Sustainable Valorization of Waste Plastics and Alternative Directions via Chemical Modification and Additive Manufacturing

The escalating accumulation of synthetic polymer waste necessitates sustainable plastic upcycling strategies that minimize risks to human health and ecosystems. This dissertation addresses this challenge and demonstrates several efficient depolymerization strategies for polyesters and polyurethanes, including a novel 'imidazolysis' approach alongside established 'glycolysis', 'alcoholysis', and 'aminolysis' methods, while driving new directions for the utilization of depolymerized products. Initially, this dissertation will demonstrate the catalyst-free depolymerization of polyethylene terephthalate (PET) using imidazoles termed "imidazolysis", which affords the bifunctional monomer 1,1'-terephthaloyl bisimidazoles (TBI) in high purity. Eight different imidazole derivatives were utilized, and it was observed that the reagents with electron-donating groups were more effective in the faster depolymerization of PET. TBIs were found to be versatile intermediates in transforming them into materials of increased value. Motivated by this outcome, we extend imidazolysis to polyurethane (PU), a ubiquitous polymer that is often neglected due to its cross-linked nature for recycling purposes. We achieved complete deconstruction of PU via imidazole, resulting in the product imidazole-carboxamide and the release of polyol. We then describe PET aminolysis to terephthalamide diols and their conversion to dichloro-terephthalamides, which serve as monomers for self-healing (SH) polyamide (PA) ionenes, compatible with fused-deposition (FDM) 3D printing. Ionenes are highly tunable materials having advantages for monomer selection from a vast library of di-(alkyl or aryl)-halides and tertiary diamines. Similarly, the dissertation demonstrates the glycolysis of PET with ethylene glycol, and further modification of this compound also led to the self-healing, tunable poly(ester-amide) ionene for 3D printing, noticeably different than the PA ionenes in terms of rigidity and self-recovery. In parallel, this dissertation presents the synthesis of novel terephthalates and carbamates (with and without allyl functional group), which were initially mass-produced from commercially available terephthaloyl chloride (TC) and methylene diphenyl diisocyanate (MDI), respectively. Subsequently, we aim to access the same products via organocatalyzed alcoholysis from waste PET and PU, enabling use in stereolithography (SLA) printing. Overall, these results highlight complementary depolymerization examples for PET and PU, demonstrating how careful reagent selection can allow us to produce commercially valuable products that link plastic circularity with additive manufacturing.