Tunable ether-functionalized protic ionic liquid for efficient glycolysis of polyethylene terephthalate

Plastics are essential to modern society, yet the imbalance between their massive production and inefficient end-of-life management results in severe energy loss and environmental burden. In this work, a green and functionally tunable protic ionic liquid ([TBD][Mea]) was designed through a hydrogen-bond acceptor strategy by neutralizing 1,5,7-triazabicyclo[4.4.0]dec-5-ene (TBD) with methoxyacetic acid (Mea). The introduction of the ether moiety enhances the hydrogen-bond accepting ability, thereby activating ethylene glycol (EG) and promoting ester bond cleavage during sustainable PET glycolysis. As a result, [TBD][Mea] catalyzed complete depolymerization of PET under mild conditions ([TBD][Mea]:PET:EG = 0.2:1:10 weight ratio, 180 °C, 1 h), affording bis(2-hydroxyethyl) terephthalate (BHET) with a high yield of 87.5%. Kinetic studies revealed a first-order reaction with an activation energy of 79.02 kJ mol −1 , consistent with DFT results showing that synergistic hydrogen–bond interactions among the ionic liquid, EG, and PET accelerate nucleophilic attack on the carbonyl carbon. This study demonstrates a metal-free, functionally tunable ionic liquid catalyst that integrates the activity of organocatalysts with the robustness of metal catalysts, offering a sustainable, solvent-based strategy for closed–loop PET recycling.