Acrylonitrile copolymerization. Sequence distribution in acrylonitrile‐styrene copolymers by ¹³C NMR: Conversion and solvent effects

Abstract

Abstract Copolymers of acrylonitrile (A) and styrene (S) were synthetized in either N , N ‐dimethylformamide (DMF) or toluene by free radical polymerization. Their sequence distribution was studied by 13 C NMR at 25, 2 MHz. The observed sequence distributions follow first order Markov statistics and may be calculated using the set of reactivity ratios r A = 0,13 and r s = 0,36 (DMF) or 0,40 (toluene) provided the copolymers remain soluble during polymerization. The reactivity ratios were calculated graphically from the experimental triad distributions observed by 13 C NMR using the method of Chiang et al. Deviations from first order Markov statistics were observed for heterogeneous polymerizations or for acrylonitrile rich initial monomer mixtures in DMF. No influence of steric hindrance on the cotacticity of the copolymer chain was noticed within the resolving power of our instrument.