高分子材料工程專業(yè)英語翻譯(DOC)

高分子材料工程專業(yè)英語翻譯Unit1Whatarepolymers?Whatarepolymers?Foronething,theyarecomplexandgiantmoleculesandaredifferentfromlowmolecularweightcompoundslike,say,commonsalt.Tocontrastthedifference,themolecularweightofcommonsaltisonly58.5,whilethatofapolymercanbeashighasseveralhundredthousand,evenmorethanthousandthousands.Thesebigmoleculesor‘macro-molecules’aremadeupofmuchsmallermolecules,canbeofoneormorechemicalcompounds.。Toillustrate,imaginethatasetofringshasthesamesizeandismadeofthesamematerial.Whenthesethingsareinterlinked,thechainformedcanbeconsideredasrepresentingapolymerfrommoleculesofthesamecompound.，可以把形成的鏈看成是具有同種化合物組成的高聚物。Alternatively,individualringscouldbeofdifferentsizesandmaterials,andinterlinkedtorepresentapolymerfrommoleculesofdifferentcompounds.另一方面，環(huán)可以大小不同、材料不同,相連接后形成具有不同化合物組成的聚Thisinterlinkingofmanyunitshasgiventhepolymeritsname,polymeaning‘many’andmermeaning‘part’(inGreek).節(jié)、基體”(希臘語中)。Asanexample,agaseouscompoundcalledbutadiene,withamolecularweightof54,combinesnearly4000timesandgivesapolymerknownaspolybutadiene(asyntheticrubber)withabout200000molecularweight.的聚丁二烯(合成橡膠)高聚物。Thelowmolecularweightcompoundsfromwhichthepolymersformareknownasepictureissimplyasfollows形成高聚物的低分子化合物稱為單體。下面簡單地描述一下形成過程：丁二烯＋丁二烯＋…＋丁二烯——→聚丁二烯(4000次)Onecanthusseehowasubstance(monomer)withassmallamoleculeweightas54growtobecomeagiantmolecule(polymer)of(54×4000≈)200000molecularweight.分子(高聚物)。Itisessentiallythe“giantness”ofthesizeofthepolymermoleculethatmakesitsbehavior(differentfromthatofacommonlyknownchemicalcompoundsuchasbenzene.)實質(zhì)上正是由于聚合物的巨大分子尺寸才使其性能不同于像苯這樣的一般化合物(的性能)Solidbenzene,forinstance,meltstobecomeliquidbenzeneat5.5℃and,onfurtherheatingboilsintogaseousbenzene.Asagainstthiswell-definedbehaviorofasimplechemicalcompound,apolymerlikepolyethylenedoesnotmeltsharplyatoneparticulartemperatureintocleanliquid.融成純凈的液體。Instead,itbecomesincreasinglysofterand,ultimately,turnsintoaveryviscous,tackymoltenmass.Furtherheatingofthishot,viscous,moltenpolymerdoesconvertitintovariousgasesbutitisnolongerpolyethylene.(Fig.1.1).合物熔融體進一步加熱，它會轉(zhuǎn)變成不同氣體，但它不再是聚乙烯(如圖1.1)Anotherstrikingdifferencewithrespecttothebehaviorofapolymerandthatofalowmolecularweightcompoundconcernsthedissolutionprocess.聚合物行為和低分子量化合物另一不同的行為為溶解過程。Letustake,forexample,sodiumchlorideandadditslowlytofixedquantityofwater.Thesalt,whichrepresentsalowmolecularweightcompound,dissolvesinwateruptoapoint(calledsaturationpoint)but,thereafter,anyfurtherquantityaddeddoesnotgointosolutionbutsettlesatthebottomandjustremainsthereassolid.解直到某一點(叫飽和點)，但進一步添加,鹽不進入溶液中卻沉到底部而保持原有Theviscosityofthesaturatedsaltsolutionisnotverymuchdifferentfromthatofwater.Butifwetakeapolymerinstead,say,polyvinylalcohol,andaddittoafixedquantityofwater,thepolymerdoesnotgointosolutionimmediately.飽和鹽溶液的粘度與水的粘度接近.但是，如果我們用聚合物，如聚乙烯醇添加到定量水中，聚合物不是馬上進入到溶液中。Theglobulesofpolyvinylalcoholfirstabsorbwater,swellandgetdistortedinshapeandafteralongtimegointosolution.