应用化学专业英语 教学课件 作者 黄忠 谢普会 付颖 主编lesson 6.ppt

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1、Unit6PolymersLesson17IntroductiontoPolymersPolymersoccurnaturallyintheformofproteins,cellulose(plants),starch(food)andnaturalrubber.Engineeringpolymers,however,areusuallysyntheticpolymers.WhatArePolymers?Apolymerisamaterialwhosemoleculescontainaverylargen

2、umberofatomslinkedbycovalentbonds,whichmakespolymersmacromolecules.Polymersconsistmainlyofidenticalorsimilarunitsjoinedtogether.Theunitformingtherepetitivepatterniscalleda"mer"or"monomer".PolymerStructuresOne-dimensionalPolymersOnedimensionalpolymersaremo

3、stcommon.Theycanoccurwhenever2reactingchainsjointomakeachain.Two-dimensionalPolymersTwodimensionalpolymersarerare,thebestexampleofonewouldbegraphite.CrystallineDiamondisanexampleofthe3-dimensionalcrystallinepolymerinwhichcarbonislinkedtofourcornersofthete

4、trahedraandthesearepackedwithlongrangeorderinspacetoformalattice.Three-dimensionalPolymersClassificationofPolymersThesearelinear,one-dimensionalpolymerswhichhavestrongintramolecularcovalentbondsandweakintermolecularVanDerWaalsbonds.Atelevatedtemperature,i

5、tiseasyto"melt"thesebondsandhavemolecularchainsreadilyslidepastoneanother.ThermoplasticPolymersThermosettingPolymersThesearethree-dimensionalamorphouspolymerswhicharehighlycrosslinked(strong,covalentintermolecularbonds)networkswithnolong-rangeorder.Rubber

6、sandElastomersFibersLiquidCrystalsThermosettingPolymersThesearethree-dimensionalamorphouspolymerswhicharehighlycrosslinked(strong,covalentintermolecularbonds)networkswithnolong-rangeorder.PolymerSynthesisStepGrowthInstepgrowthpolymerizationorcondensationp

7、olymerization,chainsofanylengthxandycombinetoformlongchains:x-mer+y-mer=(x+y)-merChainGrowthChaingrowthpolymerizationinvolvesanactivechainsitewhichreactswithanunsaturated(orheterocyclic)monomersuchthattheactivesiteisrecoveredatthechainend.TransitionsinPol

8、ymersThereisatemperature,orrangeoftemperatures,belowwhichanamorphouspolymerisinaglassystateandabovewhichitisrubbery.Thistemperatureiscalledtheglasstransitiontemperature,Tg,anditcharacterizestheamorphousphase.Molecul