All-Polyhydroxyalkanoate Triblock Copolymers via a Stereoselective-Chemocatalytic Route
Andrea H. Westlie, Sarah A. Hesse, Xiaoyan Tang, Ethan C. Quinn, Celine R. Parker, Christopher J. Takacs, Christopher J. Tassone, Eugene Y.‐X. Chen
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 ( 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.