The influence of transition metal salts in polyglycol autoxidations

The addition of small amounts of transition metal salts, e.g., CuCl2, to low molecular weight polyoxyalkylenediols results in pronounced autoxidation inhibition. This is in contrast with McGary's findings that this same class of salts accelerates the autoxidative degradation of high molecular weight polyethylene glycols. Inhibition of diethylene glycol is shown to relate to catalyzed hydroperoxide decomposition. With polyoxyethylenediol of molecular weight 600 this inhibition with CuCl2 is less pronounced, and with both polyoxyethylene diols and polyoxypropylene diols the inhibitory effect gives way to a net accelerating effect with increasing polymer molecular weight. The inhibitory effect is insensitive to increasing medium polarity and to changes in oxygen pressure, but is markedly sensitive to terminal group capping. Combinations of appropriate metal salts and organic antioxidants produce synergistic stabilization. The results may be explained by postulating a competition between the normal radical‐generating reactions of hydroperoxides with transition metal ions and the formation of specific terminal‐hydroperoxide complexes which decompose heterolytically.