The differences in the polymerization abilities of N-vinylformamide (NVF) and N-vinylisobutyramide (NVIBA) and the synthesis of their copolymers were studied. The polymerization abilities were fairly good and quite similar to those of N-vinyl-acetamide (NVA), a monomer in the same class as N-vinylalkylamides. Since the monomer reactivity ratios were r(1) = 1.08 and r(2) = 0.92 (M-1 = NVF, M-2 = NVIBA), respectively, it is clear that the comonomers definitely were converted to random copolymers. The resulting copolymers poly(NVF-co-NVIBA) exhibited the cloud points sharply. The light transmittance profiles were the same as those for poly(NVIBA) although they increased from 39 degrees C for poly(NVIBA), with an increase in the corresponding hydrophilic NVF component. Our final objective was to produce a cloud point controlled polymer material with primary amino groups. To achieve this, we examined the hydrolysis of poly(NVF), poly(NVA), poly(NVIBA), and poly(NVF-co-NVIBA) to obtain poly(vinylamine) [poly(VAm)]. The hydrolytic cleavage of poly(NVF) and poly(NVA) was promoted by an increase in temperature. However, poly(NVIBA) was not cleaved appreciably. The hydrolysis of poly(NVF-co-NVIBA) was done under controlled conditions, and amino groups selectively were introduced to only one of two components of the copolymer. The cloud point of the hydrolyzed copolymer shifted to a higher temperature than that of the copolymer.