Comparisons of Polyhedral Oligomeric Silsesquioxane Polyimides as Space-Survivable Materials

Kapton (R) 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 (R). SiO2 coatings impart remarkable oxidation resistance to Kapton (R) yet imperfections in the SiO2 application process and micrometeoroid / debris impact in orbit damage the SiO2 coating leading to Kapton (R) 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 (R) polyimide, which 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 3.5, 7.0, and 8.75 weight % Si8O11 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 (R) at a fluence of 8.5 x 10(20) O atoms cm(-2). The self-passivation of POSS-Kapton (R)-PIs has also been demonstrated by monitoring a I 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 (R) 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 (R) replacement material.