Teflon AF1600, containing perfluorinated dioxole rings, was found to be particularly susceptible to X-ray degradation, such as that occurring during X-ray photoelectron spectroscopy. Because of the presence of O, the degradation mechanism is substantially different from those of fluoropolymers containing only C and F. Each atom of a given element was found to have the same susceptibility to attack, irrespective of its position in the repeat unit, with O at least twice as susceptible as F. At any dose between 60 W* X-ray source power/5 min and 240 W/40 min, O was lost at an amount equal to that of F, which necessitated the breaking of two C-O bonds; O also degraded by breaking only one bond, in which case the oxygen was not lost but formed a free radical. The free radicals produced by the homolytic scission of C-C bonds participated in reactions leading to degradation and crosslinking. *The product of X-ray filament emission current and the potential difference between it and the X-ray anode.