Biobased bisbenzoxazine resins derived from sesamol and furfurylamine: Using natural renewable resources to access phosphorus- and halogen-free flame-retardant thermosets

Biomass derivatives are a promising class of precursors for developing natural sustainable polymers. However, biobased polymers generally possess flammable characteristic and poor thermal stability, which seriously restrain their further applications. Herein, two biobased diamines (PDFA and CPDFA) were successfully synthesized using furfurylamine and benzaldehyde/cyanobenzaldehyde as starting materials. In addition, two novel bio-bisbenzoxazine monomers, S-cpdfa and S-pdfa, were obtained via the Mannich condensation reaction from paraformaldehyde, sesamol and PDFA/CPDFA. The chemical structures of both biobased bisbenzoxazines have been confirmed by FT-IR, 1 H NMR, 13 C NMR, and 2D HMQC spectroscopies as well as high-resolution mass spectrometry (HR-MS). Moreover, the polymerization behaviors of bisbenzoxazine monomers were investigated by DSC and in situ FT-IR analyses. It is noteworthy that fully polymerized biobased thermosetting resins exhibit high thermal stability with T d10 of 373.8 °C and Y c of 63.2 % for poly(S-pdfa), and T d10 of 395.4 °C and Y c of 65.7 % for poly(S-cpdfa), respectively. Notably, poly(S-cpdfa) exhibited very low flammability and self-extinguishing performance as indicated by HRC of 13.1 J·g⁻¹·K⁻¹ and THR of 2.8 kJ·g⁻¹. This work presents a straightforward and environmentally conscious methodology to access phosphorus- and halogen-free thermosets with intrinsically flame retardancy using natural renewable resources.