Patent ID: 8153727

Claim:
A block copolymer comprised of a polymer block or blocks (A) comprising conjugated diene monomer units and a polymer block or blocks (B) comprising conjugated diene monomer units and aromatic vinyl monomer units, wherein the block copolymer satisfies the following requirements (1) through (8): (1) the polymer block or blocks (A) have a glass transition temperature in the range of −88 to −45° C., (2) the polymer block or blocks (B) have a glass transition temperature in the range of 30 to 90° C., (3) the content of aromatic vinyl monomer units in the block copolymer is in the range of 30 to 52% by weight based on the total weight of the block copolymer, (4) the block copolymer has an aromatic vinyl block ratio of smaller than 69% by weight based on the total weight of the block copolymer, (5) the viscosity of a 5% by weight solution of the block copolymer in styrene is at least 5 mPa·s but smaller than 30 mPa·s, (6) the polymer block or blocks (B) contain conjugated diene monomer units and aromatic vinyl monomer units, at a ratio in the range of 1/99 to 50/50 by weight, (7) the content of vinyl bond in the portion of conjugated diene monomer units in the block copolymer is in the range of 2 to 40% based on the total conjugated diene monomer units in the block copolymer, and (8) the ratio of the polymer block or blocks (A) to the polymer block or blocks (B) is in the range of 1.0 to 9.0 by weight.