2,3-Dihydroxypropyl methacrylate and 2-hydroxyethyl methacrylate hydrogels: gel structure and transport properties

The drying kinetics were examined in four cross-linked polymers that form hydrogels: 2,3-Dihydroxypropyl methacrylate (DHPMA) and 2-hydroxyethyl methacrylate (HEMA) and two random copolymers, with one-to-one and three-to-one HEMA-to-DHPMA molar ratios. The hydrogels were saturated with buffered, isotonic saline solution and deionized water; weight loss kinetics were monitored at temperatures from 16 to 37 °C at 30 and 60% relative humidity under air flow. While there are numerous studies of diffusion in hydrogels, this is one of few studies examining the initial evaporative drying period. The analyses of this short time data revealed that increasing the DHPMA content decreased water volatility; the percent water loss rate decreased with DHPMA content. Long time desorption data coupled with differential scanning calorimetry (DSC) results suggest that departure from Fickian desorption kinetics coincides with the onset of non-freezing water desorption. Dynamic mechanical analysis (DMA) revealed that changes in stiffness accompanying desorption are much more pronounced in HEMA containing polymers. Preliminary results indicate that the ion transport rate is greater in DMPMA containing hydrogels.