聚乙烯醇顆粒首先吸水溶脹，發(fā)生變形，經(jīng)過很長時間后，(聚乙烯醇分子)進入Also,wecanaddaverylargequantityofthepolymertothesamequantityofwaterwithoutthesaturationpointeverbeingreached.們可以將大量的聚合物加入到同樣量的水中，不存在飽和點。Asmoreandmorequantityofpolymerisaddedtowater,thetimetakenforthedissolutionofthepolymerobviouslyincreasesandthemixultimatelyassumesasoft,dough-likeconsistency.像面團一樣粘稠的混合物。Anotherpeculiarityisthat,inwater,polyvinylalcoholneverretainsitsoriginalpowderynature[astheexcesssodiumchloridedoes][inasaturatedsaltsolution].另一個特點是，在水中聚乙烯醇不會像過量的氯化鈉在飽和鹽溶液中那樣能保末狀態(tài)。Inconclusion,wecansaythat(1)thelongtimetakenbypolyvinylalcoholfordissolution,(2)theabsenceofasaturationpoint,and(3)theincreaseintheviscosityareallcharacteristicsofatypicalpolymerbeingdissolvedinasolventandthesecharacteristicsareattributedmainlytothelargemolecularsizeofthepolymer.總之，我們可以講(1)聚乙烯醇的溶解需要很長時間，(2)不存在飽和點，(3)粘度的增加是聚合物溶于溶液中的典型特性，這些特性主要歸因于聚合物大分子的尺ThebehaviorofalowmolecularweightcompoundandthatofapolymerondissolutionareillustratedinFig.1.2.rizationManyolefinicandvinylunsaturatedcompoundsareabletoformchain-likemacromoleculesthrougheliminationofthedoublebond,aphenomenonfirstrecognizedbyStaudinger.Diolefinspolymerizeinthesamemanner,however,onlyoneofthetwodoublebondsiseliminated.Staudinger首先發(fā)現(xiàn)許多烯烴和不飽和烯烴通過打開雙鍵可以形成鏈式大分子。二烯烴以同樣的方式聚合，但僅消除兩個雙鍵中的一個。Suchreactionsoccurthroughtheinitialadditionofamonomermoleculetoaninitiatorradicaloraninitiatorion,bywhichtheactivestateistransferredfromtheinitiatortotheaddedmonomer.些反應(yīng)活性中心由引發(fā)劑轉(zhuǎn)移到被加成的單體上。Inthesamewaybymeansofachainreaction,onemonomermoleculeaftertheotherisadded(2000~20000monomerspersecond)untiltheactivestateisterminatedthroughadifferenttypeofreaction.單體分子通過鏈式反應(yīng)以同樣的方式一個接一個地加上(每秒2000~20000個單體)直到活性中心通過不同的反應(yīng)方式終止。Thepolymerizationisachainreactionintwoways:becauseofthereactionkineticandbecauseasareactionproductoneobtainsachainmolecule.Thelengthofthechainmoleculeisproportionaltothekineticchainlength.OnecansummarizetheprocessasfollowRisequaltotheinitiatorradical):鏈式反應(yīng)可以概括為以下過程(R·相當與引發(fā)劑自由基)：略O(shè)nethusobtainspolyvinylchloridefromvinylchloride,orpolystyrenefromstyrene,orpolyethylenefromethylene,etc.獲得Thelengthofthechainmolecules,measuredbymeansofthedegreeofpolymerization,canbevariedoveralargerangethroughselectionofsuitablereactionconditions.分子鏈長通過聚合度測量，可以通過選擇適宜的反應(yīng)條件大為改變Usually,withcommerciallypreparedandutilizedpolymers,thedegreeofpolymerizationliesintherangeof1000to5000,butinmanycasesitcanbebelow500dover商業(yè)制備和使用的聚合物，聚合度通常在1000~5000范圍內(nèi)，但在許多情況下可Thisshouldnotbeinterpretedtomeanthatallmoleculesofacertainpolymericmaterialconsistof500,or1000,or5000monomerunits.Inalmostallcases,thepolymericmaterialconsistsofamixtureofpolymermoleculesofdifferentdegreesofpolymerization成。在幾乎所有的情況下，聚合物材料由不同聚合度的聚合物分子的混合物組成。Polymerization,achainreaction,occursaccordingtothesamemechanismasthewell-knownchlorine-hydrogenreactionandthedecompositionofphosegene.鏈式聚合反應(yīng)的機理與眾所周知的氯(氣)-氫(氣)反應(yīng)和光氣的分解機理相同。