Stereospecific anionic polymerization of N,N-dialkylacrylamides

N,N-Dimethylacrylamide (DMA), N,N-diethylacrylamide (DEA), N,N-dipropylacrylamide (DPA), N-ethylmethylacrylamide (EMA), N-acryloylpyrrolidine (APY), N-acryloylpiperidine (API), and N-acryloylmorpholine (AMO) were polymerized with 1,1-bis[(4'-trimethylsilyl)phenyl]-3-methylpentyl-lithium (1) and with 1,1-bis[(4'-trimethylsilyl)phenyl]-3,3-dipenylpotassium (2) in THF in the presence of additives. Although the polymers produced directly with 1 or 2 have broad molecular weight distributions, the addition of Et2Zn to the polymerization systems leads to slow propagation reaction and narrow molecular weight distributions of the polymers. The poly(N,N-dialkylacrylamides) produced with 1 are rich in isotactic configuration, while the addition of Et2Zn reduces isotacticity and increases the degree of syndio- and heterotacticity. In particular, the poly(DEA)s generated with 1/Et2Zn and 1/LiCl are highly syndiotactic and isotactic, respectively. Although the broad distributions of triad sequence are observed for the polymers produced with 2, the highly heterotactic poly(DEA) is formed with 2/Et2Zn at 0 degrees C. The additive effects of Et2Zn on the molecular weight and tacticity are supposed to be caused by the coordination of Et2Zn with the propagating enolate anion.