BLOCK COPOLYMERS CONTAINING BOTH POLYSTYRENE AND LOW VINYL CONTENT POLYDIENE HARD BLOCKS

摘要

The present invention provides block copolymers which have reduced solvent sensitivity and which overcome the foregoing disadvantages. In one embodiment of the present invention, there is provided an asymmetric block copolymer of the structure A-B-C-A wherein each A block is formed of a vinyl aromatic hydrocarbon, preferably styrene, and has a weight average molecular weight of 5,000 to 50,000. B is a polybutadiene block having a weight average molecular weight of 1,000 to 15,000 and a vinyl content of less than 25% by weight, and C is an elastomeric conjugated diene polymer block having a weight average molecular weight of 25,000 to 200,000 and has a vinyl content of 30 to 90%, preferably 35 to 80%, and most preferably 35 to 70% by weight. In the second embodiment of the present invention, there is provided a hydrogenated block copolymer of the formula A-B-C-B-A wherein A, B, and C have the definitions set forth above.