Competing Interfacial and Hydrotrope-like Behavior of Co-Surfactants in Miniemulsion Copolymerization

In conventional miniemulsion polymerization, stabilized miniemulsion droplets serve as individual sites for polymer particle formation. The present study shows that the cosurfactants linalool (LO) and benzyl acetate (BAc) follow distinct molecular redistribution pathways in templating miniemulsion, thus redirecting nucleation during copolymerization. In the studied miniemulsion copolymerization of styrene (St) and a highly hydrophobic high oleic soybean oil-based acrylic monomer (HOSBM), LO and BAc were used in combination with sodium dodecyl sulfate (SDS). Replacing up to 70 wt % of the SDS with BAc resulted in successful latex formation, high monomer conversion, and monomodal particle size distribution. In contrast, increasing LO fractions led to reduced conversion, increased coagulum formation, and bimodal latex particle distribution. Assessment of the apparent interfacial activity of LO and BAc in model systems revealed hidden redistribution pathways depending on the mixing regime with the St phase. LO likely provides spontaneous compartmentalization of St within aqueous domains. These interactions are consistent with hydrotrope-like behavior, which promotes the formation of competing nucleation sites. In contrast, upon mechanical agitation BAc partitioned preferentially into the St-rich phase, supporting droplet-templated polymerization. The experimental strategy presented here provides a framework for resolving competing molecular interactions and redistribution pathways in evolving emulsion systems.