The water equilibrium concentration has been determined for three aromatic polysulfones differentiated essentially by the sulfone concentration, in the 0-0.9 activity range, at temperatures of 50, 60, and 70 degrees C, using a dynamic vapor sorption apparatus. In all the cases, Henry's law was obeyed. The corresponding solubility S and heat of dissolution H-s were determined and their relationships with structure were investigated. The fact that S increases nonlinearly with the sulfone concentration and that H-s is also an increasing function of the latter leads one to abandon classical approaches to polymer-water interactions and propose a model in which water is doubly bonded. Then, S depends on the distribution of distances between polar groups, characterized by a function P(r) and H-s depends on both P(r) and the hydrogen bond potential U(r). (C) 2008 Wiley Periodicals, Inc.