Development of Hydroxytyrosol-Derived Benzoxazine Resins with Excellent Heat-Resistance and Flame Retardancy by a Solvent-Free Method

Simultaneously achieving high performance and green benzoxazine resins is challenging yet highly significant. In this work, a bifunctional benzoxazine monomer, HT-fa, was successfully synthesized using a green strategy with hydroxytyrosol as the phenol source and furylamine as the amine source, and the monomer demonstrated excellent processability. Cured HT-fa resin, poly(HT-fa), exhibited a high glass transition temperature (Tg) of 297 °C and an initial decomposition temperature (Tdi) of 354 °C. Additionally, it demonstrated exceptional flame retardancy, with a limiting oxygen index (LOI) of 44.1%, a heat release capacity (HRC) of 21.3 J/g·K, a total heat release (THR) value of 2.9 kJ/g, and a flame-retardant rating of UL-94 V-0. Notably, its LOI, HRC, and THR were superior to those of all benzoxazines synthesized using biomass-derived amine and phenolic sources and a solvent-free method. The excellent properties of HT-fa and poly(HT-fa) are due to their unique rigid-flexible molecular structures. In addition, HT-fa can be used as a modifier for the commercially available bisphenol A/aniline based benzoxazine (BA-a). The addition of HT-fa not only significantly reduces the curing temperature of BA-a but also enhances the heat-resistance and flame-retardant properties of the cured resins. Poly(HT-fa) and these copolymers have potential applications in the field of halogen- and phosphorus-free flame-retardant materials.