IMPROVED HYDROGENATED STYRENE/CONJUGATED DIENE/STYRENE BLOCK COPOLYMER AND PROCESS FOR PRODUCTION THEREOF

摘要

The invention relates to a hydrogenated styrene/ conjugated diene/styrene block copolymer excellent in toughness, heat distortion temperature and moldability, a process for producing the copolymer, and optical materials made by using the same. The block copolymer is one which is prepared by hydrogenating a styrene/conjugated diene/styrene block copolymer constituted mainly of styrene polymer blocks and a conjugated diene polymer block and which has (i) a content ratio by weight of hydrogenated styrene polymer block to hydrogenated conjugated diene polymer block of 75/25 to 97/3, (ii) a degree of hydrogenation of 90 % or above, and (iii) a number-average molecular weight of 30,000 to 200,000 g/mol as determined by GPC method, and contains (iv) 1 to 20 wt% of high-molecular weight components whose molecular weights are at least three times the number-average molecular weight as determined by GPC method.