Ultrafast and selective recycling of poly(p-dioxanone) to monomers by using Brønsted–Lewis acidic ionic liquids as solvents/catalysts

Abstract

In recent years, chemical recycling to monomer (CRM) has emerged as an advanced strategy to deal with post-consumer plastics. However, because it usually takes a long time to react at a relatively high temperature, CRM suffers from side reactions and energy consumption issues. In this work, a Brønsted–Lewis acid ionic liquid/polyhydroxy-compound system ([Et₃NH][ZnCl₃]/pentaerythritol) was developed as a bifunctional reagent for dissolving poly(p-dioxanone) (PPDO) and highly efficiently catalysing its CRM. In situ addition of the polyhydroxy-compound significantly prevented the formation of byproduct, i.e., cyclic PPDO, by converting it back to depolymerizable linear PPDO. Therefore, both the CRM efficiency and selectivity were obviously improved. At 160 °C, PPDO was almost fully depolymerized to the PDO monomer in only 8 minutes with 99.9% GC purity of yield. Moreover, [Et₃NH][ZnCl₃]/pentaerythritol could be reused at least 5 times without post-processing and its chemical structure and efficiency remained intact. According to the kinetic study, the activation energy of depolymerization was calculated to be 64.81 kJ mol⁻¹, half lower than the traditional method. Based on NMR titration, the catalytic mechanism was discussed. Importantly, according to the assessment of the energy economy factor, environmental factor, and environmental energy impact factor, the strategy developed in this work is better than all of the related works in greenness.