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 degreesC in a transparent homogeneous solution system below the 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 the 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 pKa), the copolymers clearly exhibited LCSTs. Above pKa, 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 degreesC 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.