Method for producing conjugated diene rubber

A method for producing a conjugated diene rubber, comprising the steps of:

• (a) forming a polymer block (A) by polymerizing a monomeric mixture with a polymerization initiator in an inert solvent, the polymer block (A) having an active terminal and containing 80 to 95% by weight of an isoprene monomeric unit and 5 to 20% by weight of an aromatic vinyl monomeric unit, the monomeric mixture containing isoprene and an aromatic vinyl monomer;
• (b) preparing a conjugated diene polymer chain having an active terminal and having the polymer block (A) and a polymer block (B), the polymer block (B) being formed continuously with the polymer block (A) through the continuation of a polymerization reaction caused by mixing of the polymer block (A) having the active terminal and either 1,3-butadiene or a monomeric mixture containing 1,3-butadiene and an aromatic vinyl monomer, the polymer block (B) having an active terminal and containing 50 to 100% by weight of a 1,3-butadiene monomeric unit and 0 to 50% by weight of an aromatic vinyl monomeric unit, and optionally further forming another polymer block after forming the polymer block (B);
• and
• (c) bringing a denaturant into reaction with the active terminal of the conjugated diene polymer chain having the active terminal, the denaturant having three or more groups per molecule, the three or more groups being each at least either group selected from among an epoxy group and an alkoxy group, the reaction taking place insofar as the total molar ratio of an epoxy group(s) and/or an alkoxy group(s) in the denaturant with respect to the polymerization initiator used in the polymerization ranges from 0.1 to 1.