STUDY OF THE FROZEN WATER POLY(VINYL ALCOHOL) SYSTEM BY H-2 AND C-13 NMR-SPECTROSCOPY

2H and 13C NMR techniques were used to investigate the thermodynamic state of water molecules and of poly(vinyl alcohol) (PVA) chain segments in frozen 10% PVA solutions in 99.8% and 8.5% 2H2O in the ‐66 to 3°C temperature range. The minimum amount of water not entering into the structure of ice is shown to correspond to a ratio of three water molecules to four PVA hydroxyl groups. The quantity of unfrozen water in the investigated systems was observed to change in the 5‐6°C range next to the melting point of pure water. The measurements show that, within the same temperature interval, the temperature decrease is accompanied by a sharp decrease in the 2H spin‐lattice relaxation time T1, whereas 13C T1 and the width of the 13C NMR signals increase up until the resolved PVA signals disappear. The correlation time of the motion of water deuterons and the PVA chain segments was calculated from the 2H and 13C T1 data. The interrelation between the data obtained and the cryostructurization processes leading to the formation of gels in frozen aqueous PVA solutions is discussed. Copyright © 1990 John Wiley & Sons, Ltd.