Influence of the hydrophobic phase on the thermal transitions of water sorbed in a polymer hydrogel based on interpenetration of a hydrophilic and a hydrophobic network

An interpenetrating polymer network with a low cross-linking content (so that phase separation appears) based on interpenetration of a hydrophobic, poly(ethyl acrylate), PEA, and a hydrophilic, poly(hydroxyethyl acrylate), PHEA, network is synthesized, swollen with different amounts of water, and subjected to cooling and heating scans in a differential scanning calorimeter. Results are compared with those of a pure hydrophilic network for the same water contents. Three qualitatively different kinds of thermograms are found in both cases, but in the case of the IPN, the hydrophobic component of the IPN significantly perturbs the melting process of water sorbed in the hydrophilic phase of the hydrogel. The hydrophobic component of the IPN has no appreciable influence on the specific (per unit hydrophilic component mass) water sorption, which remains almost the same as in the pure hydrophilic network, but it hinders the first-order transitions of water in the hydrogel and controls their temperature.