BLOCK COPOLYMER COMPOSITION

A block copolymer composition comprising (A) a tri-branched block copolymer (I) having a molecular weight of 150,000 to 450,000 represented by the general formula (A - B)3X wherein A represents a polymer block of an aromatic vinyl monomer, B represents a polymer block of a conjugated diene monomer, and X represents a residue of a tri-functional or tetra-functional alkoxysilane coupling agent, and the weight ratio of the polymer block A to the polymer block B is from 10/90 to 30/70, (B) a di-branched block copolymer (II) having a molecular weight of 100,000 to 300,000 represented by the general formula (C - D)2Y wherein C represents a polymer block of an aromatic vinyl monomer, D represents a polymer block of a conjugated diene monomer, and Y represents a residue of a di-functional to tetra-functional coupling agent, and the weight ratio of the polymer block C to the polymer block D is from 10/90 to 30/70, and (C) a linear diblock copolymer (III) having a molecular weight of 50,000 to 150,000 represented by the general formula E - I wherein E represents a polymer block of an aromatic vinyl monomer, and I represents an isoprene polymer block, and the weight ratio of the polymer block E to the polymer block I being from (10/90) to (30/70), the weight ratio of the copolymers (I), (II) and (III) satisfy the following relation (I)/(II) = (20/80) - (90/10) and [(I)+(II)]/(III) = (45/55) - (80/20).