Hybrid inorganic-organic materials based on a 6FDA-6FpDA-DABA polyimide and silica: physical characterization studies

A series of hybrid polyimide--silica composites were fabricated from a functionalized fluorinated polyimide and tetramethoxysilane (TMOS), methyltrimethoxysilane (MTMOS), and phenyltrimethoxysilane (PTMOS) via a sol--gel process. Polyimides were solution imidized employing 4,4'-hexafluoroisopropylidenediphthalic anhydride (6FDA), and various amounts of 4,4'-hexafluoroisopropylidene dianiline (6FpDA) and 3,5-diaminobenzoic acid (DABA). The degree of cross-linking between the silica structures and the polyimide matrixes, as well as the morphology of the hybrid systems were highly dependent on the type and content of the alkoxide employed. The higher functionality and reactivity of TMOS alkoxide gave rise to highly cross-linked, homogeneous hybrid systems, while the MTMOS and PTMOS based hybrid systems were phase separated and the silica structures largely uncondensed. Although the thermal stability changed a little, incorporation of the silica structures in the polyimide matrix increased the rigidity and mechanical strength of the hybrid materials, particularly at elevated temperatures.