Thermal and microwave assisted polymerization of vinyl acetate catalyzed by cyclometalated ruthenium (II) complexes

Polymerization of vinyl acetate (VAc) was carried out with four different cyclometalated ruthenium(II) catalysts, using CCl4 as initiator under conventional heating and microwave irradiation. The thermo-polymerizations were solvent-dependent and proceeded to limited conversions without control. Only the polymerization in DMSO mediated by [Ru(η6-C6H6)(C6H4-2-CH2NMe2)(MeCN)]PF6 (1) showed dependence of the molecular weights on conversion. Besides, this complex was the only one active under microwave irradiation. The microwave assisted polymerization was much faster than that under conventional heating, maintaining an increase of the molecular weights with conversion. The chain extensions were quite successful under both conventional heating and microwave irradiation, confirming the participation of ATRP mechanism. The complex 1 was active in atom transfer radical addition of CCl3Br to VAc substrate providing the adduct in high yield. Mechanistic studies demonstrated the importance of the presence of a labile benzene ligand to increase the catalytic activity of the ruthenium complexes.