Condensation polymers, such as poly(ethylene terephthalate) (PET), polyamides, polyurethanes, polycarbonate, polysulfone, and polyimide, comprise ~30% of the global plastic production. Although there has been some progress on chemically upcycling condensation polymers, especially PET, most condensation polymers are not recycled because of the difficulty in depolymerization to pure building blocks in an energy efficient manner. Catalysts are typically used to facilitate their deconstruction, however, catalytic deconstruction of condensation polymers has many challenges including limited reactivity, yields, and control over product selectivity. Consequently, deconstruction of condensation polymers typically requires high temperatures that lead to formation of small unselective fragments due to thermodynamically controlled processes. New processes and catalysts are needed to lower the energy requirements and temperature for deconstruction of condensation polymers. Ionic liquids hold great potential to address these challenges due to their unique physical and chemical properties, including good miscibility with polymers, high thermal stability, low vapor pressure, tailorable functionality and catalytic activity. Thus, the overarching goal of this proposal is to unravel the fundamental principles for precise deconstruction of condensation polymers using ionic liquids as both solvent and organocatalyst while establishing approaches for their reconstruction. To achieve the overarching goal, the following three specific aims will be pursued. Aim 1: Develop low energy depolymerization pathways for condensation polymers by tailoring functionality, structure, and composition of ionic liquids as solvents and catalysts. Aim 2: Develop design principles for ionic liquid organocatalysts that generate well-defined deconstructed intermediates. Aim 3: Understand and control the product selectivity in the deconstruction of mixed streams of condensation polymers using designed ionic liquids and unravel the pathways for reconstruction. Tailored IL catalysts will provide lower activation energies for depolymerization, control of product selectivity, and pathways for immediate reconstruction using well-defined deconstructed building blocks. To address these scientific challenges, a strong team has been assembled with expertise in reaction mechanism, precision synthesis, polymer chemistry, catalysis, ionic liquid chemistry, large-scale simulations and in situ/operando characterization. Successful implementation of this proposal will deliver the fundamental knowledge to establish the design principles for energy efficient polymer deconstruction and lay a versatile platform for polymer reconstruction with tailored composition, topology and functionality. These upcycled polymers can be recycled to establish an energy efficient closed loop recycling pathway for condensation polymers.