Low-Viscosity, Dynamic Amidoamine Hardeners with Tunable Curing Kinetics for Epoxy Adhesives

To address the irreversible cross-linking of amidoamine (AA) hardeners, dynamic alternatives have been developed, but high viscosities and nontunable curing kinetics limit practical applications. We present a novel strategy to reduce the viscosity of dynamic AAs by several orders of magnitude and simultaneously tune their curing kinetics with epoxy compounds. Specifically, polysuccinamide- and polyglutarimide-based curing agents were synthesized from bulk chemicals and end-capped with secondary amine functionalities. The curing kinetics of the amidoamine-epoxy system were tuned via the chemical environment of the secondary amine, while the viscosity of the hardeners was controlled by varying the average amidoamine chain length. The versatility of these dynamic hardeners was investigated in conventional bulk adhesive formulations. Tensile and lap-shear experiments on these resins demonstrated strong adhesion (up to 11 MPa) and excellent rebonding capabilities. This straightforward synthetic strategy enables an attractive drop-in technology toward rebondable amidoamine-epoxy hardeners, starting from low-viscosity formulations with tunable curing kinetics.