Theinitiationreaction,whichistheactivationprocessofthedoublebond,canbebroughtaboutbyheating,irradiation,ultrasonics,orinitiators.Theinitiationofthechainreactioncanbeobservedmostclearlywithradicalorionicinitiators.楚地進行研究用自由基型或離子型引發(fā)劑引發(fā)的鏈式反應(yīng)。heseareenergyrichcompoundswhichcanaddsuitableunsaturatedcompounds(monomers)andmaintaintheactivatedradicalorionicstatesothatfurthermonomermoleculescanbeaddedinthesamemanner.這些是高能態(tài)的化合物，它們能夠加成不飽和化合物(單體)并保持自由基或離子活性中心以致單體可以以同樣的方式進一步加成。Fortheindividualstepsofthegrowthreactiononeneedsonlyarelativelysmallactivationenergyandthereforethroughasingleactivationstep(theactualinitiationreaction)alargenumberofolefinmoleculesareconverted,asisimpliedbytheterm化反應(yīng)(即引發(fā)反應(yīng))即可將許多烯類單體分子轉(zhuǎn)化成聚合物，這正如連鎖反應(yīng)這個樣。Becauseverysmallamountsoftheinitiatorbringabouttheformationofalargeamountofpolymericmaterial(1:1000to1:1000),itispossibletoregardpolymerizationfromasuperficialpointofviewasacatalyticreaction.因為少量的引發(fā)劑引發(fā)形成大量的聚合物原料(1：1000~1：10000)，從表面上看反應(yīng)。Forthisreason,theinitiatorsusedinpolymerizationreactionsareoftendesignatedaspolymerizationcatalysts,eventhough,inthestrictestsense,theyarenottruecatalystsbecausethepolymerizationinitiatorentersintothereactionasarealpartnerandcanbefoundchemicallyboundinthereactionproduct,i.e.,thepolymer.應(yīng)的催化劑進入到反應(yīng)內(nèi)部而成為一部分，同時可以在反應(yīng)產(chǎn)物，既聚合物的末端發(fā)現(xiàn)催化劑，所以嚴格地講它們不是真正意義上的催化劑，Inadditiontotheionicandradicalinitiatorstherearenowmetalcomplexinitiatorswhichcanbeobtained,forexample,bythereactionoftitaniumtetrachlorideortitaniumtrichloridewithaluminumalkyls),whichplayanimportantroleinpolymerizationreactions(Zieglercatalysts),Themechanismoftheircatalyticactionisnotyetcompletelyclear.除離子引發(fā)劑和自由基引發(fā)劑外，還有金屬絡(luò)合物引發(fā)劑(可以通過四氯化鈦或三氯化鈦與烷基鋁的反應(yīng)得到)。它們在聚合反應(yīng)中起到了重要作用(齊格納引發(fā)劑)。它們催化活動的機理還不是十分清楚。NITStepGrowthpolymerizationManydifferentchemicalreactionsmaybeusedtosynthesizepolymericmaterialsbystepgrowthpolymerizationTheseincludeesterification,amidation,theformationofurethanes,aromaticsubstitution,etc.化、氨基甲酸酯、芳香族取代物的形成等。Polymerizationproceedsbythereactionsbetweentwodifferentfunctionalgroups,e.g.,hydroxylandcarboxylgroups,orisocyanateandhydroxylgroups.Allstep-growthpolymerizationfallintotwogroupsdependingonthetypeofmonomer(s)employed.Thefirstinvolvestwodifferentpolyfunctionalmonomersinwhicheachmonomerpossessesonlyonetypeoffunctionalgroup.體，每一種單體僅具有一種官能團。Apolyfunctionalmonomerisonewithtwoormorefunctionalgroupspermolecule.Thesecondinvolvesasinglemonomercontainingbothtypesoffunctionalgroups.Thesynthesisofpolyamidesillustratesbothgroupsofpolymerizationreactions.Thus,polyamidescanbeobtainedfromthereactionofdiamineswithdiacidsorfromthereactionofaminoacidswiththemselves.之間的反應(yīng)得到。Thetwogroupsofreactionscanberepresentedinageneralmannerbytheequations兩種官能團之間的反應(yīng)一般來說可以通過下列反應(yīng)式表示Reaction.1)illustratestheformer,while(3.2)isofthelattertype.反應(yīng)(3.1)說明前一種形式，而反應(yīng)(3.2)具有后一種形式。