Organic azides are a common functional group in polymer chemistry. Upon irradiation, they form nitrenes which are usually exploited for crosslinking based on their “universal” reactivity allowing insertion into nearby C–H bonds. Herein, it is demonstrated that polymer-bound perfluorophenyl azide groups selectively form sulfoximines when irradiated in the presence of an excess of sulfoxide, without observable crosslinking. Poly(4-azido-2,3,5,6-tetrafluorobenzyl methacrylate) (carrying an azide group in every repeat unit) is prepared through azide–para-fluoro postpolymerization modification of a 2,3,4,5,6-pentafluorobenzyl-functional precursor. Samples of the azide-functional polymer are irradiated (𝝀max = 254 nm) in dichloromethane in the presence of varying amounts of five different sulfoxides. Products are characterized by 1H and 19F NMR spectroscopy, Fourier transform infrared spectroscopy, size exclusion chromatography, and differential scanning calorimetry. Irradiations for 7 h

with a 40–70-fold molar excess of sulfoxides gave soluble products with azide-to-sulfoximine conversions of 89–96%. This first example of a selective nitrene-based reaction in the polymer arena shows that sulfoxide solvents must be avoided if crosslinking is desired and provides access to novel sulfoximine-functional materials.