| abstract |
A process for producing predominately four-armed asymmetric radial block copolymers which contain predominately, on average, two copolymer arms of a conjugated diene and a vinyl aromatic hydrocarbon and two conjugated diene homopolymer or copolymer arms, comprising:n (a) anionically polymerizing at least one conjugated diene monomer and at least one vinylaromatic hydrocarbon monomer to form a set of living polymer arms, (b) anionically polymerizing at least one conjugated diene monomer to form another set of living polymer arms, (c) coupling one set of living polymer arms with a coupling agent which is either tetramethoxysilane or γ-glycidoxypropyltrimethoxysilane, (d) substantially completing the coupling reaction while leaving, on average, two unreacted coupling sites on the coupling agent, (e) coupling the other set of living polymer arms to the first coupled set of polymer arms, and (f) optionally, partially or fully hydrogenating the coupled polymer. |