Miniemulsion polymerisation initiated using an ultrasonic field at 25°C has now been reported for various monomers including methacrylates, acrylates, styrene and vinyl acetate. Typically, a latex with a particle size of ~100 nm diameter is produced with a conversion of 80-90% in around 60 min of sonication. More recently, ultrasonically initiated copolymerisations have been studied, along with the use of these miniemulsion reactions for the encapsulation of water-insoluble molecules (such as dyes) or other inorganic pigments (including gold nanoparticles).

The ultrasonically initiated batch miniemulsion copolymerisations of methyl methacrylate (MMA) and butyl acrylate (BA) are studied at different MMA:BA ratios (including homopolymerisations) and the physical properties and chemical composition of the polymers formed investigated. Trends in the evolution of the particle number are rationalised with reference to the mechanical properties of the polymer particles, with the number concentration of the softer, BA-rich particles reducing with continued sonication. Molecular weight data are consistent with high radical fluxes entering the particles, with the radical entry frequency calculated from the peroxide yield in a model system to be ~1.5 × 10^-2 s^-1. The copolymer composition is also consistent with those predicted by standard models for dispersed phase polymerisations.

The use of miniemulsion polymerisations to encapsulate water insoluble dyes and pigments is a natural extension to this work. Since particle formation in a miniemulsion polymerisation occurs by droplet nucleation, the incorporation of fluorescent dyes into the latex particles is relatively straightforward. Similarly, gold nanoparticles (~10nm in size, synthesised using either sonochemical or chemical reduction methods) may be encapsulated into the latex particles.

With reference to the basic mechanisms of dispersed phase polymerisations, methods by which the performance of these reactions may be improved will also be discussed.