25 Synthetic Polymers

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1、Chapter25SyntheticPolymersApolymerisalargemoleculemadebylinkingtogetherrepeatingunitsofsmallmoleculescalledmonomersChain-growthpolymers,alsoknownasadditionpolymers,aremadebychainreactionsStep-growthpolymers,alsocalledcondensationpolymers,aremadebycombiningtwomoleculesbyremovingasmallmol

2、eculeChain-GrowthPolymersChain-growthpolymersproceedbyoneofthreemechanisms:radicalpolymerizationcationicpolymerizationanionicpolymerizationRadicalPolymerizationThemolecularweightofthepolymercanbecontrolledbyaprocessknownaschaintransferChain-growthpolymerizationofmonosubstitutedethylenes

3、exhibitsamarkedpreferenceforhead-to-tailadditionHead-to-tailadditionofasubstitutedethyleneresultsinapolymerinwhicheveryothercarbonbearsasubstituentHead-to-tailadditionisfavoredforstericreasonsGroupsthatstabilizeradicalsalsofavorhead-to-tailadditionBranchingofthePolymerChainBranchedpolym

4、ersaremoreflexibleCationicPolymerizationthealkenemonomerreactswithanelectrophileThecarbocationintermediatesformedduringpolymerizationcanundergorearrangementMonomersthatarebestabletoundergocationicpolymerizationarethosewithelectron-donatingsubstituentsAnionicPolymerizationNonterminatedch

5、ainsarecalledlivingpolymersThechainsremainactiveuntiltheyarekilledRing-OpeningPolymerizationStereochemistryofPolymerizationsubstituentsonthesamesidesubstituentsregularlyalternateonbothsidesLong,unbranchedpolymerscanbepreparedusinganaluminum–titaniuminitiator(Ziegler–Nattacatalyst)Polyme

6、rizationofDienesSynthesisofSyntheticRubberTheproductresultingfrompolymerizationofdifferentmonomersiscalledacopolymerFourTypesofCopolymersProgressofaStep-GrowthPolymerizationNylon6isanexampleofastep-growthpolymerformedbyamonomerwithtwodifferentfunctionalgroupsTheincorporationofaromaticri

7、ngsintopolymersimprovesthephysicalstrengthofthepolymersPolyestersarestep-growthpolymersinwhichthemonomerunitsarejoinedtogetherbyestergroupsPolyesterswithtwoestergroupsbondedtothesamecarbonareknownaspolycarbonatesEpoxyresinsarethestrongestadhesiveknownAurethane(carbamate)isacomp