PHOTOCHEMISTRY AND PHOTODEGRADATION OF POLYCARBONATE

Photophysical and photochemical techniques were used to investigate th e photodegradation of Bisphenol A polycarbonate (PC), with diphenyl ca rbonate as a model compound. UV excitation of these compounds leads to a fluorescence band with a maximum around 300 nm. The triplet state o f PC is also observed both by transient absorption and by phosphoresce nce 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 da ta of the photointermediates and products of photolysis of diphenyl ca rbonate to those of polycarbonate indicated that degradation of the po lymer, which is enhanced by oxygen, is mainly due to photooxidation ra ther than to a photo-Fries rearrangement. Generation of singlet oxygen in PC does not lead to degradation, and studies showed that the tripl et state of the polymer was not involved in the degradation process. I t is suggested that C-C bond scission occurs from the short-lived sing let excited state of polycarbonate.