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 () 8-membered diolides (-8DL; R denotes the two substituents on the ring). Depending on the composition of the soft B block, originated from -8DL (R = Et, Bu), and its ratio to the semicrystalline, high-melting hard A block, derived from -8DL, the resulting all-PHA tri-BCPs with high molar mass ( up to 238 kg mol) and low dispersity ( = 1.

Installing Controlled Stereo-Defects Yields Semicrystalline and Biodegradable Poly(3-Hydroxybutyrate) with High Toughness and Optical Clarity.

Stereo-defects present in stereo-regular polymers often diminish thermal and mechanical properties, and hence suppressing or eliminating them is a major aspirational goal for achieving polymers with optimal or enhanced properties. Here, we accomplish the opposite by introducing controlled stereo-defects to semicrystalline biodegradable poly(3-hydroxybutyrate) (P3HB), which offers an attractive biodegradable alternative to semicrystalline isotactic polypropylene but is brittle and opaque. We enhance the specific properties and mechanical performance of P3HB by drastically toughening it and also rendering it with the desired optical clarity while maintaining its biodegradability and crystallinity.

Effect of Chain Stereoconfiguration on Poly(3-hydroxybutyrate) Crystallization Kinetics.

Poly(3-hydroxybutyrate) (PHB) is naturally accumulated by bacteria but can also be synthesized chemically. Its processability is limited, as it tends to degrade at temperatures above its melting temperature; hence, investigation into crystallization kinetics and morphology of PHB materials of both natural and synthetic origins is of great need and interest to get a better understanding of structure-property relationship. Accordingly, this contribution reports a first study of the crystallization and morphology of synthetic PHB materials of different molecular weights.

Polyolefin Innovations toward Circularity and Sustainable Alternatives.

The unprecedented growth and socioeconomic impacts of polyolefins clearly outline a major success story in the world of polymer science. Polyolefins revolutionizes industries such as health care, construction, and food packaging. Despite the benefits of polyolefins, there is a rising concern for the environment due to high production volume (i.

Biodegradable Polyhydroxyalkanoates by Stereoselective Copolymerization of Racemic Diolides: Stereocontrol and Polyolefin-Like Properties.

Bacterial polyhydroxyalkanoates (PHAs) are a unique class of biodegradable polymers because of their biodegradability in ambient environments and structural diversity enabled by side-chain groups. However, the biosynthesis of PHAs is slow and expensive, limiting their broader applications as commodity plastics. To overcome such limitation, the catalyzed chemical synthesis of bacterial PHAs has been developed, using the metal-catalyzed stereoselective ring-opening (co)polymerization of racemic cyclic diolides (rac-8DL , R=alkyl group).

Stereosequenced crystalline polyhydroxyalkanoates from diastereomeric monomer mixtures.

Stereoselective polymerization of chiral or prochiral monomers is a powerful method to produce high-performance stereoregular crystalline polymeric materials. However, for monomers with two stereogenic centers, it is generally necessary to separate diastereomers before polymerization, resulting in substantial material loss and added energy cost associated with the separation and purification process. Here we report a diastereoselective polymerization methodology enabled by catalysts that directly polymerize mixtures of eight-membered diolide (8DL) monomers with varying starting ratios of chiral racemic () and achiral diastereomers into stereosequenced crystalline polyhydroxyalkanoates with isotactic and syndiotactic stereodiblock or stereotapered block microstructures.