Vapor pressures of polymer solutions. II. Vapor pressure of the poly(vinyl alcohol)‐water system

Vapor pressures were measured for the system, poly(vinyl alcohol)‐water at 30°C. with the apparatus reported in the preceding paper. Fractionated samples were used in the form of thin films, carefully dried under high vacuum at room temperature. The degree of crystallinity of these samples was about 0.2, and the degrees of polymerization were 1530 and 335. The relation between the activity of the water and the composition of the gel phase is discussed. The interaction parameter χ12 is evaluated assuming that the crystalline regions are not affected by the water and correspond to the crosslinks in an amorphous network polymer; also that the chain length between two crosslinks is not changed with the composition of the system. χ12 increases with increasing polymer concentration. This behavior is discussed with the aid of heat of dilution data from the literature. The anomalous concentration dependence of the entropy and energy contributions to χ12 may be explained as resulting from the mutual orientation of water molecules and the hydroxyl groups along the polymer chain.