Polymerization of 1,3‐butadiene with MgCl 2 ‐supported cobalt catalysts activated by ordinary alkylaluminums

MgCl 2 ‐supported CoBr 2 catalysts were prepared from mixture of MgCl 2 and CoBr 2 L 2 (L = triphenylphosphine or pyridine) in toluene. Polymerization of 1,3‐butadiene was conducted over the catalysts combined with ordinary alkylaluminums as cocatalyst. The CoBr 2 (PPh 3 ) 2 /MgCl 2 catalyst gave polybutadiene with approximately 80% of 1,2 units, whereas cis ‐1,4‐poly‐butadiene was obtained with the CoBr 2 (C 5 H 5 N) 2 /MgCl 2 catalyst. Addition of triphenylphospine to the latter catalyst caused a marked increase in the content of 1,2 units. The content of 1,2 units could be thus controlled in the range from 0 to 80% by changing the amount of triphenylphosphine. On the other hand, the CoBr 2 (PPh 3 ) 2 /MgCl 2 catalyst with very low content of CoBr 2 (PPh 3 ) 2 hardly displayed any activity. Addition of dimethoxydiphenylsilane to the catalyst gave polybutadiene containing 90 % of 1,2 units with a fairly high activity.