A novel multiscale method for the prediction of the volumetric and gas solubility behavior of high-Tg polyimides

A multiscale method for the evaluation of the fluid solubility in glassy polymers with high glass transition temperature Tg is presented and applied to the case of two polyimides, Ultem and Kapton. The method adopts Molecular Dynamics (MD) to simulate the polymer pressure–volume–temperature (pVT) behavior at temperatures above Tg not experimentally accessible. Such values are used to obtain the polymer parameters for the Perturbed Chain Statistical Associating Fluid Theory (PC-SAFT) Equation of State (EoS) required to calculate the gas solubility in the polymers below Tg with the Non Equilibrium PC-SAFT model. The MD-simulated polymer density values agree with the experimental and simulated data available, and the solubility calculated with the Non Equilibrium model represents correctly the experimental values for CH4, N2, O2 and CO2 sorption in Ultem, and the CO2 and SO2 solubility in Kapton at different temperatures. The approach can be applied to other high-Tg glassy polymers.

► NpT-MD simulations of pVT data for Ultem and Kapton above and below Tg are validated.
► Simulated pVT data above Tg are used to obtain the polymer parameters for PC-SAFT EoS.
► The NE-PC-SAFT model allows to represent gas sorption in glassy Ultem and Kapton.
► CO2 sorption in Kapton and Ultem is predicted (kij = ksw = 0) with errors below 20%.
► SO2 sorption in Kapton up to 55 °C is calculated (kij = 0) with errors below 21%.