Amine-Structure-Regulated Vanillin-Derived Imine-Cross-Linked Networks for Reprocessable, Self-Healing, and Chemically Recyclable Thermosets

Abstract

Developing vanillin-derived thermosets that combine mechanical robustness with repairability and chemical recyclability remains a central challenge in replacing petroleum-derived cross-linked polymers. Vanillin offers a renewable aromatic platform for this purpose because it can introduce rigidity while providing functional groups for dynamic network construction. Here, we report a series of vanillin-derived imine-cross-linked polymer networks (VD-TAM) prepared from a benzoxazine-containing dialdehyde monomer (VD), decanediamine (DM), and tris(2-aminoethyl)amine (TAM). By fixing the aldehyde/amine functional-group ratio at 1:1 and the VD content while varying the relative contributions of flexible DM segments and trifunctional TAM junctions, the network structure was systematically regulated. This design allowed the amine structure-dependent balance between network rigidity and imine-exchange dynamics to be evaluated. Increasing the TAM content raised the glass-transition temperature from 49.3 to 72.2 °C, the DMA-derived effective cross-link density from 5.31 × 10–4 to 16.43 × 10–4 mol cm–3, and the tensile strength from 40.37 to 56.33 MPa, while decreasing the elongation at break from 124.47 to 7.29%. Stress-relaxation analysis confirmed thermally activated network relaxation associated with imine exchange, with apparent activation energies for macroscopic network relaxation increasing from 35.83 to 49.22 kJ mol–1 as the network became more constrained. The dynamic imine network further enabled thermal reprocessing, shape-memory behavior, and efficient self-healing, with VD-TAM-50 showing a representative tensile-strength recovery of 93.5% after healing at 90 °C for 20 min and retaining 90.9% of its tensile strength after two reprocessing cycles. In addition, acid-triggered imine hydrolysis allowed recovery of the VD monomer, indicating a potential route toward monomer recovery and future closed-loop material design. These results demonstrate that amine-structure regulation provides an effective strategy for designing vanillin-derived imine networks with balanced mechanical performance, dynamic adaptability, and chemical recyclability.