Dihydroxyterephthalate-A Trojan Horse PET Counit for Facile Chemical Recycling

Here, low-energy poly(ethylene terephthalate) (PET) chemical recycling in water: PET copolymers with diethyl 2,5-dihydroxyterephthalate (DHTE) undergo selective hydrolysis at DHTE sites, autocatalyzed by neighboring group participation, is demonstrated. Liberated oligomeric subchains further hydrolyze until only small molecules remain. Poly(ethylene terephthalate-stat-2,5-dihydroxyterephthalate) copolymers were synthesized via melt polycondensation and then hydrolyzed in 150-200 degrees C water with 0-1 wt% ZnCl2, or alternatively in simulated sea water. Degradation progress follows pseudo-first order kinetics. With increasing DHTE loading, the rate constant increases monotonically while the thermal activation barrier decreases. The depolymerization products are 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 show 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.

Automated summary

This study demonstrates low-energy poly(ethylene terephthalate) (PET) chemical recycling in water, where PET copolymers undergo selective hydrolysis at diethyl 2,5-dihydroxyterephthalate (DHTE) sites, catalyzed by neighboring group participation. The depolymerization products can be used to regenerate virgin polymer. The composition-optimized copolymers show a significant reduction in depolymerization time and the recycling process is environmentally friendly using only water.