Exploiting the homogeneous expansion limit of CO2-expanded media for the synthesis of polymeric nanoparticles

This paper describes a novel method for the direct synthesis of polymeric nanoparticles based on the CO2-expanded liquid concept. This technique exploits the anti-solvent effect of dense CO2 to induce an emulsion in a polymer solution at a point known as the homogeneous expansion limit (HEL). Polymerization is carried out in the dispersed phase which consists mainly of polymer and monomer. Herein, we report on nanoparticle formation via polymerization of methyl methacrylate using a macroazoinitiator in CO2-expanded ethanol at 70 °C and 10 MPa. It is shown that polymerization at the HEL leads to well defined polymeric nanoparticles with diameters of around 100 nm. The nanoparticles are generally smaller and more uniform in size than those obtained in the corresponding CO2-free approach (dispersion polymerization).