Bridgestone Tire Company Limited

Japan Synthetic Rubber Co., Ltd.

Isamu Shimizu

Noboru Oshima

Tatsuo Fujimaki

Yoshito Yoshimura

Seisuke Tomita

Shinsuke Yamaguchi

Mikio Takeuchi

Tomoharu Yamada

A branched styrene-butadiene copolymer and a pneumatic tire using the same as a tread base rubber are disclosed. This copolymer is produced by coupling an active styrene-butadiene copolymer anion, which is obtained by polymerizing styrene and butadiene in a hydrocarbon solvent in the presence of ether or a tertiary amine and an initiator of an organolithium compound, with a tin halide compound. In the copolymer, the ratio of branched copolymer connected with tin-butadienyl bond is at least 20% by weight, and the content of bound styrene is not less than 3% by weight but less than 25% by weight, and the content of vinyl bond in butadiene portion is not less than 30% but less than 50%.

Tire tread comprised of branched styrene-butadiene copolymers

Disclosed herein is a rubber composition comprising at least 20% by weight of styrene-butadiene copolymer based on the total weight of the rubber content. The styrene-butadiene copolymer is obtained by randomly copolymerizing styrene with 1,3-butadiene in a hydrocarbon solvent in the presence of an organolithium compound as an initiator and then subjecting to a coupling reaction with a polyfunctional coupling agent, and contains 30-70% by weight of branched polymers therein, and has the following properties:

Styrene-butadiene copolymer rubber composition

A butadiene-base polymer containing a branched polymer through tin-carbon bond and a process for producing the same are disclosed. The butadiene-base polymer is produced by polymerizing 1,3-butadiene alone or 1,3-butadiene and aromatic vinyl compound in a hydrocarbon solvent in the presence of a Lewis base using an organolithium compound as an initiator and then coupling with a tin halide, and satisfies the following requirements:

Butadiene-base polymer and a process for producing the same

Branched styrene-butadiene copolymers and pneumatic tires using the same

A styrene-butadiene copolymer having a high styrene content is disclosed, which is obtained by polymerizing styrene and butadiene in a hydrocarbon solvent in the presence of an organolithium compound and, if necessary, a Lewis base and then coupling with a tin halide compound. This copolymer contains in its main chain at least 30 wt % of polymer having a tin-carbon bond and has a bound styrene content of more than 25 wt % but not more than 60 wt % and a content of vinyl bond in butadiene portion of not less than 30% but less than 50%.

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Kameyama, Japan

Isamu Shimizu