Relative rates of photooxidation of benzil to benzoyl peroxide in various polymer matrices

Benzil (BZ), 16 wt.-%, has been irradiated (>400 nm) at ambient temperature in aerated polystyrene (PS), poly(methyl methacrylate) (PMMA), polycarbona te (PC), polysulfone (PSF) and poly(vinyl chloride) (PVC) films. The rate o f BZ consumption, leading primarily to the formation of benzoyl peroxide, w as followed by infrared spectroscopy. The rate of reaction is sensitive to the nature of the glassy polymer matrix and decreases in the order: PS > PC > PVC > PSF > PMMA. The dependence of the rate of BZ consumption on the co ncentration of dissolved molecular oxygen in the polymer matrices is rather complex. A kinetic treatment, assuming steady-state conditions, leads to t he conclusion that the sum of the rates of bimolecular formation of benzoyl peroxide and quenching of BZ triplets by molecular oxygen, (k(ox) + k(q))[ O-3(2)], represents only 0.8-13% of the sum of the unimolecular rates of ra diationless and radiative deactivation (including k(p), the pseudo first-or der rate constant for reaction of BZ triplets with the polymer), (k(d) + k( ph) + k(p)), in the various polymer matrices.