SYNTHESIS AND CHARACTERIZAITON OFSPACE-SURVIVABLE POSS-KAPTON~?-POLYIMIDES

摘要

Kapton~? is used extensively in spacecraft thermal blankets, solar arrays, and spacerninflatable structures. This material is chosen due to its thermal and physical properties,rnhowever it degrades severely in low Earth orbit (LEO) by atomic oxygen (AO). SiO_2rncoatings impart remarkable oxidation resistance to Kapton~?, yet imperfections in the SiO_2rnapplication process and micrometeoroid debris impact in orbit may damage the SiO_2rncoating and lead to Kapton~? erosion. Polyhedral oligomeric silsesquioxane (POSS) is arnsilicon and oxygen cage-like structure surrounded by organic groups. POSS-diamine andrnthe monomers of Kapton~? were polymerized and cured to form POSS-polyimide (POSSPI)rnfilms. These POSS-copolymers are self-passivating by the formation of a silica layerrnupon exposure to AO. Evidence of a SiO_2 passivation layer has been shown by X-rayrnphotoelectron spectroscopy studies on AO exposed 3.5, 7.0, and 8.75 weight % Si8O11rnmain chain (MC)-POSS-PI samples with erosion yields of 3.7, 0.98, and 0.3 percent,rnrespectively, of the erosion yield for Kapton H~? at a fluence of 8.5 × 10~(20) O atoms cm~(-2).rnThe self-passivation of POSS-Pis has also been demonstrated by monitoring a 1 micronrndeep scratch in AO-exposed main-chain-POSS-PI (MC-POSS-PI) after a secondrnexposure to AO. A study of the effect of temperature on the AO erosion of POSS-PIrnsamples showed that although the erosion of MC-POSS-Pis increased with temperature,rnthey erode significantly less than their no-POSS analogues at elevated temperatures.rnPOSS-polyimides flown for 3.9 years in low Earth orbit on the Materials InternationalrnSpace Station Experiment (MISSE) showed dramatically increased survival relative to 0