Potential Lignin-Derived Alternatives to Bisphenol A in Diamine-Hardened Epoxy Resins

This work details the synthesis and characterization of potentially lignin-derived bisguaiacols as alternatives to petroleum-derived bisphenol A (BPA) in diamine-cured epoxy resins. The variations in the number of methoxy groups of lignin facilitate the systematic chemical and thermomechanical manipulation of bisguaiacol-based thermosets to achieve desirable properties. Herein, ten bisguaiacols (including structural isomers), differing in the number of methoxy groups and regioisomer content, were synthesized from substituted bioderivable hydroxybenzyl alcohols and phenols by acid-catalyzed electrophilic aromatic substitution approaches and then functionalized with oxirane groups. These bisguaiacol diglycidyl ethers were subsequently cured with a model diamine. All cured bioderivable resins had glass transition temperatures (Tg’s) above 100 °C, 5 wt % loss temperatures above 300 °C, and room-temperature glassy storage moduli above 2.0 GPa, values that were comparable to bisphenol A diglycidyl ether (BADGE/DGEBA) cured resins. Furthermore, final cured resin Tg’s (111–151 °C) and high-temperature rubbery moduli (15–46 MPa) were easily tuned by manipulating the relative number of methoxy moieties and the regioisomer content, demonstrating the versatility and robustness of these bioinspired materials.