Organo-cobalt mediated living radical polymerization of vinyl acetate

Vinyl acetate polymerization initiated by azo radical sources in the presence of cobalt(II) tetramesitylporphyrin ((TMP)CoII) shows an induction period followed by an organo-cobalt mediated living radical polymerization (LRP). The induction period corresponds to converting (TMP)CoII to an organo-cobalt porphyrin derivative (organo-Co(TMP)). Living character at low vinyl acetate conversion is demonstrated by a linear increase in molecular weight with conversion, relatively low polydispersity homopolymers, and formation of block copolymers with methyl acrylate ((TMP)Co-PVAc-b-PMA). Deviations from ideal LRP occur by radical termination and chain transfer events at moderate conversion of vinyl acetate (VAc). Mechanistic studies demonstrate that the VAc radical polymerization is controlled by a degenerative transfer mechanism that utilizes organo-cobalt complexes as the transfer agent. Kinetic studies are utilized in comparing radical polymerization of vinyl acetate and methyl acrylate that are mediated by organo-cobalt complexes. ? 2008 American Chemical Society.