Direct One-Step Controlled Partial Depolymerization and Upcycling of Poly(ethylene terephthalate) into Hyperbranched Oligomeric Ionogel

Chemical recycling of poly(ethylene terephthalate) (PET) by depolymerization into monomers to recreate virgin-grade plastics is desirable; however, the energy-inefficient separation and purification steps needed to obtain high-purity monomers result in poor overall economic feasibility at present. Herein, we present a one-step integrated process for partial depolymerization and upcycling of PET oligomers directly into high-value products without any need for solvent recovery and purification. The key strategy for our approach is using multifunctional cleaving agents such as glycerol in the presence of ionic liquid as a catalyst for controlled partial depolymerization of PET via transesterification using N-methyl-2-pyrrolidone (NMP) as a solvent. The obtained depolymerized, oligomeric PET (DOPET) recyclate together with NMP and IL is a gel-like, ionic-conductive material, also termed as an “ionogel”, that has the potential to be used in energy storage applications or as mechanically robust electrical conductors. This is a one-step process requiring no extensive separation and purification of PET oligomers or distillation of solvent for recovery, which further simplifies the recycling process while simultaneously increasing the value of the waste product. We have further investigated the effects of the choice and amount of cleaving agent on the molecular weight and branching of the DOPET oligomers and hence the properties of the upcycled end products. Moreover, we have also shown the versatility of the abovementioned process for controlled depolymerization of other condensation polymers such as polyamides, polyurethane, and even mixed polymer products to obtain high-value functional materials.