Polyesterification,whetherbetweendiolanddibasicacidorintermolecularlybetweenhydroxyacidmolecules,isanexampleofastep-growthpolymerizationprocess.進行。Theesterificationreactionoccursanywhereinthemonomermatrixwheretwomonomermoleculescollide,andoncetheesterhasformed,it,too,canreactfurtherbyvirtueofitsstill-reactivehydroxylorcarboxylgroups.仍有活性的羥基或羧基還可以進一步進行反應(yīng)。Theneteffectofthisisthatmonomermoleculesareconsumedrapidlywithoutanylargeincreaseinmolecularweight.酯化的結(jié)果是單體分子很快地被消耗掉，而分子量卻沒有多少增加。Fig.3.1illustratesthisphenomenon.Assume,forexample,thateachsquareinFig.3.1arepresentsamoleculeofhydroxyacid.Aftertheinitialdimmermoleculesfrom(b),halfthemonomermoleculeshavebeenconsumedandtheaveragedegreeofpolymerizationDPofpolymericspeciesis2.圖3.1說明了這個現(xiàn)象。假定圖3.1中的每一個方格代表一個羥基酸分子。產(chǎn)生二聚體分子后(b)，一半的單體分子消耗了，這時平均聚合度(DP)是2。Astrimerandmoredimermoleculesform(c),morethan80%ofthemonomermoleculeshavereacted,butDPisstill2.5.Whenallthemonomermoleculeshavereacted(d),DPis4. (c)中形成三聚體和更多的二聚體，超過80%的單體分子已參加反應(yīng)，但DP僅僅還是2.5。(d)中所有的單體反應(yīng)完，DP是4。Buteachpolymermoleculethatformsstillhasreactiveendgroups;hencethepolymerizationreactionwillcontinueinastepwisefashion,witheachesterificationstepbeingidenticalinrateandmechanismtotheinitialesterificationofmonomers.繼續(xù)進行，其每一步酯化反應(yīng)的反應(yīng)速率和反應(yīng)機理均與初始單體的酯化作用相同。Thus,molecularweightincreasesslowlyevenathighlevelsofmonomerconversion,anditwillcontinuetoincreaseuntiltheviscositybuild-upmakesitmechanicallytoodifficulttoremovewaterofesterificationorforreactiveendgroupstofindeachother.反應(yīng)的水或端基難以相互反應(yīng)為止。ItcanalsobeshownthatintheA-A+B-Btypeofpolymerization,anexactstoichiometricbalanceisnecessarytoachievehighmolecularweights.Ifsomemonofunctionalimpurityispresent,itsreactionwilllimitthemolecularweightbyrenderingachainendinactive.些單官能團雜質(zhì)，由于鏈的端基失活，其反應(yīng)將限制分子量。Similarly,high-puritymonomersarenecessaryintheA-Btypeofpolycondensationanditfollowsthathigh-yieldreactionsaretheonlypracticalonesforpolymerformation,sincesidereactionswillupsetthestoichiometricbalance.形成聚合物的實用方法只能是高收率的反應(yīng)。UNIT4IonicPolymerizationIonicpolymerization,similartoradicalpolymerization,alsohasthemechanismofachainreaction.Thekineticsofionicpolymerizationare,however,considerablydifferentfromthatofradicalpolymerization.由基聚合反應(yīng)。(1)Theinitiationreactionofionicpolymerizationneedsonlyasmallactivationenergy.Therefore,therateofpolymerizationdependsonlyslightlyonthetemperature.(1)離子聚合的引發(fā)反應(yīng)僅需要很小的活化能。因此，聚合反應(yīng)的速率與溫度關(guān)系不Ionicpolymerizationsoccurinmanycaseswithexplosiveviolenceevenattemperature.below50℃(forexample,theanionicpolymerizationofstyreneat–70℃intetrahydrofuran,orthecationicpolymerizationofisobutyleneat–100℃inliquidethylene).在四氫呋喃中反應(yīng)，異丁烯的陽離子聚合在-100℃在液態(tài)乙烯中反應(yīng))。Withionicpolymerizationthereisnocompulsorychainterminationthroughrecombinationbecausethegrowingchainscannotreactwitheachother.Chainterminationtakesplaceonlythroughimpurities,orthroughtheadditionofcertaincompoundssuchaswater,alcohols,acids,amines,oroxygen,andingeneralthroughcompoundswhichcanreactwithpolymerizationionsundertheformationofneutralcompoundsorinactiveionicspecies.