Methanol diffusion in polyimides: A molecular description

In this contribution the diffusion of methanol in two commercial polyimides (6FDA-ODA and Ultem® 1000) is investigated in detail by gravimetric analysis and in-situ, time-resolved FTIR spectroscopy. Two methods of spectral data analysis are employed, namely difference spectroscopy (DS) and least-squares curve fitting (LSCF). These approaches provided complementary information about the overall diffusivity, the interactions and the dynamics of the molecular species present in the investigated systems. Spectroscopic measurements on thin film samples (2-4 μm) allowed us to identify the interaction site(s) on the polymer backbone and to propose likely structures for the H-bonding molecular aggregates.By coupling gravimetric and spectroscopic data collected in the same experimental conditions it was possible to evaluate the molar absorptivities of the different molecular species, and hence their populations, in both polyimides. The results highlighted the relevance of the H-bonding interaction and of the substrate molecular structure on the final transport properties of the systems.