive,causesburns,irritatingtorespiratorysystemMethod1.Toatwo-neckedround-bottomedflask(1L)equippedwitharefluxcondenser,thermometer,andamagneticstirrerbar,add6-chlorohexanol(100g,0.73mol),pyridine(58g,0.73mol)andaceticanhydride(306g,3mol).Heatthesolutionto130Cfor1hwhilststirring.2.PourthemixtureintoanErlenmeyerflaskcontainingalargeexcessofwatersuchthatanoillayerseparates(approximately1Lofwaterissuitableforthispurpose).Usingaseparatingfunnelisolatetheoilfromtheaqueousmate-rial.Drytheorganicphasewithanhydrousmagnesiumsulfate(ca.15g,15min).Thecrude6-chlorohexylethanoateisobtainedasayellowoilandusedinthenextstagewithoutfurtherpurification.3.Toathree-neckedround-bottomedflask(1L)equippedwitharefluxcondenser,thermometer,adroppingfunnel(250mL),andamagneticstirrerbar,adddimethylformamide(300mL)andanhydrouspotassiumcarbonate(69.1g,0.5mol).Usingapowderfunnel,addmethylp-hydroxybenzoate(60g,0.40mol)togetherwiththepotassiumiodide.Heatthesolutionto90Candadd6-chlorohexylethanoate(97.4g,0.54mol)drop-wiseoverseveralhours.Stirthesolutionforatotalof24hwhereuponTLC(silicagel,3:2petroleumether:ethylacetate)shouldindicatethecompleteconversionofstartingmaterial.218 9:LiquidCrystallinepolymers4.Coolthemixtureandpourinto3Lofwaterwhilststirringvigorouslywithaglassrod.TheresultingwhitecrystalsarefilteredusingaBuchnerflaskthroughalargesintered-glassfunnel.Theproductisthenwashedwithcopiousamountsofwateranddriedinavacuumdesiccator.Typicalyieldsofmethyl4-(6-acetoxyhexoxy)benzoateareclosetoquantitative,m.p.44–46C.5.Methyl4-(6-acetoxyhexoxy)benzoate(169g,0.57mol)isdissolvedin200mLofwarmethanolina500mLErlenmeyerflask.6.Inaround-bottomedflask(1L)equippedwithamagneticstirrerbarandrefluxcondenserdissolvepotassiumhydroxide(64.7g,1.16mol)inwater(ca.100mL),addtheethanolicsolutionofmethyl4-(6-acetoxyhexoxy)ben-zoateandstirat80Cfor2h.7.Thesolutioniscooledtoabout50Candacidifiedwithhydrochloricacid(100mL,12N)andlefttostand.aAfter6h,thewhitesolidisfilteredandwashedwithcopiousamountsofwater.Typicalyieldof4-(6-hydroxyhexoxy)benzoicacidis121.0g(89%),m.p.130–133C(lit.value8139C).aThecrystalsareparticularlyfineanddifficulttofilter,useofacoursesintered-glassfunnelandfilteringslowlyundergravityisbesthere(seeChapter4,Protocol5,Noteg).TheacidgeneratedinProtocol1isthenesterifiedwithacrylicacidasshowninScheme2.Theprocedureusesanadaptationofthewell-knownDean–Starkapparatustocontinuouslyextractwaterduringthereaction.ThisisshowninFigure9.2andallowsasolventdenserthanwatertobecontinu-ouslyrecycledthroughthesystemwhilethewateriscollectedintheside-arm.Protocol2.Synthesisofp-(6-propenoyloxyhexyloxy)benzoicacid(Scheme2)Caution!Carryoutallproceduresinawell-ventilatedfume-cupboard,wearappropriatedisposablegloves,alab-coat,andsafetyglasses.Neveruseflat-bottomedflaskswithrotaryevaporators.HO(CH2)6OCO2H3O+O(CH2)6OCO2HO4OHScheme2219 HeatsourceFig.9.2ReverseDean–Starkapparatus.220 9:LiquidCrystallinepolymersProtocol2.ContinuedEquipment●ReverseDean–Starkapparatus(1L)●TLCplates(silicagel)●Refluxcondenser●Erlenmeyerflask(3L)●Teflon-coatedmagneticstirrerbar●Buchnerflask(3L)●Hotplatestirrerandoil-bath●Sintered-glassfunnel(porosity2)●Round-bottomedflask(1L)●Beaker(1L)●Rotaryevaporator●GlassrodMaterials●4-(6-hydroxyhexyloxy)benzoicacid,16.7g,0.07moltreatashazardousmaterial●Hydroquinone,10g,0.09molpossiblecarcinogen,harmful,irritant●p-Toluenesulfonicacid,5g,0.03molirritant●Acrylicacid,55mL(largeexcess)flammable,corrosive,causesburns●Chloroform,55mLsuspectedcarcinogen,harmful●Petroleumether(b.p.40–60C),ca.6mLhighlyflammable●Ethylacetate,ca.4mLhighlyflammable●Water●Propan-2-olforrecrystallizationhighlyflammable●Diethylether,300mLhighlyflammable,mayformexplosiveperoxides●Ethanol,250mLhighlyflammable●Magnesiumsulfate,anhydrous,ca.15gMethod1.SetupthereverseDean–Starkapparatuswitharefluxcondenserandmag-neticstirrerbar.2.Add4-(6-hydroxyhexyloxy)benzoicacid(16.7g,0.07mol),hydroquinone(10g),andp-toluenesulfonicacid(5g)throughtheside-armofthereverseDean–Starkapparatus.Thenaddacrylicacid(55mL,largeexcess)andchloroform(55mL).3.Heatthemixturewithstirringuntilitbeginstoboil,maintaintheboilingatasufficientratesuchthatasteadyrateofcondensationintotheside-armisachieved(typicallyabout1droppersecond),itisoftennecessarytoinsulatetheside-armwithcottonwool.4.Continueheatinguntilnomorewateriscollectedintheside-arm.Thisisbestconfirmedbyremovingtheliquidintheside-arm;oncontinuedrefluxnomorewaterisproduced,andnotraceofturbidityremainsinthedistillate.ThelevelofconversionisthencheckedbyTLC(silicagel,3:2petroleumether:ethylacetate),atthisstagenotraceofstartingmaterialshouldbepresent.5.Themixtureiscooled,transferredtoaround-bottomedflask(1L)andthechlo-roformisremovedontherotaryevaporator.Theresidueisthenpouredintocoldwaterandawhiteprecipitateisproduced.Thewhiteprecipitateisfilteredatthepumpcollected,placedinabeaker(1L)andwarmwater(500mL,40C).Themixtureisstirredvigorouslywithaglassrod,filteredatthepump,andwashedwithwatertoremovealltracesofacrylicacid.Finallyafterdryingatthepump,theproductisrecrystallizedfrompropan-2-oltoyield19.4g,(86%)ofp-(6-propenoyloxyhexyloxy)benzoicacid,m.p.102C(lit.value892C).221 S.I.Pateletal.Thefinalstepofthissynthesisinvolvesamodificationtotheoriginalprocedure.8Amildermethodofesterificationusingdicyclohexylcarbodiimideisusedwhichavoidsthegenerationofhydrochloricacidviaacidchlorides14asshowninScheme3.Protocol3.Synthesisof4-cyanophenyl-4
