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在ATRP中梯度共聚物的链段分布与分子量分布的表征.docx

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在ATRP中梯度共聚物的链段分布与分子量分布的表征 Introduction Atomtransferradicalpolymerization(ATRP)isaversatiletechniquetosynthesizeblockcopolymersandgradientcopolymerswithprecisecontrolovermolecularweightandcomposition.ATRPhasbeenwidelyusedtopreparegradientcopolymerswithvaryingmonomercompositionsandchainsegmentsdistributions.Inthispaper,wewillfocusonthecharacterizationofthechainsegmentdistributionsandmolecularweightdistributionsofgradientcopolymerssynthesizedbyATRP. ChainSegmentDistributionCharacterization GradientcopolymerssynthesizedbyATRPconsistofamixtureofmonomerunitswithdifferentreactivities.Asthepolymerizationproceeds,thecompositionofthepolymerchainchangesfromoneendtotheother,resultinginagradientofmonomerunits.Thechainsegmentdistributionofagradientcopolymeristhedistributionofmonomerunitsalongthepolymerchain.Accuratedeterminationofthechainsegmentdistributionisessentialtoevaluatethepropertiesofgradientcopolymers. Severalmethodshavebeendevelopedtocharacterizethechainsegmentdistributionofgradientcopolymers.OnemethodistouseNMRspectroscopy.^1HNMRspectroscopycanbeusedtodistinguishdifferentmonomerunitsinthecopolymerchainbasedontheirchemicalshift.Byanalyzingthepeakintensitiesofdifferentmonomerunits,thechainsegmentdistributionofthegradientcopolymercanbeobtained.However,theaccuracyofthismethoddependsontheresolutionoftheNMRspectraandthesignal-to-noiseratio. Anothermethodistousesizeexclusionchromatography(SEC)coupledwithmulti-anglelightscattering(MALS)andrefractiveindex(RI)detectors.SECseparatespolymersbasedontheirhydrodynamicsize,andMALSmeasurestheabsolutemolecularweightandsizeofpolymersinsolution.RIdetectorsareusedtomeasuretheconcentrationofpolymerinsolution.Bycombiningthesetechniques,thechainsegmentdistributionofthegradientcopolymercanbeobtained,aswellasthemolecularweightdistribution. MolecularWeightDistributionCharacterization Themolecularweightdistribution(MWD)ofagradientcopolymersynthesizedbyATRPcanbeaffectedbyseveralfactors,suchasthefeedratioofthemonomers,thereactionconditions,andthech