Synthesis and Characterization of Space-Survivable POSS-Kapton (Trademark) Polyimides (Preprint)

Abstract : Kapton(Registered) is used extensively in spacecraft thermal blankets, solar arrays, and space inflatable structures. This material is chosen due to its thermal and physical properties, however it is degraded severely in low Earth orbit (LEO) by atomic oxygen (AO). SiO2 coatings impart remarkable oxidation resistance to Kapton(Registered), yet imperfections in the SiO2 application process and micrometeoroid debris impact in orbit may damage the SiO2 coating and lead to Kapton(Registered) erosion. Polyhedral oligomeric silsesquioxane (POSS) is a silicon and oxygen cage-like structure surrounded by organic groups. POSS-diamine and the monomers of Kapton(Registered) were polymerized and cured to form POSS-polyimide (POSS-PI) films. These POSS-copolymers are 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(Registered) at a fluence of 8.5 x 1020 O atoms cm-2. The self-passivation of POSS-PIs has also been demonstrated by monitoring a 1 micron deep scratch in AO-exposed main-chain-POSS-PI (MC-POSS-PI) after a second exposure to AO. A study of the effect of temperature on the AO erosion of POSS-PI samples showed that although the erosion of MC-POSS-PIs increased with temperature, they erode significantly less than their no-POSS analogues at elevated temperatures. POSS-polyimides flown for 3.9 years in low Earth orbit on the Materials International Space Station Experiment (MISSE) showed dramatically increased survival relative to 0 % POSS-polyimide. These results and physical property characterization of POSS-PIs exposed to AO, evidence that POSS-PIs are a viable Kapton(Registered) replacement material.