THE EFFECT OF OXYGEN PLASMA ON SOME EXPERIMENTAL POLYMERS CONTAINING SILICON AND PHOSPHORUS

As part of a NASA program on high performance polymers for space applications, polymers containing silicon and phosphorus were prepared, characterized and exposed to an oxygen plasma under vacuum. Thin films of polyimides containing pendent siloxane groups, thermosetting resins containing silicon and poly(arylene ether)s containing phenylphosphine oxide were exposed to a radio frequency generated oxygen plasma to assess their stability. The weight loss of the films was monitored as a function of exposure time and compared with that of Ultem(R) and Kapton(R) polyimide films of the same thickness exposed under identical conditions. All of the experimental materials exhibited better weight retention than either of the commercial polyimides. The thermosetting resins containing silicon and poly(arylene ether)s containing phosphine oxide exhibited only minor weight loss (0-5%) compared to that exhibited by Ultem(R) (75-100%) and Kapton(R) (35-82%). Organic polymers containing silicon are known to form silicates and silicon dioxide when exposed to atomic oxygen providing an in situ protective coating. Likewise, polymers containing phosphorus have been shown to form an inorganic phosphate surface layer which subsequently provides protection from further oxidation. The same inherent characteristics that provide the polymers with atomic oxygen resistance (i.e., high oxidation state or inorganic oxide formation) may also impart fire resistance. Materials containing phosphorus are known to exhibit good flame resistance. The chemistry, properties, limiting oxygen index and oxygen plasma resistance of these materials will be discussed.