材料科学与工程基础第四章.ppt

BRANCHEDPOLYMERS支链型Apolymerhavingamolecularstructureofsecondarychainsthatextendfromtheprimarymainchains.FIGURE4.7(b)Schematicrepresentationsofbranched,branches,consideredtobepartofthemain-chainmolecule,resultsinaloweringofthepolymerdensity.Thosepolymersthatformlinearstructuresmayalsobebranched.第29页,共53页，星期六，2024年，5月CROSSLINKEDPOLYMERS交联型Apolymerinwhichadjacentlinearmolecularchainsarejoinedatvariouspositionsbycovalentbonds.FIGURE4.7(c)SchematicrepresentationsofcrosslinkedTheprocessofcrosslinkingeitherduringsynthesisorbyanonreversiblechemicalreactionatanelevatedtemperature.Manyoftherubberarecrosslinkedcalledvulcanization,硫化高温不可逆的第30页,共53页，星期六，2024年，5月NETWORKPOLYMERS网络型Apolymercomposedoftrifunctionalmerunitsthatformthree-dimensionalmolecules.Trifunctionalmerunits,FIGURE4.7(d)SchematicrepresentationsofnetworkThesematerialshavedistinctivemechanicalandthermalproperties.Epoxiesandphenol-formaldehydebelongtothisgroup.环氧的苯甲醛三功能链节第31页,共53页，星期六，2024年，5月FIGURE4.8Classificationschemeforthecharacteristicsofpolymermolecules.同质异构立体异构几何异构全同立构间同立构不同立构独立体贯穿结构第32页,共53页，星期六，2024年，5月4.9ThermoplasticandThermosettingPolymersThermoplasts(orthermoplasticpolymers):Apolymericmaterialthatsoftenswhenheatedandhardensuponcooling.Whileinthesoftenedstate,articlesmaybeformedbymoldingorextrusion.processesarereversibleandmayberepeated.Mostlinearpolymersandthosehavingsomebranchedstructureswithflexiblechainsarethermoplastic.热塑性和热固性聚合物可逆的第33页,共53页，星期六，2024年，5月thermosets(orthermosettingpolymers)Apolymericmaterialthat,oncehavingcured(orhardened)byachemicalreaction,willnotsoftenormeltwhensubsequentlyheated.热固性塑料Thermosetpolymersaregenerallyharderandstrongerthanthermoplastics,andhavebetterdimensionalstability.Mostofthecrosslinkedandnetwork