Synthesis of benzoxazine from eugenol and its co-polymerization with a gallic acid-based epoxy resin for flame retardant application

Polybenzoxazines (PBz) are a new type of resin belonging to the category of phenolic resins. As polybenzoxazines are addition-curable polymers, this obviates many of the shortcomings associated with conventional phenolic resins while endowing them with excellent thermal, physical, and thermo-physical properties and surpass the features of many conventional and state-of-the-art polymers. They even possess excellent design flexibility. In this study, a benzoxazine monomer was successfully synthesized from eugenol (Eu), ethylenediamine, and paraformaldehyde utilizing a solventless approach. The synthesized benzoxazine resin was characterized for its structural elucidation via FTIR, 1H, and 13C NMR spectroscopy and was used for crosslinking a petroleum-based epoxy and a gallic acid-based epoxy. The effects of the presence of benzoxazine on the thermal and flame retardant properties of the films were evaluated using TGA and DSC analysis and the LOI and UL 94 tests, respectively. It was found that the benzoxazine in the epoxy systems led to an increase in thermal stability and flame retardancy. The gallic acid-based epoxy system showed better thermal and flame retardant properties compared to the petroleum-based epoxy system, thus showing potential to replace the petroleum-based epoxy for high-performance applications.