高分子链的结构

高分子材料加工技术

专业英语高分子物理

高分子链的结构高分子的链结构1ChainStructureofPolymer1.1高分子结构的特点和分类Characteristicandclassificationofpolymerstructure1.1.1高分子的结构特点Characteristicsofpolymerstructure

Polymeriscomposedofmanystructuralunitslinkedbychemicalbonds.(聚合物由许多结构单元通过化学键连接而构成。)

Themolecularweightofpolymerisveryhighandhaspolydispersity.(聚合物的分子量很大并具有多分散性。)

Themainchainsofpolymercanrotate,leadingtoflexibilityofpolymerchains.Duetothermalmotion,theshape(conformation)ofpolymerchainschangewithtime.(聚合物主链上的化学键可以旋转，是聚合物链柔性的来源。同时，由于热运动，聚合物链的形状(构象)会随时间发生变化。)

TheVanderwallsforceamongstructuralunitsisveryimportant.(聚合物分子链间的范德华作用力非常重要！)

Crosslinkingmaygreatlychangepropertiesofpolymers.(交联可以明显地改变聚合物的性能。)

Theaggregatestateofpolymermaybecrystallineoramorphous.Theorderofpolymerincrystallinestateissmallerthanthatofsmallmolecules，buttheorderinamorphousstateishigherthanthatofsmallmolecules.(聚合物的聚集态结构可以是结晶态或无定型态。聚合物结晶态的有序度比小分子晶体要低，但无定形高分子的有序度要比非晶小分子要高。)1.1.2高分子的结构层次链结构高次结构(织态结构)聚集态结构(三次结构)近程结构(一次结构)远程结构(二次结构)chemicalcompositionregioisomerismstereoisomerismbranching&crosslinkingbondingsequenceincopolymersize(molecularweightanddistribution)conformation(flexibilityandrigidity)crystallinestateliquidcrystallineamorphousstateorientationstate高分子结构ConfigurationclassificationofpolymerstructureShortrange

structureLongrangestructureChainstructureAggregatestructuretexturalstructuretexturalstructureShortrangestructurestructuralunitsorlocalchainsegmentsareinvolvedLongrangestructureentiresinglepolymerchainsareinvolvedAggregatestructurelotsofpolymerchainsareinvolvedHowaboutdoublehelixstructureofDNA?Polymerstructuresatdifferentlevelsaredifferentbutcorrelated!!!Polymerstructureisthesumofstructuresatdifferentlevels,whichcontributetoapparentpolymerproperties.stereo-regularitystructureofmonomersequenceofcomonomermolecularweightcrystallizability;etc.conformation;liquidcrystal;etc.phaseseparation;crystallizability;etc.miscibility;meltingtemp.;etc.(低次结构决定高次结构！）Regulationandimprovementofpolymerpropertiescanbeapproachedbychangeofpolymerstructuresatdifferentlevels.

synthesis：

processing：

blending：shortrangestructureandlongrangestructurelongrangestructureandaggregatestructuretexturalstructure1.2高分子链的近程结构Short-rangestructureofpolymerchain1.2.1结构单元的化学组成

CompositionofstructuralunitStructuralunitMainchainSidechaingrouporsubstituente.g.poly(vinylchloride)-

PVCPolymerizationdegree1.2.2分子构造单链SinglechainMoleculararchitecture梯型聚合物LadderchainCarbonfiberFeaturesofladderpolymers:excellentthermalstability.Whensinglechaininaladderringisbrokenuponheating,themolecularweightofthepolymerisunaffected.BranchingEffectsonpolymerproperties:crystallinity,flexibility,hardness,density,meltingtemperature,etc.

shortbranches—regularity,crystallinity,

density,meltingtemperature

longbranches—dissolvingpropertyandrheologyinthemeltInfluenceofgraftingandcrosslinkingonthepropertiesofpolyethyleneTypePropertiesHDPELDPEXPECrystallinity,%9560~70Density,g/ml0.95~0.970.91~0.940.93~1.40Meltingpoint,

