Synthesis and in-situ atomic oxygen erosion studies of space-survivable hybrid organic/inorganic polyhedral oligomeric silsesquioxane polymers

Polymeric materials offer many advantages for low Earth orbit applications including ease of processing and reduced payload-to-orbit costs derived from a reduction in weight. However, over the last two decades it has been well established that polymers used in the construction of space vehicles undergo severe degradation resulting in reduced spacecraft lifetimes. These materials degrade because spacecraft surfaces must endure a high atomic oxygen (AO) flux, bombardment by low and high-energy charged particles, and thermal cycling along with the full spectrum of solar radiation. Recent testing of polymers containing the nanostructured Si-O frameworks known as POSS (polyhedral oligomeric silsesquioxanes) has revealed promising AO resistant properties. These POSS frameworks are comprised of a three dimensional inorganic core with a 3:2 O-Si ratio, surrounded by tailorable organic groups. Incorporation of POSS nanocomposites into polymers results in increased use and decomposition temperatures, improved mechanical properties, and oxidation resistance. This dissertation presents several characterization studies of the surfaces of newly synthesized POSS-containing polymers before and after exposure to AO. It also describes the synthesis of POSS-polyimides and the development of a new efficient route for synthesizing POSS-aniline monomers used for polyimide copolymerization. These POSS-polymers were exposed to AO produced by a unique hyperthermal oxygen atom source capable of producing a neutral, steady state flux of oxygen atoms devoid of any contaminating species or background radiation. A variety POSS-containing copolymers were examined because they have diverse properties and might perform well in different space-related applications. The exposed surfaces were characterized using X-ray photoelectron spectroscopy, and atomic oxygen erosion rates were calculated using stylus surface profilometry. Experiments were carried out in-situ because air exposure modifies the reactive surfaces formed during exposure to AO. Analysis reveals that these POSS-polymers rapidly form a ceramic-like, passivating SiO₂ layer that prevents further degradation of the underlying virgin polymer. The data indicates that a just a 1 mole addition of POSS can result in over a tenfold improvement in the AO erosion rate. These studies provide insight on how AO induces chemical state changes on these polymer surfaces and will enable future development of other novel space survivable materials.