Emulsion polymerization of styrene in coacervating and noncoacervating soap–electrolyte systems

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Abstract
An attempt is made here to delineate some of the consequences of the special properties of coacervating soaps when the soaps are used in the emulsion polymerization of styrene. In dilute solutions an essential difference between a coacervating soap and a noncoacervating soap is the critical suppression of the micellar ionization in coacervating systems when relatively small amounts of simple electrolytes are added to the systems. A direct correlation between the polymerization rates and polymer molecular weights with the state of micellar ionization has been demonstrated. The highest polymerization rates and highest polymer molecular weights occur in solutions in which the coacervating soaps show a maximum ionization. In soap solutions in which the micellar ionization is critically suppressed there is evidence of soap desorption from polymer particles, resulting in the generation of an increasing number of particles during the course of the polymerization. Two coacervating systems and two noncoacervating systems were used in this investigation. For the anionic noncoacervating K laurate–KCl system, where the micellarsize remains practically constant with the addition of electrolyte, the following relationship between the polymerization rate and KCl concentration, up to 1M KCI, has been found: R = R0 + B√C. The effects of the charge properties of soap micelles on the course of the polymerization of styrene have been associated with two effects. (a) For highly ionized micellar systems the micelle periphery presents an open structure due to the coulombic repulsion of the charged polar hydrophilic groups of the soap molecules. This open structure facilitates the diffusion of monomer to the loci of polymerization. (b) Where the micellar ionization is suppressed, monomer diffusion to the loci of polymerization is impeded. Extensive suppression of micellar ionization results in micelles of enhanced stability. In the highly stabilized systems when the loci of polymerization are polymer particles there is competition for soap molecules between the adsorption sites on the polymer particle and soap micelles. The influence of soap concentration on the emulsion polymerization for different soaps and electrolyte concentrations has been investigated. For the coacervating Hyamine 1622 soap at zero electrolyte concentration, the rate of polymerization has been found to be proportional to the 0.5 power of the soap concentration. This relationship is not maintained when electrolyte is added to the polymerization system.