Eugenol-derived bio-benzoxazine resins: Synthesis, characterization, and exceptional thermal stability

In this study, we succesfully synthesized bio-benzoxazine resins using eugenol, a bio-based phenolic compound, in combination with three distinct functional amines: ethanamine, aniline, and hexane-1,6-diamine. Characterization of the resulting bio-benzoxazine resins, namely E-ea (eugenol, ethanamine), E-a (eugenol, aniline), and E-dh (eugenol, hexane-1,6-diamine), was performed through H-1 NMR spectroscopy, FTIR spectroscopy, high-resolution mass spectrometry, and elemental analysis. Thermal properties were investigated using thermogravimetric analysis (TGA) for both the eugenol-derived bio-benzoxazines (E-ea, E-a, E-dh) and their corresponding polybenzoxazines (PE-ea, PE-a, PE-dh). Notably, all eugenol-based polybenzoxazines exhibited excellent thermal stability with very similar characteristics. Our findings suggest that the presence of allyl groups in eugenol promoted a more cross-linked network structure compared to other functional groups on amines. As a result, eugenol-derived bio-benzoxazines demonstrated superior thermal properties, illustrated by their impressive char yields: PE-ea; 45.6%, PE-a; 45.1%, and PE-dh; 44.1%.