The colorless polyimides LaRC (TM)-CP1 (6FDA-4BDAF) and LaRC (TM)-CP2 (6FDA-APB), which are frequently used in the aerospace industry, were exposed to UV photo-oxidation at atmospheric pressure. XPS data show a significant increase in the oxygen concentration and decrease in the carbon concentration as a result of treatment. There are slight, but significant, increases in the concentrations of nitrogen and fluorine as a result of treatment indicating ablative degradation of low molecular weight carbon-containing compounds. The increase in the concentration of oxygen appears to be primarily due to the O=C-O moiety. (C) Koninklijke Brill NV, Leiden, 2012