PROCESS FOR THE PREPARATION OF A BLOCK COPOLYMER COMPOSITION AND BLOCK COPOLYMER COMPOSITION

摘要

A process is provided for preparing block copolymer compositions, which process comprises the subsequent steps of: (1) polymerizing vinyl aromatic monomer in an inert hydrocarbon solvent in the presence of an organolithium initiator until substantially complete conversion; (2) adding conjugated diene monomer to the polymerization mixture and allowing said conjugated diene monomer to polymerize until substantially complete conversion; (3) adding a second portion of organolithium initiator, followed by the addition of a second portion of conjugated diene monomer and allowing said conjugated diene monomer to polymerize until substantially complete conversion; (4) adding a second portion of vinyl aromatic monomer and allowing said vinyl aromatic monomer to polymerize until substantially complete conversion; and (5) adding a terminating agent. Furthermore, a block copolymer composition is provided comprising: (i) a triblock copolymer A-B-B'-A' having two different or equal polymer endblocks A and A' derived from vinyl aromatic monomer and one polymer midblock B-B' derived from conjugated diene monomer, and (ii) a diblock copolymer B'-A' having one polymer block B' derived from conjugated diene monomer and one polymer block A' derived from vinyl aromatic monomer, wherein the molar weight ration A' (triblock)/A'(diblock) is in the range of from 0.9 to 1.1, wherein both block copolymers are obtained by sequential polymerization and wherein the triblock copolymer as well as the diblock copolymer have a vinyl aromatic content of 55 % by weight or less based on the total weight of the triblock copolymer and diblock copolymer, respectively.