Anionic Ring-opening Polymerization: Stereospecificity for Epoxides, Episulfides and Lactones

The first report of the stereospecific polymerization of propylene oxide (PO) was published by Pruitt and Baggett1 in 1955. Their catalyst was a reaction product of iron (III) chloride with propylene oxide. A few years later, various types of stereospecific catalyst for PO polymerization were found and developed almost simultaneously: aluminum isopropoxide/zinc chloride by Price and Osgan;2 zinc alkyl/water (or alcohol) by Furukawa and Tsuruta;3 aluminum alkyl/water by Colclough, Gee et al.;4 and aluminum alkyl/water/acetylacetone by Vandenberg.5 A zinc alkyl/water system was used by Sigwalt and co-workers in 19656 for the stereospecific polymerization of propylene sulfide. In 1967, Osgan and Teyssie7 reported the synthesis of a bimetallic catalyst, μ-oxoalkoxide (RO)2AlOZnOAl(OR)2, and noted its high activity.