Fabrication of polyimide/titania nanocomposites containing benzimidazole side groups via sol–gel process

Abstract

In recent years, polyimide (PI) hybrid materials have received considerable attention owing to the dramatic enhancements over their pristine state in thermal stabilities, mechanical properties and other special features by introducing only a small fraction of inorganic additives. In this investigation, hybrid nanocomposite films of titanium dioxide (TiO2) in PI were successfully fabricated by an in situ sol–gel process starting from tetraethyl orthotitanate in the solution of poly(amic acid) in N,N-dimethylacetamide. Neat PI was prepared from the polymerization of 2-(3,5-diaminophenyl)-benzimidazole and pyromellitic dianhydride. The hybrid films were obtained by the hydrolysis–polycondensation of moisture-sensitive titania precursor in poly(amic acid) solution, followed by the elimination of solvents and imidization process. The chelating agent, acetylacetone, was used to reduce the gelation rate of titanium alkoxide. The complete imidization temperature of the poly(amic acid) was delayed; furthermore, the thermal stability of PI was enhanced through the incorporation of the inorganic moieties in the hybrid materials. The chemical and morphological structures of the hybrid materials were characterized by Fourier transform infrared spectroscopy, X-ray diffraction, field emission scanning electron microscopy and transmission electron microscopy. The results show that the TiO2 particles are well dispersed in the PI matrix with particle size between 15 and 30nm in diameter.