Synthesis and Functionalities of Poly(N-vinylalkylamide). 13. Synthesis and Properties of Thermal and pH Stimuli-Responsive Poly(vinylamine) Copolymers

摘要

The thermoresponsive and pH-responsive intelligent copolymers of N-vinylformamide (NVF) and N-vinylisobutyramide (NVIBA), and their derivatives with primary amino groups, were synthesized. Hydrolysis of poly(NVF), poly(NVIBA), and poly(NVF-co-NVIBA) to obtain poly(vinylamine) [poly(VAm)] was carried out under acidic conditions, at 30 deg C in a transparent homogeneous solution system below teh lower critical solution temperature (LCST) of poly(nviba). Poly(NVIBA)'s chemical structure was not affected at all by dissolution in 2 N HCl for 3 weeks, with complete retention of teh side chains, whereas poly(NVF) was completely hydrolyzed after 2 weeks in 2 N HCl. The NVF unit of poly(NVF-co-NVIBA) was able to hydrolyze selectively, and it has become feasible to make poly(VAm-co-NVIBA). Aqueous hydrolyzed copolymer solutions (0.2 wt %) did not show LCSTs below pK_a=10.0, although they became slightly turbid, whereas in the pH 12.0 (above pK_a), the copolymers clearly exhibited LCSTs. Above pK_a the LCST increased successively depending on the poly(VAm) content of the copolymer. Hydrogels with stimuli-responsive property were prepared by hydrolysis of poly(NVF-co-NVIBA) hydrogel (NVF content; 30 mol %) in 2N HCl solution at 30 deg C for 12 h. The hydrolyzed copolymers were found to exhibit thermal and/or pH responsiveness. The primary amine-containing polymers are intelligent polymers and can act as chemical modifiers.