Water absorption by uncrosslinked polymers, networks and IPNs having medium to high polarity

The water absorption characteristics of five epoxy networks, one vinylester network and two interpenetrated networks resulting from the blending of the vinylester with two of the epoxy resins, have been studied in the 50–100 °C temperature range. In all of the cases, the water solubility follows the Arrhenius law. The pre-exponential factor S0 and the heat of dissolution Hs have been determined and compared with previously reported values for other networks and linear polymers. These results show that water absorption increases with the polymer polarity and is higher for interpenetrating polymer networks than for the individual network components but it is less dependent on the large-scale network structure The correlation between the logarithm of S0 and Hs indicates the existence of a compensation phenomenon, with a compensation temperature of Tc=376 K. This phenomenon may be explained by the fact that the number of hydrophilic sites is determined not only by the number of polar groups, but is also influenced by the spatial distribution of the polar groups and their ability to form H-bonds with water molecules.