化合物進行加成而發(fā)生，且一般來說(鏈終止反應(yīng))可通過這樣的化合物來進行，這種化合物可以和活性聚合物離子進行反應(yīng)生成中性聚合物或沒有聚合活性的離子型聚Iftheinitiatorsareonlypartlydissociated,theinitiationreactionisanequilibriumreaction,wherereactioninonedirectiongivesrisetochaininitiationandintheotherdirectiontochaintermination.在一個方向上進行鏈引發(fā)反應(yīng)，而在另一個方向上則發(fā)生鏈終止反應(yīng)。Ingeneralionicpolymerizationcanbeinitiatedthroughacidicorbasiccompounds.通常離子聚合反應(yīng)能通過酸性或堿性化合物被引發(fā)。Forcationicpolymerization,complexesofBF3,AlCl3,TiCl4,andSnCl4withwater,oralcohols,ortertiaryoxoniumsaltshaveshownthemselvestobeparticularlyactive.ThepositiveionsaretheonesthatcausechaininitiationForexample:BFAlClTiClSnCl叔烊鹽的絡(luò)合物活性特別高。正離子產(chǎn)生鏈引發(fā)。例如：However,alsowithHCl,H2SO4,andKHSO4,onecaninitiatecationicpolymerization.Initiatorsforanionicpolymerizationarealkalimetalsandtheirorganiccompounds,suchasphenyllithium,butyllithium,phenylsodium,andtriphenylmethylpotassium,whicharemoreorlessstronglydissociatedindifferentsolvents.但BF3與HCl、H2SO4和KHSO4也可以引發(fā)陽離子聚合反應(yīng)。陰離子聚合反應(yīng)的引發(fā)劑是堿金屬和它們的有機金屬化合物，例如苯基鋰、丁基鋰和三苯甲基鋰，它們在溶劑中高度離解。TothisgroupbelongalsothesocalledAlfincatalysts,whichareamixtureofsodiumisopropylate,allylsodium,andsodiumchloride.所謂的Alfin催化劑就是屬于這一類，這類催化劑是異丙醇鈉、烯丙基鈉和氯化鈉的混合物。WithBFandisobutyleneasthemonomeritwasdemonstratedthatthepolymerizationispossibleonlyinthepresenceoftracesoftracesofwateroralcohol.BF3為引發(fā)劑(異丁烯為單體)，在痕量水或乙醇下聚合反應(yīng)才可以進行。Ifoneeliminatesthetraceofwater,BF3alonedoesnotgiverisetopolymerization.WateroralcoholsarenecessaryinordertoallowtheformationoftheBF3-complexandtheinitiatorcationaccordingtotheabovereactions.However,oneshouldnotdescribe如果消除痕量的水，BF3單獨不會引發(fā)聚合反應(yīng)。對于上述反應(yīng)，水或乙醇對于形ononecanalsopreparecopolymersbyionicpolymerization,forexample,anioniccopolymersofstyreneandbutadiene,orcationiccopolymersofisobutyleneandstyrene,orisobutyleneandvinyethers,etc.與自由基聚合反應(yīng)一樣，通過離子聚合反應(yīng)也能制備共聚物，例如，苯乙烯-丁二等。Ashasbeendescribedindetailwithradicalpolymerization,onecancharacterizeeachmonomerpairbyso-calledreactivityratiosr1andr2.UNIT5IntroductiontoLivingRadicalPolymerizationTraditionalmethodsoflivingpolymerizationarebasedonionic,coordinationorgrouptransfermechanisms.活性聚合的傳統(tǒng)方法是基于離子，配位或基團轉(zhuǎn)移機理。Ideally,themechanismoflivingpolymerizationinvolvesonlyinitiationandpropagationsteps.理論上活性聚合的機理只包括引發(fā)和增長反應(yīng)步驟。Allchainsareinitiatedatthecommencementofpolymerizationandpropagationcontinuesuntilallmonomerisconsumed.Atypeofnoveltechniquesforlivingpolymerization,knownasliving(possiblyuse“controlled”or“mediated”)radicalpolymerization,isdevelopedrecently.最近開發(fā)了一種叫做活性自由基聚合的活性聚合新技術(shù)。ThefirstdemonstrationoflivingradicalpolymerizationandthecurrentdefinitionoftheprocessescanbeattributedtoSzwarc.Uptonow,severallivingradicalpolymerizationprocesses,includingatomtransferradicalpolymerization(ATRP),reversibleaddition-fragmentationchaintransferpolymerization(RAFT),nitroxide-mediatedpolymerization(NMP),etc.,havebeenreportedoneafteranother.