Synthesis and copolymerization of fully bio-based benzoxazines from guaiacol, furfurylamine and stearylamine

Two fully bio-based benzoxazine monomers, 3-furfuryl-8-methoxy-3,4-dihydro-2H-1,3-benzoxazine (Bzf) and 3-octadecyl-8-methoxy-3,4-dihydro-2H-1,3-benzoxazine (Bzs), have been successfully synthesized via a solventless method. Their structures have been confirmed by FTIR spectroscopy, NMR spectroscopy, and elemental analysis. Copolymerization of the monomers has been investigated by differential scanning calorimetry (DSC) measurements. The results reveal that they undergo homogeneous copolymerization when the Bzf-Bzs molar ratio exceeds 1 : 2. The furan moiety of Bzf was found to have beneficial effects on the copolymerization, including an accelerating effect on the curing process, improvement of the cross-linking density, and enhancement of the thermal properties of the copolymerized resins. Based on the mechanism of ring-opening polymerization of benzoxazines, these effects may be attributed to the electrophilic aromatic substitution of the furan ring structure. These findings have significant implications for the design of new fully bio-based polybenzoxazines with desirable properties.