Trojan Horse PET Counits for Facile Chemical Recycling

In this talk I will review our efforts to develop PET copolymers designed for low-energy chemical recycling. For example, 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. Copolymers were synthesized via melt polycondensation and then hydrolyzed in 150-200 °C water with. Degradation progress was tracked via measurement of retained solids and quantiative analysis of the aqueous phase. 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. Thermomechanical properties were in general similar to PET, with increased tensile strength and reduced extensibility the most notable differences. This approach is readily extended to other "Trojan Horse" counits that provide internal cataylsis for facile hydrolysis, methanolysis, or glycolysis.