An interaction mechanism for a bisphenol-A-based polybenzoxazine resin exposed to ultraviolet radiation is proposed. Fourier transform infrared spectroscopy indicated that a carbonyl-containing species was formed when cured 6,6'-bis(2,3-dihydro-3-methyl-4H-1,3-benzoxazinyl)isopropylidene (BA-m) resin was exposed to ultraviolet radiation (lambda > 290 nm) in the presence of ambient air at room temperature. The isopropylidene linkage was the reactive site of cleavage and oxidation. It was apparent from model compound studies that this structure was severed, resulting in the formation of a 2,6-disubstituted benzoquinone. Model compound studies also demonstrated that; the BA-m polymer backbone structure, the Mannich bridge, which was present in and characterized all the polybenzoxazines, neither cleaved nor oxidized in the presence of ultraviolet radiation in a detectable manner under the conditions of this study.