Molecular dynamics (MD) simulations of more than 40 model systems of dry and hydrated poly(pyromellitimide-1,4-diphenyl ether) (PMDA-ODA) polyimide, also known as Kapton, were undertaken in order to study the specific interactions between water and a glassy polymer matrix. Dry amorphous Kapton models were generated using a hybrid pivot Monte Carlo-MD single-chain sampling technique and were found to reproduce many features found experimentally. Water was subsequently introduced into the polyimide systems with weight percentages ranging from 1.4 to 10 wt % at 373 K. At the lower concentrations, water is found to occupy the pre-existing void space in the polymer matrix. On the other hand, there are significant changes in the volumetric, energetic, and conformational properties of the chains for water contents above ∼3%. The static and dynamic properties of the hydrogen bonds have been analyzed. In all cases under study, water is preferentially hydrogen-bonded to two sites, thus forming bridges. These water bridges, whose occurrence depends on the weight percentage of the penetrant, can link either two polymer sites, one polymer site and another water, or two other waters. Water clusters have been analyzed and found to be in agreement with findings from NMR, dielectric, and infrared attenuated total reflection (ATR) measurements. Their geometries are more chainlike and at high water contents approach a cocontinuous network. Such a characterization at the molecular level calls into question the commonly used interpretation of solubility curves based on the Zimm−Lundberg theory.

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Molecular dynamics (MD) simulations of three polysulfones (poly(ether sulfone) PESU, poly(phenylene sulfone) PPSU and polysulfone PSU) in dry and hydrated states were undertaken in order to study the specific interactions between water and glassy polymer matrices of the same structural family. Dry polysulfone models were generated using a hybrid pivot Monte Carlo‐MD single‐chain sampling technique and the resulting relaxed densities were found to be in close agreement with experimental data. Hydrated systems are found to reproduce quite well volumetric changes experimentally observed. The concentrations of sulfonic groups can explain qualitatively their different water solubilities. Water is preferentially hydrogen‐bonded to two sites which either link two polymer sites, or one polymer site and another water, or two other waters. A detailed analysis of these water bridges that are formed is presented. Only a small quantity of potential bridging sites are occupied for water contents near the experimental saturation. The free fractional volumes, the probe accessible volumes, the swelling of the polymers, the water‐polymer interactions and the hydrogen bond lifetimes, are also presented for these polysulfones. Water‐water interactions and water clusters are found to be more important in the more hydrophilic PESU in comparison to the less hydrophilic PSU. © 2010 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys, 2010