Stereospecificity in the polymerization of acrylonitrile using anionic initiators including dialkylmagnesium

Abstract

An attempt was made to synthesize stereoregular polyacrylonitrile (PAN) by anionic polymerization. Dialkylmagnesium was found to be the most effective as an initiator for this purpose when used in aromatic hydrocarbons. The triad tacticities (i.e., the content of mm, mr, and rr (m, meso; r, racemo)) of the polymers obtained was analyzed by 13C NMR and their viscosity-average molecular weight, Mv, was determined by viscometry in dimethyl sulfoxide at 25ŶC using Kamide et al.舗s Mark-Houwink-Sakurada equation. When the polymerization temperature Tp was in the range of 蜢78舑40ŶC, only atactic PAN was obtained although mm content slowly increased with Tp. In the range of Tp=40舑110ŶC, the meso-selectivity of propagation reaction increased remarkably with Tp, yielding isotactic polymer with mm content of 0.50ŷ0.02. The molecular weight, Mv, increased, after passing through a minimum at about 40ŶC, with Tp approaching to an assymptotic value at 120ŶC. Analysis of the pentad tacticity of isotactic PAN by anionic polymerization method revealed that their sequence distribution can be simply represented by neither Bernoulli nor 1st-order Markov statistics. This sharply contrasts with the results by Kamide et al. previously obtained for PAN by े-ray irradiation on urea canal complex at 蜢78ŶC [Polym. J., 17, 1291 (1985)]. © 1992, The Society of Polymer Science, Japan. All rights reserved.