Generating innovative methods to functionalize fibers and interfaces are important strategies for developing coatings that impart new or improved properties to a given material. In this work, we present a method for functionalizing highly inert poly(p-phenylene terephthalamide) (Kevlar速) fibers via thermal generation of an electrophilic nitrene, while preserving the mechanical properties of the aramid. Because of the high affinity of the sulfonyl nitrene singlet state for aromatic rings, the use of a sulfonyl azide-based copolymer allows the covalent grafting of a wide variety of common commercial polymers to Kevlar. Also, by using reactive ester copolymers, an avenue for the attachment of more exotic or delicate functionalities like small molecules, dyes, and biomolecules through postpolymerization modification is described.