A series of hybrid polyimide-SiO2-TiO2 nanocomposites were fabricated from functionalized multi-block [6FDA-6FpDA]-[6FDA-DABA] polyimides, tetraethyl orthosilicate (TEOS), and titanium isopropoxide (TIP). Compatibility and interfacial interactions between organic and inorganic phases were dependent on the nature of metal alkoxide and polyimide carboxylic acid functional group concentration. These interactions served to retard polymer segmental motions, inhibit the packing of polymer chains, and potentially create more accessible free volume in the hybrid system without defects. The fractional free volume was estimated based upon density results and had 29% increase for [6F-DABA]-[SiO2-TiO2] composites compared with pure polyimide. WAXS revealed a significant increase in hybrid composite average domain spacing from 9.63 Å to 26.5 Å. The DMTA results pointed to the interfacial interactions existing between TiO2 and SiO2-TiO2 based inorganic materials and functionalized multi-block polyimides. Carboxylic group -OH bending changes were notable at 1456 and 1403 cm-1, and swelling/dissolution experiments using THF demonstrated that TiO2 networks prevented dissolution, but pure SiO2 systems readily dissolved in the solvent. The mean TiO2 domain size within these composites was 102 nm, which was 10 times smaller than SiO2 (1194 nm). Simultaneous improvements in selectivity and permeability were observed in those hybrid materials with favorable interactions. For [6F-DABA-50]-[SiO2-TiO2] series hybrids, the He permeability was greatly enhanced from 58 Barrers (pure polyimide) to 83 Barres and the He/CH4 selectivity was increased from 221 (pure polyimide) to 334. The gas separation performance was compared to Robeson “upper bound” and exceeded the boundary in some cases.

Hybrid organic-inorganic polyimide SiO2-TiO2 nanocomposites: Structure, physical properties, and gas seperation

253rd National Meeting (2017)

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