Brian J. Petteys

Atomic Oxygen Effects on POSS Polyimides in Low Earth Orbit

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.

Polyimides with attached chromophores for improved performance in electro-optical devices

A method of chemical synthesis that allows for the facile attachment of a wide variety of chemical compounds, including highly active nonlinear optical chromophores, to polyimides has been developed recently at the Naval Air Warfare Center, Weapons Division. The synthesis of these compounds is presented, along with a discussion of their relevant physical and chemical properties, alone and in comparison to equivalent guest/host materials. Examples of attached chromophores include the well-known Disperse Red 1, along with high-activity chromophores of more recent interest such as FTC and CLD. The synthesis of structures that contain both attached chromophores and chemical functionalities that enable thermal cross-linking of the polyimides is also discussed.

Multifunctional polyimides for tailorable high-performance electro-optical devices

Progress in the development of a new class of multi-functional polyimides for use in electro-optical devices is reported. These polyimides contain hydroxymethyl-functional side-groups attached to the polymer backbone, allowing for the attachment of a wide variety of molecular species. It is shown that multiple types of organic molecules may be attached to the polymer simultaneously, with a quantitatively controllable distribution, to tailor the physical properties of the material. Methods for cross-linking the polyimides are presented, based on both modification to the backbone and the addition of difunctional additives (such as isocyanates) to solutions of the polymer during spin casting. Processing studies using spectroscopy to track the cross-linking reaction and its effects on organic nonlinear optical materials indicate that the latter method is compatible with poling processes for polymer guest/host systems with high nonlinear optical activities. Further studies using a novel thermomechanical analysis method demonstrate that the cross-linking reactions increase the glass transition temperature and inhibit physical relaxation processes in the cross-linked guest/host films.