Keteniminium-Mediated Postpolymerization Modification: Unlocking Emergent Properties in Polyacrylamides

Postpolymerization modification (PPM) is a powerful strategy for expanding the functionality of synthetic polymers beyond what is accessible through direct polymerization. Current PPM approaches for poly(acrylamide)s often require activated monomers or strong metal nucleophiles, thus limiting their accessibility. Herein, we present an amide activation strategy that enabled the direct PPM of unactivated poly(acrylamide)s via keteniminium ion intermediates. Treatment of poly(dialkylacrylamide)s with trifluoromethanesulfonic anhydride (Tf₂O) resulted in the generation of keteniminium ions that, upon nucleophilic quenching, enabled selective conversion of pendant amides to aryl ketones. Molecular characterization confirmed the formation of poly(acrylamide-<i>co</i>-vinyl ketone) random copolymers with tunable functionalities. Interestingly, copolymers composed of aryl vinyl ketone repeat units underwent controlled photodegradation under UV irradiation, including broad spectrum sunlight, due to Norrish Type II radical fragmentation at the ketone units. This strategy provides a new approach to the PPM of unactivated polymers that leverages unique reactive intermediates, expands the scope of poly(acrylamide) functionalization, and introduces a new path toward designing degradable synthetic polymers with emergent properties.