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1、4SynthesisofMacromoleculesbyStepGrowthPolymerization4.1CondensationPolymerization(Polycondensation)Condensationpolymerizations(polycondensations)arestepwisereactionsbe•tweenbifunctionalorpolyfunctionalcomponents,witheliminationofsmallmoleculessuchaswater,alcoh
2、ol,orhydrogenandtheformationofmacromo-lecularsubstances.Forthepreparationoflinearcondensationpolymersfrombifunctionalcompounds(thesameconsiderationsapplytopolyfunctionalcom•poundswhichthenleadtobranched,hyperbranched,orcrosslinkedcondensa•tionpolymers)thereare
3、basicallytwopossibilities.Oneeitherstartsfromamonomerwhichhastwounlikegroupssuitableforpolycondensation(ABtype),oronestartsfromtwodifferentmonomers,eachpossessingapairofidenticalreactivegroupsthatcanreactwitheachother(AABBtype).AnexampleoftheABtypeisthepolycon
4、densationofhydroxycarboxylicacids:O-(n-1)H20O^^(CH2)x^OH^Hf^CH2)xc^HAnexampleoftheAABBtypeisthepolycondensationofdiolswithdicarbo-xylicacids:OO^-(2n-1)H20"%CH2).-^^-HO^CH^LyOAH-^^.(CH2)x-o'^(CH2)y-^'OHnTheformationofacondensationpolymerisastepwiseprocess.Thus,
5、thefirststepinthepolycondensationofahydroxycarboxylicacid(ABtype)istheforma•tionofadimerthatpossessesthesameendgroupsastheinitialmonomer:oo^^VH2)XAOH^Z^^HO-^^^2^Y^"(^^2)X^OHoTheendgroupsofthisdimercanreactinthenextstepeitherwiththemon-omericcompoundorwithanoth
6、erdimermolecule,andsoon.Themolecular2644SynthesisofMacromoleculesbyStepGrowthPolymerizationweightoftheresultingmacromoleculesincreasescontinuouslywithreactiontime,unlikemanyadditionpolymerizations,e.g.,radicalpolymerizations.Theintermediatesthatareformedininde
7、pendent,individualreactions,areoligo-mericandpolymericmoleculeswiththesamefunctionalendgroupsasthemonomericstartingcompound.Inprinciple,theseintermediatescanbeisolat•edwithoutlosingtheircapabilityforfurthergrowth.Thus,allreactionsMi+Mj-^Mj+icanoccur,whereM,,M:
8、denoteoligomericorpolymericspeciescontaining/,;monomericunits,respectively.Theformationofareactionschemethattakesintoaccountthemultitudeofpossiblereactionsbetween/-mersand;-mers,wi
