Early Developments in Anionic Polymerization

The modem concept of linear polymers was introduced in 1920 by Staudinger, who fully recognized the idea of chain addition reaction yielding long molecules composed of monomeric units linked by covalent bonds. He was also the first to understand the anionic character of formaldehyde polymerization initiated by bases such as sodium methoxide4. In fact, studies of this reaction led him to the notion of linear macromolecules. Polymerization of ethylene oxide initiated by alkali metals and reported as early as 18785 could also be interpreted in these terms. 

Further developments in the field of chain polymerization were centered on radical poly-addition. Its mechanism was firmly established in the 1930 s and attracted much attention. The interest in anionic polymerization was marginal and the activities in this field were centered at that time around Ziegler in Germany and Lebedev in Russia. Both groups were interested in polymerization of styrene and dienes initiated by sodium metal and their work led to industrial production of synthetic rubber marketed by I. G. Far-benindustrie as Buna . 

Systematic studies allowed Ziegler to formulate the initiation step as the addition of two sodium atoms to a monomer with formation of two covalent Na-carbon bonds6, e.g., 

The concept of carbanions and ion-pairs was at its infancy at that time. The isolation of such adducts eluded him. Nevertheless, he argued for their existence by demonstrating the formation of butene-2 in reaction performed in the presence of an excess of methyl-aniline63, a compound that does not react directly with sodium metal. Since two moles of 

Our modem description would probably follow the line 

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