Mismatched Hydrogen Bond Donor‐Acceptor Stoichiometry Strategy Enables High‐Strength, Crack‐Resistant, and Recyclable Thermosetting Polyurethane Elastomer

Abstract Thermosetting polyurethane elastomers, despite their widespread application in various industries, confront critical developmental constraints due to their non‐recyclability and the strength‐toughness trade‐off. Herein, a molecular engineering strategy is proposed to tackle these challenges. The incorporation of acylsemicarbazide (ASC) moieties (oxalyl dihydrazide, 1,3‐diaminourea) with mismatched hydrogen bond donor‐acceptor stoichiometry within boroxine covalent networks enables precise tuning of binding energies, effectively circumventing excessive hydrogen‐bond aggregates and optimizing energy dissipation to resist external stress. This strategy significantly enhances and toughens the thermosetting polyurethane, demonstrating ultrahigh tensile strength and elongation at break (69.15 MPa and 1559%, respectively), along with a remarkable toughness value of 461.8 MJ m −3 . The dynamic dual‐networks endow this high‐performance thermosetting polyurethane with excellent fatigue resistance and impact resistance during long‐term tensile cycles. Additionally, it exhibited excellent recyclability and notable self‐healing capability. In summary, the proposed strategy of hydrogen bond donor‐acceptor quantity mismatch provides a feasible molecular design approach for synthesizing thermosetting polyurethane elastomers that simultaneously possess superior mechanical performance and high dynamic properties.