Styrene Crosslinked Vinylesters II: Water Sorption, Water Diffusion and Cohesive Properties

The sorption characteristics (water equilibrium concentration W _m and coefficient of diffusion D) were determined gravimetrically for six styrene crosslinked vinylester networks at 30, 40 and 50°C, 95 % RH. The equilibrium water concentration (0.5 -1.8% by weight) is independent of the temperature and appears to be closely related to the concentration of polar groups (especially hydroxyls) in the polymer. It is an increasing function of the solubility parameter. The water diffusivity is of the same order of magnitude as that of unsaturated polyesters but considerably higher than that of hydrophilic amine crosslinked epoxies. There is no apparent correlation between D and volumetric properties such as the packing density, crosslink density or local mobility determined from viscoelastic spectra. In contrast, the fact that D is a decreasing function of the hydrophilicity for all the systems under consideration (including unsaturated polyesters and epoxies) seems to indicate that water diffusion is kinetically controlled by the strength of polymer-water interactions.