Water vapor transport in a series of polyarylates

Water vapor sorption and transport properties are presented for a series of polyarylates. The effect of making various structural changes in the polymer backbone has been studied, by comparing the transport properties to those of the base polymer bisphenol A isophthalate. All the polymers exhibit an upturn in the sorption isotherm at moderate to high activities, which in most cases is caused by plasticization of the polymer by water vapor. The response of water vapor to the structural changes is compared to that of the permanent gases reported previously for these materials. A good correlation is established between the diffusion and permeability coefficients and the fractional free volume. A similar behavior is seen in gases. However, the solubility coefficient, which decreases with increase in the fractional free volume, shows an opposite effect. Water vapor has the ability to hydrogen bond with itself and interact strongly with the polymer. In the case of solubility, the water vapor–polymer interaction plays an important role and overrides the effect of the increase in fractional free volume. The structural changes described here have similar effects on the permeation of water in a series of polysulfones reported earlier, as seen here for the polyarylates.