Synthetic biodegradable polyhydroxyalkanoates (PHAs): Recent advances and future challenges

This article reviews the advances made over the past five decades of research in developing effective chemocatalytic pathways to synthesize polyhydroxyalkanoates (PHAs), a prominent class of biodegradable polyesters found in nature and considered as sustainable alternatives to petroleum-based non-degradable plastics. Focused in this review are recent efforts that seek to address the key challenges facing the biosynthetic routes by taking advantage of precision in synthesis, expedient tunability in polymer stere-omicrostructures and structures of monomers and molecular catalysts, as well as scalability and speed in polymer production that chemical catalysis can offer. This article is organized by poly(3-hydroxybutyrate) (P3HB) stereomicrostructures (tacticities), from isotactic to syndiotactic to atactic P3HB materials, followed by other PHA homopolymers and copolymers. Under each type of stereochemically defined PHAs, monomers, catalysts, and polymerizations employed for the synthesis, as well as mechanistic aspects when possible, are described. Next, recent advances in expanding the PHA scope and developing functionalized, uncommon or unnatural PHAs, inaccessible by biological methods, especially block and stereoblock or stereosequenced PHAs, are highlighted in their synthetic methods and advanced materials properties. Lastly, four key remaining challenges, and thus corresponding future directions directed at addressing those challenges, are discussed. (C) 2022 Elsevier B.V. All rights reserved.

Automated summary

This article reviews the advances in synthesizing polyhydroxyalkanoates (PHAs), a class of biodegradable polyesters, over the past five decades. It focuses on the recent efforts to address key challenges in biosynthesis by utilizing precision in synthesis, tunability in polymer structures, and scalability in polymer production offered by chemical catalysis. The article also discusses expanding the scope of PHAs and developing functionalized and uncommon PHAs through synthetic methods. It concludes with the remaining challenges and future directions in the field.