All-Polyhydroxyalkanoate Triblock Copolymers via a Stereoselective-Chemocatalytic Route

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 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 (<i>rac</i>) 8-membered diolides (<i>rac</i>-8DL^R; R denotes the two substituents on the ring). Depending on the composition of the soft B block, originated from <i>rac</i>-8DL^R (R = Et, ^<i>n</i>Bu), and its ratio to the semicrystalline, high-melting hard A block, derived from <i>rac</i>-8DL^Me, the resulting all-PHA tri-BCPs with high molar mass (<i>M</i>_n up to 238 kg mol^-1) and low dispersity (<i>Đ</i> = 1.07) exhibit tunable mechanical properties characteristic of a strong and tough thermoplastic, elastomer, or a semicrystalline thermoplastic elastomer.