Ube Industries, Inc.

Chikara Kotani

Nobuhiro Tsujimoto

Takefumi Yano

Kazuhiro Akikawa

Kei Tsukahara

A high cis-1,4-polybutadiene is produced, with reduced gel formation, by preparing a catalyst from (A) a cobalt compound, (B) a trialkyl (C.sub.1-10) aluminum compound, (C) a halide compound selected from those of formulae (1) and (2): (1) AlR.sup.2.sub.m X.sub.3-m, and (2) R.sup.3 --X, wherein R.sup.2 =C.sub.1-10 hydrocarbon, X=halogen, m=0 to 2, R.sup.3 =C.sub.1-40 hydrocarbon, and (D) water in an amount of 0.77 to 1.45 moles per mole of total Al in components (B) and (C); and polymerizing 1,3-butadiene in the presence of the resultant catalyst in a polymerization medium including an alkane, cycloalkane and/or olefin hydrocarbon.

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Ichihara, Japan

Chikara Kotani