PREPARATION OF A NEW CLASS OF POLYIMIDE SILICA HYBRID FILMS BY SOL-GEL PROCESS

A new class of polyimide-silica hybrid films were successfully prepared by the sol-gel reaction starting from tetraethoxysilane (TEOS) in the solution of polyamic acid in N,N-dimethylacetamide. The hybrid films were obtained by the hydrolysis-polycondensation of TEOS in the Polyamic acid solution, followed by heating at 270-degrees-C. Fairly flexible films were obtained up to 70 wt% of silica content. The films containing the silica less than 8 wt% were yellow and transparent, whereas the films with higher silica content were yellow and opaque. The density of the silica in the hybrid films was estimated to be 1.65 gcm-3. The Si-29 nuclear magnetic resonance spectrum indicated that the silica in the films consisted of non-hydroxy, monohydroxy, and dihydroxy siloxane structures. Silica particles with diameter of around 5-mu-m were observed in the hybrid films by scanning electron microscopy. The density, decomposition temperature, and modulus of the hybrid films increased with increasing the silica content, whereas the tensile strength and elongation at break of the films decreased in this order. The glass transition temperature of the hybrid films showed the minimum at 8 wt% of silica content. The linear thermal expansion coefficient of the silica in the hybrid films was estimated to be 1.3 x 10(-5) K-1.