Review and kinetic analysis of the photodegradation of UV absorbers

Ultraviolet absorbers (UVA's) undergo photodegradation with quantum yields on the order of 10^?6 even in glassy, unreactive matrices such as poly(methyl methacrylate) (PMMA). The kinetics of UVA loss in a film or coating can be described by the equation: A = log₁₀(1-T_o)10 + 1] where A is the absorbance at time t, T_o is the initial transmission, A_o is the initial absorbance, and k is an “infinite absorption” zero order rate constant. The derivation and implications of this equation and a general review of UVA degradation chemistry are discussed.