Characterization of the network properties of poly(ethylene glycol)-acrylate hydrogels prepared by variations in the ethanol-water solvent composition during crosslinking copolymerization

The characteristics of poly(ethylene glycol) (PEG)-acrylate hydrogel networks were investigated as a function of the ethanol-water solvent composition during free-radical crosslinking copolymerization. Macromonomer (88% ω-methoxy-PEG-acrylate and 10% ω-phenoxy-PEG-acrylate) and crosslinker (2% PEG-diacrylate) concentrations were kept constant. As the copolymerization progressed, the polymer solution in 100% ethanol became increasingly turbid, indicating the development of a heterogeneous network structure. In 100% water, however, the initially turbid polymer solution became increasingly transparent as the crosslinking copolymerization progressed. All the gels were optically clear upon equilibration in water. Kinetic studies, with attenuated total reflectance-infrared, showed a long induction period, along with a lowered reaction rate, in 100% ethanol, and a decrease in conversion with an increase in ethanol content. These results agree with the UV analysis of the sol fractions, which indicated an increase in the amounts of unreacted PEG-acrylates with an increase in the ethanol content. The gels which were formed with a high ethanol concentration exhibited lower Young'S modulus and higher swelling ability, suggesting that the network structure was significantly affected by the solvent composition during free-radical crosslinking copolymerization. From the stress-strain and swelling experiments, the Flory-Huggins interaction parameter was evaluated. The creep characteristics of the hydrogels were modeled with two Kelvin elements.