"Evolution of Chain Structure during the Glycolysis of Poly(ethylene terephthalate)"

Polyethylene Terephthalate (PET) is one of the most used commercial polymers and has the potential to be chemically recycled industrially. The industrial heterogeneous depolymerization of PET via glycolysis is often described as a surface reaction, where reaction rate is dependent on the available surface area of PET flakes. Moreover, the depolymerization is often pushed to formation of monomer, which requires extensive time and energy. Our research seeks to track the evolution of chain structure during the depolymerization process to test the presumption that the depolymerization is a surface reaction and to offer insight into the availability of intermediates in the depolymerization process. Our results show that the heterogenous reaction is governed by the diffusion of the glycol into the polymer, not the PET surface area. We will also present NMR and GPC data that documents the decrease in Mn with little loss in product yield, as well as DSC results that document the isolation of highly crystalline polymer mid depolymerization. This is consistent with the reaction of the glycol with inter-crystalline tie chains in the amorphous phase. Chain scission of tie chains lowers the dispersity of the depolymerized intermediates. This mechanism is also supported by the slow conversion of end groups to two alcohol groups. When all end groups of PET chains are converted to alcohol groups, the PET flakes break apart into highly crystalline and less disperse polymer. This understanding of the evolution of chain structure during the depolymerization process offers pathways to well characterized intermediates that can be used as feedstock for value added materials.