Renewable Thermoplastics Based on Lignin-Derived Polyphenols

A series of renewable triphenylmethane-type polyphenols (TPs) were synthesized from lignin-derived guaiacols (methylguaiacol and propylguaiacol) and aldehydes (4-hydroxy­benzaldehyde, vanillin, and syringaldehyde). By converting guaiacols to catechols through ortho-demethylation, the newly formed phenolic para site remarkably improved the reactivity as reflected by conversion of TPs. Optimized reagent molar ratios were aldehyde/catechol (1:4) and aldehyde/H2SO4 (1:3). A typical TP (VAN-M-CAT) was converted to glycidyl ether (GE-VAN-M-CAT) to examine its feasibility as precursor to epoxy thermosets. The resulting network exhibited excellent glassy modulus (12.3 GPa), glass transition temperature (167 °C), and thermal stability, which were attributed to the rigid triphenylmethane framework, high functionality (n = 5), and high cross-link density. A fully biobased epoxy comonomer (VAN-LIN-EPO), which was prepared by esterification of VAN-M-CAT with linoleic acid followed by epoxidation, could tune the material properties. This study widens the synthesis route of fully biobased polyphenols, which can yield polymers with excellent properties.