RAFT polymerization with phthalimidomethyl trithiocarbonates or xanthates. On the origin of bimodal molecular weight distributions in living radical polymerization

Phthalimidomethyl trithiocarbonate reversible addition-fragmentation chain transfer ( RAFT) agents are effective in imparting living characteristics to radical polymerizations of butyl acrylate ( BA) and N-isopropylacrylamide ( NIPAM) and provide a route to end-functional polymers with predictable molecular weight and narrow molecular weight distributions ( e. g., number-average molecular weight for PBA ((M) over bar (n))) 21 300 and polydispersity ((M) over bar (w)/(M) over bar (n))) 1.1 at 96% conversion). End group determination suggests that bimodal molecular weight distributions and long chain branches in PBA arise by copolymerization of a PBA macromonomer formed by backbiting,beta-scission. The S-phthalimidomethyl xanthates provide good control over polymerizations of the less-activated monomers N- vinylpyrrolidone (NVP) and vinyl acetate (VAc). In the case of PBA with a trithiocarbonate end or PVAc with a xanthate end, the C-S bond to the thiocarbonylthio end group can be homolyzed by thermolysis at > 180 C leaving the phthalimidomethyl end group and the ester side groups intact providing macromonomers, with omega end group -CH2-C(CO2C4H9)(=CH2) or -CH2-C(O2CCH3)(=CH2) respectively, as the main products.