Synthesis and characterization of hydrogels based on poly(vinyl alcohol)-g-poly(styrene) copolymers

A useful hydrogel for supporting and/or entrapping living microorganisms has been developed by the syntheses of graft copolymers based on vinyl alcohol and styrene, PVOH-g-PS, and through the formation of macro- and microporous structures formed under the slow evaporation of a toluene/dimethyl sulfoxide, DMSO, mixture of solvents. The PVOH-g-PS copolymer was obtained by the methanolysis of the vinyl acetate part of a previously bulk-polymerized poly(vinyl acetate)g-poly(styrene) copolymer, PVAc-g-PS. To produce the so-called PVOH-g-PS hydrogel, polymer films formed by the evaporation of a toluene/DMSO mixture were subjected to different freeze/thaw cycles in order to crystallize the PVOH part of the copolymer. Calorimetric studies carried out on these types of hydrogels show melting endothermic transitions that correspond to fusion of the PVOH, and the crystallization areas increase with the number of freeze/thaw cycles. The low-vacuum scanning electron microscopy and atomic force microscopy images reveal that the PVOH-g-PS copolymer can form films with homogeneous macro- and micropore size distributions interconnected by a cheese-like structure where the microorganisms can be supported and/or entrapped.