-(6-propenoyloxyhexanoxy)benzoate(Scheme3)Caution!Carryoutallproceduresinawell-ventilatedfume-cupboard,wearappropriatedisposablegloves,alab-coat,andsafetyglasses.Neveruseflat-bottomedflaskswithrotaryevaporators.O(CH2)nOCO2HO4(1)DCC(2)HOCNOO(CH2)nOOOCN5Scheme3Equipment●Round-bottomedflask(250mL)●Buchnerflask(250mL)●Rotaryevaporator●Sintered-glassfunnel(porosity2)●Ice–salt-bathMaterials●4-(6-propenoyloxyhexanoxy)benzoicacid,10g,34mmoltreatashazardousmaterial●Dichloromethanetoxic,carcinogenicinanimals,harmfulvapour,skinirritant●4-Dimethylaminopyridine,0.410g,3.4mmoltoxicincontactwithskinandifswallowed,irritatingtoeyesandskin●4-Cyanophenol,4g,34mmolharmful,irritant●Dicyclohexylcarbodiimide,7g,34mmoltoxic,corrosive,sensitizing●Hydrochloricacid(0.5N),200mLcorrosive,causesburns,irritatingtorespiratorysystem●Sodiumbicarbonatesolution(aqueous,saturated)●Magnesiumsulfate●Propan-2-olforrecrystallizationhighlyflammableMethod1.Add4-(6-propenoyloxyhexanoxy)benzoicacid(10g,34mmol)toa250-mLround-bottomedflasktogetherwith50mLofanhydrousdichloromethane,stirandcoolto0Cinanice–saltbath.222 9:LiquidCrystallinepolymers2.Whenthesolidmaterialhasdissolvedthenadd4-dimethylaminopyridine(0.410g,3.4mmol)and4-cyanophenol(4g,34mmol)tothestirredsolution.Dicyclohexylcarbodiimide(7g,34mmol)isaddedtothepaleyellowsolu-tion.Theresultingwhitemixtureisstirredfor5minat0Cand4hatroomtemperature.3.After4hfiltertheprecipitatedureaundergravity(washingwithalittledichloromethane)andconcentratethefiltrateusingtherotaryevaporator.Dissolvethewhiteresidueinalittledichloromethane,washwith0.5Nhydrochloricacid(2100mL),sodiumbicarbonatesolution(100mL),drywithmagnesiumsulfateandfilterundergravity.4.Concentratethesolutionbyrotaryevaporationandrecrystallize4-cyanophenyl-4
-(6-propenoyloxyhexanoxy)benzoatefrompropan-2-olasfinecolourlesscrystals,9.0g(68%).Themonomercanbepolymerizedinachain-growthprocessinitiatedbyazobisisobutyronitrile(AIBN)usingtheproceduredescribedinChapter2(Protocol1).IntheexamplegiveninProtocol4belowthematerialiscopoly-merizedwithasmallproportion(typically6%)ofhydroxyethylacrylate.Thiscomonomerprovidessitesforsubsequentcross-linking(seeProtocols11and12)Protocol4.Copolymerizationof4-cyanophenyl-4
-(6-propenoyloxyhexanoxy)benzoatewith2-hydroxyethylacrylate(Scheme4)Caution!Carryoutallproceduresinawell-ventilatedfume-cupboard,wearappropriatedisposablegloves,alab-coat,andsafetyglasses.+AIBNOOOOOOOOOHOHOOOOOO5CN6CNScheme4223 S.I.Pateletal.Protocol4.ContinuedEquipment●Dualmanifold(nitrogen/vacuum)●Sourceofdrynitrogen●Polymerizationtube●Blastscreen●Protectivenettingforpolymerizationtube●Round-bottomedflask(100mL)●Dewar●Rotaryevaporator●Thermostattedwater-bath●Erlenmeyerflasks(varioussizes)●Vacuumpump●VacuumovenMaterials●4-Cyanophenyl-4
-(6-propenoyloxyhexanoxy)benzoate,treatashazardousmaterial1g,2.5mmol●2-Hydroxyethylacrylate,18mg,0.15mmoltoxicincontactwithskin,causesburns,maycausesensitizationbyskincontact,harmfultoaquaticorganisms●AIBN4mg,0.03mmoltoxic,harmful,explosive,highlyflammable●Chlorobenzene20mLflammable,harmfulbyinhalation●Nitrogengas(drywhitespot)asphyxiationhazard●Liquidnitrogenforcoolingextremelycoldliquid,vapourcancauserapidsuffocation●Dichloromethaneforpurificationtoxic,carcinogenicinanimals,harmfulvapour,skinirritant●Methanolforpurificationhighlyflammable,toxicbyinhalationandifswallowed●Diethyletherforpurificationextremelyflammable,mayformperoxidesMethodPreparation:2-Hydroxyethylacrylateshouldbepurifiedtoremoveinhibitorspriortouse.Thisisdonebydistillationunderreducedpressure.1.Placethe4-cyanophenyl-4
-(6-propenoyloxyhexanoxy)benzoate(1g,2.5mmol)and2-hydroxyethylacrylate(18mg,0.15mmol)inthepolymeriza-tiontube.AddAIBN(4mg,0.03mmol)andfinallyaddchlorobenzene(20mL).Placeaprotectivenettingoverthetubetominimizedangerfromglassshouldthetubeshatter.AttachthetubetothemanifoldandclosetheYoung’stapatthetopofthetube.2.Carryoutthefreeze–thaw–degassingprogrammeoutlinedinChapter2,toensurealloxygenisremovedfromthesystem.IsolatethetubefromthemanifoldbyclosingtheYoung’stapwhilethesystemisundervacuum.3.Placethetubeinathermostattedwater-bathat55Cfor24h.Thisprocedureshouldbecarriedoutbehindablastscreen.4.Removethetubefromthewater-bathandallowtocooltoroomtemperature5.Transfertheresultingpolymersolutionintoaround-bottomedflask(100mL)andremovethemajorityofthechlorobenzeneusingarotaryevaporator.Thenre-dissolvethepolymerintheminimumvolumeofdichloromethaneanddroptheresultingviscoussolutionintocoldmethanol(150mL)inanErlenmeyerflask(500mL).Theflaskisallowedtostandfor30minandtheliquiddecanted.Thesolidisallowedtodryinthefume-cupboardandthenre-dissolvedindichloromethane(minimumvolume).Onceagainthepolymersolutionisprecipitated,thistimeintodiethylether.Thepolymeristhenisolatedasaboveandafurtherprecipitationintoetherundertaken.Thepolymeris224 9:LiquidCrystallinepolymersthenplacedinthevacuumovenanddriedat50Cforseveralhourstoremoveanyresidualsolventandwater.Thepolymersaresubsequentlycharacterizedbydifferentialscanningcalorimetry(DSC)todeterminethephasetransitiontemperatures.3.Thehydrosilylationreaction:ausefulprocedureforthepreparationofavarietyofside-chainpolymersThemainstructuralfeaturesofaside-chainpolymeraregiveninFigure9.3andalthoughthepolymerbackboneandflexiblespacergroupareimportantindeter-miningthethermalandphysicalpropertiesofthesepolymers,potentialapplica-tionsaredeterminedmainlybytheside-group.Forexample,iftheside-chainpolymeristobeusedasanon-linearoptical(NLO)devicethenthestructureoftheside-groupmightbeasshowninFigure9.3(a),forliquidcrystaldisplaydeviceapplicationsstructuressuchasshowninFigure9.3(b)or(c)maybeused.Graftingoftheside-groupontoapreformedpolymerbackbonehasbeenaveryusefulandhighlyproductivewayofmakingalargevarietyofside-chainpolymersfordisplaydeviceapplications.Suchpolymersshouldhavelowglasstransition(Tg)temperatures,andforthatreasonmanyoftheseside-chainliquidcrystallinepolymersarepreparedfrompreformedpoly(siloxane)back-bones.ThepolymerbackbonescomeinavarietyofdifferentformsexamplesofwhichareshowninFigure9.4.Theproceduredescribedhereinvolvesthepreparationofaferroelectricside-chainliquidcrystalofstructure13,inthiscaseacyclicsiloxanetetramer,however,thisprocedurecanbesimplyadaptedtopreparearangeofside-chainliquidcrystallinepoly(siloxanes)andelastomers(seelater).Theprocedureisperformedusingthehydrosilationreactionofthepreformedcyclicsiloxanetetramer11withthemesogenicside-group10inanhydroustolueneinthepresenceofthecatalystplatinum(0)-1,3-divinyl-1,1,3,3-tetramethyldisiloxanecomplex12atroomtemperature.(a)X(CH2)6ONNNO27(b)ONOX(CH2)10OO*N8O(c)CH3XC(CH2)10OO2CO2CHCO2Et9Fig.9.3Themainstructuralfeaturesofaside-chainpolymer.225 S.I.Pateletal.