Synthesis and characterization of block copolymers from 2-oxazolines

Poly(2-isopropyl-2-oxazoline) and block copolymers of 2-isopropyl-2-oxazoline (ISOXA) and ester derivative 2-oxazoline (Methyl 3-(oxazol-2-yl)propionate) (ESTER-OXA) were prepared by a cationic ring-opening polymerization. The lower critical solution temperature (LCST) of the aqueous polymer solutions was investigated. While the LCST of poly(2-isopropyl-2-oxazoline) was 44.7°C, slightly higher values were found for the block copolymers. The segment of poly(ESTER-OXA) of the block copolymers was hydrolyzed under mild conditions so that only hydrolysis of ester groups took place, avoiding hydrolysis of the amide groups. The values of LCST of the hydrolyzed block copolymers showed only weak pH sensitivity due to the relatively short segment of poly(ESTER-OXA) in comparison with the segment of poly(ISOXA) and to the fact that the poly(ISOXA) and poly(ESTER-OXA) segments are in separated blocks. In addition to turbidimetric experiments, diffusion and relaxation were measured by NMR for studying the molecular motions of the polymers in aqueous solutions in a broad temperature range covering the LCST, and to determine the variation in hydrodynamic radius of the molecules.