Characterization On Molecular Weight Distribution And Chain Segment Distribution Of Gradient Copolymer Via Atom Transfer Radical Copolymer

The copolymers of styrene(St)and methyl acrylonitrile(AN)were prepared using atom transfer radical polymerization(ATRP)catalyzed by CuBr/2,2'-bipyridine(bpy) in bulk at 90℃.Plots of Mn vs monomer conversion were linear,and the value of copolymer polydispersities was low.The results show that copolymerization was "living".Reactivity ratios r_S=0.33 r_A=0.03 were obtained by ¹H-NMR spectra.It turned out that the gradient copolymers be obtained due to the difference of reactivity ratios of the two monomers.The distortionless enhancement by polarization transfer(DEPT)technique for the generation of CH ¹³C-NMR was used to analyze the sequence structure of gradient copolymers at various conversions.The triad concentrations were obtained by the spectra.A dynamic Monte Carlo simulation program is developed to get the results about sequence structure.When getting rid of the nominal structure related to dormancy in the chain,the remained chain corresponds to an average molecular chain.The results indicate that the existence of the dormancy affects neither the instant composition nor the instant sequence distributions of products.Both are identical with that of conventional copolymerization.Especially,theoretical conclusion has got to prove the dormant state can't change segment length distribution or accumulated composition. It contributes the solution of MWD.According to the model above,we use paramount from the polymerization experient to research the conversion and reactivity ratios affection on the segment length distribution and average segment length and their relations.Statistic is carried on under certain conversions,so segment length distribution, average composition in polymers and various of triads are available and relations between the given parameters(reactivity ratios,initiator selectivity to monomers and initial feed composition,etc.)and the concentration of triads are achieved.Other results show that the segment length distribution is a novel one different from Flory distribution. In order to obtain the function of MWD,we define a parameter,l,which is the number of section in one monomer,and define a parameter,μ,which is the expected value of the section number in one molecula.Though l andμto work out MWD,the solution has been simplified.The result can also explain some important characterization of CRP.This work gives great supports on the CRP dynamic research.