Dihydroxyterephthalate - a Trojan Horse PET Counit for Facile Chemical Recycling.

Here we demonstrate low-energy PET chemical recycling in water: PET copolymers with diethyl 2,5-dihydroxyterephthalate (DHTE) undergo selective hydrolysis at DHTE sites, autocatalyzed by neighboring group participation (NGP). Liberated oligomeric subchains further hydrolyze until only small molecules remain. Poly(ethylene terephthalate-stat-2,5-dihydroxyterephthalate) (PEDHT) copolymers were synthesized via melt polycondensation and then hydrolyzed in 150-200 °C water with 0-1 wt % ZnCl 2 , or alternatively in simulated sea water. Degradation progress followed pseudo-first order kinetics. With increasing DHTE loading, the rate constant increased monotonically while the thermal activation barrier decreased. The depolymerization products were ethylene glycol, terephthalic acid, 2,5-dihydroxyterephthalic acid, and bis(2-hydroxyethyl) terephthalate dimer, which could be used to regenerate virgin polymer. Composition-optimized copolymers showed a decrease of nearly 50% in the Arrhenius activation energy, suggesting a 6-order reduction in depolymerization time under ambient conditions compared to that of PET homopolymer. This study provides new insight to the design of polymers for end-of-life while maintaining key properties like service temperature and mechanical properties. Moreover, this chemical recycling procedure is more environmentally friendly compared to traditional approaches since water is the only needed material, which is green, sustainable, and cheap. This article is protected by copyright. All rights reserved.