RAFT polymerization of methyl acrylate in carbon dioxide

Reversible addition fragmentation chain transfer (RAFT) polymerizations of methyl acrylate (MA) in solution containing either 22 vol.-% CO2 or toluene were performed at 80 degrees C and 300 bar using cumyl dithiobenzoate (CDB) at concentrations between 1.8 x 10(-3) to 2.5 x 10(-2) mol (.) L-1 as the RAFT agent. Product molecular weight distributions and average molecular weights indicated the successful control of MA polymerization in CO2, even at low CDB concentrations. RAFT polymerization rates were strongly retarded by CDB and were in CO2 than in toluene solution. The enhanced fluidity associated with the addition of CO2 to the polymerizing system provided access to mechanistic details of RAFT polymerization. The data of the present study into MA, together with our recent results on RAFT polymerization of styrene in solution of CO2 and of toluene, suggest that self-termination of intermediate RAFT radicals is responsible for retardation in case of high concentrations of this intermediate and in case of enhanced fluidity, which may be achieved by polymerization in solution of CO2.