Atomic Oxygen-Resistant Epoxy-Amines Containing Phenylphosphine Oxide as Low Earth Orbit Stable

Atomic oxygen (AO) attacks carbon-fiber reinforcing polymers on the surfaces of spacecraft in low Earth orbit and threatens safe spacecraft operation and service life. Incorporating phenylphosphine oxide (PPO) groups into polymer chains offers a self-regenerating method of protection from AO but remains poorly understood. Herein, epoxies containing PPO groups were synthesized with increasing concentrations of phosphorus [P] from 0 to 8 wt % to investigate their AO resistance. Thin films of PPO-containing epoxies were exposed to AO via oxygen plasma etching and characterized by interferometry, X-ray photoelectron spectroscopy, and atomic force microscopy—infrared spectroscopy. Measurements confirmed that the exposure of these materials to AO produces a passivation phosphate (POx) layer on the surface of the sample, resulting in up to 100X decrease in AO erosion rates. Furthermore, key insights into the relationship between initial [P], passivation layer surface topology, and polymer depth profiles were obtained. Crucially, the results indicate that these materials advantageously did not exhibit linear erosion rates when exposed to AO, in contrast to most organic polymers, and their AO resistance can be readily tuned via synthetic incorporation of monomers with varying [P]