54高分子化学课件

4MolecularweightsandSizes高分子的分子量与尺寸PolymerPhysics高分子物理4.1Molecularweightsandmolecularweightdistribution分子量与分子量分布Characteristicsofpolymermolecularweights高分子的分子量的特点•Themolecularweightsareveryhigh,rangingfromabout10,000to1,000,000g/molorhigher.•Themolecularweightofordinarysizemoleculesisfixed(e.g.,benzenehasamolecularweightof78g/molregardlessofitssource).Mostpolymermolecularweights,ontheotherhand,varygreatlydependingonthemethodofpreparation.•Mostpolymersarepolydisperse;thatis,thesamplecontainsmorethanonespecies.•分子量分布是聚合物最基本的结构参数之一，它对于高分子材料加工条件的控制均有重要意义：•①高分子材料加工条件的控制•②高分子材料使用性质•③聚合反应机理•④溶液性质分子量达到一定值后（临界分子量）高分子材料才具有机械强度极性聚合物临界聚合度40非极性聚合物临界聚合度80StrengthMolecularWeightPolarNonpolar分子量过高(DP600~700)，强度达到极限，但熔体粘度过大，加工困难塑料与橡胶分子量分布宜适当放宽，以提高加工性能；大分子量组分提高强度，小分子量组分起增塑作用纤维分子量分布宜窄Averagemolecularweight平均分子量MolecularweightM1M2…MiNumberN1N2…NiWeightforeachchainm1m2…miiiiMNmiiiiiiiinMxnMnMNumberaveragemolecularweightWeightaveragemolecularweightiiiiiiiiwMwmMmMApolymerconsistsofamixtureofthreemono-dispersepolymerswithmolarmasses250000,300000and350000g/molintheratio1:2:1bynumberofchains.molarmass:250000300000350000number:N2N1N(∑Ni=4N)No.fraction:¼½¼weight:2.5X105N3X105NX23.5X105N(∑mi=12X105N)Wt.fraction:2.5/12½3.5/12Mn=(1/4*2.5X105+1/2*3X105+1/4*3.5X105)=3X105Mw=(2.5/12*2.5X105+1/2*3X105+3.5/12*3.5X105)=3.042X105Z-averagemolecularweightViscosity-averagemolecularweightiiiiiiiiiiiizMwMwMNMNM223aiiiiaiivMNMNM/11Schematicofasimplemolecularweightdistribution,showingthevariousaveragesMzMwMvMnMolecularweightdistribution分子量分布1222nwnnnnMMMMM1222wzNumber-averagedistributionwidthWeight-averagedistributionwidthPolydispersity高分子分子量的多分散性wznwMMMMPolydispersityindexMethodPolydispersityStereospecificityNaturalProteins1.0PerfectAnionicPolymerization1.02-1.5NoneFreeRadicalPolymerization1.5-3NoneStepPolymerization2.0-4NoneZiegler-NattaPolymerization2-40HighCationicPolymerizationBroadNone•离散型分子量分布只含有限个级分，可粗略地描述各级分的含量和分子量的关系。•分子量分布的连续函数表示微分分布曲线：重量微分分布曲线数量微分分布曲线M或或M)(MN)(MN)(MW)(MW1M2M1M2M•积分分布曲线：MM数量积分分布曲线重量积分分布曲线1)()()()(00dMMWMIdMMWMIM1)()()()(00dMMNMIdMMNMIM)(MI)(MI聚合物的分子量分布函数聚合物的分子量分布用某些函数表示模型分布函数理论或机理分布函数假设一个反应机理，推出分布函数，实验结果与理论一致，则机理正确。不论反应机理如何，实验结果与某函数吻合，即可以此函数来描述分子量分布。Schulz-Flory最可几分布Schulz分布Poisson分布（1）理论分布（2）模型分布Gaussian分布Wesslau对数正态分布Schulz-Zimm分布函数Tung分布函数聚合物的分子量及分子量分布对其使用性能和加工性能都有很大影响。