Vanillin-Based Covalent Adaptable Networks with Ultralow Graphene Content for Enhanced Mechanical Robustness, Photothermal Self-Healing, and Corrosion Protection

Designing partially bio-based covalent adaptable networks that combine mechanical robustness with thermally or optically triggered healing and reprocessability remains challenging because network reinforcement typically reduces dynamic chain mobility. Herein, we report a vanillin-derived imine-based network reinforced by silane-functionalized graphene oxide nanosheets covalently grafted at an ultralow loading of 0.5 wt %. The covalent anchoring of graphene oxide at the network interface raises the apparent activation energy of stress relaxation from 45.0 to 73.7 kJ mol-1 while preserving Arrhenius-type temperature dependence, consistent with increased network constraint rather than enhanced intrinsic exchange kinetics. The composite retains 84.1% of its tensile strength after three hot-press reprocessing cycles. Under near-infrared irradiation, the grafted graphene oxide enables photothermal heating that locally compensates for the reduced intrinsic chain mobility, allowing surface scratches to heal within 5 min. As a protective coating, the composite maintains an impedance modulus above 109 Ω cm2 after 130 d of saline immersion, with the improved barrier performance attributed to combined effects of tortuous diffusion pathways and reduced network free volume. These results demonstrate that an ultralow fraction of covalently grafted nanofiller can simultaneously introduce mechanical reinforcement, photothermal responsiveness, and prolonged barrier function without eliminating the dynamic character of the network.