(227c) Trojan Horse Implants for Triggered Depolymerization of Polyethylene Terephthalate (PET)

Polyethylene terephthalate occupies the lion’s share in the realm of plastics, with an annual production capacity exceeding 32MMTs. This quotidian presence can be attributed to its perfect mishmash of desirable thermomechanical, chemical, barrier, and optical properties due to its robust chemical structure comprising rigid hydrophobic terephthalic units spaced by aliphatic glycols. This structure provides thermomechanical ease in processing with excellent resistance to most solvolytic attacks, fortified by the terephthalic units. Chemical resilience manifests as recalcitrance; however, it has been observed that this initial barrier to depolymerization can be overcome by relatively inconspicuous tweaks to the polyester backbone, significantly alleviating the energetic demand for chemical recycling. The premise of the study revolves around mirroring molecular reactivity at macromolecular scales by introducing chemically reactive moieties nicknamed trojan horses as a comonomer in the chain. These moieties are then activated through different mechanisms to initiate depolymerization. Mass transfer barriers on the bulk and the molecular scales greatly diminish with molecular weight as the trojan horse snips the chains stochastically along the backbone resulting in oligomers. These oligomers have a high chain end concentration and are more susceptible to solvolytic scission at milder conditions resulting in a depolymerization cascade that culminates into monomers. The depolymerized monomers and trojan horse cocktail can be repolymerized to produce polymer sans deterioration in performance properties. Several trojan horse candidates have been considered, each initiating depolymerization uniquely. Some of the mechanisms explored in the study focus on accentuated solvolysis, neighboring group participation, and oxidative hydrolysis. The trojan horses can be recycled or valorized into commercial products. Alleviated energetic demands for chemical recycling are expected to result in a paradigm shift in the industry towards molecular recycling, making atom economy viable at realizable scales.