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.