Sustainable access to biobased biphenol epoxy resins by electrochemical dehydrogenative dimerization of eugenol

Abstract

Limited fossil resources require innovative monomers and polymers derived from renewable feedstocks such as plant biomass. Thermosetting epoxy resins largely rely on petrochemical bisphenol-type monomers, which give high performance materials but are controversial due to their effects on human health. Herein, we present two biobased epoxy resins by direct dehydrogenative dimerization of eugenol, the main component of clove oil. Taking the Principles of Green Chemistry into account, we developed electrochemical dehydrodimerization at reticulated vitreous carbon (RVC) electrodes using methanol as environmentally benign solvent. Thus, fluorinated solvents such as 1,1,1,3,3,3-hexafluoroisopropanol (HFIP) or commonly used oxidizers such as potassium ferricyanide (K₃[Fe(CN)₆]) are avoided and a high reaction mass efficiency (RME) of 47% is obtained. Alkylation and epoxidation gave two epoxy resins MDDE-2E and ADDE-4E with 2 and 4 epoxy functionalities, respectively. Curing with MHHPA gave durable epoxy materials with T_g's of 153 °C for MDDE-2E (for DGEBA: 151 °C) and an extraordinary 216 °C for ADDE-4E, reflecting the increased network density of the cured epoxy material. Thermal degradation under nitrogen and air was observed at temperatures above 300 °C with T_10% of 304 and 347 °C, respectively. In contrast to DGEBA, high char rates and slower degradation above 400 °C indicate flame-retarding properties of the eugenol-derived epoxy resins.