Behavior of Water during Temperature-Induced Phase Separation in Poly(vinyl methyl ether) Aqueous Solutions. NMR and Optical Microscopy Study

The behavior of water during the temperature-induced phase separation in PVME/D 2 O solutions was investigated by 1 H NMR methods and optical microscopy. A fast exchange between water (HDO) bound in mesoglobules and free water was found from 1 H NMR spin−spin relaxation measurements at temperature above the LCST transition for semidilute PVME/D 2 O solutions where the exchange time is 1.2 ms for c = 6 wt %. In contrast, there is a slow exchange between bound and free water in highly concentrated PVME solutions and the residence time of the bound water 2 s was found for concentrations c = 20−50 wt % using one-dimensional NOE 1 H NMR experiment. A 3 order of magnitude slower exchange in highly concentrated PVME/D 2 O solutions is in accord with our optical microscopy findings that globular-like structures are here approximately 20 times larger than in PVME solution with c = 6 wt %.