到目前為止，一些活性自由基聚合過程，包括原子轉(zhuǎn)移自由基聚合，可逆加成-斷裂鏈轉(zhuǎn)移聚合，硝基氧介導(dǎo)聚合等聚合過程一個接一個被報道。Themechanismoflivingradicalpolymerizationisquitedifferentnotonlyfromthatofcommonradicalpolymerizationbutalsofromthatoftraditionallivingpolymerization.Itreliesontheintroductionofareagentthatundergoesreversibleterminationwiththepropagatingradicalstherebyconvertingthemtoafollowingdormantform：Thespecificityinthereversibleinitiation-terminationstepisofcriticalimportanceinachievinglivingcharacteristics.這種特殊的可逆引發(fā)-終止反應(yīng)對于獲得分子鏈活性來說具有決定性的重要意義。Thisenablestheactivespeciesconcentrationtobecontrolledandthusallowssuchaconditiontobechosenthatallchainsareabletogrowatasimilarrate(ifnotsimultaneously)throughoutthepolymrization.使得在整個聚合反應(yīng)過程中(只要沒有平行反應(yīng))所有的分子鏈都能夠以相同的速度增Thishas,inturn,enabledthesynthesisofpolymerswithcontrolledcomposition,architectureandmolecularweightdistribution.這樣就可以合成具有可控組成，結(jié)構(gòu)和分子量分布的聚合物。Theyalsoprovideroutestonarrowdispersityend-functionalpolymers,tohighpurityblockcopolymers,andtostarsandothermorecomplexarchitecture.方法。ThefirststeptowardslivingradicalpolymerizationwastakenbyOstuandhisleaguesinIn1985,thiswastakenonestepfurtherwiththedevelopmentbySolomonetal.ofnitroxide-mediatedpolymerization(NMP).Thisworkwasfirstreportedinthepatentliteratureandinconferencepapersbutwasnotwidelyrecognizeduntil1993whenGeorgesetal.appliedthemethodinthesynthesisofnarrowpolydispersitypolystyrene.報道，但是直到1993年Georges等把這種方法應(yīng)用在窄分子量分布聚苯乙烯之后，才得以廣泛認知。ThescopeofNMPhasbeengreatlyexpendedandnew,moreversatile,methodshaveappeared.NMP的領(lǐng)域已經(jīng)得到很大的延展，出現(xiàn)了新的更多樣化的方法。Themostnotablemethodsareatomtransferradicalpolymerization(ATRP)andpolymerizationwithreversibleadditionfragmentation(RAFT).最引人注目的方法是原子轉(zhuǎn)移自由基聚合和可逆加成斷裂聚合。Upto2000,thisareaalreadyaccountedforonethirdofallpapersinthefieldofradicalpolymerization,asshowninFig.5.1.Naturally,therapidgrowthofthenumberofthepapersinthefieldsince1995oughttobealmosttotallyattributabletodevelopmentinthisarea.。ghtanditsDistributionsofPolymersThemolecularweightofapolymerisofprimeimportanceinitssynthesisandapplication.對聚合物的合成和應(yīng)用而言，聚合物的分子量是最重要的。Theinterestingandusefulmechanicalpropertieswhichareuniquelyassociatedwithpolymericmaterialsareaconsequenceoftheirhighmolecularweight.些性能是聚合物的高分子量帶來的。聚合物材料的高分子量帶來了令人感興趣的和具用價值的力學(xué)性能。Mostimportantmechanicalpropertiesdependonandvaryconsiderablywithmolecularweight.最重要的力學(xué)性能取決于分子量，而且隨著分子量變化而發(fā)生很大的變化。Thus,strengthofpolymerdoesnotbegintodevelopuntilaminimummolecularweightofabout5000~10000isachieved.因此,直到最小分于量增大到大約5000~10000以后,聚合物的強度才開始顯示Abovethatsize,thereisarapidincreaseinthemechanicalperformanceofpolymersastheirmolecularweightincreases;theeffectlevelsoffatstillhighermolecularweights.Leveloff…達到平衡，變平緩，趨緩分子量大于這個值的時候，隨著分子量的增加，聚合物的機械性能快速增加;達到更高的分子量的時候，這種效應(yīng)才變平緩。