(a)CH3CH3CH3SiOSiOSi(CH3)3CH3Hn(b)CH3CH3CH3CH3SiOSiOSiOSi(CH3)3CH3HCH3nm(c)CH3SiOHnFig.9.4Differenttypesofpolymerbackbone:(a)homopolymers;(b)copolymers;(c)cyclicpolymers.Protocol5.Useofthehydrosilylationreactiontoformaside-chainliquidcrystallinecyclictetramer(Scheme5)Caution!Carryoutallproceduresinawell-ventilatedfume-cupboard,wearappropriatedisposablegloves,alab-coat,andsafetyglasses.Neveruseflat-bottomedflaskswithrotaryevaporators.Equipment●Dualmanifold(nitrogen/vacuum)●Sourceofdrynitrogen●Three-necked,round-bottomedflask(100mL)●Rotaryevaporator●Pressure-equalizingdroppingfunnel●TLCplates(silicagel)●Rubbersepta●Teflon-coatedmagneticstirrerbar●Inlettube●Disposablesyringefilter(PTFE,0.45m)●Syringeandneedle●Centrifuge●Magneticstirrer●CannulaneedleMaterials●Nitrogengas(whitespot,dry)asphyxiationhazard●Dryaircaution,gasunderpressure●Toluene,anhydrous,60mLflammable,toxicbyingestion,harmfulvapour●Cyclicsiloxanetetramer11,0.15g,0.5mmolflammable,harmfulbyinhalationoringestion●Compound10,1.5g,2.6mmoltreatashazardousmaterial226 9:LiquidCrystallinepolymersCH3CH2CH(CH2)11OCO2CO2CH2CHCH2CH3*10CH3SiOO[Si(CH3)2CHCH2]2PtH41211CH3SiO4CH3(CH2)11OCO2CO2CH2CHCH2CH3*13Scheme5Useofthehydrosilylationreactiontoformaside-chainliquidcrystallinecyclictetramer.●Catalyst12(solution),10Lflammable,harmful,hydrolyticsensitivity●Dichloromethane,anhydroustoxic,carcinogenicinanimals,harmfulvapour,skinirritant●Methanol,anhydroushighlyflammable,toxicbyinhalationandifswallowed●Petroleumether(b.p.40–60C)highlyflammable●Diethyletherextremelyflammable,mayformperoxidesMethodPreliminarystage:Allglasswaremustbedriedinanovenat120Cfor1h.1.The100-mLthree-neckedflaskissetupforreflux,withthepressure-equalizingdroppingfunnelinthecentralneckandtheseptumandtheinlettubeoccupyingtheoutertwonecks.2.Sweeptheapparatuswithdrynitrogen,viatheinlettube,for2min.3.Replacetheinlettubewithastopperandplacethenitrogenbubblerontopofthepressure-equalizingdroppingfunnel,allowingaslow,steadystreamofdrynitrogentopassoverthetop.4.Addcompound10(1.5g,2.6mmol)andthecatalyst12(20L)totheflaskand,byusingthesyringeandneedle,transferanhydroustoluene(50mL)fromtheSure-Sealbottletotheflaskviatheseptum.227 S.I.Pateletal.Protocol5.Continued5.Addthecyclicsiloxanetetramer11(0.15g,0.5mmol),dissolvedinanhyd-roustoluene(10mL),tothepressure-equalizingdroppingfunnelandstartthestirrer.6.Exchangethestopperfortheinlettubeandbubbledryairthroughthereac-tionmixturefor20s.a7.Replacethestopperandaddslowly,drop-wise,thecyclicsiloxanetetramertothereactionmixture.8.Whentheadditionhasbeencompleted,leavethereactionmixturestirringatroomtemperaturefor24h.b,c9.TheprogressofthereactioncanbemonitoredbyIRspectroscopybyremovingasmallquantityofthereactionmixtureusingasyringeandneedle(viatheseptum),andexaminingtheIRspectrumintheregion2000–2200cm1.Thedisappearanceofthebandat2155cm1(Si–Habsorptionband)indicatescompletionofthehydrosilylationreaction.10.Filteroffanyundissolvedmaterialandremovethetoluenebydistillationunderreducedpressure(rotaryfilmevaporator).11.Dissolvetheside-chainliquidcrystallinecyclictetramerintheminimumamountofdrydichloromethaneandprecipitatethetetramerbytheadditionofdrymethanol(usuallyaboutfourorfivetimesthevolumeofthedichloromethane).d12.Placethesuspensionoftheside-chainliquidcrystallinecyclictetramerintocentrifugetubesandspinthemat10000rpmfor15min.13.Carefullydecantofftheliquidandcheckthepurityoftheside-chainliquidcrystallinecyclicsiloxanetetramerbyTLC(silicagel,9:1petroleumether:diethylether),againststartingmonomer10.14.Ifthemonomerisstillpresent,repeatsteps11–13untiltheproductisfreeofmonomer.15.Iftheside-chainliquidcrystallinecyclicsiloxanetetramerispureandfreeofstartingmonomer,redissolvethetetramerintheminimumamountofdrydichloromethaneandfilterusingadisposablesyringefilter(PTFEmem-brane0.45m)toremoveanysmallparticulates.Thesolventcanthenbecarefullyremovedbydistillationunderreducedpressure(rotaryfilmevap-orator)anddriedinvacuoovernight.aOxygenfromthedryairwillaidthehydrosilylationreaction.bHeatmayberequired(40–50C)tocompletethehydrosilylationreaction.cThecatalyst,hydrogenhexachloroplatinate(IV)hydrate,(HPtCl)maybeusedinthehydrosilylation26reaction.Ifthiscatalystisusedthenthereactionmixturemustbeleftstirringat60–70Covernight.dSometimesatraceamountofcolloidalplatinummaybepresentintheside-chainliquidcrystalcyclicsiloxanetetramer.Thiscanberemovedbyaddingasmallamountoftriphenylphosphine(0.1g)atstep11.228 9:LiquidCrystallinepolymers4.PhotochemicalpreparationofliquidcrystallineelastomerswithamemoryofthealignedcholestericphaseThefollowingprotocols(6–10)describethesynthesisofsomecholesterol-basedacrylatesandtheirphotopolymerizationinanalignedcholestericphase.TheprotocolsutilizeamodificationofasystempreviouslydescribedbyShannon.15,16Intheabsenceofadiacrylatecomonomer,thecholestericphaseproducedinitiallyoncopolymerizationisnotstableandrevertstoasmecticphaseonasinglecycleofheatingandcooling.Inthepresenceofthediacrylatethefirst-formedphaseisstable.Thisisoneexampleofhowcross-linkingcanstabilisetheliquidcrystalphaseinliquidcrystallineelastomers,othersinclude,theso-called,polymer-stabilizedliquidcrystals17andthosedescribedinthelaterprotocols.Protocol6.Synthesisofcholesteryl2-(acryloyloxy)ethylcarbonate(Scheme6)Caution!Carryoutallproceduresinawell-ventilatedfume-cupboard,wearappropriatedisposablegloves,alab-coat,andsafetyglasses.Neveruseflat-bottomedflaskswithrotaryevaporators.OOOH+15OClO14PyridineOOOOCholDichloromethaneO16Scheme6Equipment●Two-necked,round-bottomedflask(250mL)●Erlenmeyerflask(500mL)●Pressure-equalizingdroppingfunnel(50mL)●Rotaryevaporator●Teflon-coatedmagnetstirrerbar●Erlenmeyerflask(250mL)●HotplatestirrerMaterials●2-Hydroxyethylacrylate,7mL,60mmoltoxicincontactwithskin,causesburns,maycausesensitizationbyskincontact,harmfultoaquaticorganisms●Pyridine,3.6mL,44molhighlyflammable,harmfulbyinhalation,incontactwithskinandifswallowed229 