高分子化学浙江大学polymer2-3Measurementofratecoefficients课件

18.Measurementofratecoefficients2HistoryUptothelate1980sterminationandpropagationratecoefficientswereaccessibleonlyintheircoupledform,kp/kt0.5orindividuallyviacombinationwithpseudoflickeringtechniquesliketherotatingsectororspatiallyintermittentpolymerizationmethodsincombinationwithstationarypolymerizationmeasurements.Thesituationhasdramaticallyimprovedwiththeinventionofthepulsedlaserpolymerization(PLP)techniqueinthelate1980s.Sincethen,thistechniquehasbeenextensivelyusedtocollatepropagationandterminationratecoefficientsforvarioushomo-andcopolymerizations.38.1MethodsfortheMeasurementofkdRd=fkd[I]Theconcentrationcanbemeasuredviaanyquantitytowhichitisdirectlyproportional,suchasaspectroscopicinfrared(红外光谱)absorptionthatcanbeeasilyfollowedwithreactiontime.

Infraredspectroscopyhasbeenusedextensivelyinthepasttostudythedecayoforganicperoxidesinvariousreactionmedia.568.2MethodsfortheMeasurementofkpElectronSpinResonanceSpectroscopy-StationaryPolymerization(ESR)(电子自旋共振)78.2MethodsfortheMeasurementofkpQuenchedInstationaryPolymerizationSystems(QUIPS)Aphotopolymerizablemixturepassesthroughacapillarysystem,isirradiatedataspecificlocation,andpolymerizesinthecapillaryduringawell-defineddarkperioduntilitdropsintoaquenchingbathwithaninhibitor(nitroxylradicals).Measuringthechainlengthdistributionbysize-exclusionchromatographythatallowsdeterminationofkpinaccordancewiththeequation.L=kp[M]t098.4MethodsfortheMeasurementofktSinglePulse–PulsedLaserPolymerization(SP-PLP)10Applyingpulsedlaser-polymerization(PLP)inconjunctionwithinfraredornear-infraredspectroscopicmeasurementofmonomerconversioninducedbyasinglelaserpulse(SP-PLP)allowsforthedeterminationoftheratioofterminationtopropagationratecoefficients,kt/kp,inwiderangesoftemperature;pressure;andmonomerconversion.118.5DeterminingtheModeofTermination:

DisproportionationversusCombinationIdentificationandquantificationofchainendsarenotsimpleastheygiveonlysmallsignals(relativetotherestofthepolymerchain)inaspectroscopicanalysis.Thiscanbeovercometosomeextentbyisotopiclabelingoftheinitiatorendgroupsby14CorbyusinginitiatorfragmentscontainingfluorineorphosphorusasNMR-sensitivemolecules.Theapplicationofthematrix-assistedlaserdesorptionionizationtime-of-flightmassspectroscopy(MALDI-TOF-MS)totheproblemofend-groupanalysisofpolymersbroughtsomepromisingresultstothisfieldofpolymerizationkinetics.1314Someratecoefficients

159.MolecularWeightDistribution

分子量分布179.1.DistributionfordisproportionationorchaintransferConsideronlychainswhosegrowthisterminatedbyeitherdisproportionationorchaintransfer.Notethatinboththecases,thenumberofchainsproducedisequaltothenumberofchainterminated.18Letp=probabilityofaddingamonomertoagrowchain.apolymerchainwiththelengthnisformedbyn-1

propagationstepsandonechainstopping(terminationortransfer)eventofprobability(1-p).Sotheprobabilityoffindingachainoflengthnis:numberofchainsofsizentotalnumberofchainsInstantaneousnumber-fractiondistributionnumber-fractiondistribution19weight-fractiondistribution

weightofchainsoflengthn:Wn=mnNnweightofallchains:W=mN0InitialnumberofmonomersMWofmonomerSinceoneterminationresultsinonechain,so21Averagemolecularweightaccordingtodefinition:22Averagemolecularweightaccordingtocalculation:polydispersityindex(多分散性指数),PDI23Thereare(n-1)differentwaystoformachainoflengthnfromthecombinationoftwochains,so9.2.DistributionforCombinationConsiderachainoflengthnformedbycombiningmmonomerswith(n-m)monomers.Forchainoflengthm,hereare(m-1)additionstepsand1terminationForchainoflength(n-m),hereare(n-m-1)additionstepsand1terminationProbabilityoffindingachainoflengthnis:25Molecularweightdistributioncurve26ComparisonAveragemolecularweight

