Photocurable, Thermally Reprocessable, and Chemically Recyclable Vanillin-Based Imine Thermosets

Two vanillin-based photocurable, thermally reprocessable, and chemically recyclable imine thermosets were successfully designed. The vanillin vitrimer resins were synthesized through a protocol with a two-step reaction: methacrylation and imination with diamine or triamine. The obtained vinyl ester resins with imine bonds and vinyl groups could be photocured into thermosets in 10 min at room temperature. The cured thermosets had good solvent resistance against common solvents, good thermal stability up to about 250 °C as measured by thermogravimetry, and high storage modulus (1.6–3.4 GPa as determined by dynamic mechanical analysis). Owing to the reversibility of the imine bond, both thermosets exhibited typical vitrimer behavior including stress relaxation and thermal reprocessability, while their activation energy for the imine exchange reaction and recovery ratio of tensile stress after reprocessing varied due to different cross-linking densities. Furthermore, both thermosets could be chemically recycled in hexylamine through an imine exchange reaction. The presented new strategy, thus, paves the way for production of fast-curing, chemically and thermally stable, but still thermally reprocessable and chemically recyclable imine vitrimers from abundant biobased building blocks.