Commercially available Kapton polyimide commonly used in various kinds of spacecrafts travelling in Low Earth Orbits (LEO) is severely degraded upon atomic oxygen (AO) exposure. An effective approach is to introduce the AO resistant component i.e., phenylphosphine oxide (PPO) in polymer. A series of copolyimide films has been successfully synthesized from random copolymerization of a PPO based monomer bis[4-(3-aminophenoxy)phenyl] phenylphosphine oxide (mBAPPO), 4,4′-diaminodiphenyl ether (4,4′-ODA) and 3,3′,4,4′-biphenyl tetracarboxylic dianhydride (sBPDA). The glass transition temperature (Tg) and mechanical properties were examined by differential scanning calorimetry and universal mechanical testing machine, respectively. The tensile strength, elongation, and Tg of the copolyimide films decreased with the increase of PPO content. The effects of PPO content on the morphology and structure evolvement of copolyimide films were also studied. AO exposure tests were performed using a ground-based AO effects simulation facility. Phosphorus-containing polyimide composite films formed a layer of dense polyphosphate network on the PI film after AO exposure protecting the underlying polymers from further degradation. This layer decreased the mass loss rate and outstandingly improved the AO resistance of PI films. The results of all the studies indicate that these phosphorus-containing copolyimide films can achieve great potential as polymeric materials for potential space applications in LEO and a space durable replacement for Kapton.
