Thermo- and pH-responsive copolymer of N-isopropylacrylamide with acryloylvaline: synthesis and properties in aqueous solutions

N-acryloyl-L-valine (AV) was synthesized as a pH-sensitive monomer possessing both acrylamide and isopropyl sequences similar to the chemical architecture of N-isopropylacrylamide (NIPAAm). Poly(NIPAAm-co-AV) copolymer contained 5.03 mol % randomly introduced AV units was prepared and analyzed. The sample with molar mass Mw = 24,000 g/mol was studied in aqueous solutions using static and dynamic light scattering and optical transmittance methods. Temperature dependences of scattered light intensity and turbidity as well as hydrodynamic radii of dissolved species and their relative contributions to the light scattering were obtained to determine the temperatures of phase separation in aqueous media of various acidities. The dependence of the phase separation onset temperatures on pH corresponded to that obtained for anionic pH-responsive polymers. Aggregated structures were observed in solutions; moreover, in a strongly acidic medium, with an increase in temperature, the compaction of aggregates predominated, and with an increase in pH, the formation of new aggregates dominated over their compaction.