N-Vinylamide derivatives, such as N-n-butyl-N-vinylformamides and N-isobutyl-N-vinylformamides were synthesized and copolymerized with N-vinylformamide and N-methyl-N-vinylacetamide. Lower critical solution temperature values of the copolymers were observed over a wide range of temperatures. The thermosensitive behaviors of copolymers were controlled not only by the induction rate of alkylation of N-vinylamides at the amide position but also by the chemical structures, including the hydrogen atom of the secondary amide group.