The metal catalysed oxidation of high polymers

Several reviews and original papers on the oxidation of polymers [Refs. 48, 142, 274, 318, 349, 448, 524, 542, 605, 619, 641, 685] and elastomers [Refs. 17, 72, 365, 366, 403, 566] discuss various aspects of the metal-catalysed oxidation. 

Any polymer produced on an industrial scale contains many metallic impurities. The impurities are introduced into the polymers either from the catalysts, for example, Ziegler—Natta catalysts, or from the apparatus used in the synthesis. The metallic impurities found in commercial rubber are listed, as an example, in Table 8. In practical applications, moreover, the polymers come into direct contact with a number of metals, metallic oxides and salts for example, the polymers used in the manufacture of cables with a copper core, or polymers coloured with pigments. 

Hansen et al. [269] found that copper is an active catalyst for the oxidation of polypropylene. In the presence of copper, the autocatalytic period is completely absent and the oxidation itself is then catalysed. The experiments suggest that cuprous oxide is responsible for the catalysis and not metallic copper. Cuprous oxide is considerably more active as a catalyst than cupric oxide or freshly reduced copper. A similar result was obtained by Meltzer et al. [415]. 

A number of workers [Refs. 82, 199, 203, 351, 393, 559, 609] have reported that Ti02 greatly increases the rate of oxidative photodegradation of nylon-6,6. At least three possible roles can be suggested for this phototendering effect. 

It was found that zinc oxide catalyses the formation and decomposition of peroxides under the influence of UV radiation [Refs. 117, 395, 396, 543, 640]. The most likely mechanism involves the capture of a photo-excited electron by a molecule of absorbed oxygen, as suggested by 

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