Abstract
Cobalt(II) bipyridine bisphenolate (CoII(BpyBph)) was applied to mediate the controlled/living radical polymerization of vinyl acetate (VAc), methyl acrylate (MA), and other vinyl monomers such as N-vinylpyrrolidone (NVP) and acrylonitrile (AN). In the polymerization of VAc, the molecular weight of polymer chains raised linearly to conversion of monomers. The PDI value was 1.48 at 53.9% conversion. The temperature and initiator concentration affected the VAc polymerization mainly via changing radical concentration. The polymerization of VAc was proposed to be mediated by degenerative transfer (DT) process. In other words, all CoII(BpyBph) transform to CoII(BpyBph)-R during induction period. The polymerization of MA mediated by CoII(BpyBph) was also studied. The poly(methyl acrylate) (PMA) with a relative low PDI value (1.17) at 80% conversion was obtained. The ratio of cobalt(II) and organo-cobalt(III) species during MA polymerization was followed by UV-vis spectroscopy and the equilibrium constant (Keq) was determined to be 1.2 × 10-8 M (Keq = [CoII][R•]/[CoIII-R]). The polymerization of MA should be mainly controlled by the reversible termination (RT) process. The living character of the polymerization was further determined by the synthesis of block copolymer poly(vinyl acetate)-block-poly(N-vinylpyrrolidone).