Kinetic study of the mini-emulsion polymerization of styrene

A broad particle-szie distribution in mini-emulsion polymerization is generally attributed to the long induction period and homogeneous nucleation in the aqueous phase. In this study, the high dissociation rate of the interfacial redox initiator system cumene hydroperoxide/ferrous ion/ethylenediaminetetraacetic acid/ sodium formaldehyde sulfoxylate (CHP-Fe²⁺-EDTA-SFS), which could produce hydrophobic radicals and decrease homogeneous nucleation in the aqueous phase, was used to prepare the mini-emulsion polymerization. Polystyrene particles of narrow size distribution were obtained, and their molecular weights were also very narrow (polydispersity index = 1.5-2.0). The effects of the initiator concentration, the ratio of surfactant/cosurfactant (sodium lauryl sulfate/cetyl alcohol, SLS/CA), the styrene concentration and the reaction temperature in the mini-emulsion polymerization of styrene were also investigated. When higher CHP and SFS concentrations or higher reaction temperature were used in the mini-emulsion polymerization, the polymerization rate and conversion became higher. The order of SLS : CA ratios for preparing polymer particles of high stability was 1:3 > 1:10 > 1:1 > 1:6 > 1:0.