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-diethylacry lamide (DEA) proceeded slowly and steadily with 1,1-diphenyl-3-methylpentyl lithium (DPPLi) and with diphenylmethylpotassium (Ph2CHK) in the presence o f triethylborane (Et3B) in THF even at 30 degrees C to afford the polymers having the predicted molecular weights and very narrow molecular weight dis tributions in quantitative yields. The result of the postpolymerization of DEA with Ph2CHK/Et3B confirmed the formation of a living polymer with heter otactic configuration at 30 degrees C. The poly(DMA) and poly(DEA) produced with DPPLi/Et3B were highly syndiotactic, while the isotactic polymers wer e formed in the absence of Et3B. The additive effects of Et3B on retarded r eaction rate and stereospecificity of the polymerization are attributed to the coordination of Et3B with the propagating enolate anion.