Semibatch emulsion polymerizations are predominately run in “starve-fed” mode, but what does that really mean? It is generally understood to mean that the monomer concentration in the particles is maintained at a level well below its maximum (saturation) value, which is ~5-7 M, depending on the monomers. Typically monomer concentration in the particles is kept at ~0.5-1 M by varying the monomer feed rate, but this can vary significantly depending on the specific process. There are two main reasons for running in “starve-fed” mode, and your selection of how starved you want to run your process depends on the relative value you attach to each objective:
However, other factors are also important and should be considered. The overall reaction rate is roughly proportional to the number of particles, so for a given heat-removal capacity in your reactor, smaller size particles (higher particle number) require lower monomer concentration in the particles. This means that a change in particle size likely requires a change in monomer feed rate.