Synthesis and functionalities of poly(N-vinylalkylamide). 13. Synthesis and properties of thermal and pH stimuli-responsive poly(vinylamine) copolymers

The thermoresponsive and pH-responsive intelligent copolymers of N-vinylfor mamide (NVF) and N-vinylisobutyramide (NVIBA), and their derivatives with p rimary 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 degreesC in a transparent homogeneous s olution system below the lower critical solution temperature (LCST) of poly (NVIBA). Poly(NVIBA)'s chemical structure was not affected at all by dissol ution in 2 N HCl for 3 weeks, with complete retention of the side chains, w hereas 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 b ecome feasible to make poly(-VAm-co-NVIBA). Aqueous hydrolyzed copolymer so lutions (0.2 wt %) did not show LCSTs below pK(a) = 10.0, although they bec ame slightly turbid, whereas in the pH 12.0 (above pKa), the copolymers cle arly exhibited LCSTs. Above pKa, the LCST increased successively depending on the poly(VAm) content of the copolymer. Hydrogels with stimuli-responsiv e property were prepared by hydrolysis of poly(NVF-co-NVIBA) hydrogel (NVF content; 30 mol %) in 2N HCl solution at 30 degreesC for 12 h. The hydrolyz ed copolymers were found to exhibit thermal and/or pH responsiveness. The p rimary amine-containing polymers are intelligent polymers and can act as ch emical modifiers.