Solvent-Free Seeded Dispersion Polymerization toward Core-Shell Particles and Microcapsules

Core/shell particles have been synthesized using a seeded dispersion/emulsion polymerization strategy, which enables the controlled deposition of a polymer shell around preformed seed particles. The seeded dispersion/emulsion polymerization developed is a versatile method toward the core/shell particles but has been so far conducted in liquid media in the presence of a colloidal stabilizer, which is required for realization of colloidal stability during polymerization. In this study, we developed solvent-free seeded dispersion polymerization without any colloidal stabilizer. Specifically, polypyrrole (PPy) shells were successfully formed on micrometer-sized cubic sodium chloride (NaCl) seed particles by solvent-free oxidative seeded dispersion polymerization of the pyrrole (Py) monomer. The Py monomer, oxidant, and NaCl seed particles were separately placed in a sealed reactor, allowing Py vapor to diffuse and polymerize selectively on the surface of the seed particles. The resulting NaCl/PPy core/shell particles exhibited a uniform morphology with a controllable PPy shell thickness depending on the polymerization time. Subsequent dissolution of the NaCl cores in water led to the formation of PPy microcapsules while preserving the original cubic geometry of the seeds. To evaluate the versatility of this method, other water-soluble salts with different shapes, including potassium chloride, magnesium chloride, calcium chloride, and aluminum chloride, were employed as alternative templates. The results demonstrated that this approach enables the fabrication of not only core/shell particles/microcapsules with cubic shapes but also those with various shapes depending on the template used.