High performance intrinsically flame-retardant bio-benzoxazine resin derived from 2,5-furandimethylene amine and sesamol: Synthesis and investigations of structure-property relationship

Conventional benzoxazines are largely limited by the dependence on non-renewable resources, insufficient thermal stability, and poor flame retardance properties. This study presents two high-performance monofuran-diamine-type difunctional bio-benzoxazine monomers (MDOPH-fda and DMOPH-fda), whiche were synthesized by reacting 2,5-bis(aminomethyl)furan and paraformaldehyde with either sesamol or 3,4-dimethoxyphenol. The benzoxazine structure was validated using FT-IR, 1 H NMR, 13 C NMR, HMQC NMR, and HR-MS. The polymerization behavior of the monomers was monitored by DSC and in situ FT-IR. The results demonstrated that the polymerization temperatures of the two benzoxazine monomers were close. The thermal stability and thermomechanical properties of polymers derived from the two benzoxazines were evaluated by TGA and DMA). Due to the monofuran-diamine linking structure that leads to the formation of two oxazine rings, both poly(MDOPH-fda) and poly(DMOPH-fda) exhibit good thermal stability. Their respective Td₁₀ values are 374.8 °C and 330.4 °C, and their char yields at 800 °C are 63.5% and 52.8%, respectively. Due to the benzodioxole structure, poly(MDOPH-fda) exhibit superior thermal stability. Regarding thermomechanical properties, the storage modulus of poly(MDOPH-fda) is 3364.8 MPa, while that of poly(DMOPH-fda) is 3856.1 MPa. Their glass transition temperatures (Tg) are 260 °C and 272 °C, respectively. While these values are close, both are higher than those of commercial benzoxazine resins. Experiments using a Microscale Combustion Calorimeter (MCC) and a vertical combustion test (UL-94) confirmed that the sesamol-based benzoxazine resin, poly(MDOPH-fda), exhibits excellent flame retardance. Its heat release capacity (HRC) is 38.7 J·g -1 ·K -1 , and its total heat release (THR) is as low as 0.7 kJ·g -1 , reaching the UL-94 V0 level in the vertical combustion test. Analyses of the surface morphology and chemical composition of the residues after combustion using Scanning Electron Microscopy (SEM), X-ray Photoelectron Spectroscopy (XPS) and Raman Spectroscopy (LRS) show that poly(MDOPH-fda) is conducive to the formation of a dense graphitized carbon layer at high temperatures. This makies it a strong competitor in the field of high-performance flame-retardant resins.