Synthesis of well-defined graft copolymers via coupled living anionic polymerization and living ROMP

Well-characterized polystyrene macromonomers containing a norbornene unit 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 produce 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 macromonomers with molecular weights of 3500 and 4900 (<(DP)over bar>s of 32 and 46, respectively) also goes to completion even at comparatively high macromonomer:initiator molar ratios of 100:1. This produces relatively long polynorbornene backbone chains with relatively short polystyrene grafts. On the other hand, macromonomers with number average molecular weights of 10200 and 13200 (<(DP)over bar>s of 96 and 127) are completely polymerized only up to macromonomer:initiator molar ratios of 20 and 10:1, respectively. Beyond this stage polymerization stops without destruction of the living chain ends before complete consumption of macromonomers, giving short polynorbornene backbone chains with relatively long polystyrene grafts. (C) 1998 Published by Elsevier Science Ltd. All rights reserved.