Swelling of oligomer-polymer particles. New methods of preparation

The stabilization of polydisperse aqueous emulsions towards degradation by molecular diffusion is discussed. A new method for preparation of stable monomer emulsions by diffusion, based on the physicochemical principles underlying said stabilization, is described. After homogenization of a highly water insoluble compound with water and emulsifier, the dispersed phase is swollen with more than 200 times its own volume of monomer. With stable, finely dispersed monomer emulsions, the monomer droplets may become center for particle initiation even in case one applies a water soluble initiator. The kinetics of the polymerization of such emulsions is discussed in terms of the Smith-Ewart theory, taking into account that the monomer concentration at the reaction center decreases from the start of reaction. Polymer particles consisting of pure polymer are only capable of absorbing 0.5 to 5 times their own volume of low molecular weight compounds. Calculations based upon an extended Flory-Huggins equation predict that if the particles contain a substantial amount of an oligomer which is water insoluble and has a relatively low molecular weight, one may expect an enormous increase in the swelling capacity of such particles for monomer. Methods are described where the polymer particles have been swollen with monomer up to a v/v ratio of > 1000. The principles outlined above have been used to prepare monodisperse particles with very large sizes, including monodisperse, porous particles.