Branched styrene-butadiene copolymers and pneumatic tires using the same.

摘要

A branched styrene-butadiene 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 comprising an organolithium compound, with a tin halide compound. In the copolymer, the ratio of branched polymer connected with tin-butadienyl bonds 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 bonds in the butadiene portion is not less than 30% but less than 50%.

There is also disclosed a pneumatic tire having a tread base rubber which contains at lest 20 parts by weight of a branched styrene-butadiene copolymer rubber produced by coupling a styrene-butadiene copolymer anion with a tin halide.