WATER INTERACTION WITH OLIGO-(ETHOXY) ETHYLENE GLYCOLS

The amount of water sorbed by oligo-(ethoxy)ethylene glycols of the ho mologous series HO(CH2CH2O)(n)H, E-n, with n = 1...8 was determined by the isopiestic method at constant relative humidities RH from 11% up to 97% at 25 degrees C. We found that the sorption isotherms extracted can be described using a regular solution theory used for poly-(ethox y)ethylene glycols. For the amount of water sorbed at constant RH we f ound an approximately linear dependence on the number of ether oxygens per glycol, indicating a constant number of water molecules per group , which was estimated for all RH. Furthermore, spin-lattice relaxation times of deuterium oxide ((H2O)-H-2) in a large concentration range o f ethylene glycols in heavy water were measured at the same temperatur e and for all glycols the free energy of water binding was deduced fro m these measurements using a two-state model. (C) 1997 Published by El sevier Science B.V.