A reinvestigation of electrolyte effects in the emulsion polymerisation of styrene

• Published in: Polymer international 1994-12, Vol.35 (4), p.379-387
• Main Author: Said, Ziad F. M.
• Format: Article
• Language: English
• Subjects: adsorption; Applied sciences; electrolyte; Exact sciences and technology; latex; Organic polymers; particle size; Physicochemistry of polymers; polydispersity; Polymerization; Preparation, kinetics, thermodynamics, mechanism and catalysts; rate of polymerisation
• ISSN: 0959-8103; 1097-0126
• DOI: 10.1002/pi.1994.210350411

The effects of adding potassium chloride in concentrations below that required to coagulate the latex to recips of emulsion polymerisation of styrene have been investigated using different concentrations of potassium octadecanoate, which has a low critical micelle concentration (CMC), and potassium dodecanoate, which has a moderately high CMC. At relatively high concentration of octadecanoate the final particle size is significantly increased; the rate of polymerisation is initially increased but later retarded. The effects of increasing micelle size and increased rate of coalescence are dominant. At lower concentration of this emulsifier, the rate is reduced from the onset of interval II. With dodecanoate, concentrations of electrolyte up to 0.3 M accelerate the rate. No significant change in the particle size was observed up to 0.2M electrolyte, thereafter it slightly increased. The increase in micellar concentration can only partially account for these effects. It is believed that the increase in the amount of solubilised monomer inside the micelles, and later inside the latex particles, and the resistance to coalescence (because of the favourable adsorption mechanism of this emulsifier) may account for these observations. With both emulsifiers, electrolyte reduces the induction period and latices with narrow particle size distributions are produced.