Degradation of stable thermosetting epoxy resins mediated by bases in amide solvents

Abstract

Thermosetting epoxy resins are widely used in our society for adhesives, electronic devices, and building materials owing to their hardness and chemical stability; however, their robustness hinders their ability to chemically degrade to monomers and related low-molecular-weight molecules. Herein, we report the degradation of various thermosetting epoxy resins prepared from bisphenol A diglycidyl ether as a typical epoxy agent and various curing agents, such as diamino arenes, dithiols, and acid anhydrides. The degradation proceeded smoothly when sodium tert-butoxide was used as an activator in a 1,3-dimethyl-2-imidazolidinone solvent at 150 °C to form bisphenol A as a monomer precursor in high yields without any pretreatment. The proposed degradation method was successfully applied to cross-linked thermosetting epoxy resins derived from 4,4’-diaminodiphenylsulfone, a heat-resistant curing agent, commercially available adhesives, and carbon fiber-reinforced composite materials. When composite materials are used, the carbon fibers can be recovered intact. The degradation of various thermosetting epoxy resins prepared from bisphenol A diglycidyl ether as a typical epoxy agent and various curing agents, such as diamino arenes, dithiols, and acid anhydrides proceeded smoothly with sodium tert-butoxide in 1,3-dimethyl-2-imidazolidinone (DMI) solvent at 150 °C to form bisphenol A in high yields. Amide solvents effectively promoted depolymerization and allowed insoluble cross-linked thermosetting epoxy resins to undergo the reaction.