The thermal oxidation of poly(propylene oxide) and its complexes with LiBr and LiI

The thermal volatilisation of pure poly(propylene oxide) (PPO) is greatly accelerated by oxygen. The process of thermal oxidation is dominated by the initial formation of hydroperoxides, which appear to form at the secondary (in preference to the tertiary) carbon atoms in the polymer backbone. The volatile products of degradation, which include acetaldehyde, acetone and methanol (but not unsaturated hydrocarbons, in contrast to purely thermal decomposition), can be accounted for by decomposition of the hydroperoxides. In the presence of alkali metal salts the conversion of PPO to volatile products during thermal oxidation is strongly retarded. A similar effect was observed previously with poly(ethylene oxide). Stabilisation by the salt can be attributed to a combination of effects: (i) retardation of hydroperoxide formation due to strengthening of C-H bonds adjacent to complexed metal cations, and (ii) chemical decomposition of hydroperoxides by the salt. (C) 1996 Elsevier Science Limited.