Ring-opening polymerization of five lactones catalyzed by Candida antarctica lipase B in ionic liquids yielded poly(hydroxyalkanoates) of moderate molecular weights up to Mn = 13,000. In the ionic liquid 1-butyl-3-methylimidazolium bis(trifluoromethane)-sulfonimide and with a low weight ratio of enzyme to lactone (1:100) we obtained polymers from β-propiolactone, δ-valerolactone, and ε-caprolactone with degrees of polymerization as high as 170, 25, and 85, respectively; oligomers from β-butyrolactone and γ-butyrolactone with degrees of polymerization of 5; and a copolymer of β-propiolactone and β-butyrolactone with a degree of polymerization of 180. Water-immiscible ionic liquids were superior to water-miscible ionic liquids. Reducing the water content of the enzyme improved the degree of polymerization by as much as 50% for β-propiolactone and ε-caprolactone.
Bibliographical noteFunding Information:
We thank Altus Biologics, Inc. for the generous gift of enzymes. We thank Rick Knurr in the Department of Geology and Geophysics at the University of Minnesota for the ICP-AES analysis and Dr. Ted Labuza in the Department of Food Science and Nutrition at the University of Minnesota for use of his Karl–Fisher titration apparatus. We thank the Initiative for Renewable Energy and the Environment (IREE) at the University of Minnesota and the National Institutes of Health Biotechnology Training Grant for financial support.
- Ionic liquids
- Ring-opening polymerization