1H NMR study of temperature-induced phase transitions in aqueous solutions of poly(N-isopropylmethacrylamide)/poly(N-vinylcaprolactam) mixtures

Abstract

1H NMR spectroscopy was used to investigate the temperature-induced phase transitions in aqueous solutions of poly(N-isopropylmethacrylamide)/poly(N-vinylcaprolactam) (PIPMAm/PVCL) mixtures to find out if the phase transition of the given component (PIPMAm or PVCL) is affected by the presence of the second component. Our results that PVCL and PIPMAm transitions are in polymer mixtures shifted by ~2 K towards higher temperatures in comparison with neat polymers and depend on polymer concentration show that such effect exists. Spin–spin relaxation times of water (HDO) indicate that in solutions with c ≥ 1 wt% a portion of water is predominantly bound in PVCL mesoglobules even at temperatures above the LCST transition of PIPMAm component. Water is with time released from these mesoglobules without any induction period so indicating that it is mostly indirectly bound water. We assume that there is a direct connection between character of the bound water and the transition temperatures.