Physicochemical characterization of hydrogels based on polyvinyl alcohol-vinyl acetate blends

Hydrogels made of polyvinyl alcohol-vinyl acetate and its blends with water soluble polymer were studied in terms of swelling behavior, microstructure , and dynamic mechanical properties. Hydrogels prepared by blending polyvin yl alcohol-vinyl acetate with either polyacrylic acid or poly(4-vinyl pyrid ine) exhibited a strong pH dependency. When poly(vinyl pyrrolidone) was use d for blending, an unusual pH dependency was observed. An increase in the e quilibrium water content in all systems resulted in an increase in the free zable water as determined by DSC. Critical point drying led to a striated s urface on polyacrylic acid-polyvinyl alcohol-vinyl acetate hydrogels, where as a porous structure was observed on the freeze-dried poly(vinyl pyrrolido ne)-polyvinyl alcohol-vinyl acetate gels. Hydrogels with elevated storage m odulus were obtained when either polyvinyl alcohol-vinyl acetate alone or p olyacrylic acid-polyvinyl alcohol-vinyl acetate blends were thermally treat ed at high temperatures (i.e., 150 degreesC). Low storage modulus was obser ved for both poly(vinyl pyrrolidone) and poly(4-vinyl pyridine)-containing hydrogels. Temperature dependency of storage modulus from 20 to 60 degreesC was observed only for poly(4-vinyl pyridine)-polyvinyl alcohol-vinyl aceta te hydrogels. (C) 2001 John Wiley & Sons, Inc.