1H NMR study on the hydration during temperature-induced phase separation in concentrated poly(vinyl methyl ether)/D2O solutions

A certain portion of spatially restricted bound water (HDO) was established for concentrated PVME/D2O solutions at temperature above the LCST transition from the measurements of H-1 NMR spectra and H-1 spin-spin relaxation times T-2 of HDO. The fast and slow exchange regime between bound and free water was revealed for polymer concentrations c = 2 - 10 wt % and c = 20 - 60 wt %, respectively. For the latter case, the residence time of bound HDO tau >> 2.7 ms and relatively weak hydrogen bonding follow from the position of the separate NMR signal of bound HDO. For polymer concentrations c = 20 - 60 wt %, the spin-spin relaxation time T-2 of bound HDO and the molar ratio [PVME monomeric unit]/[bound D2O] remain virtually constant and equal to T-2 congruent to 40 ms and [PVME]/[bound D2O] congruent to 2.7 on average, thus indicating a direct connection of the fraction of bound water with the conformational structure of phase-separated PVME.