A Multifunctional Polyurethane Containing <scp>UPy</scp> and <scp>PPG</scp> Side Chains Achieves Synergistic Reinforcement of Epoxy Adhesives Through an Interpenetrating Network

ABSTRACT Conventional epoxy adhesives suffer from excessive brittleness and poor toughness due to their high crosslinking density, which severely limits their engineering applications. To address this, this study proposes a “dual‐network synergistic crosslinking” strategy. A functionalized polyurethane prepolymer terminated with UPy (dynamic hydrogen‐bonding units) and epoxy groups was designed and incorporated into a bisphenol‐A epoxy resin/anhydride curing system. The resulting composite adhesive achieves simultaneous enhancement in strength and toughness. After optimization, the material exhibits a shear strength of 27.73 MPa, tensile strength of 32.67 MPa, and impact strength of 31.4 kJ/m 2 , representing improvements of 118%, 106%, and 243%, respectively, compared to the pure epoxy system. The dynamic hydrogen‐bonding network (UPy‐epoxy interfacial interactions) and flexible PPG segments synergistically enhance toughness through energy dissipation and stress relaxation, while the stoichiometrically controlled dual‐network crosslinking structure ensures a balance between strength and toughness. This work provides an innovative solution to overcome the longstanding “strength‐toughness trade‐off” dilemma in epoxy adhesives.