Bio-Based Liquid Latent Curing Agent Integrating Intrinsic Toughening and Superior Latency for Epoxy Resins

We report a highly biobased, room-temperature liquid latent curing agent (DAMIM) for sustainable one-component epoxy resins─synthesized via a mild, solvent-free reaction of imidazole, biosourced dimethyl itaconate, and dimer acid (C 36 fatty acid from plant oils). DAMIM exhibits low viscosity (9.6 Pa·s at 25 °C), full miscibility with DGEBA, and high activation energy (65 kJ mol –1 by Ozawa method), and exceptional latency, with a gel time ∼20 times longer than that of the imidazole control at 100 °C. Rheology confirms slow viscosity rise below 90 °C, enabling a wide processing window (60–100 °C). Crucially, the flexible aliphatic chain of dimer acid imparts intrinsic toughening: Compared with the EP-IM system, the impact strength of the EP-DAMIM system is significantly improved, while the flexural strength and tensile strength are essentially maintained. Unlike nanoparticle- or plasticizer-toughened systems, DAMIM covalently integrates toughness into the network without compromising structural integrity or introducing migration risks. This work delivers a scalable, molecularly engineered solution that simultaneously addresses dispersion limitations of solid biocuring agents, brittleness of epoxies, and fossil-dependence─which directly promotes the development of green thermoset manufacturing in alignment with global dual-carbon goals.