Selective Lanthanide-Organic Catalyzed Depolymerization of Nylon-6 to ϵ-Caprolactam.

Area of Science:

• Polymer chemistry
• Catalysis
• Materials science

Background:

• Nylon-6 recycling remains a challenge due to its robust chemical structure.
• Existing depolymerization methods often require harsh conditions or lack selectivity.
• Development of efficient catalysts for selective polymer degradation is crucial for sustainable materials management.

Purpose of the Study:

• To investigate the efficacy of lanthanide trisamido catalysts for Nylon-6 depolymerization.
• To determine the optimal conditions for selective conversion of Nylon-6 to ϵ-caprolactam.
• To explore the catalytic activity trend across different lanthanide elements.

Main Methods:

• Utilized commercially available lanthanide trisamido catalysts, Ln(N(TMS)₂)₃.
• Conducted solvent-free depolymerization experiments with post-consumer Nylon-6 and mixed plastic waste.
• Employed experimental kinetics and Density Functional Theory (DFT) for mechanistic analysis.

Main Results:

• Achieved selective depolymerization of Nylon-6 to ϵ-caprolactam using lanthanide catalysts.
• The process demonstrated near-quantitative yields, high selectivity, and operated at the lowest reported temperatures.
• Catalytic activity correlated with the Ln³⁺ ionic radius; effectiveness extended to mixed plastic streams.

Conclusions:

• Lanthanide trisamido catalysts offer a highly efficient and selective method for Nylon-6 depolymerization.
• The solvent-free, low-temperature process is effective for both pure and mixed post-consumer Nylon-6.
• Mechanistic insights suggest a catalytic cycle involving N-H deprotonation and chain-end back-biting.