Fully Bio-Based Benzoxazine Adhesive with Enhanced Strength via Synergistic Supramolecular and Covalent Cross-Linking

Adhesive technology plays a crucial role in enabling durable and efficient bonding across a wide range of industries, from consumer goods to high-tech fields such as electronics and aerospace. Traditional adhesive materials are predominantly derived from petroleum-based products, leading to significant environmental and energy challenges due to overreliance on nonrenewable resources. In response, the development of eco-friendly adhesives from renewable biobased materials has gained considerable attention. However, fully biobased adhesives often exhibit lower adhesion strength compared to their petroleum-derived counterparts, presenting a significant challenge in the field. In this study, we report the design and synthesis of a fully biobased benzoxazine adhesive (FBBA) with superior adhesion properties, excellent solvent resistance, and antifreeze capabilities. The adhesive is derived from vanillyl alcohol (VA) and difurfurylamine (DIFFA) through a solvent-free Mannich reaction, resulting in the benzoxazine monomer DIFFA-VA. Upon heating, DIFFA-VA undergoes solvent-free ring-opening polymerization, forming a robust polymer network, Poly(DIFFA-VA), which is stabilized through the synergistic combination of supramolecular hydrogen bonds and covalent heterocyclic cross-linking. This innovative strategy achieves an adhesive with remarkable ambient bonding strength (8.0 MPa), outstanding antifreeze performance (4.0 MPa at −196 °C), and excellent resistance to aqueous solutions and common organic solvents. Given its ultrastrong bonding strength, solvent resistance, and ability to withstand extreme temperatures, this adhesive shows great potential for applications in sectors such as electronics, aerospace, and automotive, where durability and environmental resistance are crucial. The development of this ultrastrong, antifreeze, and solvent-resistant adhesive from renewable feedstocks not only addresses critical environmental concerns but also provides valuable insights into the synergistic effects of covalent and supramolecular interactions on the properties of biobased polymers.