Ziegler, Karl formation

Until 1953, most addition polymers were made by free-radical paths, which produce atactic polymers. In that year, however, the Nobel laureates Karl Ziegler and Giulio Natta introduced a new technique for polymerization using a type of catalyst that permits control of the stereochemistry of a polymer during its formation. 

A notable exception to the emphasis on free-radical polymerization studies was provided by Karl Ziegler and his co-workers who extended the study of the alkali metal polymerization of dienes to include metals other than sodium and various metal alkyls. Of particular interest were the results obtained with the simplest Group I alkali metal, lithium. It was found that when lithium metal was used as a polymerization initiator 1,4- structures predominated over 1,2-polymers. It was also found that polymerization in hydrocarbon solvents further favoured production 1,4- structures whilst polymerization in polar liquids such as ethers and amines often favoured the formation of 1,2- units. It was also found that reaction of lithium with monomer led to the production of an organo-lithium compound which made feasible homogeneous polymerization—a discovery which eventually led to commercial exploitation. 

Karl Ziegler describes the formation of alkyl aluminum oxides and the subsequent reaction of the primary produced dialkyl aluminum hydroxide [28]. It was also recognized that bis(diethylaluminum)oxide decomposes by disproportionation into triethyl-aluminum and a solid, non-volatile compound [29]. Bis(dimethylaluminum) oxide is mentioned in the hterature but not exactly described [30]. 

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