Exploring enzymatic degradation, reinforcement, recycling, and upcycling of poly(ester)s-poly(urethane) with movable crosslinks

Enzymes are highly efficient, chemoselective, and sustainable biocatalysts, standing out as eco-friendly tools to advance the circular plastics economy. Herein, we explored enzymatic reactions of poly(ε-caprolactone)-poly(urethane) (PCL-PUs) in organic solvent under different reaction conditions using Novozym 435 (immobilized lipase) as the enzyme. PCL-PUs with triacetylated γ-cyclodextrin (TAcγCD)-based movable crosslinks (PCL-γCD-PU) not only exhibited excellent mechanical properties due to effective energy dissipation, but also efficient enzymatic degradation that was optimized for increases in TAcγCD content. Under reaction time control, molecular weight and mechanical properties of PCL-γCD-PU were enhanced by a novel enzymatic reinforcement strategy. Without sorting, the degraded products are versatile resources that can be enzymatically closed-loop recycled by switching reaction concentration or enzymatically upcycled into value-added polymers by mixing with selective substrates. The facile polymer structure design combined with enzymatic reactions is expected to provide a broad approach for toughening various polymeric materials and advancing their development as sustainable resources.