Water vapor sorption and transport in polysulfones and their blends

Water sorption and transport properties of homogeneous blends of a water soluble polymer with a relatively hydrophobic polymer were investigated. Specifically, a series of miscible blends of hydrophobic bisphenol A polysulfone and water soluble poly (vinyl pyrrolidone), as well as hydrophobic polyethersulfone and water soluble polyethyloxazoline, were studied. The effects of polymer repeat unit structure on the water sorption and transport properties of a series of polysulfones based on bisphenol A polysulfone were also analyzed.; The accurate measurement of water vapor sorption and permeation in polymers is complicated because water has a tendency to adsorb on high energy surfaces, a relatively high heat of vaporization, and a high solubility in most polymers. These issues and the difficulties they cause in the design of sorption and permeation equipment are reviewed, and some new approaches to circumvent these problems are described and employed in the design of the equipment used in this study.; The equilibrium solubility of water in a polymer, unlike permanent gases, does not have a simple dependence on free volume but correlates more strongly with the frequency of hydrogen bonding sites on the polymer. Thus, the solubility of water in the polymer blend films increases with increasing water soluble polymer content. Structural modifications to the repeat unit of bisphenol A polysulfone which enhance the ability of the polymer to hydrogen bond also generally increase the solubility of water in the polymer.; For all systems studied, water diffusivity is directly dependent on polymer fractional free volume. For the blend systems studied, the addition of the water soluble polymer decreases the fractional free volume of the polymer blend, resulting in a diffusion coefficient that generally decreases with increasing water soluble polymer content in the blend. Structural modifications to bisphenol A polysulfone that increase the polymer fractional free volume tend to increase the diffusion coefficient of water in the polymer.; Water permeability is equal to the product of the solubility and the diffusivity. Thus, in all of the systems studied, water permeability broadly correlates with the polymer free volume, but a favorable water-polymer interaction can be an overriding factor.