Emulsion Polymerization of Styrene Using the Homopolymer of a Reactive Surfactant

Abstract

The emulsion polymerization of styrene using the homopolymer of sodium dodecyl allyl sulfosuccinate as a polymeric surfactant (poly(TREM)) was studied in terms of the polymerization kinetics, the nucleation mechanisms, and the properties of the final latexes. It was found that the relationship between the maximum rate of polymerization and the final number of polymer particles was one-to-one under all experimental conditions (Rp ∝ Np1.0). The dependencies of these on the initiator and polymeric surfactant concentrations varied, depending on experimental conditions (Rp ∝ Np1.0 ∝ [E]0.2-0.4; Rp ∝ Np1.0 ∝ [I]0.6-0.8). These variations were attributed to the increased ionic strength effects with increasing concentration of poly(TREM), a polyelectrolyte, and its properties as a polymeric surfactant. It was inferred from the polymerization kinetics (Rp vs time) that homogeneous nucleation was dominant using poly(TREM) even with concentrations exceeding its critical micelle concentration. This differs from the monomeric TREM LF-40 surfactant. Characterization of the amount of poly(TREM) bound to the polymer particles was carried out by serum replacement studies and ion exchange/conductometric titration measurements. Evidence is given that more than half of the poly(TREM) was bound to the polymer particles, either by grafting of the poly(TREM) and/or irreversible adsorption. The amount of bound poly(TREM) increased with increasing surfactant concentration and increasing initiator concentration (i.e., decreasing particle diameter). Contact angles of water measured on films formed from the latexes showed that the poly(TREM) does not migrate significantly to the surface of the films, which is consistent with the latex surface characterization results.