Seulchan Lee

Plastic and elastomer wastes are abundant, carbon-rich feedstocks. At the same time, carbon capture requires sorbents that perform under realistic temperatures, humidity, dilute CO2, and repeated regeneration. This review surveys feedstock-driven chemical upcycling routes that transform waste polymers into CO2 sorbents, while treating carbonization-derived physisorbents as a comparative benchmark and pragmatic fallback for chemically intractable or highly heterogeneous feedstocks. We frame “waste-to-sorbent” conversion as a feedstock-driven design problem in which inherited constitutional chemistry, network and morphology, formulation, and acquired chemistry—collectively termed chemical memory—govern feasible transformations and capture performance. We organize the literature by major feedstocks—PET, PVC, polystyrene, rubbers/tires, polyolefins, and mixed plastics—and compare physisorption- and chemisorption-dominant architectures with emphasis on binding-site accessibility, transport limits, humidity effects, impurity tolerance, oxidative stability, and regeneration windows. Because cross-study comparison is often hindered by inconsistent testing conditions and incomplete characterization of both starting feedstocks and resulting sorbents, we propose a mechanism-aware benchmarking framework and minimum reporting protocol centered on feedstock descriptors, application-relevant CO2 partial pressures, working capacity, accessible-site metrics (e.g., effective nitrogen/amine efficiency), ultramicropore descriptors, and durability under humid/impure cycling. These guidelines connect feedstock chemistry to deployable sorbent design and accelerate translation beyond headline capacities.

Reversible ring-opening metathesis polymerization (ROMP) of cyclooctene (COE) derivatives remains a challenge due to their high ring strain energies (RSEs). While previous strategies rely on fused bicyclic systems to reduce RSEs, depolymerization of non-bicyclic COE polymers has proven difficult. Here, we demonstrate efficient reversible ROMP of non-bicyclic COE derivatives by introducing conformational constraints via geminal tert-butyl and hydroxy substituents. These tailored monomers enable depolymerization efficiencies exceeding 90%, achieving near-quantitative monomer recovery under optimized conditions. Experimental and computational analyses reveal that intramolecular OH-π interactions stabilize cyclic conformations in hydroxy-containing monomers, while steric hindrance in the ring-opened form is also critical for efficient depolymerization. This work highlights the interplay between substituent effects, steric control, and molecular conformation in enabling chemical recyclability. It offers an alternative molecular design strategy for developing sustainable materials through reversible polymerization, challenging the conventional reliance on bicyclic systems.

Thermosets possess exceptional thermochemical stability and mechanical performance, but their irreversible crosslinked structures render them unrecyclable, posing severe environmental concerns. Although dynamic adaptable networks, including coordination-adaptable networks (CooANs), have emerged as sustainable alternatives, most rely on network rearrangement rather than true monomer recovery. Here, we develop a CooAN by integrating ring-opening metathesis polymerization of a vicinal-diol-functionalized cyclohexene monomer with dynamic Fe(III)–diol coordination. The resulting network enables mechanical reprocessing through reversible metal–ligand exchange and complete chemical recycling via ring-closing metathesis depolymerization of cyclohexene backbone, achieving 79% monomer recovery. The material exhibits high tensile strength (> 25 MPa), large elongation (> 600%), and distinct shape-memory behavior. It can also be extended to form conductive composites while retaining full recyclability. Precisely tuned ring-strain energy facilitates efficient depolymerization under mild conditions. This work establishes a sustainable molecular design strategy for fully recyclable thermosets that unite mechanical robustness, functional adaptability, and closed-loop chemical circularity.

The development of environmentally sustainable processes for polymer recycling is of paramount importance in the polymer industry. In particular, the implementation of chemical recycling for thermoset polymers via covalent adaptable networks (CANs), particularly those based on the dynamic hindered urea bond (HUB), has garnered intensive attention from both the academic and industrial sectors. This interest stems from its straightforward chemical structure and reaction mechanism, which are well‐suited for commercial polyurethane and polyurea applications. However, a substantial drawback of these CANs is the requisite use of toxic isocyanate curing agents for their synthesis. Herein, we propose a new HUB synthesis pathway involving thiazolidin‐2‐one and a hindered amine. This ring‐opening reaction facilitates the isocyanate‐free formation of a HUB and enables sequential reactions with acrylate and epoxide monomers via thiol–Michael and thiol–epoxy click chemistry. The CANs synthesized using this methodology exhibit superior reprocessability, chemical recyclability, and reutilizability, facilitated by specific catalytic and solvent conditions, through the reversible HUB, thiol–Michael addition, and transesterification processes.

The development of environmentally sustainable processes for polymer recycling is of paramount importance in the polymer industry. In particular, the implementation of chemical recycling for thermoset polymers via covalent adaptable networks (CANs), particularly those based on the dynamic hindered urea bond (HUB), has garnered intensive attention from both the academic and industrial sectors. This interest stems from its straightforward chemical structure and reaction mechanism, which are well‐suited for commercial polyurethane and polyurea applications. However, a substantial drawback of these CANs is the requisite use of toxic isocyanate curing agents for their synthesis. Herein, we propose a new HUB synthesis pathway involving thiazolidin‐2‐one and a hindered amine. This ring‐opening reaction facilitates the isocyanate‐free formation of a HUB and enables sequential reactions with acrylate and epoxide monomers via thiol–Michael and thiol–epoxy click chemistry. The CANs synthesized using this methodology exhibit superior reprocessability, chemical recyclability, and reutilizability, facilitated by specific catalytic and solvent conditions, through the reversible HUB, thiol–Michael addition, and transesterification processes.

A highly efficient, direct C(sp³)–H cyanation was developed under mild photocatalytic conditions. The method enabled the direct cyanation of various C(sp³)–H substrates with excellent functional group tolerance. Notably, complex natural products and bioactive compounds were efficiently cyanated.

Palladium catalysts modified with iminopyridine ligands were employed for ethylene/CO and styrene/CO copolymerization and ethylene/styrene/CO terpolymerization. Our studies revealed that the steric and electronic effects of the catalysts play key, yet distinct roles in these polymerization reactions. The thermal properties of the polyketones were engineered by varying the styrene content in terpolymers derived from ethylene, styrene, and CO sources, with increased styrene ratios yielding reduced polyketone crystallinity.