THE EFFECT OF HYDROGEN-BONDING ON VAPOR DIFFUSION IN WATER-SOLUBLE POLYMERS

Water-vapor transport in poly( acrylic acidi (PAA), poly(N-vinyl-2-pyr rolidone) (PVPo), and their 2 : 1 interpolymer complex was measured be tween 30 and 50 degrees C. It was found that the formation of interpol ymer hydrogen bonding not only caused the T-g of the complex to be hig her than those of the individual components, but also affected vapor-s orption behaviors. In the high vapor pressure region (P-r > 0.5), sorp tion isotherms in pure PAA and PVPo follow the Flory-Huggins solution theory and the sorbed water molecules may form clusters around the COO H groups in PAA and C=O groups in PVPo. However, sorption in the compl ex is almost linear for the entire range of water activities. The bina ry polymer-polymer interaction parameter between PAA and PVPo in the c omplex, chi(PAA-PVPo), is less than zero, which is indicative of favor able interaction between PAA and PVPo. At lower water activities, sorp tion behaviors for water in the three polymers can be approximated by Henry's law and vapor-diffusion coefficients can be ranked as PVPo > c omplex > PAA. The water vapor diffusion coefficients in each system de crease with increasing P-r in the region of P-r > 0.5 because the prop ortion of immobilized water molecules increases with vapor concentrati on. (C) 1997 John Wiley & Sons, Inc.