Additive Effect of Triethylborane on Anionic Polymerization of N,N-Dimethylacrylamide and N,N-Diethylacrylamide

Anionic polymerizations of N, N -dimethylacrylamide (DMA) and N,N -diethylacrylamide (DEA) proceeded slowly and steadily with 1,1-diphenyl-3-methylpentyllithium (DPPLi) and with diphenylmethylpotassium (Ph 2 CHK) in the presence of triethylborane (Et 3 B) in THF even at 30 °C to afford the polymers having the predicted molecular weights and very narrow molecular weight distributions in quantitative yields. The result of the postpolymerization of DEA with Ph 2 CHK/Et 3 B confirmed the formation of a living polymer with heterotactic configuration at 30 °C. The poly(DMA) and poly(DEA) produced with DPPLi/Et 3 B were highly syndiotactic, while the isotactic polymers were formed in the absence of Et 3 B. The additive effects of Et 3 B on retarded reaction rate and stereospecificity of the polymerization are attributed to the coordination of Et 3 B with the propagating enolate anion.