Synthesis and Properties of Isoliquiritigenin‐Based Main‐Chain Type Benzoxazine Resins

ABSTRACT In this study, two main‐chain type benzoxazines (poly(ILG‐ddm) main and poly(ILG‐pdfa) main ) based on isoliquiritigenin were successfully synthesized, and their structures and properties were systematically characterized and evaluated. FT‐IR and NMR analyses confirmed the chemical structures of benzoxazines, verifying the successful formation of the oxazine ring. DSC studies showed that both bio‐based thermosetting systems exhibited lower curing temperatures compared to traditional petroleum‐based benzoxazines. Notably, poly(ILG‐pdfa) main displayed a significantly lower apparent activation energy (~127 kJ/mol) than poly(ILG‐ddm) main (~148 kJ/mol), indicating its easier curing and superior processability. TGA results demonstrated that the resulting cured sample, poly(ILG‐ddm) main X , possessed higher thermal stability ( T d5 = 352°C, char yield at 800°C = 58.4%). Although poly(ILG‐pdfa) main X showed slightly lower thermal stability ( T d5 = 319°C, char yield = 49.8%), it still maintained excellent performance among fully bio‐based polymeric materials. DMA analysis revealed that poly(ILG‐pdfa) main X exhibited high storage modulus and a high glass transition temperature (266.2°C) due to the strong intermolecular forces and π–π stacking between the furan and chalcone structures. The isoliquiritigenin‐derived polybenzoxazines exhibit an optimal balance between low polymerization temperature and high thermal stability, providing a robust matrix for their application in high‐performance and sustainable composites.