Catalyst Design to Address Nylon Plastics Recycling

Rational tailoring of catalytic systems offers highly desirable transformations targeting the growing environmental challenges associated with plastics pollution. For example, the identification of efficient catalysts to address alarming end-of-life Nylon pollution remains underexplored. Nylon-6 is a non-biodegradable high-performance engineering plastic with centuries of chemical persistence, resulting in millions of tons of waste accumulation. Here we report the rational manipulation of organolanthanide catalyst structure to achieve an exceptionally efficient, solventless, and scalable Nylon-6 depolymerization process, affording monomer ε-caprolactam in ≥99% yield. Specifically, catalyst Cp*₂LaCH(TMS)₂ (Cp* = η₅-C₅Me₅, TMS = SiMe₃) operates at catalyst loadings as low as 0.2 mol% and temperatures as low as 220 °C. For efficient deconstruction of more recalcitrant commodity Nylon-6 end-of-life articles such as fishing nets, car-pets, and clothing, the robust, thermally stable ansa-metallocene catalyst Me₂SiCp’’₂YCH(TMS)₂, (Cp’’ = η₅-C₅Me₄) effects >99% conversion of these items into ε-caprolactam. The collected product can be readily re-polymerized to afford pristine Nylon-6 with higher molecular masses and comparable structural regularity, providing a superior upcycling pathway for end-of-life Nylon plastics. Experimental mechanistic studies reveal intriguing and effective depolymerization pathways, such as catalytic intrachain “unzipping” enabled by the catalyst π-ancillary ligand steric constraints. Effective interchain “hopping” mechanisms, as well as chain-end deactivation are also demonstrated and supported by DFT analyses.