All-Polyhydroxyalkanoate Triblock Copolymers via a Stereoselective-Chemocatalytic Route.

Biodegradable polyhydroxyalkanoate (PHA) homopolymers and statistical copolymers are ubiquitous in microbially produced PHAs, but the step-growth polycondensation mechanism the biosynthesis operates on presents a challenge to access well-defined block copolymers (BCPs), especially higher-order tri-BCP PHAs. Here we report a stereoselective-chemocatalytic route to produce discrete hard-soft-hard ABA all-PHA tri-BCPs based on the living chain-growth ring-opening polymerization of racemic ( rac ) 8-membered diolides ( rac -8DL R ; R denotes the two substituents on the ring). Depending on the composition of the soft B block, originated from rac -8DL R (R = Et, n Bu), and its ratio to the semicrystalline, high-melting hard A block, derived from rac -8DL Me , the resulting all-PHA tri-BCPs with high molar mass ( M n up to 238 kg mol -1 ) and low dispersity ( Đ = 1.07) exhibit tunable mechanical properties characteristic of a strong and tough thermoplastic, elastomer, or a semicrystalline thermoplastic elastomer.