Chemically circular, mechanically tough, and melt-processable polyhydroxyalkanoates

• Published in: Science (American Association for the Advancement of Science) Vol. 380; no. 6640; pp. 64 - 69
• Main Authors: Zhou, Li, Zhang, Zhen, Shi, Changxia, Scoti, Miriam, Barange, Deepak K., Gowda, Ravikumar R., Chen, Eugene Y.-X.
• Format: Journal Article
• Language: English
• Published: United States The American Association for the Advancement of Science 07.04.2023; AAAS
• Subjects: Carbonyl compounds; Carbonyls; Monomers; Polyhydroxyalkanoates; Polyhydroxyalkanoic acid; Polymers; Science & Technology - Other Topics
• ISSN: 0036-8075; 1095-9203; 1095-9203
• DOI: 10.1126/science.adg4520

Polyhydroxyalkanoates (PHAs) have attracted increasing interest as sustainable plastics because of their biorenewability and biodegradability in the ambient environment. However, current semicrystalline PHAs face three long-standing challenges to broad commercial implementation and application: lack of melt processability, mechanical brittleness, and unrealized recyclability, the last of which is essential for achieving a circular plastics economy. Here we report a synthetic PHA platform that addresses the origin of thermal instability by eliminating α-hydrogens in the PHA repeat units and thus precluding facile cis-elimination during thermal degradation. This simple α,α-disubstitution in PHAs enhances the thermal stability so substantially that the PHAs become melt-processable. Synergistically, this structural modification also endows the PHAs with the mechanical toughness, intrinsic crystallinity, and closed-loop chemical recyclability. Polyhydroxyalkanoates are a promising class of plastics accessible chemically or microbially from relatively sustainable feedstocks. However, their performance properties lag behind commercial petrochemically derived alternatives. Zhou et al . report that replacing reactive carbonyl-adjacent hydrogens in the monomer with methyl groups produces a polyhydroxyalkanoate that is more robust in multiple respects (see the Perspective by Guillaume). The dimethyl polymer is both crystalline and ductile, structurally sound during melt processing, and subject to efficient degradation to recover the monomer on treatment with base. —JSY Replacing reactive hydrogens in the monomer improves the properties of a type of polyester in multiple respects.