REVIEW AND KINETIC-ANALYSIS OF THE PHOTODEGRADATION OF UV ABSORBERS

Ultraviolet absorbers (UVA's) undergo photodegradation with quantum yi elds on the order of 10(-6) even in glassy, unreactive matrices such a s poly(methyl methacrylate) (PMMA). The kinetics of UVA loss in a film or coating can be described by the equation: A = log(10)[(1-T-0)10((A 0-kt)) + 1] where A is the absorbance at time t, T-0 is the initial tr ansmission, A(0) is the initial absorbance, and k is an ''infinite abs orption'' zero order rate constant. The derivation and implications of this equation and a general review of UVA degradation chemistry are d iscussed.