Hybrid organic-inorganic 6FDA-6pFDA and multi-block 6FDA-DABA polyimide SiO2–TiO2 nanocomposites: Synthesis, FFV, FTIR, swelling, stability, and X-ray scattering

Abstract A series of hybrid polyimide-SiO 2 –TiO 2 nanocomposites were fabricated from functionalized multi- block polyimides, tetraethyl orthosilicate (TEOS), and titanium isopropoxide (TIP). Polyimides were solution imidized utilizing 4,4′-hexafluoroisopropylidene diphthalic anhydride (6FDA), and stoichiometric amounts of 4,4′-hexafluoroisopropylidene diamine (6FpDA) and 3,5-diaminobenzoic acid (DABA). Organic and inorganic phase compatibility and interfacial interactions were dependent upon metal alkoxide type and polyimide carboxylic acid functional group concentration (COOH). The glass transition temperature (Tg) of [6F-DABA-25] composites increased 25 °C from 334 °C to 359 °C as measured with dynamic mechanical analysis (DMA). Polyimide swelling experiments using THF demonstrated that TiO 2 created interpenetrating networks within the hybrid nanocomposite preventing dissolution, but pure SiO 2 systems readily dissolved in the solvent. The mean TiO 2 domain size within these composites was 102 nm, which was 10 times smaller than SiO 2 (1194 nm). WAXS revealed a significant increase in hybrid composite domain spacing from 9.63 A to 26.5 A. This led to a reduction in the polyimde's effective density within the composites from 1.45 g/cm 3 to 1.35 g/cm 3 , which was attributed to increasing interchain distance and decreasing chain packing density. These results are attributed to enhanced interactions between functionalized polymer chains and inorganic domains containing TiO 2 and SiO 2 –TiO 2 versus SiO 2 .