Ionic complex of Vanadyl(IV) in the polymerization of 2-hydroxyethyl methacrylate as probed by EPR

The vanadyl ionic complex VO(DMSO)5(ClO4)2 (I) exhibits high catalytic activity in the polymerization of 2-hydroxyethyl methacrylate (HEMA). The changes in the vanadium oxidation state during polymerization under argon and in the presence of oxygen were studied by EPR. Under aerobic conditions, the HEMA chain propagation radical was detected; this indicates the presence of a radical chain polymerization pathway caused by the ability of I to perform one-electron reduction of molecular O2. The radical generation rate is controlled by the initial concentration of I: its increase results in the formation of inactive species, presumably, μ-peroxo complexes Vv-O-O-Vv. It was shown by kinetic methods that the radical-chain pathway initiated by the reaction of I with O2 is not crucial in the HEMA polymerization.