| abstract |
A block copolymer composition comprising n (A) a tri-branched block copolymer (I) having a molecular weight of 150,000 to 450,000 represented by the general formula n n (A-B).sub.3 X n n 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, n (B) a di-branched block copolymer (II) having a molecular weight of 100,000 to 300,000 represented by the general formula n n (C-D).sub.2 Y n n 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 agents, and the weight ratio of the polymer block C to the polymer block D is from 10/90 to 30/70, and n (C) a linear diblock copolymer (III) having a molecular weight of 50,000 to 150,000 represented by the general formula n n E-I n n 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 n n (I)/(II)=(20/80) to (90/10) and n n n [(I)+(II)]/(III)=(45/55) to (80/20). |