GLASS LIQUID TRANSITION AND CALORIMETRIC RELAXATION OF GLASSY AQUEOUS-SOLUTIONS IMBIBED IN POLY(2-HYDROXYETHYL METHACRYLATE) - A COMPARISON WITH BULK BEHAVIOR

Differential scanning calorimetric measurements of ethylene glycol and aqueous solutions of ethylene glycol (EG) and LiCl in hydrogels of poly(2-hydroxyethyl methacrylate) have been made and the results compared against the corresponding study of their bulk states. For increasing concentrations of EG solutions, the glass transition temperatures, T(g), in the bulk and in the hydrogels approach the same value at about 22 mol % of EG, but for LiCl solution they do not. The minimum in T(g) that appears at the low concentration of the solute in the bulk solutions vanishes when the solutions are imbibed in the hydrogel, and the glass transition endotherm becomes remarkably broader. Activation enthalpies for calorimetric relaxation at T(g) are in the range 80 +/- 20 kJ mol-1.