The implementation of covalent adaptable networks as reprocessable thermosets is often hindered because of the trade-off between their stability and reprocessability. In epoxy resins, β-amino amide-based curing agents provide reprocessability and high dimensional stability but typically require elevated temperatures for (re)processing. In contrast, β-amino ester motifs, despite their lower creep resistance, enable (re)processing and debonding at lower temperatures, which is particularly advantageous for debondable structural adhesive applications. In this study, we aim for a comprehensive combination of the advantages of these two dynamic covalent chemistries for epoxy-based covalent adaptable networks and their derived debondable adhesives, by designing a poly(β-amino amide-co-β-amino ester) hybrid dynamic curing agent. The use of such a hybrid dynamic curing agent for the epoxy curing reaction results in processable cross-linked materials with a stress relaxation activation energy of 147 kJ/mol, compared to 165 and 140 kJ/mol for the amide and ester counterparts, thus highlighting the contribution of β-amino ester motifs. We further employ the hybrid dynamic curing agent for debondable adhesive formulations, demonstrated on varying substrates including metal, wood, and composite. An excellent adhesive lap shear strength of up to 16 MPa is achieved with enhanced debonding capability that facilitates the nondestructive disassembly of bonded components, especially advantageous for heat-labile wooden and composite materials.
Nguyen et al. (Sun,) studied this question.