INTERACTION OF WATER WITH POLY(VINYL METHYL-ETHER) IN AQUEOUS-SOLUTION

Near-infrared, viscometric, and calorimetric measurements were made on aqueous poly(vinyl methyl ether) (PVME) solutions at temperatures between 15 and 43-degrees-C. We found a hydrogen-bonded structure of water around the polymer chain (a polymer-water complex), which is characterized by two distinct hydration numbers (i.e., 2.7 and 5.0 water molecules on each monomer unit of the chain) by analyzing the concentration dependence of endothermic enthalpies at a cloud point temperature, ca. 35-degrees-C. In particular, the 2.7 water-polymer complex has been suggested to be cooperatively formed by using data of the near-infrared (nir) absorption spectrum around 1930 nm. Furthermore, the peak-wavelength of the nir spectrum has been observed to change drastically at the cloud point when the temperature is raised. This can be interpreted as a cooperative collapse of the hydrogen-bonded water structure to free water, resulting in the aggregation of the polymer chains due to the exposure of their hydrophobic groups at the cloud point. (C) 1994 John Wiley & Sons, Inc.