Electronic and steric ligand effects in the radical polymerization of vinyl acetate mediated by β-ketoiminate complexes of cobalt(II)

Complexes Co[OC(Ph)CHC(Me)NAr]₂ [Ar=Ph, 1; o,o′-C ₆H₃Me₂ (Xyl), 2; p-C₆H ₄CF₃, 3] are tested in the polymerization of vinyl acetate (VAc) initiated by V-70 (0.8 equiv) at 30°C. Polymerization occurs without any notable induction time yielding PVAc with relatively low polydispersity, but with higher than expected Mn values, which indicates inefficient trapping processes. The appar- ent 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(β-diketonato) complexes allows a separate assessment of ligand electronic and steric effects in the ability to control polymerization.