C135105Workingtemperature,

C12080~100100~135TensileStrength,MPa20~4010~2010~100Elongation,%50~40050~80050~600XPE:交联聚乙烯Crosslinkingpolymers:un-dissolvable,un-meltablestrength,thermalstabilityThermosetresinandvulcanizedrubberarecrosslinkingpolymermaterials.交联crosslinkingVulcanizationofrubberCureofthermosetplasticsCrosslinkingofsaturatedpolyolefins:

radicalattack(forexample：irradiationcrosslinking)1.2.3键接异构BondorderisomerRegio-selectivityofstructuralunitsinpolymerization

vinylmonomers(CH2=CHR)

head-headtail-tailhead-tailaffectingcrystallizability,mechanicalpropertiesandthermalstability头尾头头+ZnZnCl286%Head-tailstructureisthemajorityinpolymersofvinylmonomers.Head-to-tailHead-to-headHead-headandtail-tailstructuresleadingtomorehydroxylleft,thustheabilityofwaterabsorptionincreasesandstrengthisreduced.Dienemonomers？Howtodetermineregio-regularity?NMR,IR,chemicalreaction,Pyro-GC,etc.1.2.4立体异构Stereoisomerism旋光异构OpticalisomerismAfterpolymerization,achiralcarbonatomisproducedforvinylmonomers,thustherearetwoopticalisomers.(Forsinglepolymerchain,theopticalactivityisveryweakduetothesmalldifferencebetweenthetwolongchaingroup.)Howtoprepareapolymerwithopticalactivity?三种类型Isotactic全同立构Atactic无规立构Syndiotactic间同立构Polymerchainsarecomposedofsingleopticalisomers.uniformandcrystallizable.Polymerchainsarecomposedoftwoalternativeopticalisomers,uniformandcrystallizable.Polymerchainsarerandomlycomposedoftwoopticalisomers.Theformertwoarestereo-regularPP,andthelastoneisstereo-irregularPP.non-uniformand

usuallynon-crystallizableStereo-configurationaffectspolymerpropertiesPS：

isotacticPS：crystallizable，Tm=240C

，uneasytodissolve

atacticPS：softtemperature80C

，solubleinbenzenePP：

isotacticPP：Tm=175C

，highstrength,usedasfiberandengineeringplastic

atacticPP：soft,additiveforpavingasphaltIsstereoregularitythenecessaryconditionforpolymercrystallization?Undermostcasesitis,butsomeexceptions:poly(fluoroethylene)poly(vinylalcohol)poly(trichlorofluoroethylene)similarsizesofFandHstrongHbondClisslightlylargerthanF，ButstrongrepulsionbetweenFatoms.几何(顺反)异构Geometrical(cis-/trans-)isomerismFor1,4-additionofdienemonomerscis-1,4-butadiene,rubbertrans-1,4-butadiene,crystalline,plastics天然橡胶Naturalrubber杜仲胶Gutta-percha

Stereo-isomerismandregio-isomerismmayoccursimultaneously!1.2.5共聚物的序列结构Sequencestructureofcopolymerscopolymerizationcanimprovesomespecificpropertiesofpolymers

PMMA:

poorflowbehaviorandnotsuitableforinjection-molding(strongintermolecularinteraction).

MMA+Scopolymer:

improvedflowbehavior,suitableforinjectionmolding

S+ANcopolymer:

impactresistance,thermalstabilityandchemicalresistanceareimproved(canbeusedasoil-resistantparts).

无规共聚物(randomcopolymer)Twoormoremonomerunitsdistributealongthepolymerchainrandomly

ABAABABBAAABABBAAA

Poly(A-co-B)Theinteractionamongstructuralunitsandtheintermolecularinteractionarealtered.Thesolutionproperties,crystallizabilityandmechanicalpropertiesofthecopolymeraredifferentfromthecorrespondinghomopolymers.Forexample:PEandPP

areplastics,butEPrandomcopolymerisrubber.PTFE(聚四氟乙烯)isaplastics.Moltenprocessingisimpossible,butcopolymerof

tetrafluoroethyleneandhexafluoropropyleneisathermoplastic.嵌段共聚(blockcopolymer)

AAAAAAAAABBBBBBBBB

polyA-b-polyBorpoly(A-b-B)

SBS:poly(styrene-b-butadiene-b-styrene)preparedbylivinganionicpolymerizationHardHardSoftSBS：thermoplasticelastomer

hightemp:canflowandcanbeprocessedbyinjectionmolding.lowtemp:likecrosslinkingrubber(PSchainsatbothendsareglassy,“physical”crosslinking).PSPBQuestion:IsBSBblockcopolymerathermoplasticelastomer?接枝共聚

(graftcopolymer)polyA-g-polyB

(注意顺序：主链在前，侧链在后)ABS(acrylonitrile-butadiene-styrene):

ternarycopolymerpreparedbycombinationofrandomcopolymerizationandgraftingpolymerization.