S.I.Pateletal.Protocol6.Continued●Dichloromethane,275mLtoxic,carcinogenicinanimals,harmfulvapour,skinirritant●Cholesterylchloroformate,18.0g,40mmolcorrosive●Magnesiumsulfate●Petroleumether(b.p.40–60C)highlyflammableMethod1.Toatwo-neckedround-bottomedflask(250mL)equippedwithadroppingfunnelandamagneticstirrerbar,add2-hydroxyethylacrylate(7mL,60mmol)andpyridine(3.6mL,44mmol)indichloromethane(35mL).Coolthemixtureto0Cinanice-bath.2.Tothedroppingfunnel,addasolutionofcholesterylchloroformate(18.0g,40mmol)indichloromethane.Addthesolutionofcholesterylchloroformatedrop-wisetothecontentsoftheround-bottomedflask.3.Removetheice-bathtoallowthemixturetowarmtoroomtemperatureandcontinuestirringfor19h.4.Dilutethemixturewithdichloromethane(240mL)beforeaddingtoanErlenmeyerflask(500mL).Drythesolutionovermagnesiumsulfate,filter,andconcentratebyrotaryevaporator.5.Recrystallizethesolidfrompetroleumether60–80inanErlenmeyerflask(250mL).ThesecondcomonomerisproducedinproceduresasoutlinedinProtocols7–9.Protocol7.Synthesisof11-bromoundecanoylchloride(Scheme7)Caution!Carryoutallproceduresinawell-ventilatedfume-cupboard,wearappropriatedisposablegloves,alab-coat,andsafetyglasses.Neveruseflat-bottomedflaskswithrotaryevaporators.SOCl2Br(CH2)10CO2HBr(CH2)10COCl1718Scheme7Equipment●Round-bottomedflask(250mL)●Hotplatestirrer●Pressure-equalizingdroppingfunnel(50mL)●Rotaryevaporator●Teflon-coatedmagnetstirrerbarMaterials●11-Bromoundecanoicacid,21.2g,80mmol●Thionylchloride,12g,100mmolreactsviolentlywithwater,harmfulbyinhalationandifswallowed,contactwithwaterliberatestoxicgas,causessevereburns230 9:LiquidCrystallinepolymersMethod1.Toasingle-neckedround-bottomedflask(250mL)equippedwithadroppingfunnelandamagneticstirrerbar,add11-bromoundecanoicacid(21.2g,80mmol).2.Tothedroppingfunneladdthionylchloride(12g,100mmol).3.Slowlyaddthecontentsofthedroppingfunneltotheround-bottomedflaskwhilststirring;continuestirringforafurther20h.4.Removetheexcessthionylchlorideontherotaryevaporator.Protocol8.Synthesisofcholesteryl11-bromoundecanoate(Scheme8)Caution!Carryoutallproceduresinawell-ventilatedfume-cupboard,wearappropriatedisposablegloves,alab-coat,andsafetyglasses.Neveruseflat-bottomedflaskswithrotaryevaporators.20Br(CH2)10COCl+19HOOPyridineCholBr(CH2)10O21Scheme8Equipment●Round-bottomedflask(250mL)●Separatingfunnel(500mL)●Teflon-coatedmagnetstirrerbar●Erlenmeyerflask(250mL)●Hotplatestirrer●RotaryevaporatorMaterials●Cholesterol(38.6g,0.1mol)●Pyridine(10mL)highlyflammable,harmfulbyinhalation,incontactwithskin,andifswallowed●Chloroform(ethanolfree)asuspectedcarcinogen,harmful,shouldbestoredinthedarktopreventformationofphosgene●11-Bromoundecanylchloride,35.7g,124mmoltreatashazardousmaterial●Hydrochloricacid(1N),100mLcorrosive,causesburns,irritatingtorespiratorysystem●Magnesiumsulfate●Petroleumether(b.p.40–60C)highlyflammable●Ethanolhighlyflammable231 S.I.Pateletal.Protocol8.ContinuedMethod1.Toasingle-neckedround-bottomedflask(250mL)equippedwithamagneticstirrerbar,addasolutionofcholesterol(38.6g,100mmol),pyridine(10mL),andethanolfreechloroform(200mL).Coolto0Cinanice-bathandstir.2.Addasolutionof11-bromoundecanylchloride(35.7g,124mmol)inchloroformover30min.Continuestirringfor2hat0Candafurther16hatroomtemperature.3.Dilutethemixturewithchloroform(100mL)andwashwith1Nhydrochloricacid(250mL)andwaterinaseparatingfunnel(500mL).SeparateanddrytheorganiclayerinanErlenmeyerflask(250mL)drywithmagnesiumsul-fateandfilterundergravity.4.Concentratethemixtureinasingle-neckedround-bottomedflask(250mL)usingarotaryevaporator.5.Recrystallizethesolidfroma1:1v/vmixtureofpetroleumetherandethanol.aEthanol-freechloroformisobtainedbypassingthroughacolumnofalumina.Protocol9.Synthesisof11-acryloyloxy-undecanoicacidcholesterylester(Scheme9)Caution!Carryoutallproceduresinawell-ventilatedfume-cupboard,wearappro-priatedisposablegloves,alab-coat,andsafetyglasses,UV-safewhereappropriate.K⊕OOOODMF(CH2)10OCholChol+Br(CH2)10OO2122Scheme9Equipment●Round-bottomedflask(250mL)●Hotplatestirrer●Teflon-coatedmagneticstirrerbar●Buchnerflask(3L)●Oil-bath●Sintered-glassfunnelMaterials➊Potassiumacrylate,16.5g,150mmoltreatashazardousmaterial●Cholesteryl11-bromoundecanoate,31.7g,50mmoltreatashazardousmaterial●2,6-Di-tert-butyl-4-methylphenol,0.75g,3.4mmolharmful,irritant●N,N-Dimethylformamidetoxictoreproductiveorgans,harmfulincontactwithskin,irritatingtoeyes232 9:LiquidCrystallinepolymers●Petroleumether(b.p.40–60C)highlyflammable●EthanolhighlyflammableMethod1.Toasingle-neckedround-bottomedflask(250mL)equippedwithamagneticstirrerbar,addpotassiumacrylate(16.5g,0.15mol),cholesteryl11-bromoundecanoate(31.7g,0.05mol)and2,5-di-tert-butylcresol(0.75g,3.4mmol)anddissolveindimethylformamide.2.Heatthesolutionto100Candstirfor21hwiththeuseofanoil-bathandhotplatestirrer.3.CoolthemixturetoroomtemperatureandfilteratthepumpthroughaBuchnerfunnel(500mL)andsinteredfunnel.4.Recrystallizethesolidfroma1:1v/vmixtureofpetroleumetherandethanol.Protocol10.CholestericalignmentandphotopolymerizationCaution!Carryoutallproceduresinawell-ventilatedfume-cupboard,wearappropriatedisposablegloves,alab-coat,andsafetyglasses.Glasswaretosupportsamples;hollowtoallowtheflowofwaterthroughoutandmaintaintemperature.UVsourcePhotochemicalsafetycabinetWateroutWaterinfrompumpFig.9.5Experimentalset-upforthephotopolymerizationofalignedcholestericsamples.233 S.I.Pateletal.Protocol10.ContinuedEquipment●Glassvial(30mL)●Waterpump●GlassPasteurpipettes,disposable●Waterbath●Borosilicateglassslides●Photochemicalsafetycabinet●Hotplate●125WHgarclamp(mediumpressure)●Photopolymerizationglassware(Figure9.5)14Materials●Cholesteryl-2-(acryloyloxy)ethylcarbonate,53mg,0.1mmoltreatashazardousmaterial●11-Acryloyloxy-undecanoicacidcholesterylester,63mg,0.1mmoltreatashazardousmaterial●Irgacure651,1.2mg,0.005mmoltreatashazardousmaterial●1,6-Hexanedioldiacrylate,1.0mg,2mmolirritatingtoeyesandskin,maycausesensitizationbyskincontact●Dichloromethanetoxic,carcinogenicinanimals,harmfulvapour,skinirritantMethod1.Toaglassvial(30mL)addcholesteryl-2-(acryloyloxy)ethylcarbonate(53mg,0.1mol),11-acryloyloxy-undecanoicacidcholesterylester(63mg,0.1mmol),Irgacure651(1.2mg,0.005mmol),and1,6-hexanedioldiacrylate(1.0mg,2mmol)anddissolveintheminimumamountofdichloromethane(
1mL).2.Casttheviscoussolutiontoaborosilicateslideusingaglasspipetteapplyingathinfilmfromthecentreoftheslideoutwards.3.Heattheslideonahotplate(
