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Kapton polyimde is extensively used in solar arrays, spacecraft thermal blankets, and space inflatable structures. Upon exposure to atomic oxygen in low Earth orbit (LEO), Kapton is severely eroded. An effective approach to prevent this erosion is to incorporate polyhedral oligomeric silsesquioxane (POSS) into the polyimide matrix by copolymerizing POSS monomers with the polyimide precursor. The copolymerization of POSS provides Si and O in the polymer matrix on the nano level. During exposure of POSS polyimide to atomic oxygen, organic material is degraded, and a silica passivation layer is formed. This silica layer protects the underlying polymer from further degradation. Laboratory and space-flight experiments have shown that POSS polyimides are highly resistant to atomic-oxygen attack, with erosion yields that may be as little as 1% those of Kapton. The results of all the studies indicate that POSS polyimide would be a space-survivable replacement for Kapton on spacecraft that operate in the LEO environment.

Public reporting burden for the collection of information is estimated to average 1 hour per response, including the time for reviewing instructions, searching existing data sources, gathering and maintaining the data needed, and completing and reviewing the collection of information. This review is intended to cover the more recent advances in both structure-property relationships of polymers incorporating Polyhedral Oligomeric Silsesquioxane(s) (POSS) nanostructured chemicals as well as space-survivability testing of POSS-polymers. The strategy employed for using POSS as building blocks is discussed in addition to current models and predictions pertaining to the ideal crystallite/aggregate size of the nanocomposite within the polymer matrix to provide maximum mechanical improvements. The oxidation and rapid formation of SiO2 during atomic oxygen testing leads to a passivating layer, and conclusive proof of these phenomena is presented. Also, a brief history of POSS is outlined to help readers understand how they relate to the recent boom in nanotechnology and their position in nanomaterials R&D.

A series of four new end-capped and hydroxymethyl-functionalized polyimides were prepared. Through a two-step chemical modification process (3-aminopropyl)(hepta-i-butyl) polyhedral oligomeric silsesquioxane (POSS) was covalently attached to the polymer backbone. POSS loading levels as high as 36 wt % could be obtained while maintaining excellent processability and optical clarity of thin films. Concurrent attachment of either a cyanate ester or hydroxyethyl methacrylate (HEMA) group afforded processable POSS-polyimides that underwent thermal curing to yield solvent-resistant films, both having final T g's of 251 °C. Kinetic analysis of the cure reactions yielded energy of activations of 93 kJ/mol (cyanate ester) and 103 kJ/mol (HEMA). Exposure of a POSS-polyimide containing ∼31 wt % POSS to atomic oxygen displayed no measurable level of erosion relative to a Kapton H standard.

Kapton polyimide (PI) is widely used on the exterior of spacecraft as a thermal insulator. Atomic oxygen (AO) in lower earth orbit (LEO) causes severe degradation in Kapton resulting in reduced spacecraft lifetimes. One solution is to coat the polymer surface with SiO 2 since this coating is known to impart remarkable oxidation resistance. Imperfections in the SiO 2 application process and micrometeoroid / debris impact in orbit damage the SiO 2 coating, leading to erosion of Kapton.A self passivating, self healing silica layer protecting underlying Kapton upon exposure to AO may result from the nanodispersion of silicon and oxygen within the polymer matrix. Polyhedral oligomeric silsesquioxane (POSS) is composed of an inorganic cage structure with a 2:3 Si:O ratio surrounded by tailorable organic groups and is a possible delivery system for nanodispersed silica. A POSS dianiline was copolymerized with pyromellitic dianhydride and 4,4?-oxydianiline resulting in POSS Kapton Polyimide. The glass transition temperature (Tg) of 5 to 25 weight % POSS Polyimide was determined to be slightly lower, 5 -10 %, than that of unmodified polyimides (414 ºC). Furthermore the room temperature modulus of polyimide is unaffected by POSS, and the modulus at temperatures greater than the Tg of the polyimide is doubled by the incorporation of 20 wt % POSS.To simulate LEO conditions, POSS PI films underwent exposure to a hyperthermal O-atom beam. Surface analysis of exposed and unexposed films conducted with X-ray photoelectron spectroscopy, atomic force microscopy, and surface profilometry support the formation of a SiO 2 self healing passivation layer upon AO exposure. This is exemplified by erosion rates of 10 and 20 weight % POSS PI samples which were 3.7 and 0.98 percent, respectively, of the erosion rate for Kapton H at a fluence of 8.5 x 10 20 O atoms cm -2 . This data corresponds to an erosion yield for 10 wt % POSS PI of 4.8 % of Kapton H. In a separate exposure, at a fluence of 7.33 x 10 20 O atoms cm -2 , 25 wt % POSS Polyimide showed the erosion yield of about 1.1 % of that of Kapton H. Also, recently at a lower fluence of 2.03 x 10 20 O atoms cm -2 , in going from 20 to 25 wt % POSS PI the erosion was decreased by a factor of 2 with an erosion yield too minor to be measured for 25 wt % POSS PI.