Lactone Ring-Opening Equilibria in Methanol by 1H NMR Analysis: An Assessment of the Ring-Opening Polymerizability of Lactone Monomers

Mengyuan Jin, Thomas R. Hoye

Research output: Contribution to journalArticlepeer-review

2 Scopus citations

Abstract

The purpose of this study was to learn if a convenient 1H NMR method could be developed to serve as a tool for estimating the propensity of a given lactone to participate in ring-opening transesterification polymerization (ROTEP). The methanolysis of each of 18 lactones was initially examined in CD3OD solution in the presence of sulfuric acid as a Brønsted catalyst at ambient temperature. Once equilibrium was established, the ratio of remaining lactone to the ring-opened methyl ester/alcohol could be readily measured by NMR spectroscopy. The observed thermodynamic driving force observed for the methanol ring openings is roughly in line with the extent of ROTEP for the various classes of lactones. This is the case even though the reaction conditions for these methanolyses versus ROTEP reactions are substantially different. Qualitative evaluations of the rates of the ring-opening methanolyses were also performed, and several non-obvious relative reactivities were observed. Finally, employing this simple NMR methanolysis using low concentrations of methanol in CDCl3is recommended as the preferred protocol for the initial evaluation of the polymerizability of any new lactone monomer that researchers may prepare in the future.

Original languageEnglish (US)
Pages (from-to)1122-1129
Number of pages8
JournalMacromolecules
Volume56
Issue number3
DOIs
StatePublished - Feb 14 2023

Bibliographical note

Funding Information:
Rachel Rapagnani in the laboratories of Professor Ian Tonks kindly provided the samples of lactones 7 , 12 , and 13 . This work was supported by the National Science Foundation Center for Sustainable Polymers (CHE-1901635), an NSF-funded Center for Chemical Innovation, and the Minnesota Corn Growers Association. Support for a portion of the NMR instrumentation was derived from an NIH Shared Instrumentation Grant (S10OD011952). The DFT computations were performed using the resources of the University of Minnesota Supercomputing Institute (MSI).

Publisher Copyright:
© 2023 American Chemical Society. All rights reserved.

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