化学专业英语-Polymer课件

PolymerChemistryIntroductiontopolymersSynthesisStructureandpropertiesCharacterization1.Introductiontopolymers1.1Polymer

Polymersarelargemoleculesmadeupofsimplerepeatingunits.ThenameisderivedfromtheGreek

polymeaning“many”andmer

meaning“part”.Macromoleculeisatermsynonymouswithpolymer.1.3Classificationofpolymers

1.3.1Homopolymerandcopolymer

（均聚物和共聚物）

Ifonlyonetypeofmonomerisemployedtoformthepolymertheresultingmoleculeiscalledahomopolymer.Oftenpropertiesareobtainedbyusingdifferenttypesofmonomerspecies.Inthiscasethepolymeristermedacopolymer.

1.3.2Linear,branchedandnetworkpolymer（线形，支化，网状高分子）LinearBranchedNetwork(crosslinked)1.3.3ThermoplasticandThermoset（热塑和热固塑料）

?

Whatis

thermosetting.?

?Whatisthermoplastic?

Thermoplasticpolymersarereadilymoldable

andcanbecastfromsolutiontogivefilms.1.3.4OtherClassifications

RubbersPlasticsFibersCoatingsAdhesives2.1Step-growthpolymerization

（逐步聚合）

Step-growthpolymerization,whichisoftenalsocalledcondensationpolymerization（缩聚）sinceitisalmostexclusivelyconcernedwithcondensationreactiontakingplacebetweenmultifunctionalmonomermolecules.2.1.1Condensationreaction

（缩合反应）

Atypicalcondensationreactionisthereactionbetweenaceticacidandethylalcohol

Twoimportantpointstonotearethatasmallmolecule,water,isproducedbythereaction.Alsotheproductethylacetateisknownasanester.2.1.3Carothersequation（卡罗瑟斯方程） Carothers,whowasapioneerofstep-growthpolymerizationproposedthattherewasasimplerelationshipbetweenthenumberaveragedegreeofpolymerization,andtheextentofreaction,p.

Extentofreaction（反应程度）,p

,attimetisdefinedastheprobabilitythatanyfunctionalgrouppresentinitiallyhasreacted

Thenumberaveragedegreeofpolymerization（数均聚合度）,，isgivenby2.1.4Linearstep-growthpolymerizationsystemEsterinterchangereactionSaltdehydrationRing-openingpolymerization2.1.5Non-linearstep-growth

polymerizationsystem

Ifatriolisreactedwithadiacid,abranched

ratherthanalinearchainwillform.Thebranchedchaincangoonbyfurthercondensationreactionstoformcomplexthree-dimensionalnetworkstructureswhichhavephysicalandmechanicalpropertieswhicharequitedifferentfromthoseoflinearpolymers.2.2Freeradicaladditionpolymerization（自由基加成聚合）

Additionpolymerizationisthesecondmaintypeofpolymerizationreaction.Ittakesplaceinthreedistinctsteps:initiation,propagationandtermination,andtheprincipalmechanismofpolymerformationisbyadditionofmonomermoleculestoagrowingchain.Therearesufficientdifferencesbetweenfreeradicalandionicinitiatedreactionsforthetwotypestobetreatedseparately.2.2.1FreeradicalinitiatorsFreeradicalmaybereadilyproducedbythethermaldecompositionofcertainperoxidesandazocompounds.Azocompoundswilldecomposebothwiththeapplicationofheatandbyphotolysis.Chemicalreactionssuchasredoxreactionsmaybeusedtoproduceradicalsandtheyareparticularlyusefulfortheinitiationofpolymerizationatlowtemperatureorforemulsionpolymerization.2.2.3Propagation

Chainpropagation

takesplacebytherapidadditionofmonomermoleculestothegrowingchain

andthiscanbewritten,ingeneral,ignoringtheradicalfragmentsas Theaveragelife-timeofthegrowingchainareextremelyshortandseveralthousandadditioncantakeplacewithinafewsecond.2.2.4Termination

disproportionation（歧化）chaintransfer（链转移）2.3Ionicpolymerization

（离子聚合）

Ionicpolymerization

systemshavebeendevelopedbecausesomemonomerswhichcontaindoublebondscannotbepolymerizedusingfree-radicalinitiators.Alsoionicpolymerizationgenerallytakesplaceatlowtemperaturesandcanofferbettercontrolofstereoregularityandrelativemolecularmassdistribution.2.3.1Cationicpolymerization

（阳离子聚合）

Thistypeofpolymerizationtakesplacebytheadditionofmonomermoleculestoapositivelychargedgrowingchain,knownasacarboniumion.2.3.2Anionicpolymerization

（阴离子聚合）

Anionicpolymerizationinvolvesthesuccessiveadditionofmonomerswhichcontaindoublebondstoanegativelychargedspeciesknownasacarbanion.

