Preparation and characterization of pH-sensitive,interpenetrating networks of poly(vinyl alcohol) and poly(acrylic acid)

Hydrogels with varying cross-linking ratio and ionic content were prepared from interpenetrating networks of poly(vinyl alcohol) and poly(acrylic acid). Equilibrium swelling studies were conducted and the average molecular weight between cross-links, M _c, and mesh size were determined. Hydrogels with large M _c, values were found to swell to a greater extent than those with small M _c values. It was also observed that an increase in M _c yielded faster swelling and deswelling rates, as the rates for membranes with M _c = 18,000 were about twice as fast as were the rates for membranes with M _c = 34,000. Oscillatory swelling behavior was investigated in response to changes in the pH and ionic strength of the swelling medium. A change in pH from 3 to 6 caused an ionization of the hydrogels and an increase in the weight swelling ratio, with a greater increase exhibited by IPNs with a higher ionic content. Increase in pH also caused an increase in the average mesh size. © 1995 John Wiley & Sons, Inc.