Free-standing, polysilsesquioxane-based inorganic/organic hybrid membranes for gas separations

Polysilsesquioxanes (PSSQs) are composite materials consisting of inorganic framework and organic functional groups. Their inherent dual characteristics offer various applications including microelectronics, optics and biosciences. For the first time, free standing ladder-like PSSQ films were successfully prepared for gas separations, allowing practical applications in the membrane area. In order to fabricate a free-standing PSSQ film, a novel ladder-like poly(phenyl-co-glycidoxypropyl) silsesquioxanes with phenyl:glycidoxypropyl copolymer ratio of 6:4 (LPG64) were synthesized by a base-catalyzed sol-gel reaction. Moreover, the LPG64 films were thermally crosslinked with octa(aminophenyl)-T8-silsesquioxane (OAPS) with different concentrations of OAPS. Single gas (i.e. He, H₂, CO₂, O₂, N₂, and CH₄) transport measurements were performed for the LPG64 as well as LPG64/OAPS composite membranes. The LPG64 membrane exhibited a relatively high CO₂ permeability of 47.88Barrer compared to other gases with CO₂/N₂ permselectivity of 30.5. The annealing effect on the transport results of the LPG64 membrane was negligible due to its rigid inorganic framework. Combination of our transport analysis and XRD characterization demonstrated that the addition of OAPS led to more dense chain packing, reducing permeability for all the gases tested in this work with increase in permselectivities. Especially, the LPG64/OAPS (80/20wt/wt) membrane improved He/N₂ and H₂/N₂ permselectivities by 98% and 80%, respectively, compared to those for neat LPG64 membranes.