| 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°C. 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 rs=0.33 rA=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. Chains of which the lengths obey the Poisson distribution are produced by this effective model according to the changing probabilities which are calculated by the instant concentration of monomers. Through recording the number of reacted monomers and calculating the number of left ones, instant probabilities are got when the reactivity ratios and the initiator selectivity to monomers are considered.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 characterize the gradient structure of the copolymers, we define a parameter, I, which is called gradient index. I is the ratio of ((FAAA)g/(FA)g)/( (FAAA)m/(FA)m) or ((FBBB)G/(FB)G)/ ( (FBBB)M/(FB)M). (Fa)G, (FAAA)G, (FB)G and (FBBB)G for gradient copolymer chains. Similar notation, (FA)M, (FAAA)M, (FB)M and (FBBB)M was employed for the steady Markov chains which...
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