Protocatechuic Acid–Based Benzoxazine Resin With Exceptional Thermal Stability and Flame Retardancy: Synthesis and Properties

Developing high-performance bio-based thermosets has attracted increasing attention to reduce fossil resource dependence. In this work, a novel protocatechuic acid–based benzoxazine monomer with bis-oxazine rings (NDBA-fa) was synthesized from protocatechuic acid (PCA), furfurylamine, and formaldehyde. The structure of NDBA-fa has been characterized by ¹H NMR, ¹³C NMR, and Fourier transform infrared spectroscopy. The result of curing kinetics showed that NDBA-fa had a lower activation energy than other bio-based benzoxazine resins. The cured product poly(NDBA-fa) had a higher thermal decomposition temperature (T_d5% = 363°C) and char yield (char yield = 63.5%, 800°C), and lower heat release capacity (HRC = 15.8 Jg⁻¹ K⁻¹). In addition, the NDBA-fa was introduced into the bisphenol-A-type benzoxazine resin (BA-a). When the content of NDBA-fa was 7.5%, the T_g, T_d5%, and char yield were, respectively, increased by 21°C, 14°C, and 16.8%, and the HRC decreased by 76.3 Jg⁻¹ K⁻¹ compared with traditional resin poly(BA-a). Overall, this article provides guidance for the structural design and synthesis of bio-based benzoxazines, which has important theoretical significance and application value.