Polymerization in the presence of organic compounds of alkali metals

Abstract

AbstractA study was made of the effect of the nature of the alkaline metal and of the medium on the rate of polymerization and on the structure of the polymer chain. The rate of polymerization of styrene and isoprene with an ethyllithium catalyst in hydrocarbon medium has been shown to increase on addition of polar compound triethylamine, ether, and tetrahydrofuran, to the solvent. The limiting concentration of triethylamine, above which increase in the polymerization rate in the presence of ethyllithium is no longer observed, is considerably higher in the case of isoprene than styrene. This is in agreement with the data on the kinetics of ethyllithium‐catalyzed polymerization of styrene and isoprene in hydrocarbon medium, according to which the limiting concentration of ethyllithium, above which dependence of the polymerization rate on the catalyst concentration is no longer observed, is considerably lower for isoprene than for styrene. The difference in polymerization kinetics of isoprene and styrene is explained by the fact that more amine is required to dissociate polymerization‐inactive polyisoprene‐lithium associates. By the copolymerization method it has been shown, in harmony with published data, that the mechanism of chain growth in the presence of ethyllithium changes on passing over from a hydrocarbon to a polar solvent and also on changing alkyllithium for organosodium compounds. The specific features of alkyllithium catalysts in hydrocarbon medium are interpreted as due to the participation of the lithium component of the catalyst besides the carbanion in the chain growth.