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

摘要

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 deg C for 1-3 h.The resulting poly(l)s possessed the predicted molecular weights based on the molar ratios between monomer and initiators and the narrow molecular weight distributions (A_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 HC1 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 ~1H-NMR measurement,the racemo dyad of poly(NIPAM) obtained with diphenylmethyllithium,-potassium and -cesium in the presence of Et_2Zn 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.