40C)forafewsecondsandshearthemixture(spreadthinly)inasingledirectionacrossthesurfaceoftheslideusinganothercleanborosilicateslide.4.Theslideisplacedonthephotopolymerizationglassware14(Figure9.5)andconnectedtoawaterpumpandwater-bath(setto40C).5.Withtheexperimentalsetupsafelywithinaphotochemicalsafetycabinet,a125WHgarclamp(mediumpressure)isfixedatadistanceof10cmfromthesampleslide.6.Irradiatefor30min.Thepolymerisobtainedasa(dependingonthecomposi-tion)highlycolouredfilmindicativeofacholestericphase.5.DefiningpermanentmemoryofmacroscopicglobalalignmentinliquidcrystalelastomersForthesampledescribedabove,itwasnotedthatcross-linkingenhancesthestabilityofthephasepresentatthetimeofcross-linking.Forthissample,thecross-linkingwasintroducedduringthepolymerizationprocess.Asimilarsituationexistswherecross-linkingisintroducedtointopreformedpolymerbackbones.Cross-linkingaliquidcrystallinepolymerinagloballyalignedstateintroducesapermanentmemoryofthealignmentpresentatthetimeof234 9:LiquidCrystallinepolymerscross-linking.ItshouldbenotedinpassingthatsuchbehaviouristobeexpectedfromtheexcellenttheoreticalmodelsofWarnerandhiscolleagues,18andwithouttheunderstandingprovidedbythisteammanyofthedevelopmentsdescribedbelowmightnothavecomeabout.Thefollowingexamplesdescribetwodifferentapproachestodevelopingliquidcrystallineelastomers.Thefirsttwoexamples,developedatReading,utilizetheacrylate-basedpolymerdescribedinProtocol4;thefinaltech-nique,inventedinFreiburgutilizessiloxane-basedpolymers.Thislatterprocessisparticularlyusefulwherehighlevelsoforientationarerequired(andofcourseroomtemperatureliquidcrystallinephases).Inthefirstexample,theacrylate-based,side-chainliquidcrystalpolymer,4-cyanophenyl-4
-(6-propenoyloxyhexanoxy)benzoate(CBZ6),canbeusedtoproducecross-linked,liquidcrystallinenetworks.2-Hydroxyethylacrylateisincludedat6%toprovideactivesitesforthesubsequentcross-linkingreaction(Protocol4).Thedegreeofpolymerizationis150producinganematicpolymerwithTg33CandTNI128C.Thenetworksaredefinedgloballyaligninginanexternalmagneticfieldbyaftercross-linkingwithacross-linkersuchasdiisocyanatohexane.Protocol11.Cross-linkingaliquidcrystallinepolymertoformamonodomainsampleCaution!Carryoutallproceduresinawell-ventilatedfume-cupboard,wearappropriatedisposablegloves,alab-coat,andsafetyglasses.Equipment●Volumetricflask(50mL)●Electromagnet(B1T)●Kaptonsheet(25m)●Hot-stage/ovenandtemperaturecontroller●GlassPasteurpipettes,disposable●Kaptontape●DesiccatorcontainingbothsilicagelandMaterials●Diisocyanatohexane(DCH),100mg,0.6mmolharmful,irritant,lachrymator,possible,sensitizer●Dichloromethane,anhydroustoxic,carcinogenicinanimals,harmfulvapour,skinirritant●Triethylamine,20mg,0.2mmolhighlyflammable,harmfulbyinhalationandifswallowed,causesburns●CBZ6randomcopolymera50mgtreatashazardousmaterial●Propan-2-olhighlyflammableMethodPreparation:ThepolymerissynthesizedusingthemethoddescribedinProtocol4.1.Toavolumetricflask(50mL)addDCH(100mg)andfilltothe50mLmarkwithdrydichloromethane.[triethylamine(20mg)canbeaddedasacatalysttothereaction,butisusuallynotrequired].235 S.I.Pateletal.Protocol11.Continued2.DissolveCBZ6polymer(50mg)intheminimumvolumeofdrydichloromethane(
0.25mL)andaddtherequiredamount(0.45mL)oftheabovesolutiontogivea30%molarexcessofcross-linker.3.CleantheKaptonsubstratewithpropan-2-olandallowtodrycompletely.4.Usingaglasspipette,castthefilminaboutfivesuccessivelayersallowingtimeforsolventexclusionbetweeneachlayer.Donottotouchthecastpoly-merwiththetipofthepipetteasthisintroducesbubbles.Thefilmisnowleftinadesiccatorcontainingsilicagel(toabsorbmoisture)andparaffinwax(toabsorbdichloromethane)foraround1hsuchthatthemajorityofthesolventisexcluded.5.Thefilmandsubstratearenowmountedinthemagnethot-stagebystick-ingtheedgesoftheKaptonsubstratetotheovenfloorwithKaptontape.NotethattheKaptonhasparallelgrooveswhichrunperpendiculartothedirectionthefilmcomesawayfromtheroll,itisimportanttoensurethattheselinesrunparalleltothemagneticfield(forsystemswithparallelcoupling).6.Withthemagneticfieldon,thesampleisrapidlyheatedtoabout5CaboveTNIforafewsecondsbeforecoolingtotherequiredtemperaturewithinthenematicphase.ThesolventstillcontainedinthefilmsdepressesTNItoaslowas60Contheinitialrapidheating.OnsubsequentcoolingfromaboveTNI,thesampleshowsamuchsmallerdepressionofTNIofonlyafewdegrees.Thepolymeralignsina2-Tfieldinabout5minbuttakesupto30minat0.6T(at5CbelowTNI).Thealignmenttimeisstronglytemperaturedependentincreasingto120minfor0.6Tat15CbelowTNI.Thefilmisnowheldatthistemperature(usually120C)for2–3daysforthecompletionofthereaction.7.Afterremovalfromthehot-stage,thefilmandsubstratearecooledtobelowTgonacoldsurface(e.g.anicecubewrappedintinfoil)forafewseconds.Thefilmisnowremovedfromthesubstratebyscratchinganedgeofthefilmwitharazorblade,thisactstoseparateacornerofthefilmandtherestofthesubstrateisnowcarefullypeeledfromtheelastomer.Possibleproblems1.Bubbles.(a)Thetipofthepipettewasallowedtotouchthecastfilm;(b)successivelayerswerecastbeforethepreviouslayerhadexcludedthesolvent;(c)thefilmwasnotleftforlongenoughatroomtemperatureinthedesiccator.2.Non-uniformfilmsurface.Eithernotenoughinitialpolymerforthecastareaortoomuchsolventintheconcentratedsolution.3.Opaquefilm.Causedbycross-linkingoccurringbeforecompletealign-mentwiththeappliedfieldduetoeitherahighmolecularweightpolymer236 9:LiquidCrystallinepolymers(thusslowalignment)ortoolargeanexcessofcross-linker(toofastcross-linking).Thekineticsofcross-linkingdependonthemolecularweightofthepolymerandthecross-linkerused,seebelow.Inessence,theshortaliphaticcross-linkers,reactmoreslowlythanthelongaliphaticcross-linkers,whichreactslowerthanthephenyl-containingcross-linkers.Highmolecularweightpolymersreactfasterthanlowmolecularweightpolymersandalsotakelongertoaligninthemagneticfield.Thepresenceofthetriethylaminefurtherincreasesthekineticsofthecross-linking,especiallyatlowertemperatures,thereforethelengthoftimethecastfilmisleftinthedesiccater(step4,)mustbekepttoaminimumwhenusingtriethylamine.Mw/MnCross-linkerTimeto70%gel(h)320000/45000Methylenebis(phenyl1isocyanate)MDI320000/45000Diisocyanatohexane25(DCH)160000/40000Diisocyanatohexane60(DCH)160000/40000Diisocyanatohexane50triethylamine160000/40000Diisocyanatododecane40(DCDD)160000/40000Methylenebis(phenyl1isocyanate)MDI50000/28000Methylenebis(phenyl5isocyanate)MDI4.Filmflowsorbecomesopaquewhensubsequentlyheatedup.Insufficientcross-linking.Thismaybeaproblemofapolymerwithtoolowmolecularweightpolymerorinsufficientcross-linker.Fullycross-linkedsamplesretaintheirmacroscopicshapeonheating.aAcopolymercontaining6%hydroxyethylacrylateCompound6,Protocol4,thischapter.5.1ImprintingchiralstructureinliquidcrystallineelastomersAsimilarapproachhasbeenusedtoproducematerialswithachiral(cholesteric)structurebyperformingtheexperimentsdescribedaboveinthepresenceofalowmolecularweightchiralliquidcrystallinematerial(Figure9.6).Thechiralmaterialisnotcovalentlyattachedtothenetworkandcanberemovedsubsequentlytoproduceanimprintedchiralstructure.19Asbefore,thepolymerdisplaysanematicmesophasebetweentheglasstransition(Tg33C)andthetransitiontoanisotropicfluid(TNI128C).237 