There are basically three types of particle-producing polymerization methods: emulsion, dispersion, and suspension. All three methods involve a particle of polymer stabilized by a dispersing agent of some type. In emulsion polymerization the monomer is insoluble in the polymerization medium (usually water) and the polymerization occurs within a surfactant micelle. Suspension polymerization involves the use of the monomer droplets in water and is carried out with an initiator that is soluble in the monomer. The resulting polymer particles are stabilized by a polymeric suspending agent. Dispersion polymerization differs from the other forms of heterogeneous polymerization described above in that the monomer is soluble in the polymerization medium and the polymer is not. As the polymerization proceeds, the growing chains become insoluble and precipitate from the solution. Flocculation is prevented by the presence of an amphipathic graft or block copolymer. The average particle size achieved in this type of process is smaller than the products of suspension polymerization, but larger than the products of emulsion polymerization.