1H NMR study of temperature-induced phase separation in solutions of poly(N-isopropylmethacrylamide-co-acrylamide) copolymers

1H NMR spectroscopy was applied to investigate temperature-induced phase separation in solutions of poly(N-isopropylmethacrylamide-co-acrylamide) [P(IPMAm/AAm)] random copolymers in D2O, D2O/ethanol and D2O/acetone. The NMR relaxation behaviour of water (HDO) was also examined. The effects of P(IPMAm/AAm) composition and the ethanol or acetone content in the mixed solvents on the temperature, width and extent of the phase transition as well as on the mobility of polymer segments and water molecules were characterized. For D2O solutions of the copolymers prepared with the AAm fraction in the polymerization mixture not exceeding 25 mol% 1H NMR spectra show dynamic heterogeneity of copolymer chains in mesoglobules where AAm sequences and surrounding short IPMAm sequences are hydrated and mobile, while sufficiently long IPMAm sequences are dehydrated and their mobility is strongly reduced. The obtained results are consistent with the idea that P(IPMAm/AAm) copolymer mesoglobules are rather porous and disordered.