The Role of Molecular Interactions in Controlling Methanol Diffusion in Polyimides: A Time-Resolved FTIR Spectroscopy Investigation

Polyimides are a well-known class of high-performance polymers with excellent properties and a wide range of applications, especially as membranes for gas and liquid separation. In this contribution a molecular level description of the methanol diffusion in three different polyimides is reported. Two commercial polyimides (PMDA-ODA and Ultem 1000) and a third one synthetized ad-hoc (6FDA-ODA) were examined in detail by time-resolved FTIR spectroscopy supplemented with gravimetric analysis. Complementary approaches were employed for the interpretation of the spectral data [difference spectroscopy (DS) and least-squares curve fitting (LSCF)]. Information about the overall diffusivity, the interactions and the dynamics of the molecular species in the polymer/penetrant systems were provided.