DisproportionationvsCombination29ThermodynamicsPolymerizationpossibilityIsthemonomerpolymerizable?PolymerizationequilibriumPolymerizationordepolymerization?30G<0frommonomertopolymerG>0frompolymertomonomerG=0equilibriumbetweenmonomerandpolymer31enthalpycontributionHentropycontributionSSisalwaysnegative,reflectingthelossofdegreesoffreedomofthemonomerbecomingapartofthepolymerchain.Sisaround-105~-125J/(mol*K)forpolymerizationfromR.T.to100oC,-TSisaround30~42KJ

allchainpolymerizationsareexothermic.

mostfree-radicalpolymerizationsarenegativewithtypicalvaluesrangingfrom30to80kJ/mol.

PolymerizationismainlydeterminedbyH32PolymerizationheatStericeffect:-H

Resonanceeffect:-H

Styrene(69.9)butadiene(72.8)acrylonitrile(72.4)

negativesubstitute:-H

vinylchloride(95.8)vinylidenefluoride(129.7)tetrafluoroethylene(154.8)

Hbond&solvent:-H

acrylicacid(66.9)methacrylicacid(42.3)

-33monomer -H

(kJ/mol) -S

(J/mol.K)ethylene 95.0 100.4propylene 85.8 116.3butylene-1 79.5 112.1isobutylene 51.5 119.7isoprene 72.8 85.8butadiene 73 89.0styrene 69.9 104.6-methylstyrene 35.1 103.8tetrafluroethylene 155.6 112.1vinylchloride 95.6 -methlymethacrylate 56.5 117.2acrylicacid 66.9acrylamide 82.0DataofHandS

forsomemonomers(25C)34CeilingTemperature(聚合上限温度)[M]=1.03536Forexample:

ΔH°ΔS° [M]at70oC

kJ/mol

J/(molK)MMA 56 118 4.36×10-3Styrene 73 104 2.09×10-6-Methylstyrene 45 148 7.60equil.monomerconcentrationequilibriummonomerconcentration3711.Controlled/LivingRadicalPolymerization38DisadvantagesoftraditionradicalPolymerizationSlowandcontinuousinitiationpreventssynthesisofwell-definedpolymerswithdegreesofpolymerizationpredeterminedbytheratioofconcentrationsoftheconvertedmonomertotheintroducedinitiator,withcontrolledtopologies(stars,combs)andcompositions(blocks,grafts,gradients).Thetypicallifetimeofapropagatingchainisveryshort,intherangeof1s.Molecularweightdistributionisbroad.Poorcontrolontheregio-andstereoselectivity39FeaturesofLivingPolymerizationNoterminationreaction!Linearkineticplotinsemilogarithmiccoordinates(ln([M]0/[M])vs.time),ifthereactionisfirst-orderwithrespecttothemonomerconcentration.LinearevolutionofMWwithconversion.MWispredictedby[M]/[I]0Polydispersity(Mw/Mn)shouldbeclosetounityEnd-functionalityofpolymerchainBlockpolymercanbepreparedbycontinuouspolymerizationofsecondmonomer40Controlled/LivingRadicalPolymerization41NitroxideMediatedPolymerization(NMP)Inthismechanism,thedormantchainisdissociatedintopolymerradicalP·andcappingradicalX·,whereX·isassumedtobestableenoughtoundergonoreactionotherthanthecombinationwithP·42Ni