Ion-pair cooperativity in common neutral salts promotes methanolysis of ester-containing plastics.

Methanolysis is a promising strategy for chemical recycling of ester-containing plastics, but current approaches rely on homogeneous acids/bases or heterogeneous catalysts, which suffer from corrosion and deactivation. Here we report that common neutral salts can promote plastic methanolysis via an ion-pair cooperative mechanism. In situ spectroscopy, nuclear magnetic resonance, Raman spectroscopy, molecular dynamics simulations, and density functional theory calculations reveal that Na+ coordinates with carbonyl oxygen, enhancing carbonyl electrophilicity, while Cl- interacts with methanol through O-H⋯Cl- hydrogen bonding, disrupting its hydrogen-bond network and activating the nucleophile. Extending this concept to various neutral salts establishes a clear structure-activity relationship governed by cation-mediated substrate activation and anion-mediated methanol activation. Notably, naturally occurring salts also show comparable activity, and the strategy is applicable to representative ester-containing plastics including polycarbonate (PC), polylactic acid (PLA), polybutylene terephthalate (PBT), and polyethylene terephthalate (PET). These results identify ion-pair cooperativity as a possible mechanism for polymer depolymerization and provide a feasible strategy for plastic chemical recycling.