Synthesis of two-phase polymer particles in supercritical carbon dioxide

Abstract

The synthesis of particles with discrete phases using traditional emulsion polymerisation is a well-established process. Phase-separated particles have a wide range of applications, such as in coatings, drug delivery, impact modification and as supports in catalysis. However, as a dry powder is often desired for the end application, post-polymerisation, energy intensive drying steps are usually required for the removal of water. Alternatively, dispersion polymerisation utilising supercritical carbon dioxide (scCO₂) as a reaction medium allows for the production of dry, free-flowing powders upon release of the CO₂. Here, we present the innovative use of scCO₂ to provide a novel and environmentally acceptable route for creating phase-separated particles. Particles containing a high T_g poly(methyl methacrylate) (PMMA) phase, combined with a low T_g polymer phase of either poly(benzyl acrylate) (PBzA) or poly(butyl acrylate) (PBA), were investigated. Both monomers were added to the reaction after the formation of PMMA seed particles. Benzyl acrylate (BzA) was chosen as a model low T_g monomer, with well-defined and detectable functionality when mixed with PMMA. Butyl acrylate (BA) was also used as an alternative, more industrially relevant monomer. The loading of the low T_g monomer was varied and full characterisation of the particles produced was performed to elucidate their internal morphologies and compositions.