No abstract

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 welldefined 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.