Polyimide/nano-TiO2 hybrid films having benzoxazole pendent groups: In situ sol–gel preparation and evaluation of properties

• A series of PI/TiO2 nanocomposites were fabricated via in situ sol–gel procedure.
• The influence of benzoxazole pendent groups on the properties of nanocomposites was studied.
• The chemical and morphological structures of the hybrid films were characterized.
• TiO2 NPs dispersed well in the PI matrix with particle diameters between 25 and 40 nm.
• The fire-resistance of nanocomposites was enhanced by the introduction of TiO2.

Polyimide/titania (PI/TiO2) nanocomposite films have been successfully fabricated through the in situ formation of TiO2 within a PI matrix via sol–gel method. Poly(amic acid) (PAA), which is the precursor of PI, was successfully synthesized by mixing pyromellitic dianhydride (PMDA), with equimolar amount of a diamine monomer having a pendent benzoxazole unit and two flexible ether linkages in N,N-dimethylformamide (DMF) solvent. Tetraethyl orthotitanate [Ti(OEt)4] and acetylacetone were then added to the resulted PAA. After imidization at high temperature, PI/TiO2 hybrid films were formed. The structure and morphology of the hybrid nanocomposites with different titania contents (0 wt%, 5 wt%, 10 wt%, and 15 wt%) were characterized by Fourier transform infrared spectroscopy, X-ray diffraction, and transmission electron microscopy. The results indicate that the TiO2 nanoparticles were homogeneously dispersed in the hybrid films. The thermogravimetric analysis of nanocomposites confirms the improvement in the thermal stability with the increase in the percentage of titania nanoparticle. Transmission electron microscopy showed that the nanoparticles with an average diameter of 25–40 nm were dispersed in the polymer matrix.