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Synfacts 2007(6): 0600-0600  
DOI: 10.1055/s-2007-968584
Synthesis of Materials and Unnatural Products
© Georg Thieme Verlag Stuttgart · New York

Synthesis of Cyclic Poly(Lactide) via Zwitterionic Polymerization

Contributor(s): Timothy M. Swager, Wei Zhang
D. A. Culkin, W. Jeong, S. Csihony, E. D. Gomez, N. P. Balsara, J. L. Hedrick, R. M. Waymouth*
Stanford University, University of California, Berkeley and IBM Almaden Research Center, San Jose, USA
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Publication History

Publication Date:
22 May 2007 (online)

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Significance

Zwitterionic ring-opening polymeri­zation of lactide 1 catalyzed by N-heterocyclic carbenes (NHCs, 2) provided cyclic polyesters (3) of defined molecular weight and narrow molecular weight distribution. The cyclic structure of the polymers was determined by 1H NMR spectroscopy, mass spectrometry and comparisons of the solution properties of the cyclic polymers with their linear congeners. Polymerization of optically pure l-lactide generated crystalline cyclic poly(l-lactide), indicating that the polymerization proceeds with retention of stereochemistry. These NHC-mediated zwitterionic polymerizations also display a remarkable degree of control and exhibit some features of living polymerizations.