Ube Industries, Inc.

Shotaro Sugiura

Haruo Ueno

Hideo Ishikawa

Tetsuro Matsuura

Minoru Kono

Thunehiko Tokutomi

A process for producing a polybutadiene is provided wherein, first, 1,3-butadiene is polymerized in the presence of a particular cis-1,4-polymerization catalyst and subsequently, the polymerization is continued in the presence of a particular 1,2-polymerization catalyst. The resulting polybutadiene is characterized as containing 2 to 40% of the 1,2-structure, the melting point of the 1,2-structure portion being 110.degree. to 215.degree.C, and containing 60 to 98% of the cis-1,4-structure and having an intrinsic viscosity [.eta.] of 0.9 to 8 in tetraline at 135.degree.C. A vulcanized product of the polybutadiene is characterized as possessing improved tear strength, flex-crack resistance and tensile strength.

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Ichihara, Japan

Shotaro Sugiura