STEREOSPECIFICITY IN THE POLYMERIZATION OF ACRYLONITRILE USING ANIONIC INITIATORS INCLUDING DIALKYLMAGNESIUM

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 C-13 NMR and their viscosity-average molecular weight, M(v)BAR, was determined by viscometry in dimethyl sulfoxide at 25-degrees-C using Kamide et al.'s Mark-Houwink-Sakurada equation. When the polymerization temperature T(p) was in the range of -78-40-degrees-C, only atactic PAN was obtained although mm content slowly increased with T(p). In the range of T(p)=40-110-degrees-C, the meso-selectivity of propagation reaction increased remarkably with T(p), yielding isotactic polymer with mm content of 0.50+/-0.02. The molecular weight, M(v)BAR, increased, after passing through a minimum at about 40-degrees-C, with T(p) approaching to an assymptotic value at 120-degrees-C. 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 gamma-ray irradiation on urea canal complex at -78-degrees-C [Polym. J., 17, 1291 (1985)].