We have developed a method to prepare highly porous microspheres of the conducting polymer polyaniline (PANI) and a selection of its ring-substituted derivatives. Briefly, a water-in-oil-in-water (W/O/W) double emulsion is generated when excess ammonium hydroxide is rapidly added to an acidic dispersion containing the preformed polymer and a monomer such as o-toluidine or m-toluidine. These monomers are soluble in acidic solutions, but spontaneously form immiscible droplets in sufficiently alkaline solution. Spheres are formed when the granular polymer dissolves in the monomer droplets, and pores are formed by water droplets trapped in the polymer matrix. The amphiphilic monomer serves as a single small molecular surfactant that stabilizes both the oil-water and water-oil interfaces of the double emulsion, which is rare among W/O/W systems. The granular and spherical forms have nearly identical FTIR, UV-Vis, and NMR spectra, indicating no differences in the molecular or electronic structure. However, SEM images reveal that the morphology is highly sensitive to the monomer concentration; too little yields only granular particles and too much yields an oily product. The monomer can be unconsumed reactant from the polymer synthesis (e.g. o-toluidine in poly(o-toluidine)), or specifically added to a polymer dispersion (e.g. o-toluidine in PANI). We have obtained PANI and poly(o-toluidine) microspheres using a variety of monomers. Poly(m-toluidine), poly(2-ethylaniline) and poly(3-ethylaniline) are the subject of ongoing study. The simplicity and convenience of this method combined with the unique electronic properties of the polymers suggest applications including electroactive microreactors, scaffolds for catalysis, and encapsulants for payload delivery.

Porous microspheres of polyaniline and its derivatives prepared from W/O/W double emulsions

254th National Meeting (2017)

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