Preparation of Thermally Resistant and Mechanically Strong Biomass Benzoxazine Resins via Green Strategy

Developing biomass resins with high thermal resistance and mechanical performance through a green strategy is an interesting challenge. Increasing the functionality of oxazine ring is favorable to improve the thermal resistance and mechanical strength of resins; however, no tri- or more functional benzoxazine monomers synthesized using the green strategy have been reported. Herein, two novel trifunctional benzoxazine monomers (coded as DPTA-f and DPTR-f) with very low melting points (61, 49 °C) were synthesized using biomass raw materials (diphenolic acid, tyramine, tyrosol, and furfurylamine) and green solvents (ethanol and water). The cured resins of DPTA-f and DPTR-f, designed as P(DPTA-f) and P(DPTR-f), not only exhibit high storage moduli (3600 and 3080 MPa) and high tensile strength (65.0 and 55.1 MPa) but also have high glass transition temperature (Tg = 328, 302 °C) and initial degradation temperature (351 and 350 °C), especially P(DPTA-f) exhibits bigger Tg than all benzoxazine resins prepared using the green strategy (SCI database). They also have good flame retardancy. The above excellent processing nature of DPTA-f and DPTR-f together with competitive thermal resistance and mechanical strength of two cured resins benefits from the unique chemical and aggregate state structures of the biobased benzoxazines.