S.I.Pateletal.OOO(CH2)6O0.94OCNO6OCH2CH2OH0.06CBZ6CN23CB15NCOCH2NCO24MDIFig.9.6Imprintingchiralstructureinliquidcrystallineelastomer,polymer6(CBZ6),chiraldopant23(CB15)andcross-linkingagent24(MDI).Protocol12.Caution!Carryoutallproceduresinawell-ventilatedfume-cupboard,wearappropriatedisposablegloves,alab-coat,andsafetyglasses.Equipment●Glassvials(5mL)●Mylarsheet(100mthickness,cuttoforaringwith●Volumetricflask(5mL)internaldiameter,20mmandexternaldiameter,30mm)●1mLgraduatedpipette●Teflon(PTFE)sheet●GlassPasteurpipettes,disposable●Filterpaper●Desiccatorcontainingbothsilica●Beaker(100mL)gelandparaffinwax●Screwcapjar(15mL)●Hot-stage/ovenandtemperaturecontrollerMaterials●CBZ6randomcopolymer,23mgtreatashazardousmaterial●CB15chiraldopant,35mg,0.1mmolirritant238 9:LiquidCrystallinepolymers●Dichloromethane,anhydrous10mLtoxic,carcinogenicinanimals,harmfulvapour,skinirritant●Methylenebis(phenylisocyanate),5mg(MDI)harmfulbyinhalation●KBr,anhydrous(pressedpellets:25mmdiameter,2mmthick)●Distilledwater,70mL●NitrogenAsphyxiationhazardMethod1.AddtheliquidcrystallinepolymerCBZ6(23mg)toaglassvial(5mL).2.AddthechiraldopantCB15(35mg,0.1mmol)intoanotherglassvial(5mL)andadddrydichloromethane(1mL)bypipette.3.Tothevolumetricflask(5mL)addtheisocyanatecross-linkerMBPI(5mg)andmakeupthesolutionusingdrydichloromethane(5mL).4.RemoveaportionofthesolutionofCB15indichloromethane(2mL)andaddtotheCBZ6polymergivingasolutioncontaining30mol%CB15.5.AddafractionofthesolutionofMDIindichloromethane(0.5mL)tothesolutioncontainingCBZ6andCB15togivea10%molarexcessofisocyanatetohydroxylgroups.6.WeighoneoftheKBrdiscs,placeitonthehot-stageandheatto35C.7.Usingapipette,addthesolutionofpolymer,dopant,andcross-linkerdrop-wisetotheKBrdisctoformadropletinthecentreofthedisc(15mmdiameter)andallowthesolventtoevaporate.Aflowofnitrogenoverthesamplemaybeusedatthispointtoassistinevaporationbutcompressedairshouldbeavoidedasitmayintroducemoisture.Whenthesolventhasevaporatedthefilmwillturnfromtransparenttoopaqueandtheprocessmayberepeated.Continueuntilallofthesolutionhasbeendeposited.8.Placethediscwiththepolymerfilmintoadesiccatorcontainingdryingsilica(forabsorbingmoisture)andparaffinwax(toabsorbdichloromethanevapour)andleavefor1h.9.Weighthediscandpolymerfilm,thefilmshouldbeopaqueandofrelat-ivelyuniformthicknessanybubblesmayberemovedbythecarefulappli-cationofasmallamount(lessthanonedrop)ofdrydichloromethane.10.Thediscisplacedontothehot-stageandtheMylarringaddedsuchthatitencirclesthedepositedsample.Heatthehot-stageat5Cmin1tothecross-linkingtemperature(60C).11.Oncethecross-linkingtemperaturehasbeenattained,addthesecondKBrdisctothetopofthesampleandapplypressuretodefinethesamplethickness.Ifanalignedsampleisdesiredasmall,linear,oscillatoryshearmaybeappliedatthispoint(amplitude5mm,frequency1Hz).12.Transferthesampletoanoven(preheatedto60C)andplaceamass(
50g)ontopofthesampletoensureitremainscompressedtothethick-nessoftheMylar.Leavesamplefor1–2weekstocross-link.Alteringthe239 S.I.Pateletal.Protocol12.Continueddurationofthereactionorthemolecularweightofthepolymermaybeusedtovarythedegreeofcross-linking.13.Oncompletionofthedesiredperiodofcross-linkingthesamplesandwichedbetweenthetwoKBrdiscsisremovedfromtheoven,placedintoabeakercon-tainingdistilledwater(50mL)andleftforthesubstratestodissolve(
3–4h).14.TheelastomerisremovedfromtheKBrsolutionbyfloatingitoffontoapieceofTeflonsheet.Washtheelastomertwiceindistilledwater(20mL)toremoveanyresidualKBrandcarefullypatdrywithfilterpaperwhilstontheTeflonsubstrate.15.Weighthesample;anymasslossatthispointindicateseitherthepresenceofdichloromethaneinthesampleatthetimeofcross-linkingorlossofCB15duringtheprocess.Gaininmassindicatessomeabsorptionofwaterintothesample.16.Theelastomerisplacedintoajar(
15mL)containingdichloromethane(4mL)andthejarissealedforatleastonehourtoenabletheelastomertoswellandtheCB15toberemoved.17.RemovetheelastomerfromthedichloromethanesolutionbyagainfloatingontoTeflonsheetandallowsolventtoevaporate.Caremustbetaken,astheelastomerishighlyswollenandfragileandwilladheretoitselfstronglyifpermittedtocurlupduringevaporationofthesolvent.18.Oncemostofthesolventhasevaporated,thesamplewillbecomeopaqueandmaybegentlyloosenedfromtheTeflonsurfaceandplacedintoanovenat40Ctoremoveanyresidualdichloromethane.19.TheamountofCB15extractedfromtheelastomerandthemassofthesolublefractionoftheCBZ6polymermaybedeterminedfromUVspectroscopyonthedichloromethanesolution.Inordertocarryoutthespectroscopicanalysisthesolutionmustfirstbediluted,typicallyadilutionof100isrequiredtoobtainanabsorptionofaround1butthiswillvaryslightlyfromsampletosample.Cross-linkedliquidcrystallinepolymerswiththeopticalaxisbeingmacro-scopicallyanduniformlyalignedarecalledliquidsinglecrystallineelas-tomers(LSCE).Withoutanexternalfieldcross-linkingoflinearliquidcrystallinepolymersresultinmacroscopicallynon-orderedpolydomainsam-pleswithanisotropicdirectororientation.Thenetworksbehavelikecrystalpowderwithrespecttotheiropticalproperties.Applyingauniaxialstraintothepolydomainnetworkcausesareorientationprocessandthedirectorofliq-uidcrystallineelastomersbecomesmacroscopicallyalignedbythemechan-icaldeformation.Thesamplesbecomeopticallytransparent(Figure9.7).Thisprocess,however,doesnotleadtoapermanentorientationofthedirector.Withoutstress,theelastomersrelaxtothepolydomainstructure.InordertoachieveapermanentanduniformorientationinanLSCE,theconformationof240 