Directional Depolymerization of Poly(ε-caprolactone) with High Monomer Selectivity.

Chemical recycling to monomer (CRM) is the most attractive method for achieving the closed-loop usage of polymers, in which polymers are recycled back to their starting monomers and then used to produce new polymers without loss of the virgin material properties. However, during the CRM process, the depolymerized products are usually accompanied by the formation of byproducts (e.g., cyclic oligomers) in addition to monomers. Therefore, the directional depolymerization to monomer through catalyst design is significant. Herein, we report the directional depolymerization of poly(ε-caprolactone) (PCL) to ε-caprolactone (ε-CL) under solution conditions through innovative design of catalyst structure. The (BisSalen)Al catalysts, featuring a confined cavity, demonstrated exceptional performance, enabling highly selective depolymerization of PCL with excellent monomer selectivity (>99%) and yield (93%). The mechanism of selective depolymerization was further investigated in detail through controlled NMR experiments and density functional theory (DFT) calculations. This work reveals the correlation between catalyst structure and depolymerization selectivity, providing theoretical guidance for the design of directional depolymerization catalysts.