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 polyvinyl alcohol-vinyl acetate with either polyacrylic acid or poly(4-vinyl pyridine) exhibited a strong pH dependency. When poly(vinyl pyrrolidone) was used for blending, an unusual pH dependency was observed. An increase in the equilibrium water content in all systems resulted in an increase in the freezable water as determined by DSC. Critical point drying led to a striated surface on polyacrylic acid-polyvinyl alcohol-vinyl acetate hydrogels, whereas a porous structure was observed on the freeze-dried poly(vinyl pyrrolidone)-polyvinyl alcohol-vinyl acetate gels. Hydrogels with elevated storage modulus were obtained when either polyvinyl alcohol-vinyl acetate alone or polyacrylic acid-polyvinyl alcohol-vinyl acetate blends were thermally treated at high temperatures (i.e., 150 degreesC). Low storage modulus was observed 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 acetate hydrogels. (C) 2001 John Wiley & Sons, Inc.