The basis of this polymerization method is the formation of a large amount of dispersed “microreactors” of polymerizable monomer in a continuous phase of water. The components for this reaction are:

• one or several radically polymerizable monomers
• a surfactant capable of emulsifying hydrophobic monomers in water
• a water soluble initiator that can be activated by thermal decomposition or a redox reaction to start the radical polymerization.

This technique involves mechanically dispersing monomer in a non-compatible liquid, usually water, and polymerizing the resultant monomer droplets by use of a monomer-soluble initiator. If the process is carefully controlled, polymer is obtained in the form of granular beads, which are easy to handle and can be isolated by filtration or by spray drying. A major advantage is that heat transfer is very efficient and the reaction is therefore easily controlled.

This polymerization type uses a solvent. Both the resulting resin and the monomers have to be soluble in the solvent used. Peroxides or azo compounds serve as radical initiators. The degree of polymerization and thus the molecular weight of the resulting resin molecules can be adjusted via the initiator and monomer concentrations, the polymerization temperature, chain transfer agents, or even the type of solvents used.

Reactive systems typically consist of monomer and polymer mixtures that react with each other upon triggering the polymerization by e.g. presence of metal ions, radiation or other means. Initially the monomer acts as solvent/diluent to decrease the overall viscosity of the formulation. After application, the reactive diluent is polymerized to achieve the final properties and to reduce the VOC in contrast to formulations with conventional organic solvents. Reactive diluents are for example used in low VOC lacquers, composite resins or in anaerobic adhesives. The latter are used for bonding and sealing metal.