POLYMERIZATION OF CONJUGATED DIENES INITIATED BY SOLUBLE ORGANOSODIUM COMPOUNDS IN HYDROCARBON SOLVENTS

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 mol(-1) s(-1) for butadiene and 0.065 litre mol(-1) s(-1) for isoprene polymerization in heptane at 30 degrees 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 1,2-butadiene, or 3,4-isoprene, unit content than in polymerization with other alkali metals.