Photochemistry of Azide‐functional Polymers: Soluble Sulfoximine Polymers through Selective Nitrene–Sulfoxide Addition

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 (lambda(max) = 254 nm) in dichloromethane in the presence of varying amounts of five different sulfoxides. Products are characterized by H-1 and F-19 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.