Improving Circularity via Chemical Recycling to all Rings

Aliphatic polyesters synthesized via ring-opening polymerization (ROP) have properties competitive to incumbent plastic (PE, PP), while simultaneously opening up for chemical recycling to monomer (CRM). However, not all aliphatic polyesters are prone to undergo CRM, and the ability to shift the equilibrium between polymer and monomer is tightly associated with the initial monomer structure. The standard strategy to measure CRM is to evaluate the change in free energy during polymerization (∆G_ROP). However, ∆G_ROP is only one-dimensional by assessing the equilibrium between initial monomer and polymer. But under active catalytic conditions, the depolymerization of polymers can lead to formation of larger rings, such as dimers, trimers, tetramers, and so on, via the ring-chain equilibrium (RCE), meaning that the real thermodynamic recycling landscape is multi-dimensional. This work introduces a multi-dimensional chemical recycling to all rings (CRR) via a highly active catalytic system to reach RCE. Thermodynamically ∆G_RCE is completely different from ∆G_ROP. Using ∆G_RCE instead of ∆G_ROP allows us to achieve CRR for polymers notoriously difficult to achieve CRM for, as exemplified within by CRR for poly(ε-caprolactone), poly(pentadecalactone), and mixed polymer systems. Overall, this work provides a new general concept of closing the material loop.