The dark oxidation of polystyrene and its mechanism

Cumene and other derivatives of benzene can form reversible contact charge transfer complexes (CCT) with O-2, but due to the influence of the space structure of polystyrene (PS) such as steric or electronic effect caused by the neighboring benzene ring, the O-2-CCT of PS is irreversible. High molecular weight PS(HPS) gives its maximum absorption wavelength of O-2-CCT at 278. 4nm, but low molecular weight PS(LPS) at 295.6nm as it has a similar structure of styrene due to a double bond at one end of its chain which results in the red shift of O-2-CCT absorption. The CCT formed between PS and O-2 has been considered as the initial state of the dark oxidation and it is proposed that PS as like the model compound cumene undergoes dark oxidation through O-2-CCT, CTC, H+ transfer, free radicals in cage and the formation of hydroperoxides.