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

Abstract

AbstractAn 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‐C6H13)2Mg] 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 (Mv) exceeds 1 × 105. The triad tacticities [mm, mr, and rr contents (r, racemo configuration)] of the polymers obtained were analysed by 13C NMR and their Mvs were determined by viscometry in dimethylsulphoxide at 25°C using Kamide et al.'s Mark–Houwink–Sakurada equation.Mv of PAN increased significantly by after‐treatment of the catalysts, prepared from (n‐C6H13)2Mg and alicyclic alcohols, with triethylalyminium (Et3Al). Ultra‐high molecular weight PAN samples ranging in Mv from 2 × 106 to 6 × 106 [(mm) = 0.57–0.66] were obtained in anisole at 135°C by using the above catalyst system. A main role of Et3Al 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.