Remarkable AO resistance of POSS inorganic/organic polymers

Polymeric materials offer many advantages for Low Earth Orbit applications including ease of processing and reduced payload-to-orbit costs from the reduction in weight. However, currently applied materials are limited by their severe degradation as a result of atomic oxygen (AO) impingement, vacuum-ultraviolet irradiation and thermal cycling. The Air Force Research Laboratory has dramatically improved polymer properties through the incorporaton of hybrid organic/inorganic POSS (Polyhedral Oligomeric Silsesquioxane). The POSS frameworks are comprised of a three dimensional inorganic core with a 3:2 O-Si ratio, surrounded by tailorable organic groups. POSS incorporation results in increased use and decomposition temperatures, improved mechanical properties, and oxidation resistance. Results of flammability and char motor tests have shown the rapid formation of a ceramic SiO₂ layer, making the hybrid POSS-polymers potential candidates as space resistant materials. This paper reports on the AO resistance of POSS-PDMS and POSS-polyurethanes, with the data obtained using a unique high-purity AO source coupled with in situ XPS. Experimental results show the rapid formation of a passivating SiO₂ layer, which is known to be self-annealing in the presence of VUV radiation. Discussions will be centered on the synthesis of the hybrid POSS polymers, AO testing and subsequent material characterization.