Polyimide-silica materials have been prepared via the sol-gel process by mixing tetramethoxysilane with a polyamic acid. Two polyamic acids have been used. The first is obtained with an equimolar mixture of oxydianiline (ODA) and pyromellitic dianhydride (PMDA) in dimethyacetamide. The second is prepared with a mixture of PMDA with aminopropyltrimethoxysilane (APrTMOS).
The microstructure of the materials obtained with these two polyamic acids are drastically different. The presence of both amino and methoxy side-groups on the APrTMOS enables a chemical bonding between the organic and the inorganic networks resulting in the formation of homogeneous films. On the other side, no chemical bond is provided by the ODA-PMDA polyamic acid resulting in a biphasic microstructure where pure silica particles are embedded in a polyimide matrix.
These two types of materials have been characterized in order to point out the key parameters of their microstructure. 29Si NMR, thermogravimetric analysis, scanning electron microscopy and infra-red spectroscopy have been used to study materials containing various proportions of TMOS and prepared with various hydrolysis ratios.