Novel efficient method of chemical upcycling of waste poly(ethylene terephthalate) bottles by acidolysis with adipic acid under microwave irradiation

In this work, for the first time, the reaction of post-consumer poly(ethylene terephthalate) (PET) bottles with adipic acid (AA) under microwave (MW) irradiation without catalyst was investigated. An efficient procedure to isolate various materials was proposed, namely the excess adipic acid, terephthalic acid, and novel oligo(ethylene adipate-co-terephthalate) (OEAT) with carboxylic end groups. The structure of OEAT was confirmed by FTIR, 1H-NMR, and ESI-MS. OEAT is a mixture of oligomers, containing co-oligomers of ethylene adipate and terephthalate, and nonreacted adipic acid. An explanation of the mechanism of the reaction was proposed through a concerted six-member ring formation including an O-alkyl fission process. Adipic acid and terephthalic acid were recovered and used as basic materials. OEAT was used for curing diglycidyl ether of bisphenol-A (DGEBA) resin and applied as a coating material. This upcycling method of PET showed high atom efficiency and high isolated yield reaction.