Sustainable Organocatalytic Strategies for Biodegradable Polyester Elastomers

The environmental impact of conventional plastics has driven research interest toward biodegradable alternatives, particularly aliphatic polyesters synthesized via ring-opening polymerization (ROP) of cyclic esters [1]. While tin-based catalysts (e.g., Sn(Oct)₂) remain widely used, their toxicity remains a critical aspect for the full sustainability of these materials, thus a shift toward eco-friendly catalytic systems [2] is mandatory. Recent advancements highlight urea/thiourea derivatives as effective organocatalysts, operating through hydrogen-bonding interactions to activate both monomers and initiators. This dual activation enables precise control over polymer molecular weight and architecture [3]. Among these, ureate anions, generated by deprotonating urea derivatives, have demonstrated exceptional efficiency in ROP, particularly for challenging monomers like ω-substituted lactones and macrolactones [4]. In this work, we developed bis-ureate catalysts to address polymerization difficulties of structurally complex lactones. By combining lactones of varying ring sizes and functionalities through a sequential copolymerization strategy, thermoplastic elastomers with tunable mechanical and thermal properties can be produced. The opportune selection of the initiator (e.g., monofunctional alcohols for linear chains or polyols for branched architectures) further allowed control over polymer topology. The resulting materials exhibit a biphasic morphology, integrating rigid crystalline segments of PLLA with flexible amorphous regions. This design mirrors the performance of petroleum-based elastomers while offering enhanced sustainability. Our approach provides a practical way to design biodegradable plastics that work well and are eco-friendly, supporting a circular economy [1].