Inmostinstances,thereissomemolecularweightrangeinwhichagivenpolymerpropertywillbeoptimumforaparticularapplication.Thecontrolofmolecularweightisessentialforthepracticalapplicationofapolymerizationprocess.合物的分子量。Whenonespeaksofthemolecularweightofapolymer,onemeanssomethingquitedifferentfromthatwhichappliestosmall-sizedcompounds.當人們談到聚合物分子量的時候，他所指的是和(適用于)低分子化合物的分子量完全不同的另一回事。Polymersdifferfromthesmallsizedcompoundsinthattheyarepolydisperseorheterogeneousinmolecularweight.聚合物與小分子量化合物的不同在于聚合物的分子量是多分散性的或不均勻的。Evenifapolymerissynthesizedfreefromcontaminantsandimpurities,itisstillnotapuresubstanceintheusuallyacceptedsense.仍然Polymers,intheirpurestform,aremixtureofmoleculesofdifferentmolecularweights.最純凈的聚合物是具有不同分子量的分子的混合物。Thereasonforthepolydispersityofpolymersliesinthestatisticalvariationspresentinthepolymerizationprocesses.聚合物多分散性在于聚合過程中展現(xiàn)的統(tǒng)計變化。Whenonediscussesthemolecularweightofapolymer,oneisactuallyinvolvedwithitsaveragemolecularweight.討論聚合物的分子量，準確的含義是平均分子量。Boththeaveragemolecularweightandtheexactdistributionofdifferentmolecularweightswithinapolymerarerequiredinordertofullycharacterizeit.情況。Thecontrolofmolecularweightandmolecularweightdistribution(MWD)isoftenusedtoobtainandimprovecertaindesiredphysicalpropertiesinapolymerproduct.Variousmethodsareavailablefortheexperimentalmeasurementoftheaveragemolecularweightofapolymersample.在聚合物樣品平均分子量的實驗測試中有許多方法可以利用。Theseincludemethodsbasedoncolligativeproperties,lightscattering,viscosity,ultracentrifugation,andsedimentation.這些方法基于依數(shù)性，光散射，粘度法，超速離心分離，沉降法。Thevariousmethodsdonotyieldthesameaveragemolecularweight.不同的方法得到不同的平均分子量。Differentaveragemolecularweightsareobtainedbecausethepropertiesbeingmeasuredarebiaseddifferenttowardthedifferentsizedpolymermoleculesinapolymersample.(對同一聚合物)得到了不同的平均分子量，因為所測得的性質(zhì)對試樣中不同尺寸的聚合物分子有不同的偏差。Somemethodsarebiasedtowardthelargersizedpolymermolecules,whileothermethodsarebiasedtowardthesmallersizedmolecules.一些方法對較大尺寸的聚合物分子有偏差(傾向性)，而另外一些方法則對較小尺寸的聚合物分子有偏差(傾向性)。Theresultisthattheaveragemolecularweightsobtainedarecorrespondinglybiasedtowardthelargerorsmallersizedmolecules.所獲得的平均分子量分別對較大的或較小的分子有(偏差)傾向性。Themostimportantaveragemolecularweightswhicharedeterminedarethenumber-averagemolecularweightMn,theweight-averagemolecularweightMwandtheviscosityaveragemolecularweightMv.。Inadditiontothedifferentaveragemolecularweightsofapolymersample,itisfrequentlydesirableandnecessarytoknowtheexactdistributionofmolecularweights.除聚合物樣品的不同的平均分子量外，經(jīng)常需要知道確切的分子量分布。Avarietyofdifferentfractionationmethodsareusedtodeterminethemolecularweightdistributionofapolymersample.各種各樣的不同的分級方法被用來確定聚合物樣品的分子量分布。Thesearebasedonfractionationofapolymersampleusingproperties,suchassolubilityandpermeability,whichvarywithmolecularweight.子量變化而變化。UNITUNIT7PolymerSolutionDissolvingapolymerisaslowprocessthatoccursintwostages.溶解高分子需要一個緩慢的過程，這個過程分兩步發(fā)生。First,solventmoleculesslowlydiffuseintothepolymertoproduceaswollengel.溶劑分子緩慢地擴散到高分子中產(chǎn)生溶脹凝膠。Thismaybeallthathappensif，forexample，thepolymer-polymerintermolecularforcesarehighbecauseofcrosslinking，crystallinity·orstronghydrogenbonding.