The Morphology of Polystyrene Latex Particles

Abstract

Our understanding of the factors controlling the preparation of sty rene-based latex products has recently undergone extensive revision. Brief ly, we have found that, under a wide range of conditions, the growing latex particles possess a core-shell structure in which a monomer-rich shell encapsulates a polymer-rich core. This two-phase behavior is remarkable inasmuch as styrene and polystyrene are ordinarily (in macroscopic sys tems) completely miscible in all proportions. The proposed core-shell mor phology explains the extended constant-rate behavior observed in styrene emulsion polymerization and permits extension of the Smith-Ewart The ory to conversions as high as 60%. In seed growth experiments, the added monomer actually encapsulates the original seed particles, up to their equi librium saturation content, thereby indicating that the phenomenon of interest is controlled by thermodynamic factors. We believe that encapsu lation is governed by the microscopic nature of the latex particles which has, in turn, a profound effect upon the conformational behavior of the long-chain polymer molecules as they interact with the particle-water in terface. These findings have important fundamental implications and tech nological applications in latex product design that are only beginning to be explored.