In situ charge neutralization-controlled particle coagulation and its effects on the particle size distribution in the one-step emulsion polymerization

A novel approach to prepare sub-200 nm, narrowly dispersed polystyrene latex particles is proposed for the emulsion polymerization of a ca. 40 wt% solid-content solution. The presented method exploits the cationic comonomer methacryloxyethyltrimethyl ammonium chloride (MATMAC) or the initiator 2,2′-Azobis (2-methylpropionamidine) dihydrochloride (AIBA) to generate cationic oligomeric radicals shielded the negatively charged surfactant molecules adsorbed on the particles surface, further induced particle coagulation by in situ charge neutralization. By adjusting the types and amounts of the comonomer, the extent of the in situ charge neutralization is controlled. In consequence, the extent of the particle coagulation is controlled, resulting in the production of large-size latex particles. The particle coagulation induced by in situ charge neutralization occurs at the particle nucleation stage, which extends the times of particle completive growth and reversible coagulation, and therefore, narrowed the width of the particle size distribution of the ultimate latex particles. The resulting colloidal latexes containing 40 wt% solid content are very stable by presenting the absolute value of zeta potentials larger than 40 mV. This approach is likely to be used for large-scale industrial productions of narrowly dispersed polymer particles.