Abstract: 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%.

Abstract: An alkenyl aromatic compound-conjugated diene block copolymer having a combined alkenyl aromatic compound content of 25-95% by weight, characterized in that said copolymer is represented by the formula,A--B--Awherein A represents an alkenyl aromatic compound polymer block, the total amount of A's in both ends being 50-97% by weight of the total combined alkenyl aromatic compound content; B represents a conjugated diene-alkenyl aromatic compound copolymer block, said B portion having (a) 2-10 taper blocks where the amount of the alkenyl aromatic compound increases gradually and (b) a weight ratio of alkenyl aromatic compound/conjugated diene of 3-85/97-15; and the total amount of the chains that 1-4 alkenyl aromatic compound monomers are linked is 5-30% by weight of the total combined alkenyl aromatic compound content. Said copolymer is excellent in the balance of impact strength, tensile strength and elongation.

Abstract: 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:(1) a content of a bound aromatic vinyl compound in the butadiene-base polymer is 0-40% by weight;(2) a ratio of vinyl bond-containing butadiene unit in the toal butadiene unit of the butadiene-base polymer is 30-90%;(3) a ratio of the branched polymer in the butadiene-base polymer is at least 30% by weight; and(4) a ratio of a component having a molecular weight of less than 100,000 as polystyrene in the molecular weight distribution as measured by a gel permeation chromatography is 10-20% by weight.

Abstract: 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%.

Abstract: 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%.

Abstract: High vinyl polybutadiene or styrene-butadiene copolymer obtained by polymerizing 1,3-butadiene alone or with styrene in a hydrocarbon solvent using an organolithium compound as an initiator and coupling the resulting polymer, characterized in that(1) the polybutadiene or styrene-butadiene copolymer comprises at least 20% by weight of a polymer having in its molecular chain a linkage between butadienyl and at least one metal selected from the group consisting of silicon, germanium, tin and lead,(2) the styrene content of said copolymer is 40% by weight or less, and(3) the polybutadiene or the butadiene portion of the styrene-butadiene copolymer has a vinyl content of 50 to 95%.Said polybutadiene or styrene-butadiene copolymer has low rolling resistance, high wet skid resistance, highly improved fracture property and, an excellent processability.