Synthesis and swelling behavior of acrylate-based hydrogels

The purpose of this investigation was to report the synthesis of a novel pH-sensitive acrylate-based hydrogel by polymerizing the comonomers 2-hydroxyethyl methacrylate, HEMA, acrylic acid, AA, and sodium acrylate, NaAc. The NaAc component was obtained by neutralization of AA with sodium hydroxide. Hydrogels were obtained by free radical copolymerization in aqueous solution in the presence of redox initiators, Na2S2O8/Na2S2O5, and ethylene glycol dimethacrylate, EGDMA, crosslinker. The copolymers were synthesized by varying neutralization percent of AA in the range of 10-100. The swelling behavior of the copolymeric gels were investigated as a function of pH, temperature, ionic strength, and AA neutralization percent. The polymer mesh size, xi, molecular weight between crosslinks, M-c, and crosslinking density, q, were determined by using the Flory-Rehner equation in the pH range of 2-8 as 8.78-48.8 angstrom, 209-2667 g/mol, and 0.046-0.59, respectively. The diffusional exponent value, n, of the synthesized hydrogel was found to be 0.59, indicating a non-Fickian diffusion mechanism. It can be concluded that the hydrogel demonstrated a sharp change in its water absorbency, mesh size and molecular weight between crosslinks of the network with a change in pH of the swelling media. The latter properties suggest strong consideration of these hydrogels for use as oral drug delivery systems and ion-exchangers for removal of metal ions from aqueous media, owing to the carboxylate groups within the polymeric network.