New insights on in situ charge neutralization governing particle size distribution in macroemulsion polymerization

Macroemulsion polymerization is the most widely used approach for the fabrication of the monodisperse polymer particles. During the polymerization process, particle nucleation plays a critical role in determining particle size distribution of the ultimate particles. In general, the repulsion between ionic oligomeric radicals and micelles enhances particle nucleation, resulting in smaller particle sizes. In this study, methacryloxyethyltrimethyl ammoniumchloride (MATMAC) and 2′azobis (2methylpropionamidine) dihydrochloride (AIBA) were used as the cationic species to shield the negative charges of sodium dodecyl sulfate micelle, inducing in situ charge neutralization in the nucleation period, and further decreasing the particle number, enlarging the particle size of the ultimate latex particles. The ultimate particle size of MATMAC or AIBA system reached ～ 200 nm, which is the 2 times bigger than that without any cationic species. Moreover, a narrow particle size distribution was obtained for these systems. The in situ charge neutralization between the cationic species and surfactant molecules enhanced the oligomeric radical capture rate of micelles, further narrowing the particle nucleation time and inducing primary particle coagulation.