Polyhedral Oligomeric Silsesquioxane (POSS) Polyimides as Space-Survivable Materials (Preprint)
AIR FORCE RESEARCH LAB WRIGHT-PATTERSON AFB OH TURBINE BRANCH
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Polyimides PIs such as KaptonR are used extensively in spacecraft thermal blankets, solar arrays, and space inflatable structures. Atomic oxygen AO in low Earth orbit LEO causes severe degradation of KaptonR. SiOsub 2 coatings impart remarkable oxidation resistance and have been widely used to protect KaptonR, yet imperfections in the SiOsub 2 application process and micrometeoroiddebris impact in orbit damage the SiOsub 2 coating leading to KaptonR erosion. A polyimide that is self-passivating by the formation of a silica layer upon exposure to AO has been achieved by the copolymerization of a polyhedral oligomeric silsesquioxane POSS diamine with the KaptonR monomers, pyromellitic dianhydride and 4,4-oxydianiline, resulting in POSS-KaptonR-polyimide. The self-passivating properties have been shown by monitoring a 1 micron deep scratch in POSS-PIs after exposure to AO. Kapton HR, SiOsub 2-coated Kapton HNR, and 8.75 weight Sisub 8Osub 11 cage main-chain POSS-polyimide 8.75 wt Sisub 8Osub 11 MC-POSS-PI were exposed to equivalent AO fluences before and after being scratched. During the first AO exposure and outside of the scratch, these samples eroded 5.0 microns, 0 microns, and less than 200 nm respectively. During the second AO exposure, the samples eroded an additional 5.0 microns within the scratch and outside of the scratch, 7.0 microns within the scratch and 0 microns outside of the scratch, and 200 nm within the scratch and 0 microns outside of the scratch respectively.
- Physical Chemistry
- Coatings, Colorants and Finishes