Mechanism of Narrowly Dispersed Latex Formation in a Surfactant-Free Emulsion Polymerization of Styrene in Acetone–Water Mixture

Abstract

The mechanism of narrowly dispersed latex formation in a surfactant-free emulsion polymerization (SFEP) of styrene in acetone–water was studied by a combination of transmission electron microscopy (TEM) and dynamic light scattering (DLS). The critical nuclei were experimentally observed and the formation of narrowly dispersed PS latex is proved to be originated from competitive growth kinetics. Spherical nuclei were regenerated via a microphase inversion of PS oligomer in a 50% volume fraction acetone–water mixture at 70 °C. They followed a polydispersed log-normal distribution with Rs ∼ 10.6 nm and δ ∼ 0.298, and the smallest nucleus with Rs ∼ 1.1 nm was similar to critical nuclei, with PS backbone (average chain length ∼6–7) repeat units) inside and sulfate groups to stabilize it at oligomer chain ends. Note that the spherical nuclei are not necessarily narrowly dispersed. Competitive growth kinetics makes smaller nuclei grow much faster than large nuclei in the subsequent polymerization process, resul...