One-Pot Solvent-Free Synthesis of Imine-Based Epoxidized Soybean Oil Vitrimers for Sustainable Adhesives

The traditional methods for synthesizing imine-based epoxidized soybean oil (ESO) vitrimers often rely on organic solvents, leading to issues such as incomplete raw material conversion, increased production costs, and environmental concerns, contradicting the principles of green and sustainable chemistry. To overcome these challenges, we propose an innovative one-pot, solvent-free approach for synthesizing imine-linked ESO vitrimers via a melt reaction utilizing ESO, vanillin, and diamines. In this system, three distinct reactions can occur: phenolic hydroxy-epoxy, amino-aldehyde, and amino-epoxy. Our findings indicate that the first two reactions occur more readily and rapidly than the third, facilitating the successful synthesis of the vitrimers. We employed three different diamines to tailor the chemical structure and control properties of the ESO vitrimers; aromatic diamines produced rigid vitrimers with high strength but low ductility, while aliphatic diamines yielded flexible vitrimers with lower strength but higher ductility. All vitrimers exhibited rapid high-temperature stress relaxation and excellent reprocessability and thermal stability. Notably, these vitrimers demonstrated impressive adhesive properties, achieving lap shear strengths between 4.0 and 6.7 MPa when applied to various substrates, including wood, steel, and aluminum. Moreover, the dynamic imine bonds enable exceptional recyclability, removability, and reusability, with recycled ESO vitrimers even surpassing their virgin counterparts in mechanical and adhesive performance, underscoring the significance of this work in advancing sustainable adhesive materials with enhanced functionality and circularity.