Patent ID: 7977428

Claim:
A linear block copolymer composition, comprising from 55 to 95 mass % of a vinyl aromatic hydrocarbon and from 5 to 45 mass % of a conjugated diene as monomer units; wherein: the linear block copolymer composition is a mixture comprising linear block copolymers having at least three types of polymer blocks with different molecular weights represented by the following formula: S—B—S where S is a polymer block comprising a vinyl aromatic hydrocarbon as monomer units, and B is a polymer block consisting of conjugated diene monomer units; a molecular weight distribution (Mw/Mn) of a mixture of the polymer blocks is within a range of from 3.35 to 6; in a gel permeation chromatogram of the mixture of the polymer blocks, M 1 /M 2 is within a range of from 12.5 to 25, where M 1 is a largest peak top molecular weight among peak top molecular weights corresponding to peaks forming at least 30% of a whole peak area, and M 2 is a smallest peak top molecular weight among peak top molecular weights of 50,000 or less corresponding to peaks forming at least 20% of the whole peak area; and the linear block copolymer composition is obtained by: preparing a polymer system by carrying out anionic polymerization of a first charge of a vinyl aromatic and an initiator; adding a second charge of a vinyl aromatic hydrocarbon and an initiator to the polymerization system; adding a third charge of a vinyl aromatic hydrocarbon and an initiator to the polymerization system, the first, second, and third charges resulting in formation three types of vinyl aromatic hydrocarbon blocks having different peak top molecular weights; adding a fourth charge of a conjugated diene; adding a fifth charge of a vinyl aromatic hydrocarbon; and inactivating all active terminals of the obtained polymers.