Multifunctional Biobased Benzoxazines Blended with an Epoxy Resin for Tunable High-Performance Properties

Biobased polybenzoxazines incorporate natural phenolic structures to produce polymers with near-zero shrinkage, high char yields, and high chemical and thermal resistances, garnering great interest as sustainable high-performance polymers. Herein, difunctional and trifunctional benzoxazine monomers, bisguaiacol-furfurylamine (BG-f) and triguaiacol-furfurylamine (TG-f), respectively, were synthesized from renewable guaiacol, vanillin, and furfurylamine using solventless procedures. Benzoxazines were blended with varying weights of epoxy resin and thermally cured to produce benzoxazine-epoxy (BG-f-E and TG-f-E) polymers. These polymers displayed glass transition temperatures ranging from 130 to 157 °C (peak of the loss modulus), thermal stabilities from 299 to 329 °C in both N2 and air, and char yields ranging from 35% to 58%. BG-f-E and TG-f-E with greater benzoxazine content produced stiffer materials exhibiting glassy storage moduli values upward of 3.48 and 3.69 GPa, respectively. BG-f-E polymers displayed higher molecular weight between cross-link values (646 g mol–1 to 981 g mol–1) compared to TG-f-E polymers (316 g mol–1 to 465 g mol–1) and exhibited fracture energies upward of 404 J m–2. These investigations demonstrate the utility of incorporating biobased benzoxazines into benzoxazine-epoxy resin formulations to design sustainable polybenzoxazines with tunable thermal and mechanical properties for high-performance polymer applications.