Enzymatic ring-opening polymerization of lactones in supercritical carbon dioxide: A review

Abstract

The polymerization of lactones has revealed the potential of polylactones for preparing biomaterials with attractive properties for biomedical applications. The use of green solvents and biocatalysts are fundamental steps towards the circularity of the synthesis of these polymers. Supercritical carbon dioxide has emerged as a green solvent for a variety of processes due to its hybrid liquid-gas properties, non-toxicity, and reusability. Novozym® 435 is the most widely used enzyme due to its excellent stability under high pressure. However, the high cost of this lipase is one of the limiting factors for its expansion to an industrial scale. The enzymatic polymerization of lactones in supercritical carbon dioxide is a promising technique for the production of high molar mass polyesters, although it presents challenges in becoming a completely green process. Thus, this work aims to provide an overview of the enzymatic polymerization of lactones in supercritical carbon dioxide, including the compilation and discussion of the developed research up to date. This review also presents the main challenges to overcome for the progress of this technology. In the future perspective, searching for cheaper enzymes and the development of an integrated process that allows the reuse of both the enzyme and CO₂ should be part of the research in the coming years. Furthermore, the synthesis of copolyesters employing this biosynthetic route is also a field to be explored, since the easy manipulation of the reaction conditions can offer a wider range of customized polymeric materials.