Catalyst-Free Synthesis of Next-Generation Biobased High-Toughness Polyesters Enabled by Knoevenagel Chemistry

Despite being among the most prevalent polymers, conventional thermoplastic polyesters are petroleum-derived, and their production relies on energy-intensive processes with high temperature and vacuum and involves toxic catalysts. Herein, we presented a novel biobased multiblock thermoplastic polyester material from lignocellulosic-derived monomers, i.e., vanillin-based aldehyde monomer and polycaprolactone-based cyanoacetate, via a catalyst-free Knoevenagel condensation melting polymerization under low-temperature conditions (190 °C). By precisely tuning the molecular weight (2000 and 4000 g/mol) and molar ratio of soft segments, the material demonstrated exceptional performance with a tensile strength of 30.55 MPa, elongation at break of 871%, and toughness of 138.59 MJ M–3, surpassing most commercial elastomers (e.g., SBS). Thanks to its good processing adaptability and low processing energy consumption, the resulting multiblock thermoplastic polyester material could be processed by melting spinning, thermoforming, and twin-screw extrusion and could be efficiently reclaimed from mixed plastic waste through a solvent-casting closed-loop recycling strategy. The melting-spinning fibers demonstrated notable elongation at break exceeding 600%, while regenerated films exhibited substantially enhanced toughness achieved through molecular reorganization. This work establishes a green paradigm for sustainable high-performance polymers, integrating environmental compatibility with engineering feasibility, and paves the way for the transition of biobased polyesters toward a circular economy.