PHOTOCHEMISTRY AND PHOTODEGRADATION OF POLYCARBONATE

Photophysical and photochemical techniques were used to investigate the photodegradation of Bisphenol A polycarbonate (PC), with diphenyl carbonate as a model compound. UV excitation of these compounds leads to a fluorescence band with a maximum around 300 nm. The triplet state of PC is also observed both by transient absorption and by phosphorescence studies. The PC triplet in dichloromethane solution interacts with oxygen, ferrocene, trans-piperylene, and perylene with rate constants of 6.25 x 10(8), 2.89 x 10(8), 3.05 X 10(8), and 5.60 X 10(8) M-1 s-1, respectively. A comparison of the absorption and the fluorescence data of the photointermediates and products of photolysis of diphenyl carbonate to those of polycarbonate indicated that degradation of the polymer, which is enhanced by oxygen, is mainly due to photooxidation rather than to a photo-Fries rearrangement. Generation of singlet oxygen in PC does not lead to degradation, and studies showed that the triplet state of the polymer was not involved in the degradation process. It is suggested that C-C bond scission occurs from the short-lived singlet excited state of polycarbonate.