ANOMALOUS SORPTION AND PERVAPORATION OF AQUEOUS-ORGANIC MIXTURES BY POLY (VINYL ACETAL) MEMBRANES

Various poly(vinyl butyral), poly(vinyl acetal) and poly(vinyl formal) membranes have been prepared by casting from tetrahydrofuran solutions. While these membranes swell tremendously or even dissolve in alcohols or acetic acid, they swell very little in water. Their swelling in water-alcohol or water-acetic acid mixtures is, however, appreciable, with the absorbed mixture enriched in water. Similarly, the membranes are more permselective to water than they are to alcohols and acetic acid. These anomalous phenomena are explained by suggesting that the selective adsorption of the alcohol or acetic acid molecules on the polymer, with their hydrophobic moiety in contact with the polymer molecules, hydrophilise the polymer, making the latter more compatible with water.