Tj. Bastow et al., H-1 AND C-13 NMR-STUDIES OF WATER AND HEAVY-WATER ABSORPTION IN POLY(VINYL ALCOHOL) HYDROGELS, Journal of membrane science, 131(1-2), 1997, pp. 207-215
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.