H-1 AND C-13 NMR-STUDIES OF WATER AND HEAVY-WATER ABSORPTION IN POLY(VINYL ALCOHOL) HYDROGELS

Solid state nuclear magnetic resonance measurements of slightly syndio tactic poly(vinyl alcohol) (PVOH) films have been used to explore the effect of H2O and (H2O)-H-2 absorption on hydrogen bonding, and hence molecular mobility and conformations, in these hydrogels. Gels of wate r concentration from 5 to 60 wt% were studied. H-1 NMR spectra show sw itching of methine proton conformation at similar levels (ca. 30 wt%) of water and heavy water absorption, indicative of a threshold reducti on of hydrogen bonding and increased molecular mobility. The methine C -13 NMR spectra display triad structure line narrowing at a similar le vel of absorption which is commensurate with a 1:1 matching of PVOH mo nomer units with water or heavy water molecules. H-1 NMR chemical shif ts are used to study the mobility environments (or 'states') of water and line widths are used to follow solvent mobility. Discrete environm ents of H2O and (H2O)-H-2 are observed as multiple peaks in the H-1 li ne at 4.8 ppm (5.0 ppm for (H2O)-H-2), and these results are supported by thermogravimetric measurements. The main features of the C-13 NMR spectra suggest that (polymer mobility) Line narrowing occurs due to t he break up of inter- and intra-molecular hydrogen bonding through int eraction of hydroxyl groups with H2O or (H2O)-H-2 molecules and not du e to the concomitant reduction of crystallinity.