Vikas Mittal, Polymer Nanocomposites in Emulsion and Suspension: an Overview, Chapter 1 in Polymer Nanocomposites by Emulsion and Suspension Polymerization, edited by Vikas Mittal, Royal Society of Chemistry (Great Britain), 2011, provides an excellent review of this field. The extent of cross-linking can also be increased further by postcuring (annealing) the as-polymerized beads for a brief period at an elevated temperature. The extent of cross-linking can be controlled by varying the concentration of cross-linker in the monomer mixture. Thermoset versions of the same polymers can also be produced readily in the form of spherical beads via suspension polymerization, by including one or more of many available cross-linkers (such as divinylbenzene, ethylene glycol dimethacrylate, trimethylolpropane triacrylate, 1,6-diaminohexane, p-phenylenediamine, etc.) in hydrocarbon droplets. Polystyrene, high-impact polystyrene, poly(methyl methacrylate), poly(vinyl acetate), poly(vinyl chloride), copolymers of styrene and methyl methacrylate, copolymers of methyl methacrylate and vinyl acetate, and copolymers of styrene and acrylonitrile are among the thermoplastic polymers that can be produced in the shape of spherical beads on a commercial scale with favorable process economics via suspension polymerization. The formulation often also includes one or more oil-soluble initiator(s) as well as one or more additive(s) helping stabilize the suspension and controlling its rheology. Hence each hydrocarbon droplet is like a mini-reactor in which bulk polymerization is occurring. Hydrocarbon droplets, containing the monomer(s), are suspended in an aqueous medium and then polymerized, with agitation (usually by stirring) to maintain the two-phase system during polymerization, resulting in spherical polymeric beads. Suspension polymerization is the preferred technique for manufacturing spherical polymeric beads ranging from about 50 microns to several millimeters in diameter by starting from many monomers. ![]() NANOCOMPOSITE BEADS VIA SUSPENSION POLYMERIZATION
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