POSS-Grafted PAI/MoS2 Coatings for Simultaneously Improved Tribological Properties and Atomic Oxygen Resistance

Polyamide-imide (PAI) is extensively used in onboard spacecraft mainly as a surface-protective material owing to its inherent excellent mechanical strength, chemical inertness, irradiation resistance, high-temperature stability, and high wear resistance. Nevertheless, PAI in the low earth orbit (LEO) is severely eroded by the presence of atomic oxygen (AO). To solve this problem, in this work, the octa- and mono-amino polyhedral oligomeric silsesquioxane (OMPOSS) were incorporated into the PAI matrix by covalent grafting, and the lubricating coatings were prepared using molybdenum disulfide (MoS2) as the solid lubricant. Additionally, the effects of AO exposure on pure PAI/MoS2 and POSS-reinforced PAI/MoS2 coatings were investigated. More importantly, the results indicated that the coatings exhibited outstanding tribological properties and anti-AO performance owning to the addition of octa-amino POSS (OPOSS) monomers into the main chain and mono-amino POSS (MPOSS) as the end-capping reagent of the polymer. The cooperation of OPOSS and MPOSS significantly improved the AO resistance resulting from the formation of a connected and networked silicon dioxide passivating layer on the surface. As a result, the PAI-based lubricating coating modified by OMPOSS possessing excellent tribological properties and anti-AO performance would be a novel space-suitable material in LEO.