例如,如果因交聯(lián)，結(jié)晶和很強的氫鍵而形成很大的分子間力，(聚合物的溶解過程)有可能就只停留在這一階段。Butiftheseforcescanbeovercomebytheintroductionofstrongpolymer-solventinteractions,thesecondstageofsolutioncantakeplace.段就會發(fā)生。Herethegelgraduallydisintegratesintoatruesolution.Onlythisstagecanbemateriallyspeededbyagitation.過攪拌得到明顯促進。Evenso,thesolutionprocesscanbequiteslow(daysorweeks)formaterialsofveryhighmolecularweight.雖然如此，對高分子量的材料而言，溶解過程是相當緩慢的(幾天或幾個星期)。Solubilityrelationsinpolymersystemsaremorecomplexthanthoseamonglowmolecular-weightcompounds,becauseofthesizedifferencesbetweenpolymerandsolventmolecules,theviscosityofthesystem,andtheeffectsofthetextureandmolecularweightofthepolymer.態(tài)結(jié)構(gòu)的影響等原因，高分子體系的溶解性關(guān)系比低分子量化合物要復(fù)雜得多。Inturn，thepresenceorabsenceofsolubilityasconditions(suchasthenatureofthesolvent，orthetemperature)arevariedcangivemuchinformationaboutthepolymer.當條件(溶劑的性質(zhì)或溫度)變化的時候，有無溶解性又可提供出許多關(guān)于這種聚合物的信息。Asspecifiedintheliterature，thearrangementsofthepolymerchaindifferingbyreasonofrotationsaboutsinglebandsaretermedconformations.。tionapolymermoleculeisarandomlycoilingmassmostofwhoseconformationsoccupy[‘okjupai]manytimesthevolumeofitssegmentsalone.大部分構(gòu)象占鏈段分子自身體積的許多倍。Theaveragedensityofsegmentswithinadissolvedpolymermoleculeisof10-4~10-5g/cm3.溶解聚合物分子里的平均鏈段密度是10-4~10-5g/cm3Thesizeofthemolecularcoilisverymuchinfluencedbythepolymer-solventinteractionforces.聚合物-溶劑之間的作用力對分子線團尺寸有很大的影響。Inathermodynamically“good”solvent,wherepolymer-solventcontactsarehighlyfavored,thecoilsarerelativelyextended.在熱力學(xué)上的好溶劑中，聚合物-溶劑作用較強，線團是相對伸展的。Inapoor”solventtheyarerelativelycontracted.而在不良溶劑中，線團則是相對收縮的。Itisthepurposetodescribetheconformationalpropertiesofbothidealandrealpolymerchains.使用上述方法的目的是描述理想的和真實的聚合物鏈構(gòu)象。Theimportanceoftherandom-coilnatureofthedissolved,molten,amorphous,andglassystatesofhighpolymerscannotbeoveremphasized.Manyimportantphysicalaswellasthermodynamicpropertiesofhighpolymersresultfromthischaracteristicstructuralfeature.高分子的許多重要的物理及熱力學(xué)性質(zhì)都是這個結(jié)構(gòu)特征引起的。Therandomcoil(Fig.7.1)arisesfromtherelativefreedomofrotationassociatedwiththechainbondsofmostpolymersandtheformidablylargenumberofconformationsaccessibletothemolecule.無規(guī)線團(圖7.1)一方面是由于聚合物鏈上的鍵自由旋轉(zhuǎn)而產(chǎn)生的，另一方面是由于(聚合物)分子(鏈)可達到巨大的構(gòu)象數(shù)而產(chǎn)生的。Fig.Tab.Oneoftheseconformations,thefullyextendedchainhasspecialinterestbecauseitslength,thecontourlengthofthechain,canbecalculatedinastraightforwardway.長度可以直接地計算出來。Inallothercasesthesizeoftherandomcoilmustbeexpressedintermsofstatisticalparameterssuchastheroot-mean-squaredistancebetweenitsends,(r2)1/2,oritsradiusofgyration,theroot-mean-squaredistanceoftheelementsofthechainfromitscenterofgravity,(s2)1/2.在所有其他的場合，無規(guī)線團的尺寸必須用統(tǒng)計參數(shù)來表示，如鏈末端之間距離的均方根，(r2)1/2或回旋半徑，從分子重心(質(zhì)心)到鏈節(jié)距離的均方根(s2)1/2Forlinearpolymersthatarenotappreciablyextendedbeyondtheirmostprobableshape,themean-squareend-to-enddistanceandthesquareoftheradiusofgyrationaresimplyrel