Sustainably sourced covalent adaptable networks derived from eugenol for flame retardant, transparent and self-healing coating applications

High-transparent polycarbonate (PC) is often used to replace glass in construction, but its poor flame retardancy limits its use. In recent years, materials for covalent adaptive networks (CANs) have gained much attention. The preparation of CANs and their application to flame retardant coatings is an innovative approach. In this work, a dithiol-containing borate ester (B2SH) and P-containing eugenol monomer (TEP) were synthesized. The flame retardant self-healing eugenol bio-based covalent adaptive network (TEP-SH) was prepared by copolymerizing TEP with B2SH and polythiol monomers (such as pentaerythritol tetra(3-mercaptopropionate) (4SH)) via photo-induced thiol-ene polymerization. Among these samples, TEP/B2SH/13%4SH has the best comprehensive performance, while superior flame retardancy, self-healing and shape memory properties and high transparency are preserved. TEP/B2SH/13%4SH was coated on a PC board for the cone calorimeter test. Compared with those of PC, PHRR and THR decreased by 31.3% and 24.5%, respectively, and the char yield (CY) increased from 3.5% to 16.6%. Moreover, TEP/B2SH/13%4SH exhibited excellent adhesion to PC with a high shear strength (2.77 MPa). Therefore, TEP/B2SH/13%4SH has excellent performance and can be used as a flame-retardant, transparent and self-healing coating, thus ensuring the safe application of PC in building materials.