Fabrication of Porous “Clickable” Polymer Beads and Rods through Generation of High Internal Phase Emulsion (HIPE) Droplets in a Simple Microfluidic Device

The fabrication of micrometer-sized monodisperse highly porous polymer particles, of both spherical and rodlike shapes, using a simple microfluidic setup is demonstrated. Droplets were generated in a coflow device from a water-in-oil high internal phase emulsion (HIPE), hereby creating a water-in-oil-in-water (W/O/W) emulsion. The individual droplets of monomer HIPE were polymerized downstream in the channel through photopolymerization. The polymer particles produced via this strategy possess very large macropores in comparison with the more conventional porous polymer beads synthesized by inducing in situ phase separation throughout the polymerization process through the use of porogenic solvents. Epoxy-functionalized porous particles made using the HIPE microfluidic method showed superior performance in a consecutive azide and cycloaddition “click”−“click” modification procedure monitored by IR. Our microfluidic approach led to the successful miniaturization of monodisperse submillimeter spherical poly(HIPE) beads, down to diameters of 400 μm. More strikingly is the production of poly(HIPE) rods, which were obtained by using a viscous HIPE, which in coflow emulsification formed an unstable jet that broke up into rodlike sections. These rodlike droplets maintained their shapes throughout the microfluidic channel and did not relax back into spherical droplets, allowing for production of poly(HIPE) rods upon photopolymerization. The nonspherical shape in this case is not determined by confined channel geometries, which to the best of our knowledge is unprecedented as a strategy to produce nonspherical polymer particles with microfluidics.