Chemical Recycling of End‐of‐Life Polyamide 6 via Ring Closing Depolymerization

The chemical recycling of end‐of‐life polymers, a sequence of depolymerization and polymerization reactions, enables the conserving of fossil resources and can add some value to the circular economy. In this study, a process for the depolymerization of end‐of‐life Nylon 6 via ring‐closing reactions to produce as building block N ‐acetylcaprolactam have been set up. In detail, a combination of acetic anhydride as depolymerization reagent and catalytic amounts of 4‐dimethylaminopyridine allows under microwave irradiation and within short times (15 min) the conversion of end‐of‐life Nylon 6 to N ‐acetylcaprolactam under solvent‐less conditions. Applying optimized conditions a sequence of Nylon 6 goods was transformed in good yields. The product N ‐acetylcaprolactam was converted to ϵ‐caprolactam by transfer of the acetyl functionality to 2‐aminoethanol to give N ‐(hydroxyethyl)acetamide a precursor for poly( N ‐vinylacetamide). The generated ϵ‐caprolactam can be used as monomer for the synthesis of new Nylon 6, therefore a chemical recycling of the monomeric unit of Nylon 6 is feasible.