The possibility of initiating the chain oxidation of polymers by nitrogen oxide radicals

Abstract

IT HAS been shown recently by a number of investigators that phenol and amylamine anti-oxidants can not only break oxidation reaction chains, but also initiate a chain reaction, to form active radicals. Kuz'minskii and Angert [1, 2] found that aromatic amines are able to initiate rubber oxidation. On the example of a number of anti-oxidants, Shlyapnikov, Miller and Neiman [3, 4] showed that they could initiate the oxidation of polypropylene, and also increase the probability of branching, by reaction with hydroperoxides. Recently it was suggested tha t stable imino oxide radicals could be used as anti-oxidants. In [5, 6] these radicals were found to be good stabilizers for polyformaldehyde and polycaproamide. In [7] it was found tha t imino oxide radicals of the aliphatic series easily recombine with alkyl radicals. I t might be thought that the role of stable imino oxide radicals consists only of breaking reaction chains. But in [8] it was found that phenoxide radicals could detach hydrogen from different compounds, the activation energy of this reaction depending on the C--H bond energy. Mamedova, Buchachenko and Neiman found tha t imino oxy radicals of various structures were able to detach the hydrogen at ethylbenzene with an activation energy of 15 kcal/mole and activation entropy depending on the structure of the radical. On removal of the hydrogen the radicals C6H 5 CH CH 3 are formed, which are able to combine with 02 and thus initiate the oxidation reaction. The work cited above demonstrates the possibility of the hightemperature activation of polymer oxidation by stable radicals. Now it is interesting to extend the previous results to the case of the detachment of the hydrogen atom bound with nitrogen, which could occur with the initiation of heterochain polymer oxidation by polyamides for instance. To find the answer to this question, we synthesized iminoxy stable radicals and studied their reaction with hydrazobenzene. In this reaction the radical detaches a hydrogen atom with formation of hydrazobenzene. The following radicals were prepared and studied: