Emulsion Polymerization of Voided Particles by Encapsulation of a Nonsolvent

The modification of an emulsion polymerization with a water-miscible alcohol and a hydrocarbon nonsolvent for the polymer can influence the morphology of the particles. The formation of monodispersed particles with a hollow structure or diffuse microvoids is possible. Both kinetic and thermodynamic aspects of the polymerization dictate which particle morphology is obtained. Complete encapsulation of the hydrocarbon occurs provided low molecular weight polymer is formed initially in the process. Subsequent addition of a cross-linking monomer stabilizes the morphology. The final particle size can be defined by small nucleating latex seed particles. Monodispersed hollow particles with diameters from 0.2 to 1 μm are possible. Void fractions as high as 50% are feasible. The phase separation of polystyrene within the styrene−isooctane dispersion has been modeled with the Flory−Huggins theory. The encapsulation has been discussed in terms of interaction parameters, transport processes, polymer molecular weight, and interfacial tension effects.