9:LiquidCrystallinepolymers(a)(b)Fig.9.7Liquidcrystallineelastomer(LCE):(a)polydomainsample(1.0);(b)samplealignedbyamechanicalfield(1.4)(L/L0,Llengthofthesample,L0lengthofthesamplewithoutload).1.51.41.31.21.11.00.80.91.01.1TredFig.9.8ThechangeinsamplelengthobservedwhenheatingtheLSCEfromnematictoisotropic.RelativelengthL/LisotropicofanLSCEversusreducedtemperatureTredT/Tn,i(Lisotropiclengthofthesampleintheisotropicstate,Ttemperature,Tn,iphasetrans-formationtemperature).thenetworkstrandshastobeconsistentwiththeanisotropyofthenematicphasestructure.Thiscanberealized,ifthenetworkisadditionallycross-linkedinasecondcross-linkingreactionunderload.Theadditionalcross-linkslock-intheanisotropicchainconformationandretainareversibleanduniformorientationofthenematicphasestructure.TheuniformanisotropicstructureofanematicLSCEisdirectlyreflectedinthethermalexpansionbehaviour.WhenheatingtheLSCEfromthenematicstateintotheisotropicstateastrongreductionofthesamplelengthalongtheopticalaxisisobserved(Figure9.8).Thisprocessdirectlyindicates241 S.I.Pateletal.theconformationalchangesofthenetworkchainsandthestateoforderbetweenthenematicandisotropicstate.InthefollowingthesynthesisofanematicLSCEisdescribed.20Protocol13.Synthesisofanematicliquidsinglecrystallineelastomer(Scheme10)CH3CH3CH3CH3CH3CH3CH3SiOSiOSiCH3Ptcat.CH3SiOSiOSiCH3+RCH3HCH3TolueneCH3HCH3nnPolysiloxanePHMSMesogenicgroupM4OCH3Liquidcrystallinecross-linkerV1elastomerMesogenicgroupOM4OCH3OOOMe25OOCross-linkerV1(CH2)9(CH2)926Scheme10Equipment●Glassvialwithcap(10mL)●Thermostattedcentrifuge●Water-bath●Tweezers●Teflonfilm(19.5mmtimes153mm)●Adhesivetape(tolueneresistant)●Spincastingmould(seeFigure9.8)●Metalclips●Glasssyringe(0.45mTeflonfilter)●Vacuumoven●MicrolitresyringeMaterials●MesogenM4OCH3,210.477g,1.6mmolunknown(care!)●Cross-linkerV1,220.083g,0.2mmolunknown(care!)●Poly(hydrogenmethylsiloxane)(degreeunknown(care!)ofpolymerizationn120),0.120g,2mmol,●Toluene,2mLhighlyflammable,harmfulbyinhalation●PtcatalystSML86005,6Lunknown(care!)Method1.PrepareasolutionofthemesogenicgroupM4OCH3(0.477g,1.6mmol),thecross-linkerV1(0.083g,0.2mmol)andthepoly(hydrogenmethylsiloxane)(0.120g,2.0mmol)intoluene(1.5mL).Usetheglassvialforthisstep.Dissolvethesolidsubstanceswiththehelpofthewarm(50C)water-bathifnecessary.2.PutaTeflonfilm(1.95cm15.3cm)intothemouldtomakeitpossibletoremovetheswollenelastomerafterthereaction.242 9:LiquidCrystallinepolymers3.InjectthesolutionintothemouldbyasyringewithaTeflonfilter.4.Rinsethefilterwith0.5mLtolueneandaddthefiltratetothesolutioninthemould.5.Add6LofthePtcatalysttothesolutionusingthemicrolitresyringe.6.Closethemouldandfixthecoverwithscrews.7.Mountthemouldonthespindleofthethermostattedcentrifuge(Figure9.9).Turnonthethermostatandthecentrifugeandcarryoutthereactionat60C,4000rpmfor1h.8.Turnoffthethermostatandthecentrifuge,dismountthemouldandcoolitdowntoroomtemperatureinarefrigeratororonice.FasteningnutBrasscoverScrewsTeflon-coveredsealingringTeflonfilm20.0mmElastomerfilmBrassmouldSpindleofcentrifuge49.0mmFig.9.9Schematicdiagramofthemouldusedforspincasting.AdhesivetapeTurbidElastomerTransparentTurbidmFig.9.10Theorientationprocessbyamechanicalfield.243 S.I.Pateletal.Protocol13.Continued9.OpenthemouldandremovetheswollenelastomertogetherwiththeTeflonfilmwiththehelpofapairoftweezers.10.Cuttheelastomerinthreepartsandhangitonaretortstandwiththehelpoftheadhesivetape.Makesurethattheedgesoftheelastomersarenotdam-aged.Fixametalcliptotheothersidesoftheelastomersandloadthemcarefullywith12g(e.g.30clips)eachfor30min(Figure9.10).Theelas-tomersmuststaytransparentinthemiddlepart.Ifthisisnotthecase,increasetheloadwithoutdestroyingtheelastomers.11.De-swelltheelastomersatroomtemperatureforoneweek.After24htheloadcanbereducedto5g(e.g.12clips)iftheelastomersstaytransparent.12.Drytheelastomersinvacuumat80Cfor24h.13.Characterization.DSCresults:glasstransition,T4C;C0.4Jg1K1;gpnematictoisotropicphasetransformationtemperatureTn,i71C;Hn,i1.4Jg1.X-ray:orderparameterS(25C)0.60.1.6.SummaryInthischapterwehavedescribedsomeofthepropertiesofpolymericmateri-alswithside-chainliquidcrystallineunits.Asthereaderwillinfer,thereislittletodistinguishthesynthesisofthesematerialsfromotherpolymersdescribedinearlierchapters(althoughside-groupsmaybechemicallymorecomplex).Wherecross-linkingisintroduced,however,thesematerialsexhibitinterestingproperties,whicharedeterminedbythestateatthetimeofcross-linking.Undersuchcircumstances,experimentalistsneedtothinkbeyondthepracticalitiesofformingcovalentbondsbetweenatomsandcon-siderwaysofforexamplealigningmaterialsasthesebondsareformed.Itisthroughtheuseofcombinationofskillsofteninvolvingscientistsfromarangeofdisciplines,thatthepromiseofnewmaterialssuchasthosedescribedinthischapterarebeingrealized.References1.Onsanger,L.Ann.N.Y.Acad.Sci.1949,51,627.2.Flory,P.J.Proc.R.Soc.London1956,234A,73.3.Elliot,A.;Ambrose,E.J.Discuss.FaradaySoc.1950,9,246.4.(a)Tanner,D.;Gabard,V.;Schaefger,J.R.PolymersforAdvancedTechnologies;IUPACInternationalSymposium;1988,p.384.(b)Kwolek,S.L.;Morgan,P.W.;Schaefer,J.R.;Gulrich,L.W.Macromolecules1977,10,1390.(c)DuPont(Kwolek,S.L.)BritishPatent,1,283,064.(d)Jaffe,M.;Jones,S.R.InHighTechnologyFibres,PartA;Lewin,M.;Preston,J.,eds,Dekker:NewYork;1985.(e)Morgan,P.W.Macromolecules1977,10,1381.5.Ballauff,M.Angew.Chem.Int.Ed.Engl.1989,28,253–267.244 9:LiquidCrystallinepolymers6.Finkelmann,H.InPolymerLiquidCrystals;Ciferri,A.;Krigbaum,W.R.;Meyer,R.B.,eds,AcademicPress:NewYork;1982.7.Piskunov,M.V.;Kostromin,S.G.;Stroganov,L.B.;Plate,N.A.;Shibaev,V.P.Makromol.Chem.RapidCommun.1982,3(6),443–447.8.Portugal,M.;Ringsdorf,H.;Zentel,R.Makromol.Chem.1982,183,2311–2321.9.(a)Attard,G.S.;Williams,G.Chem.Br.1986,22(10),919–924.(b)Hirai,A.;Mitchell,G.R.;Davis,F.J.NewPolym.Mater.1990,1,251–260.10.Zentel,R.Angew.Chem.Int.Ed.Engl.1989,28,1407–1415.11.Wang,X.-J.;Warner,M.J.Phys.A1987,20,713–731.12.Davis,F.J.J.Mater.Chem.1993,3(6),551–562.13.Fieser,L.F.J.Am.Chem.Soc.1953,75,4400.14.Patel,S.I.MemoryEffectsinLiquidCrystallineElastomers;PhDThesis;UniversityofReading;2001.15.Shannon,P.J.Macromolecules1983,16,1677–1678.16.Shannon,P.J.Macromolecules1984,17,1873–1876.17.(a)Broer,D.J.;Mol,G.N.Makromol.Chem.1989,190(1),19–30.(b)Brittin,M.;Mitchell,G.R.;Gilbert,A.Mol.Cryst.Liq.Cryst.2001,357,99–115.18.Warner,M.InSide-ChainLiquidCrystalPolymers;McArdle,C.B.,ed.,Blackie:NewYork;1989.19.Hasson,C.D.;Davis,F.J.;Mitchell,G.R.J.Chem.Soc.,Chem.Commun.1998,2515–2516.20.Küpfer,J.;Finkelmann,H.Makromol.Chem.RapidCommun.1991,12,717–726.21.Finkelmann,H.;Rehage,G.Makromol.Chem.RapidCommun.1980,1,31.22.Kundler,I.PhDThesis;Freiburg,Germany;1998.245 IndexPageentriesinitalicsrefertoprotocolsonthosepagesacrylonitrilecopolymerof223–225copolymerwith4-vinylpyridine61–62cross-linkingincopolymercontaining235pyrrolysisof60235–24011-acryloyloxy-undecanoicacid4,4
