Re-examination of the thermal oxidation reactions of polymers 3. Various reactions in polyethylene and polypropylene

Many hydroperoxide and peroxide transforming reactions can proceed in polymers. Pseudo-monomolecular and bimolecular hydroperoxide decomposition constitute only part of the overall possibilities. The additional reactions depend heavily on the particular polymer and the conditions of the experiments. The reaction of aldehydes with secondary hydroperoxides in polyethylene (PE) is transforming the aldehydes into acids and the hydroperoxides into ketones. With advancing oxidation acid-catalyzed hydroperoxide decomposition is expected to become increasingly important. It is particularly of interest if it involves special hydroperoxides such as alpha-keto-hydroperoxides and allylic hydroperoxides because the corresponding reactions give chain scission. The most important special structure formed in PE seems to be the alpha,gamma-keto-hydroperoxides. Their thermal decomposition gives chain scission with simultaneous formation of carboxylic acid and methyl-ketone groups. Thermal decomposition of the ozonides formed on oxidation of PE and polypropylene (PP) also involves chain scission. In PE, contrary to PP, formation of 1,2-dioxetane groups is restricted. In addition, alpha-hydroxy-hydroperoxides are expected in much smaller amount in PE than in PP. They might be the only source of chemiluminescence in PE. (C) 2002 Elsevier Science Ltd. All rights reserved.