Porous Structure and Thermal Stability of Photosensitive Silica/Polyimide Composites Prepared by Sol-Gel Process

The sol-gel method was employed to synthesize an inorganic-organic photosensitive composite material, silica/polyimide. Silica was covalently bonded to polyimide by introduction of 1,4-aminophenol as a coupling agent. A photosensitive cross-linking agent, 2-(dimethylamino) ethyl methacrylate, was used to engender UV sensitivity to the composite. Using field emission scanning electron microscope imaging at very high magnifications, the composite film was found to exhibit a porous cross-sectional structure. The pores were interconnected to form numerous continuous channels within the matrix and silica particles were attached to the pore wall of the polyimide host. Depending on the preparation conditions, the size of the silica particles could vary from 20 nm to a few mu m. The thermal degradation temperatures, dynamic mechanical properties, glass transition temperatures, thermal expansion coefficients, and dielectric constants of various silica/polyimide composites were measured, and the results indicated that incorporation of silica could improve the thermal and dimensional stabilities of the polyimide. Also, because the silica/polyimide composite had a porous interior structure, it had a rather low dielectric constant with the lowest achievable value being 1.82. (C) 2009 Wiley Periodicals, Inc. J Appl Polym Sci 114: 2019-2029,2009