-dichlorodiphenylsulphone152–156cholesterylester232–233anionicpolymerisation67–89dielectricspectroscopy23–24ofmethylmethacrylate73–75differentialinterferenceofstyrene71–72contrastmicroscopy11antimonyoxide134–135,141,142–143differentialscanningcalorimetry19–21aromaticpolyamide127–129differentialthermalanalysis18–19atomtransferfree-radicalpolymerisation(ATRP)4,4
-difluorobenzophenone147–148,150–152116–1234,4
-dihydroxybenzophenone147–148ofoligo(ethyleneglycol)methacrylate121–1231,1-diphenylethene73polyethyleneoxidebasedinitiatorfor120–121inpolymerisationofethyleneoxide84–87ofstyrene118–120divinylbenzene2atomicforcemicroscopy16–18divinylbenzene64–65,209–210doublemanifold51–52bacteria-imprintedpolymer210,211–214Durhamroute3benzylacrylatedynamicmechanicalthermalanalysis21–23frombenzylalcohol52–54polymerisationof52–55electronenergylossspectroscopy(EELS)141,2-bis(2-chloroethoxy)ethane139electronmicroscopy11–1411-bromoundecanoylchloride230–231etchingin12–13scanning13–14carbonfibres60stainsfor12chaingrowthpolymerisation43transmission11–12cholestericalignment233–234emulsionpolymerisation64,65,66–67cholesteryl11-bromoundecanoate231–232energydispersivespectrometry15cholesteryl2-(acryloyloxy)ethylcarbonateethyleneoxide229–230ininitiationofATRP120–121cholesteryl4-vinylphenylcarbonateringopeningpolymerisationof87–89polymerisationof205–207ethyleneglycoldimethacrylate205–206preparationof203–205Claytone138,142–143ferricchlorideoxidationofpyrrole167–168coordinationpolymerisation90–95flashcolumnchromatography112–113coreshellsequencingfree-radicalchainpolymerisationPAMAMdendrimers192ofbenzylacrylate52–55PEdendrimers195chain-transferagentsin473-[6-(4
-cyanobiphenyl-4-yloxyl)hexyl]pyrrolecopolymersfrom57–62polymerisationasanalignedfilm176–178asemulsionpolymerisation64,65,66–67polymerisationusingferricchloride174–176initiatorsfor46preparationof173–174mechanismof44–454-cyanophenyl-4
-(6-propenoyloxyhexyloxy)ofN-isopropylacrylamide62–63benzoateofstyrene-d756–57synthesisof222–223assuspensionpolymerisation64,64–65246 Indexgelpermeationchromatography4–7NuclearMagneticResonancegels6213Cintegratedintensity9generationsfordendrimers188monomersequences9grouptransferpolymerisation101–108tacticityfrom7–9ofablockcopolymer106–108nyloncatalystfor103–1046,6127ofmethylmethacrylate104–106ropetrick1271-hexenepolymerisation92–93octavinylcyclotetrasiloxane–ringopening3-hexylthiophenepolymerisationof87–89electrochemicalpolymerisation181–183oligo(ethyleneglycol)methacrylatepolymerisationusingnickelcatalystpolymerisationusingATRP183–185121–123hydrosilylation225–226226–228opticalmicroscopy9–114-(6-hydroxyhexyloxy)benzoicacid217–219organometalliccoupling181,183–185infra-redp-(6-propenoyloxyhexyloxy)benzoicacidmicroscopy15219–221spectroscopy15phosphorylationprocedureforpolyamideinterfacialpolymerisation136–138synthesis127–129isophthalicacid128–129photopolymerisation233–234isopreneblockcopolymerwithstyrene78–80polarisedlightmicroscopy9–11poly(aniline)178–181Kevlar1chemicaloxidation180–181electrochemicalpolymerisationlightscattering179–180detectorforGPCpoly(esterether)130–135determinationofMwusing4poly(etherketone)liquidsinglecrystalelastomer242–244cyclicoligomersfrom146–152synthesisinsolution147–148magneticfieldorientationofliquidcrystallinesynthesisunderpseudo-highdilutionelastomerusing242–244conditions150–152MALDI-ToF5–7polypyrrolemechanicalfieldorientationofliquidcrystallineelectrochemicalsynthesisof163–165,elastomerusing242–244164–165metallocene3,92–93-d5165–167methylmethacrylate2,4-dimethyl-167–168grouptransferpolymerisationof106–108polythiophene181–185polymerisationofinitiatedbypotassiumpyrrole169–1719-fluorenyllithium73–75p-phenylenediamine128–129molecularweightpseudo-highdilutionconditions150–152determinationforpolymer4–7numberaverage4Ramanmicroscopy15viscosityaverage4,5reactivityratios57–58weightaverage4ring-openingmetathesispolymerisation3,93ofnorbornene94–5N-[benzylsulphonyl]pyrrolering-openingpolymerisation44acylationof171–173ofethyleneoxide84–87hydrolysisof171–173ofoctavinylcyclo-tetrasiloxane87–89preparationof171N-isopropylacrylimide62–63Sacrificialspacer203,203–210non-periodiccrystallisation135,136scanningprobemicroscopy16–18norbornenepolymerisation94–95Schlenkflask115247 Indexsodiumnaphthaleneaniontemplate201polymerisationofstyreneby76–77tert-butylacrylatesolvents–propertiesandpurification49–50blockcopolymerwithstyrene80–82starburstdendrimers188–199hydrolysisofblockcopolymercontainingpolyamidoamine188–189,190–19382–83poly(ether)dendrimers193–196,196–1992,2,6,6-tetramethylpiperidinyl-1-oxidestep-growthpolymerisation44(TEMPO)110Stillereaction3initiatorbasedon110–114styreneinpolymerisationofstyrenecationicpolymerisation89–90114–116copolymerscontainingthermalanalysis18–23block80–83,78–80thermoplasticelastomers3random58–604,4
-thiobis(benzenethiol)152–156-d7polymerisation56–57(4-vinylphenoxy)dimethylphenylsilaneinitiationofpolymerizationbys-butyllithiumpolymerisationof209–21071–72preparationof207–208initiationofpolymerizationbysodiumnaphthaleneanion76–77Woodsmetalbath141polymerisationusingaTEMPObasedinitiator114–116X-rayscattering24–29sulphone-linkedparacyclophanes152–156smallangle28–29synthesisof152–156wideangle26–28supercapacitors2supercriticalco22Ziegler-Natta3suspensionpolymerisation64,64–65zincacetatedihydrate141,134–135syringepump151,152142–43248