Selective Low-Temperature Depolymerization of Highly Transesterified P(LLA-co-CL) Copolymers: Efficient Lactide Recovery and PCL Upcycling.

The selective chemical recycling of copolyesters remains a major challenge for achieving polymer circularity. Here we show that highly transesterified poly(L-lactide-co-caprolactone) (P(LLA-co-CL)) copolymers undergo low-temperature depolymerization with exceptional selectivity for L-lactide (LLA). Statistical copolymers prepared under SnOct2/BnOH at 130 °C feature both lactidyl and lactoyl units, reflecting extensive sequence scrambling. Upon vacuum distillation at 230°C, distillates are recovered that are highly enriched in LLA (up to 96-99 mol%), while the polymer residues reorganize into higher-molar-mass polycaprolactone (PCL) chains sporadically decorated with lactoyl units. Further heating to 250°C mobilizes these domains, affording controlled release of CL and its dimer. Importantly, no macrocyclic species incorporating caproyl-lactidyl or caproyl-lactoyl motifs were detected, in line with the thermodynamic disfavor of 10- and 13-membered ring formation. Instead, the recycling process combines the selective regeneration of virgin-quality LLA with the generation of unprecedented "upcycled PCL" architectures, distinct from conventional PCL and offering new opportunities for property design. This dual outcome establishes a practical framework for closed-loop and value-added recycling of complex copolyesters.