Polymers with intrinsic microporosity (PIMs) are of great interest in the field of gas separation membranes. Already the first synthesized PIM-1 shows extraordinary permeability and selectivity. Unfortunately, PIM-1 is susceptible to physical aging and thus gradually loses its outstanding properties. In this study a polyhedral oligomeric silsesquioxane with phenethyl substituents (PhenethylPOSS) was used as a nanofiller (0–40 wt%) in the PIM-1 matrix to potentially improve the gas transport properties and prevent physical aging. The molecular mobility of the solution-cast nanocomposite films was analyzed by Broadband Dielectric Spectroscopy (BDS). Furthermore, gas permeability was determined with the time lag method (0–20 bar upstream pressure) at 35 °C for N2, O2, CH4 and CO2.
According to basic phenomenological models describing the solution-diffusion based mechanism of penetrant diffusion in dense polymers, a connection between the diffusive transport of gas molecules in a polymeric matrix and the molecular mobility of that matrix on a certain length scale is, in principle, established for a long time. However, experimental data directly showing this correlation are rare. The investigation of a series of nanocomposites based on a polyhedral oligomeric silsesquioxane (POSS) and a polycarbonate matrix allows a systematic change of the molecular mobility on a local length scale (β-relaxation) and of the corresponding activation energy EA, both determined by broadband dielectric spectroscopy. Independently, activation energies of penetrant diffusion (ED) of these nanocomposites were determined for N2, O2, CO2, and CH4 and a clear linear correlation between the two activation energies was established for the first time.