General mechanism of polymer degradation

The oxidative degradation, involving the scission of the main polymer chain, the decrease in molecular weight and the evolution of low molecular weight reaction products, takes place during several stages of the oxidation reaction proper  

When the oxygen concentration is low, or the atmosphere is completely free of oxygen, the degradation involves the macro-radical decomposition 

At high temperatures some polymers depolymerize in an oxygen-free atmosphere with the liberation of the pure monomer [Refs. 154, 250, 389, 492] 

The depolymerization of polymethacrylonitrile for example at temperatures exceeding 200°C yields up to 100% of the monomer [252]. 

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