In the first line, styrene monomer, water, initiator, and suspending agents form the basic
charge to the suspension reactor (1). The styrene-to-water ratio varies with the type of polystyrene
required. A typical ratio is about one-quarter to one-half monomer to water volume. Initiators are
commonly used because the reaction temperature is usually too low for adequate thermal initiation of
polymerization. Suspending agents are usually protective colloids and insoluble inorganic salts.
Protective colloids are added to increase the viscosity of the continuous water phase, and insoluble
inorganic salts such as magnesium carbonate (MgCO3) are added to prevent coalescence of the drops
upon collision.