Synthesis of Water-Soluble, Intrinsically Flame-Retardant Benzoxazine Based on Renewable, Natural Resources

Against the general trend of developing hydrophobic benzoxazine resins, a novel water-soluble benzoxazine monomer with carbohydrate functionality (HP-fa) is synthesized. The synthesis and materials involved are all natural renewable raw materials that are designed to increase the concept of greenness and sustainability. The monomer was designed to improve compatibility with hydrophilic surfaces and environmental friendliness by the use of ethanol as a solvent. The structure of the synthesized monomer is verified using 1H NMR, 13C NMR, and Fourier transform infrared (FTIR) spectroscopy. The catalytic effect of hydroxyl groups in promoting polymerization is explored, which exhibits a heat of polymerization, ΔH, of 146.2 J/g and significantly low activation energies of polymerization of 25.9–97.2 kJ/mol. The differential scanning calorimetry (DSC) and thermogravimetric analyses (TGA) are employed to study the polymerization process and thermal stability. Two-dimensional nuclear magnetic resonance (2D NMR) spectroscopy is employed to elucidate the molecular structure and confirm the formation of the benzoxazine framework. The activation energy for the degradation of cross-linked HP-fa using the Flynn–Wall–Ozawa equation is determined. The flammability of the polymer derived from the synthesized monomer is determined using a microscale combustion calorimeter (MCC). The heat release capacity is observed to be very small at 25 J/(g·K), suggesting the intrinsic noncombustible nature of this polymer without added flame retardant.