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Abstract Nylon‐6 is selectively depolymerized to the parent monomer ϵ‐caprolactam by the readily accessible and commercially available lanthanide trisamido catalysts Ln(N(TMS)2)3(Ln=lanthanide). The depolymerization process is solvent‐free, near quantitative, highly selective, and operates at the lowest Nylon‐6 to ϵ‐caprolactam depolymerization temperature reported to date. The catalytic activity of the different lanthanide trisamides scales with the Ln3+ionic radius, and this process is effective with post‐consumer Nylon‐6 as well as with Nylon‐6+polyethylene, polypropylene or polyethylene terephthalate mixtures. Experimental kinetic data and theoretical (DFT) mechanistic analyses suggest initial deprotonation of a Nylon terminal amido N−H bond, which covalently binds the catalyst to the polymer, followed by a chain‐end back‐biting process in which ϵ‐caprolactam units are sequentially extruded from the chain end.
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Catalyst metal-ligand design for rapid, selective, and solventless depolymerization of Nylon-6 plastics
Developing effective catalysis to address end-of-life Nylon pollution is urgent yet remains underdeveloped. Nylon-6 is a resilient synthetic plastic and a major contributor to ocean pollution. Here, we report a metallocene catalytic system based on earth-abundant early transition and lanthanide metals that mediates Nylon-6 depolymerization at unprecedented rates up to 810 (ε-caprolactam)$ mol(Cat.)1$h1 at 240C in R99% yield. This solventless process operates with catalyst loadings as low as 0.04 mol % at temperatures as low as 220C—themildest Nylon-6 depolymerization conditions reported to date. This metallocene catalysis can be carried out in a simulated continuous process, and the resulting ε-caprolactam can be re-polymerized to higher-quality Nylon-6. Experimental and DFT analyses identify effective depolymerization pathways involving catalytic intra-Nylon-chain ‘‘unzipping’’ assisted by p-ligand effects and inter-chain ‘‘hopping.’’ A robust chelating ansa-yttrocene is particularly effective in depolymerizing diverse commodity end-of-life articles, such as fishing nets, carpets, clothing, and plastic mixtures.
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- Award ID(s):
- 2247666
- PAR ID:
- 10522742
- Publisher / Repository:
- Cell Press
- Date Published:
- Journal Name:
- Chem
- Volume:
- 10
- Issue:
- 1
- ISSN:
- 2451-9294
- Page Range / eLocation ID:
- 172 to 189
- Subject(s) / Keyword(s):
- Nylon-6 catalytic deconstruction recycling caprolactam
- Format(s):
- Medium: X Size: 2MB
- Size(s):
- 2MB
- Sponsoring Org:
- National Science Foundation
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- Free Publicly Accessible Full Text
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Accepted Manuscript1.0
- Journal Article:
- https://doi.org/10.1016/j.chempr.2023.10.022
