Suspensionpolymerisation

Suspension polymerisation, also known as suspension polymerization, is a heterogeneous free-radical polymerization method in which monomer droplets are dispersed in a continuous aqueous phase and polymerize to form solid polymer beads. It is widely used for producing particulate polymers with controlled size and morphology, such as polystyrene, polyvinyl chloride, and polymethyl methacrylate beads.

In typical suspension polymerisation, a water-based medium containing stabilizers or protective colloids (for example, polyvinyl alcohol or gelatin) forms a dispersed phase in which monomer droplets are stabilized against coalescence. The monomer, or a mixture of monomers, is emulsified or dispersed in the water by mechanical stirring to create droplets ranging from tens of nanometers to hundreds of micrometers, depending on conditions. Polymerization is initiated by a radical initiator, commonly a water-soluble source such as ammonium or potassium persulfate, which diffuses into the droplets and starts the growth of polymer chains. Heat or a redox system provides the necessary activation energy. Growth and termination occur within the droplets, producing solid beads that are then separated and washed.

Key factors that influence bead size and distribution include the stabilizer type and concentration, stir rate, monomer solubility, and temperature. Ostwald ripening can lead to drift in particle size if not controlled. The method allows good heat management and low-viscosity reaction media, enabling scalable production of uniform beads with relatively low residual monomer.

Applications of suspension polymerisation include ion-exchange resins, chromatography beads, abrasive and filler carriers, and various polymer beads used in plastics and coatings.