Kinetics and Equilibrium Swelling Properties of Hydrophilic Polymethacrylate Networks
Summary: Hydrogels were synthesized by polymerization of 2-Hydroxy ethylmethacrylate (HEMA) in the presence of ethyleneglycoldimethacrylate (EGDMA) as a crosslinking agent. Structural information and thermophysical properties of the hydrogels were analyzed using Fourier-Transform Infrared spectroscopy, thermogravimetrical analysis, and differential scanning calorimetry. The swelling behaviour of the obtained chemically crosslinked P(HEMA-EGDMA) networks in aqueous solution was investigated as a function of the pH value and concentration of crosslinking agent. Plateau values were found at equilibrium swelling for a low pH value after one day swelling, whereas increasing water uptake was obtained for pH = 6.32 even at swelling times of more than five days. For short swelling times, a linear relationship between swelling ratio and time was found. Experimental data were rationalized using Fick's second law of diffusion. For early and moderate times of diffusion, threshold values were found in all cases considered here, indicating a Fickian behaviour below and a non-Fickian diffusion mechanism above the threshold.