StructureP(BS)-g-P(SA)orP(AB)-g-PSorP(SA)-g-P(AB)-CH2-CH=CH-CH2-

Rubber-likeelasticity.HighimpactresistanceGoodformabilityChemicalresistance,hightensilestrengthandhardness交替共聚物(alternatingcopolymer)

ABABABAB

Anexample:Styrene-maleicanhydridealternatingcopolymer

Poly(A-alt-B)shortrangestructurestructureofunitcarbonchainpolymerheterochainpolymerelementaryorganic

polymerinorganicpolymermoleculararchitecturesinglechainladderchainbranchingcrosslinkingbondorderisomerismvinylmonomer：H-T;H-H;T-Tdienemonomer：1,2;1,4;3,4stereo-isomerismvinylmonomer：opticalisomerism

(isotactic,syndiotactic,atactic)dienemonomer：geometricisomersequenceofcopolymerrandomcopolymerblockcopolymergraftingcopolymeralternatingcopolymerconfiguration1.3高分子链的远程结构Long-rangestructureofpolymerchain1.3.1分子量MolecularWeightSmallmolecule：definitemolecularweightforaspecificsubstancePolymer：distributionofmolecularweight(polydispersity)Forthedetails,seeChapter4OnlywhenMWreachesacertainvalue(criticalMW),polymermaterialsexhibitusefulmechanicalstrength.polarpolymer:DPcri

40non-polarpolymer:DPcri

80StrengthMolecularWeightPolarNonpolarWhenMWisveryhigh(DP>600~700),strengthreachesalimit,butmeltviscosityistoohightoprocess.Plasticsandrubber:broadMWdistribution(highMWpartscontributetostrength,lowMWpartsimproveprocessability.)Fiber:narrowMWdistribution1.3.2内旋转构象ConformationalStaterotationofC－CsinglebondchangeofconformationlargerpolymerizationdegreeTEMofbacteria’sDNATherepeatingunitsinthemainchainareconnectedbycovalentbonds⇒noindependentmotionforsingleunit⇒polymerchainsare

poorinentropy.flexibility链段Chainsegment

consistinginmanyunits,whichcanmoveindependently.considerableconformationDuetopresenceofHandothersubstituents,energybarriermustbeovercomeforrotationofsinglebond.largerdistancesmallerrepulsionlowerenergystability:trans>gauche>cistg-g+cistrans正丁烷或聚乙烯内旋转位能图gaucheForlinearPEchain,theenergylevelofall-transconformationisthelowestT=0K:planarzig-zagconformationT>0K:gaucheconformationsappearduetothermalmotion

Forawith10,000bonds,Thenumberofarrangements310,000=104,7711.3.3分子链的柔顺性

ChainFlexibilityStaticflexibility(静态柔顺性)

flexibilityofpolymerchainatthermodynamicequilibrium

determinedbythedifferenceinthepotentialenergyof

transandgaucheconformation(

)<kT largeamountofgaucheconformation,andtheshapeofpolymerchainisrandomcoils(无规线团)

kT

transconformationisthemajority(thewholepolymerchainisflexible,butlocalisrigid.) >>kT Thepolymerchainisrigid.Dynamicflexibility(动态柔顺性)

thetransition

ratebetweendifferentconformationsdeterminedbytheenergybarrierbetweendifferentconformations(

E)

p:timefortransitionfromtranstogaucheconformationE<<kTtransitionfromtranstogaucheconformationcanbecompletedin10

11s.smallp

:gooddynamicflexibilitylargep

:poordynamicflexibilityTemperatureForceSolventExternalFacto