Interaction between water and polymer chains in poly[hydroxyethyl acrylate) hydrogels

Polymer networks of different cross-linking densities were prepared by copolymerisation of hydroxyethyl acrylate and ethylene glycol dimethacrylate. The average molecular weight between cross-links as well as the polymer chain mobility were characterised by means of dynamic-mechanical spectroscopy. Equilibrium sorption iso-therms and the water uptake in immersion in liquid water allowed the determination of the Flory-Huggins interaction parameter between water molecules and polymer chain segments, which decreased with the water activity in the hydrogel and increased with the crosslinking density as a consequence of the hydrophobic character of the cross-linking agent. Dynamic sorption and desorption experiments were used to determine the diffusion coefficient.