Polyimide-silica hybrids derived from an isoimide oligomer precursor

Organic-inorganic hybrids of a cross-linked polyimide and silica were prepared via the sol-gel route using an acetylene-terminated oligomeric isoimide and tetraethoxysilane (TEOS) precursors. Two coupling agents, gamma-mercaptopropyltrimethoxysilane (MPTMS), and triethoxysilane were employed to compatibilise the organic and inorganic components of the precursor solution mixture. Homogeneous co-continuous phase morphologies could be produced with the use of MPTMS and their properties were evaluated by rheological and analytical techniques. Dynamic mechanical tests were carried out on unidirectional carbon fibre composites based on a polyimide-silica hybrid matrix. The results indicate that the thermooxidative stability of the hybrids at high temperatures is improved considerably over that of the base polyimide. However, the compatibilisation reactions of the coupling agent with the organic precursor, prior to the isomerisation-curing stages, causes a reduction in cross-linking density and a concomitant reduction in the glass transition temperature.