Sustainable Thermoplastic Elastomers from Commercial Cyclic Esters: One-Pot Synthesis of Poly( l -lactide)- b -(δ-hexalactone- stat -ε-caprolactone)- b -( l -lactide) and Its Chemical Recycling to the Monomers

We report the one-pot synthesis of ABA triblock copolymers composed of poly(l-lactide) (PLA) as hard segments and δ-hexalactone/ε-caprolactone (HL/CL) copolymers as soft midblock. Use of an environmentally benign and highly active and living Fe(II)-based catalyst enabled precise molecular design and control over copolymer architecture, providing low-Tg, amorphous statistical HL/CL dihydroxy-terminated copolymers, which could be chain extended with l-lactide in the same reactor, resulting in poly(l-lactide)-b-(δ-hexalactone-stat-ε-caprolactone)-b-(l-lactide) triblock copolymers. The one-pot synthetic route enabled control of block composition and length, resulting in material property profiles ranging from silicone-like soft elastomers to SBS-like rubbers, and to toughened PLA. Finally, efficient chemical recycling to the pristine monomers with >90% recovery was achieved by catalytic thermal depolymerization under mild conditions.