Multifunctional Biobased Benzoxazine Resins with Balanced Processability, Thermal Stability, and Intrinsic Flame Retardancy

Multifunctional benzoxazine resins with high‑rigidity skeletons have gained widespread research interest owing to their comprehensive performance advantages, but their monomers typically suffer from high melting points and poor solubility. To address this issue, three multifunctional benzoxazines, DATR-fa, DAHT-fa, and DPAHT-fa, were synthesized in the green solvent ethanol using biomass-derived phenolic acids, phenolic alcohols, and furfurylamines. All three monomers exhibit low melting points (81, 93, and 61 ° C), which are attributed to the introduction of ester groups and short alkyl chains that weaken molecular rigidity and packing regularity. Through thermal curing, three cured resins, poly(DATR-fa), poly(DAHT-fa), and poly(DPAHT-fa), were prepared, all of which exhibit excellent heat resistance (glass transition temperatures of 266, 286, and 296 ° C), high thermal stability (initial decomposition temperatures of 353, 341, and 359 ° C), and good flame-retardant properties (heat release capacity (HRC) values of 65.4, 46.4, and 61.8 J/(g·K), total heat release (THR) values of 6.4, 4.7, and 5.0 kJ/g, and UL-94 ratings of V1, V0, and V1, respectively). Furthermore, a detailed study was conducted on the flame-retardant mechanism of these polybenzoxazine resins. This work offers new guidelines for designing multifunctional benzoxazine resins featuring balanced processability, thermal stability, and intrinsic flame retardancy.