Dynamic cross-linked latent accelerators featuring dual-dynamic urea bonds for one-component epoxy systems

Abstract

One-component epoxy resins are highly attractive for industrial use due to their simplicity, consistent quality, and low waste, yet balancing long-term room-temperature storage stability with efficient low-to-medium-temperature curing remains a major challenge in epoxy/dicyandiamide (DICY) systems. Herein, we present a series of dynamic cross-linked latent accelerators (IEM-DtBIM-x) based on dual-dynamic urea bonds (sterically hindered urea and imidazole urea). Incorporation into the epoxy/DICY system deliver outstanding storage stability (>91 days with viscosity remaining below twice the initial value, far exceeding conventional imidazole accelerators) while reducing the curing temperature by 37 °C compared with the accelerator-free system. Thermally triggered dissociation releases active imidazole, hindered amine, and isocyanate species that synergistically accelerate epoxy/DICY cross-linking and simultaneously construct a reinforced epoxy network via urethane linkages and enhanced hydrogen bonding. The resulting cured resins exhibit markedly superior thermomechanical performance compared with imidazole-promoted systems, including elevated glass transition temperatures by up to 24 °C, higher tensile strength and modulus, improved solvent resistance, and significantly enhanced lap-shear adhesion on various substrates. This dual-dynamic urea bond strategy provides an innovative route to high-performance one-component epoxies with ultralong shelf life and rapid moderate-temperature curing, with broad potential in structural adhesives, coatings, composites, and electronic packaging.