Comparisons of Polyhedral Oligomeric Silsesquioxane (POSS) Polyimides as Space-Survivable Materials (Postprint)
AIR FORCE RESEARCH LAB EDWARDS AFB CA PROPULSION DIRECTORATE
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Kaptonregistered name is used extensively in spacecraft thermal blankets, solar arrays, and space inflatable structures. Atomic oxygen AO in low Earth orbit LEO causes severe degradation of Kapton. SiO2 coatings impart remarkable oxidation resistance to Kapton, yet imperfections in the SiO2 application process and micrometeoroid debris impact in orbit damage the SiO2 coating leading to Kapton erosion. Polyhedral oligomeric silsesquioxane POSS is a silicon and oxygen cage-like structure surrounded by organic groups which can be polymerizable. POSS-diamine was polymerized with the Kapton monomers, pyromellitic dianhydride and 4.4-oxydianiline. The resulting POSS-Kapton polyimide PI is self-passivating by the formation of a silica layer upon exposure to AO. Evidence of a SiO2 passivation layer has been shown by X-Ray Photoelectron Spectroscopy studies on AO exposed samples, and erosion yields of 3.5, 7.0, and 8.75 weight Si8O11 MC-POSS-PI samples which were 3.7, 0.98, and 0.3 percent, respectively, of the erosion yield for Kapton H at a fluence of 8.5 x 10 to the 20th power oxygen atoms per square cm. The self-passivation of POSS-Kapton-PIs has also been demonstrated by monitoring a 1 micron deep scratch in MC-POSS-PI after exposure to AO. Kapton Htrade mark, SiO2 coated Kapton HNtrade mark and 8.75 wt Si8O11 MC-POSS-PI samples were exposed to AO, scratched, and re-exposed to AO. Upon the first exposure, these samples eroded 5.0 micron, 0 micron, and 200 nm respectively. Upon the second exposure the samples eroded, respectively, an additional 5.0 micron within and outside of the scratch, and 7.0 micron and 200 nm within the scratch only. Physical property characterization of POSS-PIs exposed to AO, and samples flown in LEO on the Materials International Space Station Experiment MISSE, evidence that POSS-PIs are a viable Kapton replacement material.
- Physical Chemistry
- Polymer Chemistry