3. Equipment & Techniques
* emulsion polymerization
Emulsion polymerization is a type of polymerization that takes place in an emulsion typically incorporating water, monomer, and surfactant. The most common type of emulsion polymerization is an oil-in-water emulsion, in which droplets of monomer (the oil) are emulsified (with surfactants) in a continuous phase of water. Water soluble polymers, such as certain polyvinylalcohols or hydroxyethyl celluloses, can also be used to act as emulsfiers/stabilisers.
Some of the popular emulsions available in the market include Polyvinyl acetate homopolymers and copolymers, styrene butadiene latex, and acrylic emulsions. These emulsions find applications in adhesives, paints, paper coating and textile coatings. They are finding increasing acceptance and are preferred over solvent-based products in these applications as a result of their eco-friendly characteristics due to the absence of VOC(Volatile Organic Compounds) in them.
Advantages of emulsion polymerization include:
▪ The continuous water phase is an excellent conductor of heat and allows the heat to be removed from the system, allowing many reaction methods to increase their rate.
▪ Since polymermolecules are contained within the particles, viscosity remains close to that of water and is not dependent on molecular weight.
▪ The final product can be used as is and does not generally need to be altered or processed.
Most emulsion polymerizations use a free-radical polymerization method. Emulsion poymerization can be carried out as a batch reaction, but in many cases is performed as a starve-fed reaction to insure a good distribution of monomers into the polymer backbone chain.
The leading theory for the mechanism of starve-fed, free-radical emulsion polymerization is summarized by the following: