A Catalytic Cycle of Lactone Polymerization with Anionic Ureas: A Computational Investigation

The polymerization of lactones is a common method to produce polyesters, which have many applications in industry. However, achieving efficient polymerization with minimal byproducts and high molecular weight often requires a catalyst. Catalysts that have been used for the ring-opening polymerization of lactones include metal complexes, frustrated lewis pair catalysts, and some acid catalysts. Unfortunately, many of these suffer from toxicity and high costs. Recently, a series of anionic urea catalysts have been synthesized and used to successfully polymerize a series of lactones. These catalysts can achieve high conversions with narrow molecular weight distributions quickly and at room temperatures. We are computationally probing the reactive mechanism of these catalysts using Density Functional Theory (DFT) to understand what properties lead to successful polymerization. Herein, we present an analysis of the catalytic cycle for these catalysts and an analysis of electronic and steric differences between the catalysts and their effect on reactivity. We also propose new catalysts in this class based on the steric and electronic requirements discovered in this study. Reference: Lin, B.; Waymouth, R. M. J. Am. Chem. Soc., 2017, 139, 1645-1652