4. Suspension polymerization

In this type of process, the water-insoluble monomer is suspended in droplets by vigorous mechanical agitation, stabilized by suspending and dispersing agents. The initiator used must be hydrophobic, such as benzoyl peroxide, in order to solubilize in the monomer droplets. Two cases are to be considered, depending on the solubility of the polymer in its monomer:

• if it is soluble (as in the case of styrene or methyl methacrylate), polymerization takes place in a homogeneous medium inside each droplet, which can then be considered as a mini-mass polymerization reactor;

• Otherwise, we're dealing with precipitation polymerization (as in the case of vinyl chloride) in each droplet.