Space Survivability of Main-Chain and Side-Chain POSS-Kapton Polyimides

Kapton® polyimde (PI) is extensively used in solar arrays, spacecraft thermal blankets, and space inflatable structures. Upon exposure to atomic oxygen (AO) in low Earth orbit (LEO), Kapton® is severely degraded. An effective approach to prevent this erosion is chemically bonding polyhedral oligomeric silsesquioxane (POSS) into the polyimide matrix by copolymerization of POSS‐diamine with the polyimide monomers. POSS is a silicon and oxygen cage‐like structure surrounded by organic groups and can be polymerizable. The copolymerization of POSS provides Si and O in the polymer matrix on the nano level. During POSS polyimide exposure to atomic oxygen, organic material is degraded and a silica passivation layer is formed. This silica layer protects the underlying polymer from further degradation. Ground‐based studies and MISSE‐1 and MISSE‐5 flight results have shown that POSS polyimides are resistant to atomic‐oxygen attack in LEO. In fact, 3.5 wt% Si8O11 main‐chain POSS polyimide eroded about 2 μm during the 3.9 year flight in LEO, whereas 32 μm of 0 wt% POSS polyimide would have eroded within 4 mos. The atomic‐oxygen exposure of main‐chain POSS polyimides and new side‐chain POSS polyimides has shown that copolymerized POSS imparts similar AO resistance to polyimide materials regardless of POSS monomer structure.