Synthesis of well-defined block copolymers containing poly(N-isopropylacrylamide) segment by anionic block copolymerization of N-methoxymethyl-N-isopropylacrylamide

Anionic polymerization of N-methoxymethyl-N-isopropylacrylamide (1) was carried out with diphenylmethyllithium, -potassium and -cesium in the presence of diethylzinc in THF at -78 degreesC for 1-3 h. The resulting poly(1)s possessed the predicted molecular weights based on the molar ratios between monomer and initiators and the narrow molecular weight distributions (M-w/M-n = 1.1). The methoxymethyl protecting groups were completely hydrolyzed to afford a poly(N-isopropylacrylamide) (poly(NIPAM)), having well-defined chain structures by treatment with aqueous HCl in 1,4-dioxane at room temperature for 12 h. Stereoregularity of the resulting poly(NIPAM) was strongly affected by the counterions of anionic initiator. From the H-1-NMR measurement, the racemo dyad of poly(NIPAM) obtained with diphenylmethyllithium, -potassium and -cesium in the presence of Et2Zn was found to be 75, 50 and 30%, respectively. The sequential copolymerization of styrene or isoprene with 1 and the subsequent deprotection quantitatively gave well-defined block copolymers containing poly(NIPAM) segments. The copolymers had the predicted molecular weights, compositions and the narrow molecular weight distributions, and showed the typical amphiphilic character with regard to solubility.