Classificationofcopolymers

Thereareseveralwaysinwhichmonomerscanbearrangedinthemacromolecules.RandomcopolymersAlternatingcopolymersBlockcopolymersGraftcopolymersRandomcopolymers（无规共聚物）

-A-B-A-A-B-A-B-B-B-A-A-B-

TrulyrandomcopolymersareonlyfoundunderspecificpolymerizationconditionsAlternatingcopolymers（交替共聚物）

-A-B-A-B-A-B-A-B-A-B-A-B-A-B-

Thistypeofcopolymersisformedduringcondensationpolymerizationwhentwodifferenttypesofmonomersuchasdiacidanddiolareused.Blockcopolymers（嵌段共聚物）

-A-A-A-A-A-B-B-B-B-B-A-A-A-A-A-

Sometimestheblockcopolymerismadeupofjusttwoorthreelongblocksofeachtypeofunitgivingamaterialwithinterestingandunusualproperties.Graftcopolymers（接枝共聚物） -A-A-A-A-A-A-A-A-A-A-A-A-A-A-A-A-BBBBBBBB

Ingeneralitisfoundthatblockandgraftcopolymershavepropertiesofboththehomopolymerswhereasalternatingandrandomcopolymerspossesspropertiessomewherebetweenthoseofthetwohomopolymers.3StructuresandProperties

3.1Molarmass（摩尔质量）

Molarmass(M)ofthepolymeristhe‘themassofonemoleofthepolymer’andsohasunitsofgmol-1orkgmol-1.Anormalpolymersamplecontainsmoleculeswithavarietyoflengthsanditisonlypossibletoquoteanaveragevalueofmolarmass.Oftentheterm‘molecularweight(分子量)’isstillusedinsteadofmolarmass. (1)Thenumberaveragemolarmass（数均摩尔质量）,isdefinedas‘thesumoftheproductofthemolarmassofeachfractionmultipliedbyitsmolefraction’i.e. whereXiisthemolefractionofmoleculesoflengthi,theratioofthenumberofmoleculesoflengthitothetotalnumberofmolecules.

(2)Theweightaveragemolarmass(重均摩尔质量）,

isdefinedas‘thesumoftheproductofthemolarmassofeachfractionmultipliedbyitsweightfraction’ i.e. wherewiistheweightfractionofmoleculesoflengthi,theratioofthemassofmoleculesoflengthitothetotalmassofallmolecules.

3.1.1MeasureofaveragemolarmassEndgroupanalysis（端基分析法）Cryoscopyandebulliometry（冰点和沸点测定法）Osmometry（渗透压法）Lightscattering（光散射法）Ultracentrifugation（超速离心法）Viscometry（粘度法）Viscosity（粘度）1.Relativeviscosity(相对粘度，viscosityratio) Inthisexpression,and0refertosolutionandsolventviscosity,respectively,inpoiseunitswhichareproportionaltothecorrespondingflowtimes,tandt0,throughtheviscometercapillary.

Relativeviscosityisdimensionless.

2.Specificviscosity（增比粘度）

Specificviscosityisalsodimensionless. 3.Reducedviscosity(比浓粘度，viscositynumber)

4.Inherentviscosity(比浓对数粘度，logarithmicviscositynumber)5.Intrinsicviscosity(特征粘度，limitingviscositynumber)

Concentration,C,intheaboveexpressionsisingramsper100mlofsolvent;thereforereduced,inherent,andintrinsicviscositieshaveunitsofdeciliterspergram.Mark-Houwinkequation whereKandareconstantswhichdependonthenatureofpolymerandthesolvent.IntrinsicviscosityisrelatedtomolarmassaccordingtoMark-Houwinkequation.ThemolarmassobtainedbytheMark-Houwinkrelationshipisreferredtoastheviscosityaveragemolarmass.

