Catalyst-Induced Carbamate Exchange Imparts Auxeticity to Commercial Thermoset Polyurethane Foam

Auxetic polyurethane foams (PUFs), distinguished by their negative Poisson's ratio, are prized as metamaterials for their superior damping and protection capabilities. Nevertheless, conventional auxetic PUFs face limitations: those relying on non-covalent interactions suffer from poor fatigue resistance, while covalently bonded variants demand intricate processing or specialized network designs. In this work, we introduce a facile and universal strategy to fabricate thermoset auxetic PUFs by leveraging catalyst-induced dynamic exchange of carbamate bonds, permitting structural reconfiguration via triaxial hot-pressing. The resulting foams exhibit robust auxeticity across a wide compression strain of 0-50%, and their permanent covalent networks ensure durable auxetic performance under cyclic compression, solvent exposure, and thermal aging. In addition, this strategy showcases broad applicability in the fabrication of auxetic PUFs, permitting adjustments in catalyst types, PUF formulations, and catalyst incorporation methods. Our work expands the design toolbox for auxetic metamaterials, offering opportunities for adaptive protective systems with tailored mechanical responses.