Comparisons of Polyhedral Oligomeric Silsesquioxane Polyimides as Space-Survivable Materials

Kapton® 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®. SiO 2 coatings impart remarkable oxidation resistance to Kapton®, yet imperfections in the SiO 2 application process and micrometeoroid / debris impact in orbit damage the SiO 2 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 to form POSS-Kapton® polyimide, which is self-passivating by the formation of a silica layer upon exposure to AO. Evidence of a SiO 2 passivation layer has been shown by X-Ray Photoelectron Spectroscopy studies on AO exposed 3.5, 7.0, and 8.75 weight % Si 8 O 11 main chain (MC)-POSS-PI samples with erosion yields of 3.7, 0.98, and 0.3 percent, respectively, of the erosion yield for Kapton H® at a fluence of 8.5 x 10 20 O atoms cm -2 . 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. A study of the effect of temperature on the AO erosion of POSS-Kapton® samples showed that although the erosion of MC-POSS-PIs increased with temperature, they erode significantly less than their no-POSS analogous at elevated temperatures. Physical property characterization of POSS-PIs exposed to AO, and samples flown in LEO on the Materials International Space Station Experiment (MISSE), provide evidence that POSS-PIs are a potential Kapton ® replacement material.