3.1.2MolarmassdistributionUltracentrifugation（超速离心法）Fractionalprecipitation（沉淀分级法）Fractionalsolution（溶解分级法）Gelpermeationchromatography（凝胶渗透色谱法）Thinlayerchromatography（薄层色谱法）3.2StereochemistryIn1963,ZieglarandNattawontheNobelPrizeinChemistryfortheirdiscoveriesthatledtothedevelopmentofstereoregularpolymers.3.2.1StructuralisomerismBranchingOrientations

head-to-tail head-to-head3.2.2Configurationalisomerism Forpolymerspreparedfrommonomersoftype,therearetwopossiblestereoregulararrangements-oneinwhicheachcarbonbearingtheRgrouphasthesameconfiguration,andoneinwhichalternatecarbonsbearingtheRgrouphavethesameconfiguration.Nattaproposedthetermsisotactic（全规）fortheformerandsyndiotactic（间规）forthelatter.Acompletelyrandomdistributioniscalledatactic（无规）.3.3Crystallinity（晶态）Whenapolymerhasahighlystereoregularstructurewithlittleornochainbranchingorwhenitcontainshighlypolargroupsthatgiverisetostrongdipole-dipoleinteractions,itcanexistincrystallineform.Fringedmicellemodel(缨状胶束模型)Foldedchainlamellamodel(折叠链结构模型)Switchboardmodel(插线板模型)Crystallinemeltingpoint（晶体熔点）,Tm

Forcrystallinepolymers,thetemperatureatwhichcrystallinitydisappearsisfrequentlyused.Thisiscalledcrystallinemeltingpoint,anditismostconvenientlymeasuredbyobservingthedisappearanceofcrystallinebirefringenceunderapolarizingmicroscope.Meltingpointofpolymersisalsoreferredtoasfirst-ordertransitiontemperature.3.4Glasstransitiontemperature（玻璃化温度）,Tg

Allpolymers,attemperaturesbelowacertainlevel,exhibitpropertiescharacteristicofabrittlesolidorglass.Asthetemperatureisraised,apointisreachedwherethepropertiesofthepolymerchangetothoseofarubber.Thistemperatureiscalledtheglasstransitiontemperature,Tg.Itdiffersfromthemeltingpoint,wherethepolymerchangesfromthesolidtotheliquidstate;rather,itmarksthetemperatureatwhichmajorsegmentsofthepolymerchainsgainsometranslationalfreedom.Inotherwords,thepolymerisnolongerheldinarigidstatewithmotionrestrictedtovirbrationalmovementsofindividualatoms,butsectionsofpolymerchainsbegintomove.Inadditiontostiffness,polymersexhibitmarkedchangesinotherproperties,suchasrefractiveindex,thermalconductivity,andspecificvolumeattheglasstransitiontemperature.Infact,onecanmeasureTgbyplottingspecificvolumeagainsttemperatureandnotingthetemperatureatwhichthereisachangeinslope.Moreconveniently,canbemeasuredbydifferentialthermalanalysis. BecausethechangesthatoccuratTgarenotsomuchinphysicalstate,aswithTm,butratherinthermodynamicproperties,theglasstransitiontemperatureisalsoreferredtoasthesecond-ordertransitiontemperature.3.5Flameresistant

Manypolymers–forexample,poly(vinylchloride)andotherhalogen-containingpolymers–arenotflammable.Others,suchaspolyurethanes,burnpoorlyorstopburningwhenthesourceofflameisremoved.Thelattertypearesaidtobe“self-extinguishing”.Whilethemechanismofburningisnotwellunderstood,itisknownthatcertainelements,whenincorporatedintopolymerseitherasfillersorasanintegralpartofthepolymerstructure,retardorpreventburning.Thedegreeofpreventiondepends,ofcourse,onconcentration.Amongthevariouselementsthathavebeentested,halogen,phosphorus,andantimonyhavebeenreceivedmostattention.3.6ThermalstabilityWhenorganicsubstancesareheatedtoveryhightemperature,theyhaveatendencytoformaromaticcompounds.Itfollows,then,thataromaticpolymersshouldberesistanttohightemperature.Awidevarietyofpolymershavingrepeatingaromaticunitshavebeendevelopedinrecentyearswithmuchoftheimpetuscomingfromtheneedoftheaerospaceindustriesforhigh-performancematerialsthatwillwithstandextremesoftemperature.Inadditiontothermalandoxidativestability,aromaticpolymersfrequentlydisplaymuchbetterresistancetoionizingradiationthandononaromaticpolymers.3.7ChemicalresistanceOneoftheproblemsthatoilcompaniesfacewith:petroleumstoragetanksisrustingawayofmetalbottombymoisturefromunderneath.Remedy:bysprayinginsideonthetankbottomamixtureofunsaturatedpolyesterinstyreneandchoppedglassfibersforreinforcing.

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