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

The observation that butadiene emulsion polymn. in the presence of fatty-acid emulsifiers need minimal amts. 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. Exptl. evidence is presented which shows that fatty-acid emulsifiers can actively reduce the av. no. of radicals per particle. Three components are necessary for retardation of the rate of polymn., in the absence of dodecanethiol, to occur. First, only diene monomer polymns. show retardation. Second, only peroxodisulfate-initiated polymns. show retardation. Third, retardation of the rate of polymn. 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. Exptl. evidence justifies the suggestion that reactions between a fatty-acid radical and butadiene play an important role in the promoting effec