Breaking Two Rings

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Science  14 Sep 2007:
Vol. 317, Issue 5844, pp. 1473
DOI: 10.1126/science.317.5844.1473a

Polyesters have traditionally been prepared by condensation of monomers bearing acid or ester groups: The chain grows by formation of O-C bonds with concomitant loss of water or alcohol. Choosing a cyclic monomer can eliminate formation of these small-molecule by-products, as chain growth proceeds by ring-opening, but this approach offers limited functional diversity along the polymer backbone. Jeske et al. have developed a zinc catalyst that links epoxides to cyclic anhydrides through alternating ring-opening steps and thereby introduces backbone substituents ranging from methyl and cyclohexyl to vinyl moieties by appending them to the strained three-membered rings. A cyano group on the diiminate ligand coordinated to zinc proved key to catalyst stability under the reaction conditions. The system achieved number-average molecular weights exceeding 104 and low polydispersities (1.1 to 1.5). — JSY

J. Am. Chem. Soc. 129, 10.1021/ja0737568 (2007).

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