The role of the emulsifier is to hold the growing polymer molecule inside a micelle.
Emulsion polymerization is a type of free radical polymerization that usually starts with an emulsion of water, monomer, and a surfactant ( a substance that decreases the surface tension of a liquid).
The most common type of emulsion polymerization is one in which large monomer droplets, empty micelles, and micelles with single monomer molecules are dispersed in a continuous phase of water.
The initiator diffuses into the micelle and polymerizes the monomer.
More monomer diffuses from the droplet into the micelle, so the polymer chain becomes longer.
The polymers can grow to extremely high molecular weights, especially if there is only about one initiator molecule per micelle.