Stabilization mechanisms of polyimide-metallosiloxane nanocomposites against atomic oxygen impact

The structure and properties of sol–gel filled polyimide (PI) films were investigated as a protective coating for the low orbit devices. The organosoluble PI based on 4,4′-(9-fluorenylidene)dianiline and 3,3′,4,4′-diphenyloxide tetracarboxylic acid and tris-(methyldiethoxysiloxy)aluminium (Al-siloxane) and tris-(methyldiethoxysiloxy)iron (Fe-siloxane) as precursors of nanoparticles were used. A comparative analysis of the curing of Al-siloxane and Fe-siloxane in pure state and in the polymer matrix was carried out by FTIR spectroscopy. The type of precursor metal atom has no significant influence on the thermal, mechanical, and dielectric properties of PI nanocomposites, however the filler and the type of precursor metal atom determine their resistance to atomic oxygen (AO). PI filled with nanoparticles based on Fe-siloxane (PI-[FeOSi]) exhibit a higher AO resistance than PI-[AlOSi]. The SEM imaging showed that the protection mechanism of PIs with metallosiloxanes nanoparticles against the destructive AO effect is based on the formation of an external protective layer, morphology/continuity of which is determined by the nature of the metal atom. The protective layer on the PI-[FeOSi] surface is less susceptible to microcracking compared to the outer layer formed on the PI-[AlOSi] film.