Synthesis of ultra‐high molecular weight polyacrylonitrile with highly isotactic content ( mm > 0.60) using dialkylmagnesium/polyhydric alcohol system as catalyst

An attempt was made to synthesize a catalyst having high activity for synthesis of highly isotactic polyacrylonitrile (PAN) with high molecular weight by anionic polymerization. The reaction products of di‐ n ‐hexylmagnesium [( n ‐C 6 H 13 ) 2 Mg] with alicyclic alcohols such as 1,4‐cyclohexanediol or 1,5‐decalindiol were found to be effective as polymerization catalysts for preparation of PAN samples whose triad isotacticity [the content of mm (m , meso configuration)] is about 0.64 and viscosity‐average molecular weight ( M v ) exceeds 1 × 10 5 . The triad tacticities [ mm , mr , and rr contents ( r , racemo configuration)] of the polymers obtained were analysed by 13 C NMR and their M v s were determined by viscometry in dimethylsulphoxide at 25°C using Kamide et al .'s Mark–Houwink–Sakurada equation. M v of PAN increased significantly by after‐treatment of the catalysts, prepared from ( n ‐C 6 H 13 ) 2 Mg and alicyclic alcohols, with triethylalyminium (Et 3 Al). Ultra‐high molecular weight PAN samples ranging in M v from 2 × 10 6 to 6 × 10 6 [( mm ) = 0.57–0.66] were obtained in anisole at 135°C by using the above catalyst system. A main role of Et 3 Al in these catalyst systems is considered to reduce, in advance, OH groups on the catalyst, resulting in a significant suppression of termination reactions of propagating PAN chains during the polymerization.