Epimerization-suppressed organocatalytic synthesis of poly-L-lactide in supercritical carbon dioxide under plasticizing conditions

Abstract Herein, an efficient (> 95% yield, > 99.0% ee) Bronsted acid-catalyzed synthetic method of poly-L-lactide (PLLA) in supercritical carbon dioxide (scCO2) under plasticizing conditions is presented. High-performance liquid chromatography analysis of the PLLA hydrolysis products indicated that, as opposed to the case of organic solvents, the use of a nucleophilic catalyst in scCO2 suppressed the epimerization. The highly stereochemically pure PLLA prepared by the developed method under metal-free conditions meets the criteria of medicinal/engineering applications.