SYNTHESIS OF WELL-DEFINED GRAFT-COPOLYMERS VIA COUPLED LIVING ANIONIC-POLYMERIZATION AND LIVING ROMP

Well-characterized polystyrene macromonomers containing a norbornene u nit at the chain end were prepared by capping living polystyrene with exo-5-norbornene-2-carbonyl chloride. The macromonomers were then ring opened polymerized using well-defined Schrock molybdenum initiators, Mo(N-2,6-i-Pr2C6H3)(OCMe3)(2)(CHR) where R is CMe3 or CMe2Ph, to produ ce well-defined graft copolymers. Well-characterized graft copolymers with polystyryl grafts of average degrees of polymerization 15, 22, 35 , 50, 100 and 130 were successfully prepared. Ring opening metathesis polymerization (ROMP) of macromonomers with a molecular weight of 1550 (<(DP)over bar> = 13) goes to completion at a macromonomer:initiator molar ratio of 200:1. Ring opening metathesis polymerization of macrom onomers with molecular weights of 3500 and 4900 (<(DP)over bar>s of 32 and 46, respectively) also goes to completion even at comparatively h igh macromonomer:initiator molar ratios of 100:1. This produces relati vely long polynorbornene backbone chains with relatively short polysty rene grafts. On the other hand, macromonomers with number average mole cular weights of 10200 and 13200 (<(DP)over bar>s of 96 and 127) are c ompletely polymerized only up to macromonomer:initiator molar ratios o f 20 and 10:1, respectively. Beyond this stage polymerization stops wi thout destruction of the living chain ends before complete consumption of macromonomers, giving short polynorbornene backbone chains with re latively long polystyrene grafts. (C) 1998 Published by Elsevier Scien ce Ltd. All rights reserved.