Thermoplastic elastomer of butadiene-styrene block copolymer and its production

This invention relates to thermoplastic elastomeric block copolymers and process for the preparation thereof. According to this invention, the block copolymers obtained through block copolymerization process at higher temperature and adding butyllithium in twice during copolymerization are mixed block copolymer of A1-B-A2/B-A2 and B-A2/B-A2(where A represents monovinyl aromatic monomer; B represents conjugated diene monomer) having different blocks, higher elongation and appropriate melt index. The process of this invention is simple and efficient. The copolymers of this invention are particularly useful for various applications of typical styrene butadiene block copolymer, especially plastic modifier.