Patent ID: 7332542

Claim:
A process for the preparation of a linear A1B1A2 block copolymer having two mono alkenyl arene polymer blocks and one controlled distribution block of a conjugated diene and a mono alkenyl arene, comprising the steps; a. polymerizing a mono alkenyl arene in a reactor in the presence of an inert hydrocarbon solvent and an organolithium initiator whereby a living polymer block A1 terminated with a lithium ion is formed; b. prior to the completion of the polymerization in step a, adding to the reactor in one aliquot between 40 and 60% of the conjugated diene monomer desired in the copolymer block B1, and a distribution agent and continuing the polymerization of the mono alkenyl arene monomer and conjugated diene monomer; c. after about 20 to about 60 mol % of the monomers in step b has been polymerized, gradually adding the remaining amount of conjugated diene monomer and mono alkenyl arene monomer to the reactor at a rate that maintains the concentration of the conjugated diene at no less than about 0.1% weight until about 90% of the monomers in block B1 have been polymerized, thereby forming a living copolymer block copolymer A1B1; d. adding additional mono alkenyl arene monomer to the reactor, thereby forming a living copolymer A1B1A2, wherein the A1block and the A2 block each has a number average molecular weight of about 3,000 to about 60,000 and the B1 block has a number average molecular weight of about 30,000 to about 300,000.