Copolymerization in N-vinylcaprolactam-N-vinylpyrrolidone and N,N-diethylacrylamide-N,N-dimethylacrylamide systems: The effect of composition and spatial structure of copolymers on their thermal sensitivity

Factors that affect the temperature-responsive properties of water-soluble polymers were revealed by studying the copolymerization of two pairs of monomers: N-vinylcaprolactam-N-vinylpyrrolidone and N,N-diethylacrylamide-N,N-dimethylacrylamide. In each pair, the first monomer forms a temperature-responsive polymer and the second gives a polymer soluble in water up to the boiling point. It was found that in all cases, the addition of the second (more hydrophilic) monomer resulted in a monotonous increase in the phase separation temperature in an aqueous copolymer solution, with the temperature rise being comparatively slow in the initial stage and sharply accelerating after the addition of more than 40–50 mol % second monomer. The phase-separation temperature versus copolymer composition curves for N,N-diethylacrylamide-N,N-dimethylacrylamide copolymers of iso-and heterotactic structure synthesized via anionic polymerization are rather similar. At the same time, the copolymers of both types prepared via radical polymerization are characterized by steeper curves, a pattern that may be due to a high content of the syndiotactic structure, however, changes in the copolymer spatial structure have a lesser effect on the phase separation temperature than the presence of units of a more hydrophilic monomer. The addition of a relatively low amount (20–25 mol %) of a less hydrophilic monomer imparts temperature sensitivity to polymers, such as polyvinylpyrrolidone or polydimethylacrylamide, which do not possess this property in the pure form.