Accessing Chemically Recyclable Polyamides with Tunable Properties via Geminal Dimethyl Substitution

The development of new chemically recyclable polymers could serve as a means of reducing the plastic pollution and alleviating global energy crisis and monomer design strategy has driven the innovation in this field. In this contribution, α-dimethyl substituted caprolactam (α-DMCL) and γ-dimethyl substituted caprolactam (γ-DMCL) were prepared to evaluate the substitution position effect on chemical recyclability and material performance in polycaprolactam (PCL) system. The introduction of geminal dimethyl substitution to ε-caprolactam (CL) at α and γ position endowed the resulting polyamides P(α-DMCL) and P(γ-DMCL) with distinct thermal and mechanical properties. Remarkably, thermal depolymerization of P(γ-DMCL) in presence of potassium caprolactamate (CL-K) could be carried out at 200 °C and converted to γ-DMCL in 91% yield. The recovered γ-DMCL was capable of repolymerization to P(γ-DMCL) without a decrease in reactivity, demonstrating the proof-of-concept recyclability of P(γ-DMCL).