Functional polymers for colloidal applications. V. Novel behavior of polymeric emulsifiers in emulsion polymerization

The polymeric emulsifier poly(dodecyl acrylate-co-acrylic acid) i.e., the sodium salt (PDA)] and monomeric emulsifier sodium dodecyl glutarate (SDG) have been synthesized. PDA and SDG are used as emulsifiers in the emulsion polymerization of styrene with both the water-soluble initiator potassium persulfate (K₂S₂O₈) and the oil-soluble initiator 2,2′-azobisisobutyronitrile (AIBN). The PDA/K₂S₂O₈ system showed a bimodel distribution of particle sizes (2 and 0.05 μm). A bimodel particle distribution was also found for the PDA/AIBN system, but the distribution for the large particles was wide (0.1–10 and 0.07 μm). The SDG/K₂S₂O₈ system displayed only one kind of particle size (0.05 μm), but the SDG/AIBN system also showed a bimodel distribution of particle sizes (0.05 and 5 μm). These bimodel distribution results for the PDA/K₂S₂O₈, PDA/AIBN, and SDG/AIBN systems indicate that the polymerization sites are both in oil droplets and in micelles (polymer aggregates). This mechanism is interpreted in terms of the formation of polymer aggregates, which is supported by the results of pyrene solubilization, pyrene fluorescence, surface tension, and pyrene excimer experiments. © 1993 John Wiley & Sons, Inc.