Preparation and Evaluation of Gas Transport Properties of Poly(ether imide)–Polyhedral Oligomeric Silsesquioxane Nanocomposite Membranes

A series of poly(ether imide)–POSS (PEI–POSS) nanocomposite membranes were prepared by varying the weight percentage (2, 4, 6, 8 and 10 wt%) of aminoethylaminopropylisobutyl functionalized polyhedral oligomeric silsesquioxanes (POSS–NH₂). The membranes were characterized by DSC, TGA, AFM, FESEM, XRD etc. There was no significant change in the thermal and mechanical properties of the membranes for lower POSS content, but with higher POSS content thermal stability and mechanical strength decreases. X-ray diffraction study showed amorphous morphology of the PEI–POSS membranes. FESEM and AFM studies revealed that the POSS molecules were well distributed and exhibited no significant increase of the roughness of the membranes for lower loading. At relatively higher loading of POSS some small aggregates were found and roughness of the membrane also increases. Gas transport properties through these PEI–POSS membranes with four gases CO₂, O₂, N₂ and CH₄ were successfully measured. The effects of incorporation of POSS into the fluorinated PEI membranes on their gas transport properties were investigated at three different temperatures (35 °C, 45 °C and 55 °C) and at an applied pressure of 3.5 atm. The nanocomposite membranes showed enhanced gas permeability. The PEI–POSS membranes with 2 wt% POSS loading (BPI-6FDA-2P) exhibited a significant increase in permeability compared to the pure PEI membrane (CO₂ permeability increase is 13.8%) with comparable selectivity for different gas pairs. The permeability of all the gases was increased significantly with increase in POSS loading with the reduction in permselectiviy for different gas pairs compared to the corresponding pure PEI membrane. Temperature dependence of permeation and diffusion coefficients were utilized to calculate the activation energies of the permeation and diffusion processes for different gas molecules through the PEI–POSS membranes from the slopes of the respective Arrhenius plots.