Synthesis of highly isotactic ( mm > 0.70) polyacrylonitrile by anionic polymerization using diethylberyllium as a main initiator

An attempt was made to synthesize steroregular polyacrylonitrile (PAN) with a high triad isotacticity (i.e. the content of mm (m, meso) ) exceeding 0.70 by the anionic polymerization method. In the stereospecific polymerization of acrylonitrile (AN) initiated by diethylberyllium (Et 2 Be) in xylene at 130°C, the ( mm ) content as well as the viscosity‐average molecular weight (MÞ v ) of PAN increased by addition of diisobutylaluminum hydride (i‐C 4 H 9 ) 2 AlH) as an additive to the polymerization system. Maximum ( mm ) content, attained in the molar ratio region of (i‐C 4 H 9 ) 2 AlH/Et 2 Be > 1.0, was about 0.73. The stereospecific polymerization of AN was also initiated using a mixture of Et 2 Be and di‐ n ‐hexylamagnesium ((Et 2 Be/( n ‐C 6 H 13 ) 2 Mg system), where both Et 2 Be and ( n ‐C 6 H 13 ) 2 Mg can induce the stereospecific polymerization of AN at 130°C. The ( mm ) content of the PAN sample prepared using the Et 2 Be/( n ‐C 6 H 13 ) 2 Mg system (( mm ) = 0.64) was higher than that of PAN samples synthesized using Et 2 Be alone (( mm ) = 0.56) and ( n ‐C 6 H 13 ) 2 Mg alone (( mm ) = 0.51) under the same conditions except initiator. A significant difference in 13 C chemical shifts of α‐carbons between Et 2 Be (1.35 ppm) and ( n ‐C 6 H 13 ) 2 Mg (10.72 ppm) dissolved in hydrocarbon solvent at 110°C leads us to the conclusion that when Et 2 Be induces the stereospecific polymerization in the Et 2 Be/( n ‐C 6 H 13 ) 2 Mg system as initiator, the main role of ( n ‐C 6 H 13 ) 2 Mg is considered to be the suppression of the association of Et 2 Be (active site) itself.