Non-equilibrium compressible lattice theories accounting for hydrogen bonding interactions: Modelling water sorption thermodynamics in fluorinated polyimides

In this contribution the sorption thermodynamics of water in glassy fluorinated polyimides has been interpreted by using two non-equilibrium lattice models, accounting for hydrogen bond formation, which have been developed by extending, respectively, the Panayiotou–Sanchez (PS) and the Non-Random Hydrogen Bonding (NRHB) equilibrium models to the case of glassy polymers. The procedure used to extend the equilibrium models follows the same line of thought utilized by Doghieri and Sarti in deriving the Non-Equilibrium Thermodynamics for Glassy Polymers (NET-GP) model. The approach has been found to be successful in interpreting experimental water sorption isotherms in two different perfluorinated polyimides, namely 6FDA-ODA and 6FDA-6FpDA. The models have been also found to be capable of supplying a good qualitative and quantitative estimate of the number of water–water and water/polymer hydrogen bonds, as emerged from the comparison of theoretical predictions with experimental data obtained by means of previous IR spectroscopic measurements.