Guanidine-Zinc/Epoxide Catalyzed Ring-Opening Polymerization of ε-Caprolactone and Aminolysis Recycling of PCL

Poly(ε-caprolactone) (PCL), as a typical aliphatic biodegradable polyester, holds significant application prospects in biomedical and advanced manufacturing fields due to its excellent biocompatibility and processability. However, existing catalytic systems still face challenges in simultaneously achieving high activity, low catalyst loading, and high molecular weight under high-temperature bulk conditions. In this study, a guanidine-based zinc complex was employed as the catalyst, and epoxide was introduced as the co-initiator to efficiently catalyze the bulk ring-opening polymerization of ε-caprolactone (ε-CL). Techniques including Proton Nuclear Magnetic Resonance（¹H-NMR）, gel permeation chromatography (GPC), and differential scanning calorimetry (DSC) were employed to study the structures of the complexes, along with the molecular weights and thermal properties of the polymers. This catalytic system achieved efficient monomer conversion with an extremely low catalyst loading (n(ε-CL)∶n(CHO)∶n(cat.) = 10000∶2500∶1), delivering a turnover frequency (TOF) as high as 49.3×10² h⁻¹. Under optimized conditions (n(ε-CL)∶n(CHO)∶n(cat.) = 5000∶500∶1, 60 min), PCL with a maximum M_n of 81.8 kg/mol could be obtained. Furthermore, the obtained PCL could be completely depolymerized into high value-added hydroxyamide derivatives under catalyst-free, mild conditions via ethanolamine aminolysis, demonstrating promising potential for chemical circularity. This catalytic system provides a novel approach that is efficient, cost-effective, and environmentally friendly for the industrial preparation of biodegradable polyesters and the chemical recycling of waste plastics.