The first vinyl organometallic monomer containing tungsten, (η6-vinylcyclopentadienyl)tricarbonylmethyltungsten (4), was homopolymerized and copolymerized with styrene, acrylonitrile, methyl methacrylate, and N-vinyl-2-pyrrolidone, using azobis(isobutyronitrile) (AIBN) as the initiator. Reactivity ratios for the styrene (M2) copolymerization of 4, initiated by AIBN in benzene solutions, were = 0.16 and r2 = 1.55 from which the Alfrey-Price parameters e = -1.98 and Q = 1.66 were calculated. Thus, (η5-vinylcyclopentadienyl)tricarbonylmethyltungsten is an exceptionally electron-rich vinyl monomer, closely resembling vinylferrocene, (η5-vinylcyclopentadienyl)tricarbonylmanganese, and (η5-vinylcyclopentadienyl) dicarbonylnitrosylchromium in this respect. This is the first vinyl monomer known to have an M-CH3 (M is a transition metal) bond. Styrene polymerizations in the presence of (η5-cyclopentadienyl)- tricarbonylmethyltungsten were carried out to evaluate the possibility that the methyl group is a good hydrogen atom donor (thereby serving as an inhibitor or a chain transfer agent). No evidence was obtained for significant chain transfer activity. Similarly, neither (η5-cyclopentadienyl)tricarbonylmanganese nor poly(η6-vinylcyclopentadienylRricarbonylmanganese acted as efficient chain transfer agents in styrene polymerizations.