Emulsion polymerization of voided particles by encapsulation of a nonsolvent

The modification of an emulsion polymerization with a water-miscible alcoho l and a hydrocarbon nonsolvent for the polymer can influence the morphology of the particles. The formation of monodispersed particles with a hollow s tructure 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 w eight polymer is formed initially in the process. Subsequent addition of a cross-linking monomer stabilizes the morphology. The final particle size ca n be defined by small nucleating latex seed particles. Monodispersed hollow particles with diameters from 0.2 to 1 mu m are possible. Void fractions a s 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 effe cts.