SYNOPSIS
Two kinds of water-insoluble PVA-MA hydrogel films were prepared from PVA-MA, an esterification product of poly(viny1 alcohol) and maleic anhydride, by heat treatment and a crosslinking reaction, respectively. Both films changed their dimensions upon environmental pH changes. The crosslinked gel expanded to approximately 230% of its original length, with most changes occurring in the pH range of 2-7. The heat-treated PVA-MA film swelled stepwisely, with about 45% of the total expansion occurring a t pH 2-7 and the remaining 55% at p H 9-12. Results from IR spectra analysis and acid-base titration suggest that the ionization of carboxylic acid accounts for the pH-induced gel swelling irrespective of the differences in the swelling behavior of these two gels. The pK, values of the heat-treated PVA-MA gel increased from 4 to 10 while the degree of dissociation varied from 0 to 80%, whereas that of the crosslinked PVA-MA film is limited in a range of 3.3-4.2. The permeability of glucose across the crosslinked PVA-MA film increased when pH was raised from 2 to 7. No significant change of permeability was noticed between pH 7 and 12. For the heat-treated PVA-MA film, glucose permeability increased when pH was changed from 2 to 7 and from 7 to 1 2 . 0 1996 John Wiley & Sons, Inc.