Hydrogels Obtained via γ-Irradiation Based on Poly(Acrylic Acid) and Its Copolymers with 2-Hydroxyethyl Methacrylate

Abstract

Hydrogels containing both carboxyl and hydroxyl functional groups have been prepared by γ-irradiation of either aqueous solutions of acrylic acid (AA) and mixtures of AA and 2-hydroxyethyl methacrylate (HEMA) in different ratios, or aqueous solutions of poly(AA), PAA, and poly(AA-co-HEMA) obtained via solution polymerization. A higher absorbed dose is required in order to prepare hydrogels from monomer solutions, compared with those from polymer solutions. The range for the absorbed doses was chosen so that the probability of crosslinking reactions is higher than that of degradation ones. As the radiation energy deposited in a sample increases, the equilibrium swelling degree and the average molar mass between crosslinks diminishes. Chemical transformations induced by radiation were investigated by means of FTIR spectroscopy and thermal analysis of polymers before and after irradiation. For all these systems, the formation of a three-dimensional network enhances the glass transition temperature and thermal stability, but a further increase in the crosslinking degree may have the reverse effect on the glass transition temperature. Depending on the preparation protocol and/or hydrogel composition, superabsorbent materials that can bind different compounds throughout side functional groups may be obtained.