Effect of introducing amide groups into alkyl side chains of POSS for thermally stable and atomic-oxygen resistant coatings

Atomic oxygen (AO) exposure in very low Earth orbit (VLEO) severely degrades polymer substrates on satellite surfaces. While alkyl-substituted polyhedral oligomeric silsesquioxane (POSS) coatings without covalent crosslinking are widely studied for AO protection, their limited thermal durability restricts their applicability under VLEO thermal cycling conditions. To enhance thermal resistance, we focused on introducing noncovalent interactions through hydrogen bonding by incorporating amide groups into alkyl-substituted POSS and designed a C 8 -amide-S 9 -POSS molecule. This molecule exhibits a high melting point of approximately 140 °C, exceeding the ±100 °C fluctuations typical of the space environment. Spin-coated C 8 -amide-S 9 -POSS films formed smooth surfaces on polyimide substrates and were evaluated using a laser-detonation AO beam. Surface analyses confirmed that the films retained smooth morphology after AO exposure. Microbalance measurements revealed that AO-induced mass loss was lower for C 8 -amide-S 9 -POSS-coated films than for alkyl-substituted hexadecyl POSS coated films. Owing to its smooth coating, C 8 -amide-S 9 -POSS effectively protects the underlying polyimide substrates from AO-induced erosion. These results demonstrate that incorporating amide groups into alkyl-substituted POSS enhances thermal stability and improves film-forming properties, leading to improved AO protection of polyimide substrates. This molecular design strategy provides an effective approach to space coatings that require both high melting points and AO resistance.