Bifunctional diazirine reagent for covalent dyeing of Kevlar and inert polymer materials†

We report a convenient bifunctional diazirine reagent that is capable of photochemically modifying inert polymers, particularly those used in fibers and textiles for ballistics and blast protective gear, such as para-aramid and ultra-high molecular weight polyethylene (UHMWPE). The reagent's structure features a trifluoromethyl diazirine group as a precursor to a carbene that binds the textile surface. On the reagent's other terminus, a benzyl bromide group acts as a site accessible for substitution reactions. As a bench-stable liquid, this bifunctional diazirine can be prepared on gram-scale quantities and rapidly activates under long-wave UV light. A series of fabrics made from Kevlar, Spectra, Dyneema, etc. were functionalized with this diazirine reagent, then subsequently dyed by binding nucleophilic dyes. The resulting coloration was found to be robust and colorfast with respect to water, organic solvent, and simulated laundering with detergent, and the strength of the fibers or fabrics was retained through the dyeing process, as shown through TGA and mechanical break testing. Overall, this carbene-based method provides a general, mild strategy for the covalent attachment of small molecules to textiles made from inert polymers, particularly para-aramids and UHMWPE, as well as nylon and fiber blends of these materials, and has potential use in next-generation protective outerwear.