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

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.