Effect of addition of organoaluminum and organoboron compounds in the stereospecific polymerization of acrylonitrile using dialkylmagnesium as catalyst

An attempt was made to clarify the effect of addition of organoaluminum and organoboron compounds in the stereospecific polymerization of acrylonitrile (AN) initiated by dialkylmagnesium (R 2 Mg) above 100°C. The triad isotacticity (i.e. the content of mm ( m : meso)) as well as the viscosity‐average molecular weight ( M̄ v ) of polyacrylonitrile (PAN) increased when trialkylaluminum (R 3 Al) and trialkylboron (R 3 B) were used as additives. Diisobutylaluminum hydride [(i‐C 4 H 9 ) 2 AlH] was found to be the best additive. in the stereospecific polymerization of AN, giving PAN with higher ( mm ) content (0.63), higher M̄ v value (5.2 × 10 4 ), and a yield approximately double that obtained using ( n ‐C 6 H 13 ) 2 Mg alone. When the ( n ‐C 6 H 13 ) 2 Mg/(i‐C 4 H 9 ) 2 AlH system was used, the yield, ( mm ), and M̄ v of PAN increased with polymerization temperature ( T p ); maximum values of yield, ( mm ), and M̄ v were obtained at c . 130°C. The optimum amount of additives was approximately equimolar to R 2 Mg as initiator. The 13 C chemical shift of α‐carbon in R 2 Mg at 90°C shifted by mixing with R 3 Al and R 3 B, respectively, indicating the existence of interaction between R 2 Mg and the additives. The main role of the additives is considered to be suppression of the self‐association of R 2 Mg by strong interaction with R 2 Mg.