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

Abstract

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-Pr 2C 6H 3)(OCMe 3) 2(CHR) where R is CMe 3 or CMe 2Ph, 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=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 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 10 200 and 13 200 ( DP 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.