Particle growth in butadiene emulsion polymerization, 4. The promoting effect of mercaptans

Abstract

AbstractThe observation that butadiene emulsion polymerizations in the presence of fatty acid emulsifiers need minimal amounts of tertiary or n‐dodecanethiols to polymerize at a reasonable rate is often referred to as the promoting effect of mercaptans and is evaluated in this paper. Experimental evidence is presented which shows that fatty acid emulsifiers can actively reduce the average number of radicals per particle. In this paper it will be shown that three components are necessary for retardation of the rate of polymerization in the absence of dodecanethiol to occur: (1) Only diene monomer polymerizations show retardation. (2) Only peroxodisulfate‐initiated polymerizations show retardation. (3) Retardation of the rate of polymerization only occurs in the presence of fatty acid emulsifiers. These three components are combined for the first time in a reaction scheme which is an extension of a reaction scheme proposed by Kolthoff in 1951. Experimental evidence justifies the suggestion that reaction between a fatty acid radical and butadiene play an important role in the promoting effect.