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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.

Water transport in a densely crosslinked epoxy network, TGDDM–HHPA, was investigated by coupling time-resolved FTIR spectroscopy and gravimetric measurements. Vibrational analysis yielded information on the different water species present in the system and allowed a quantitative estimation of their population at sorption equilibrium. The transport of water molecules was found to follow a Fickian behaviour characterized by an effective diffusion coefficient which increases with total water concentration. The dependence of the effective diffusion coefficient, D eff ( C ), on concentration, as obtained from integral sorption curves, was interpreted by introducing a concentration dependent term, D ( C ), and an “interaction factor”, ϕ , which accounts for the effect of the molecular interactions which effectively slow down the diffusion process. The results were compared with those obtained on another epoxy network, TGDDM–DDS, characterized by the presence of stronger interacting sites. Differences and similarities of the spectroscopic and gravimetric results are critically discussed in the light of the structure of the two networks.

The diffusion of low molecular weight penetrants through films of a PMDA-ODA polyimide and a corresponding polyimide-silica bicontinuous nanocomposite (organic–inorganic hybrid) was monitored using time-resolved FTIR spectroscopy and gravimetric analysis. A reacting and a non-reacting penetrant, ammonia and water vapour, were used in the study in order to evaluate their relative interactions with the components of the polyimide-silica hybrid from sorption and diffusion measurements. In the experiments with water vapours the sorption equilibrium was measured with activity levels varying from 0.1 to 0.75. The state of water molecules was examined on the basis of a simplified H-bonding association model. From the experiments using ammonia as the penetrant, it was possible to separate the physical diffusion component from the reaction-determined transport rate by using different sample thickness and penetrant pressure. A remarkable catalytic effect of the silica phase on the reaction of ammonia with the polyimide was observed.

In this contribution we analyse sorption and transport of several gases in semicrystalline syndiotactic polystyrene with nanoporous crystalline δ form. Investigation was performed on amorphous samples and on samples characterized by different degrees of crystallinity. Sorption isotherms of carbon dioxide, nitrogen and oxygen in the crystalline phase have been determined starting from experimental results obtained for semicrystalline and amorphous samples. Corresponding isosteric heats of sorption were evaluated for the crystalline and amorphous phase. Permeation tests were also performed to gather information on mass transport properties of semicrystalline samples, evaluating average diffusivities of carbon dioxide and oxygen, in the limit of small concentrations as function of degree of crystallinity.