The results of the investigation of polymerization and copolymerization processes of hydrocarbon monomers initiated by compounds of alkaline-earth metals are summarized. Experimental data on the synthesis of initiators, stereospecifity, kinetics and mechanism of the processes are considered. The pecularities of the processes studied are discussed and compared with those of the polymerization initiated by alkali metals, the importance of bimetallic species in polymerization processes being emphasized.

Polymerization of butadiene and isoprene in hydrocarbon solvents initiated by unsolvated organosodium compounds was studied. It was found that the polymer molecular weight and the MWD are determined mainly by chain transfer to solvent and polymer, and no chain transfer to monomer was observed even in the case of isoprene. The overall polymerization rate is proportional to the concentrations of the monomer and the initiator. Apparent chain propagation rate constants were found to be 0.11 litre mo1-ls-l for butadiene and 0.065 litre mol-ls-' for isoprene polymerization in heptane at 30°C. It is suggested that associated (dimeric) forms of polydienylsodium active centres play an important role in chain propagation, being responsible for a stronger chain transfer and a greater l,Zbutadiene, or 3,4-isoprene, unit content than in polymerization with other alkali metals.

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