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 (Ph2CHK) in the presence of triethylborane (Et3B) in THF even at 30 degrees 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 Ph2CHK/Et3B confirmed the formation of a living polymer with heterotactic configuration at 30 degrees C. The poly(DMA) and poly(DEA) produced with DPPLi/Et3B were highly syndiotactic, while the isotactic polymers were formed in the absence of Et3B. The additive effects of Et3B on retarded reaction rate and stereospecificity of the polymerization are attributed to the coordination of Et3B with the propagating enolate anion.