Formaldehyde-Free Synthesis of Fully Bio-Based MultifunctionalBisbenzoxazine Resins from Natural Renewable Starting Materials

Although bio-based benzoxazines (BZs) have beenexplored widely as sustainable thermosetting resins, few high-performance BZs have been prepared completely from naturalrenewable resources. In this study we synthesized a fully bio-basedmultifunctional bisbenzoxazine (AP-fa-BZ) in high yield and purityfrom apigenin (AP), furfurylamine (fa), and benzaldehyde by usingboth solvent and solventless approaches. Fourier transforminfrared (FTIR) spectroscopy, high-resolution mass spectrometry,and one- and two-dimensional nuclear magnetic resonancespectroscopy confirmed the chemical structure of AP-fa-BZ. Wethen used dynamic mechanical analysis, differential scanningcalorimetry (DSC), thermogravimetric analysis, andin situFTIR spectroscopy to examine the thermal characteristics of AP-fa-BZ before and after its ring-opening polymerization (ROP). DSC revealed that the temperature required for the formation ofpoly(AP-fa-BZ) through ROP (236.3 degrees C) was significantly lower than that of a typical 4-phenyl-3,4-dihydro-2H-1,3-benzoxazine(Pa-type) monomer due to the positive catalytic effect of the phenolic OH groups in the AP structure. After thermal polymerizationat 250 degrees C, the resulting poly(AP-fa-BZ) possessed a high thermal decomposition temperature (Td10= 395 degrees C), a high char yield (52wt %), and a high glass transition temperature (Tg= 283 degrees C). Contact angle measurements revealed the tunable surface properties ofAP-fa-BZ. Finally, the AP-fa-BZ resin functioned as an antibacterial agent against bothStaphylococcus aureusandEscherichia coli.

Automated summary

In this study, a fully bio-based multifunctional resin AP-fa-BZ was successfully synthesized and demonstrated high thermal stability, tunable surface properties, and antibacterial activity against Staphylococcus aureus and Escherichia coli.