Universal Base-Catalyzed Aza-Michael Addition: A General Platform for Transforming Polyurethanes into...

Postpolymerization functionalization (PPF) of polyurethanes remains a persistent challenge, typically requiring the preinstallation of specialized reactive handles during initial synthesis. This limitation restricts the upcycling and advanced modification of existing, industrial-scale polyurethane materials. Herein, we report a universal and scalable strategy to transform "off-the-shelf" polyurethanes by leveraging the ubiquitous carbamate moiety (RO-C(═O)-NH-R) as a direct chemical handle for aza-Michael addition. Catalyzed by the phosphazene superbase P₂-tBu, this method achieves high degrees of functionalization (up to 99%) across a diverse substrate scope, including various acrylates and vinylphosphonate. Using this platform, we engineered a new class of comb-like poly(alkylene oxide) thermogels whose branched topology imparts transformative viscoelastic properties. These materials exhibit a 5-fold decrease in viscosity under shear, significantly outperforming the industry standard Pluronic F-127, while requiring 3-fold lower extrusion forces through 27-gauge needles, ensuring superior injectability. Furthermore, the branched architecture enables exceptionally sustained therapeutic release with a cumulative drug release of only 59% over 324 h compared to the rapid 52-h depletion of Pluronic F-127. This work establishes a general, handle-free pathway for the precision engineering of functional polyurethanes, bridging the gap between commodity plastics and high-performance biomaterials.