Control of Particle Size in the Dispersion Polymerization of Sterically Stabilized Polymer Colloids

Abstract

The two principal methods of preparing polymer particles in a liquid medium are emulsion and suspension polymerization. While both preparative techniques utilize heterogeneous reactions, the locus of the polymerization in these two systems differs dramatically. In emulsion polymerization the reaction proceeds within micelles in solution with the emulsion droplet functioning as a reservoir for the monomer, while in suspension polymerization the reaction takes place within the monomer droplet. These procedures usually lead to small particles of 0.1 – 2.0µm diameter for emulsion polymerized particles while suspension polymerization usually yields coarse particles that exhibit a wide particle size distribution. Both of these particle polymerization techniques are usually carried out in polar media such as water, although considerable progress has been made in polymerizing water soluble monomers in hydrocarbon fluids using the inverse emulsion technique¹. Although conventional emulsion polymerization usually leads to submicron size particles, major advances have been made by the Ugelstad² and the Vanderhoff and El-Aasser³ research groups in preparing monodisperse polymer particles up to 100µm in diameter. Ugelstad et al² have achieved this by utilizing a sequential swelling process followed by polymerization of the latex while Vanderhoff and El-Aasser have achieved the same objective by preparing the particles using a seeded emulsion polymerization in the gravity free environment of space.