线形缩聚物的Flory分布（Flory应用统计方法、根据官能团等活性概念而推导出来）•x聚体的数量分布函数为：•x聚体的重量分布函数为：)1(10PPNNxx21)1(PxPWxxnxNNNNNNNP111110000Pxn11•由Flory分布函数可以推导出平均分子量Pxn11PMMn10PPxw11PPMMw11022141PPPxz220141PPPMMzPMMdnw1•尼龙66经实验分级后，由实验测得的分子量分布求出，等，与上述理论推导结果颇为接近，许多逐步聚合物的接近2，证明了理论的正确性•但要用以上Flory分布的前提是：官能团的活性与分子的大小无关，即等活性理论。wxnxnwMMdB加聚反应中用schulz分布：•歧化终止时：•偶合终止时：21)1(PxPWxx312)1(21PPxWxx聚合物分子量的测定方法化学方法Chemicalmethod端基分析法Endgroupanalysis,orendgroupmeasurement热力学方法Thermodynamicsmethod佛点升高，冰点降低，蒸汽压下降，渗透压法Osmoticmethod光学方法Opticalmethod粘度法Viscosimetry，超速离心沉淀Ultracentrifugalsedimentationmethod及扩散法Diffusion其它方法Othermethod电子显微镜Electronmicroscope，凝胶渗透色谱法Gelpermeationchromatography(GPC)动力学方法Dynamicmethod光散射法Lightscatteringmethod4.2Determinationofthenumber-averagemolecularweight数均分子量的测定End-groupanalyses端基分析•Manytypesofsynthesesleaveaspecialgroupononeorbothendsofthemolecule,suchashydroxylandcarboxyl.Thesecanbetitratedoranalyzedinstrumentallybysuchmethodsasinfrared.niiiiiiiiiMNMNNWNWMH2N(CH2)5CO[NH(CH2)5CO]nNH(CH2)5COOH•Formolecularweightsaboveabout25,000g/mol,themethodbecomesinsensitivebecausetheendgroupsarepresentintoolowaconcentration•Molecularweightdeterminedbyend-groupanalysesisnumber-averagemolecularweightColligativemethods依数性方法•Thecolligativepropertiesinclude:–Boilingpointelevation–Meltingpointdepression–Vaporpressurelowering–Osmoticpressure....122cAMHRTcTvbEbulliometry沸点升高法BoilingpointelevationSolventdensityLatentheatsofvaporizationpergramofsolventSoluteconcentrationingramspercubiccentimeterGasconstantTemperatureBoilingpointelevationMKMHRTcTvbc1lim200cbcTKMniiiiiiiiiiiiicbMKcMNNKccMcKcMcKT0证明：沸点升高法测定的是数均分子量nffcMHRTcT1lim20Cryoscopicmethod冰点降低法FreezingpointdepressionSolventdensityLatentheatsoffusionpergramofsolventSoluteconcentrationingramspercubiccentimeterGasconstantTemperatureMeltingpointdepression201101XPPPVapor-phaseosmometry(VPO)气相渗透压法VaporpressureofthepuresolventMolefractionofthesoluteVaporpressureofthesolutionVaporpressurelowering...12cAMKcT0ccTKMSchematicofvapor-phaseosmometersolventsolventsolutionTnMMembraneosmometry膜渗透压法OsmoticpressurencMRTc0limSchematicillustrationofanosmometer...1232cAcAMRTcSchematicillustrationofthedependenceofosmoticpressureonconcentration2122/102/1cccc2=MnA2膜的选择•使聚合物分子不能透过•溶剂分子透过速率较大•不与聚合物和溶剂发生化学作用(不适合未分级的含有大量低分子的聚合物)若部分聚合物分子透过半透膜，所测分子量偏高还是偏低？Comparisonofcolligativemethods依数性方法的比较PropertyValueVaporpressurelowering4103mmHgBoilingpointelevation1.3103℃Freezingpointdepression2.5103℃Osmoticpressure15cmso