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, O-Z absorption and formation of intermediate and final products a conclusion has been made that the pol ystyrene photo-oxidation process involves two mechanisms: a photochain (sim ilar to 90%) and a hydroperoxide (similar to1%) one. The photochain mechani sm is based on the reaction of excited peroxide macroradicals dissociation (the kinetic chain length is 10(2)-10(3) units), leading directly to format ion 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 conv erted, includes an RO2. reaction with a macromolecule and hydroperoxide for mation. A subsequent ROOH decomposition results in the scissions of the pol ymer chains and the formation of high-molecular oxidation products (carbony ls, alcohols, ethers). (C) 2001 Elsevier Science Ltd. All rights reserved.