Editing Emulsion polymerization (section)

==Process considerations==
Emulsion polymerizations have been used in [[batch production|batch]], semi-batch, and [[continuous production|continuous]] processes. The choice depends on the properties desired in the final polymer or dispersion and on the economics of the product. Modern [[process control]] schemes have enabled the development of complex reaction processes, with ingredients such as initiator, monomer, and surfactant added at the beginning, during, or at the end of the reaction.

Early [[styrene-butadiene]] rubber (SBR) recipes are examples of true batch processes: all ingredients added at the same time to the reactor. Semi-batch recipes usually include a programmed feed of monomer to the reactor. This enables a [[starve-fed]] reaction to ensure a good distribution of monomers into the polymer [[backbone chain]]. Continuous processes have been used to manufacture various grades of synthetic rubber.

Some polymerizations are stopped before all the monomer has reacted. This minimizes chain transfer to polymer. In such cases the monomer must be removed or [[stripping (chemistry)|stripped]] from the dispersion.

[[Colloid]]al stability is a factor in design of an emulsion polymerization process. For dry or isolated products, the polymer dispersion must be isolated, or converted into solid form. This can be accomplished by simple heating of the dispersion until all water [[evaporates]]. More commonly, the dispersion is destabilized (sometimes called "broken") by addition of a multivalent [[cation]]. Alternatively, acidification will destabilize a dispersion with a [[carboxylic acid]] surfactant. These techniques may be employed in combination with application of [[Shearing (physics)|shear]] to increase the rate of destabilization. After isolation of the polymer, it is usually washed, dried, and packaged.

By contrast, products sold as a dispersion are designed with a high degree of colloidal stability. Colloidal properties such as particle size, particle size distribution, and viscosity are of critical importance to the performance of these dispersions.

[[Living polymerization]] processes that are carried out via emulsion polymerization such as iodine-transfer polymerization and [[RAFT (chemistry)|RAFT]] have been developed.

Controlled coagulation techniques can enable better control of the particle size and distribution.<ref>{{Cite journal |last=Kostansek |first=Edward |date=2004-01-01 |title=Controlled coagulation of emulsion polymers |url=https://doi.org/10.1007/s11998-004-0023-1 |journal=JCT Research |language=en |volume=1 |issue=1 |pages=41–44 |doi=10.1007/s11998-004-0023-1 |issn=1935-3804|url-access=subscription }}</ref>