Biorenewable Epoxy Resins Derived from Plant-Based Phenolic Acids

Plant-derived phenolic acids are attractive substitutes for petroleum sources for the derivation of polymers, due to their rigid aromatic rings and chemical groups amenable to functionalization. Difunctional phenolic acids were investigated as replacements for the diglycidyl ether of bisphenol A (DGEBA) in anhydride-cured epoxy resins. Functionalization of each phenolic acid was carried out through allylation, followed by epoxidation. Epoxy resins were synthesized through reaction of either epoxidized salicylic acid (ESA) or epoxidized 4-hydroxybenzoic acid (E4HBA) with the curing agent methylhexahydrophthalic anhydride (MHHPA) (catalyzed by 1-methyl-imidazole, 1-MI). The MHHPA anhydride curing agent (catalyzed by 1-MI) was chosen due to the resulting high conversion and advantageous high polymer glass transition temperature. ESA and E4HBA had similar curing behavior to that of DGEBA when cured with MHHPA. A two-step protocol was developed to avoid monomer evaporation and polymer vitrification during curi...