Butadiene-base polymer and a process for producing the same

A process for the production of a vulcanized rubber composition comprising a butadiene-base polymer containing a branched polymer and satisfying the following requirements:

• (1) a content of a bound aromatic vinyl compound in the butadiene-base polymer is 0-40% by weight;
• (2) a content of a vinyl bond-containing butadiene unit in the total butadiene unit of the butadiene-base polymer is 30-90%;
• (3) a content of the branched polymer in the butadiene polymer is at least 30% by weight;
• and
• (4) a content of a component having a molecular weight of less than 100,000 as polystyrene in the molecular weight distribution as measured by gel permeation chromatography is 10-20% by weight, which process comprises the steps of:
• (A) polymerizing 1,3-butadiene alone or 1,3-butadiene and an aromatic vinyl compound in a hydrocarbon solvent in the presence of Lewis base using an organolithium compound as an initiator, while continuously or intermittently adding a hydrocarbon solvent containing an active hydrogen-containing compound selected from the group consisting of water, alcohols and phenols in an amount of 0.01-0.20 mol per one atomic equivalent of lithium atom in the organolithium initiator at such a stage that the conversion rate reaches 10-90%;
• (B) coupling the resulting butadiene-base polymer with a lithium atom at the terminal thereof with a tin halide;
• and
• (C) vulcanizing said polymer.

A process for the production of a vulcanized rubber composition comprising a butadiene-base polymer containing a branched polymer and satisfying the following requirements:

• (1) a content of a bound aromatic vinyl compound in the butadiene-base polymer is 0-40% by weight;
• (2) a content of a vinyl bond-containing butadiene unit in the total butadiene unit of the butadiene-base polymer is 30-90%;
• (3) a content of the branched polymer in the butadiene-base polymer is at least 30% by weight;
• and
• (4) a content of a component havin a molecular weight of less than 100,000 as polystyrene in the molecular weight distribution as measured by gel permeation chromatography is 10-20% by weight, which process comprises the steps of:
• (A) polymerizing 1,3-butadiene alone or 1,3-butadiene and an aromatic vinyl compound in a hydrocarbon solvent in the presence of a Lewis base using as organolithium compound as an initiator, while continuously or intermittently adding a compound selected from the group consisting of .alpha.-acetylenes, allenes, active hydrogen-containing compounds and halogen compounds in an amount of 0.1-2.0 mol per one atomic equivalent of lithium atom in the organolithium initiator at such a stage that the conversion rate reaches 10-90%;
• (B) coupling the resulting butadiene-base polymer with a lithium atom at the terminal thereof with a tin halide;
• and
• (C) vulcanizing said polymer.