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Polyimide/silica–titania (PI/SiO2–TiO2) hybrid films were prepared via an in situ sol–gel process. The PI precursor, poly(amic acid) (PAA), which contains 2,2'-bis[4-(4-aminophenoxy)-phenyl]propane (p-BAPPP), 3,3',4,4'- benzophenetetracarboxylic anhydride (BTDA) and 3-aminopropyltrimethoxysilane (APrTMOS), was first synthesized; this was followed by the addition of phenyltrimethoxysilane (PTMS) and/or tetraethyl orthotitanate (Ti(OEt)4) to fabricate PI/SiO2–TiO2 films. The relative content of SiO2 to TiO2 has remarkable effects on the crosslink structure and resultant properties of the hybrids. XPS results confirm that the amount of Si on the surface of the hybrids is higher than that in the bulk. The distribution of Ti in the hybrid films is contrary to the above trend because of the formation of three-dimensional SiOSi, SiOTi, and TiOTi networks. The SiO2 content of the hybrids containing only silica significantly affects their refractive index, contact angle, and dielectric constant. The films with added PTMS show higher contact angles than pure PI because nonpolar segments, C2H6 or benzene groups, tend to distribute on the surface. Upon the addition of (Ti(OEt)4), some hydrophilic segments on the surface of the hybrids are induced because of the formation of a crosslinked structure. The denser crosslinked molecular structure, and consequently lower CTE and higher Tg are obtained from hybrids containing more TiO2. By comparing the above properties and flexibility, the best composition of metal oxides (SiO2/TiO2) in hybrids is 20/80. That is, an optimum ratio of metal oxides in PI hybrids induces superior properties for advanced practical applications. © 2012 Wiley Periodicals, Inc. J. Appl. Polym. Sci., 2013 |
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