Metal-Free Synthesis of Tough PLLA- <i>b</i> -PCVL- <i>b</i> -PLLA Triblock Polyester Thermoplastic Elastomers from Mixed Monomers

High Resolution Image Download MS PowerPoint Slide Designing thermoplastic elastomers (TPEs) that are simultaneously biodegradable, metal-free, and mechanically robust remains a major challenge. Here, we report a one-pot organocatalytic ring-opening polymerization strategy that converts a mixed feed of ε-caprolactone (CL), δ-valerolactone (VL), and l -lactide (LLA) into high-molecular-weight PLLA- b -PCVL- b -PLLA triblock copolyesters without metal catalysts. By exploiting the intrinsic reactivity differences among the monomers and switching from diphenyl phosphate (DPP) to tert -butyl phosphazene ( t -BuP 2 ), well-defined triblocks with M n up to 300 kg mol –1 and tunable PLLA contents were obtained. The optimized material exhibits an outstanding combination of tensile strength (61 MPa), elongation at break (>2200%), and toughness (653 MJ m –3 ). Small- and wide-angle X-ray scattering analyses, together with in situ tensile scattering measurements, indicate strain-induced structural reorganization and alignment during deformation. These triblocks also show good elastic recovery and high thermal stability ( T d,5% > 350 °C), reprocessability, and enzymatic degradability. This work provides a metal-free, mixed-monomer, one-pot route to high-performance biodegradable triblock polyester elastomers and offers a promising platform for sustainable elastomeric materials.