Photo-oxidation of polymers 4. The dual mechanism of polystyrene photo-oxidation: a hydroperoxide and a photochain one

By comparing the quantum yields of initiation, O2 absorption and formation of intermediate and final products a conclusion has been made that the polystyrene photo-oxidation process involves two mechanisms: a photochain (∼90%) and a hydroperoxide (∼1%) one. The photochain mechanism is based on the reaction of excited peroxide macroradicals dissociation (the kinetic chain length is 102–103 units), leading directly to formation of the main final products, H2O and CO2, whose yield is comparable with the quantity of the absorbed oxygen. The ordinary hydroperoxide mechanism, by which up to 10% of the radicals formed in the initiation stage are converted, includes an RO2• reaction with a macromolecule and hydroperoxide formation. A subsequent ROOH decomposition results in the scissions of the polymer chains and the formation of high-molecular oxidation products (carbonyls, alcohols, ethers).