Cobalt Bipyridine Bisphenolate Complex in Controlled/Living Radical Polymerization of Vinyl Monomers

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). The living characters of linear increased molecular weight with monomer conversion, relatively narrow molecular weight distribution, and the synthesis of block copolymer demonstrated by the formation of PVAc-b-PNVP were all observed. The polymerization of VAc was proposed to be mediated by the degenerative transfer (DT) process, but the polymerization of MA should be mainly controlled by the reversible termination (RT) process since the equilibrium constant (Keq = [CoIII–R]/[CoII][R•]) between cobalt(II) and organocobalt(III) was measured as 8.6 × 107 M–1. The correlation between Keq and the redox potential (E1/2) of cobalt complexes was preliminarily observed as a higher E1/2 leading to a larger Keq.