Electronic and Steric Ligand Effects in the Radical Polymerization of Vinyl Acetate Mediated by β‐Ketoiminate Complexes of Cobalt(II)

Abstract

Complexes Co[OC(Ph)CHC(Me)NAr](2) [Ar=Ph, 1; o,o'-C(6)H(3)Me(2) (Xyl), 2; p-C(6)H(4)CF(3), 3] are tested in the polymerization of vinyl acetate (VAc) initiated by V-70 (0.8 equiv) at 30 degrees C. Polymerization occurs without any notable induction time yielding PVAc with relatively low polydispersity, but with higher than expected M(n) values, which indicates inefficient trapping processes. The apparent polymerization rate constant varies in the order 2>1>3. Controlled polymer growth is also observed when the polymerization is conducted in the presence of a much higher V-70/1 ratio, demonstrating that this system can also function as a transfer agent in a degenerative transfer process. Competition between chain growth and catalyzed chain transfer (CCT) is also observed, the latter prevailing at higher temperatures. Comparison of these results with previous reports on bis(beta-diketonato) complexes allows a separate assessment of ligand electronic and steric effects in the ability to control polymerization.