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

摘要

Benzil (BZ), 16 wt.-, has been irradiated (>400 nm) at ambient temperature in aerated polystyrene (PS), poly(methyl methacrylate) (PMMA), polycarbonate (PC), polysulfone (PSF) and poly(vinylchloride) (PVC) films. The rate of BZ consumption, leading primarily to the formation of benzoyl peroxide, was 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 concentration of dissolved molecular oxygen in the polymer matrices is rather complex. A kinetic treatment, assuming steady-state conditions, leads to the 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)~3O_2, represents only 0.8-13 of the sum of the unimolecular rates of radiationless and radiative deactivation (including k_p, the pseudo first-order rate constant for reaction of BZ triplets with the polymer), (k_d + k_(ph) + k_p), in the various polymer matrices.