Variables analysis in the gelation of alkoxysilane solutions for the production of polyimide-silica hybrids

An investigation was carried out to study the effect of formulation variables on the gelation behaviour of alkoxysilane solutions based on tetraethoxysilane (TEOS) and that of corresponding polyimide-based hybrid solutions compatibilised by means of organofunctional trialkoxysilane coupling agents. The polyimide precursors used were from commercial sources, specifically a polyamic acid and an acetylene-terminated isoimide oligomer. Formulation parameters, such as the nature of the solvent and the catalyst, the nature and amount of the coupling agent, and the type of organic polymer precursor were found to have a dominant role in the gelation behaviour of the alkoxysilane solutions. The volumetric fill ratio used for the sol-gel reactions in a closed system was also found to have a significant effect on the gelation rate of the solutions. In addition, it was established that the nature of the coupling agent used for the compatibilisation of hybrids affects the relationship between gel time and concentration. The order in which gelation is ranked in relation to formulation variables is reversed, however, in the presence of the polyimide precursor used in the alkoxysilane solution for the production of the corresponding hybrids.