Compare four free radical polymerization methods and the sites of polymerization. Examples

The four free-radical polymerization methods are propriety polymerization, solution polymerization, suspension polymerization, and emulsion polymerization.

Intrinsic polymerization is the polymerization without any other medium, only the monomer under the initiator, heat, light, radiation and other initiation. Gaseous, liquid, solid monomers can be carried out in the body of the polymerization, the liquid monomer of the body of the polymerization is the most important.

Solution polymerization monomer and initiator dissolved in a suitable solvent for the polymerization method called solution polymerization. The use of solvents in the solution polymerization process reduces the viscosity of the system, so mixing and heat transfer is easier, the temperature is easy to control, less gel effect, and local overheating can be avoided.

The monomer dissolved in the initiator is suspended in water in the form of droplets for free radical polymerization as suspension polymerization. The overall view of the water as a continuous phase, the monomer is a dispersed phase. Floating polymerization system generally has monomer, initiator, water, dispersant four basic components. Monomer insoluble in water under the action of strong stirring, was crushed and dispersed into small droplets, with the reaction, the dispersion of the droplets may be condensed into a block, the system must be added to the dispersant.

Emulsion polymerization is a unique method that can be used for certain free radical polymerization reactions, which involves the polymerization of monomers in the form of an emulsion. The composition of an emulsion polymerization system is complex, and generally consists of four components: monomer, dispersing medium, initiator, and emulsifier. The monomer of classical emulsion polymerization is oil-soluble, the dispersion medium is usually water, and water-soluble initiators are selected.

Extended information

The body polymerization method of polymerization heat is difficult to disseminate the problem, the industrial production of more than two-stage polymerization process. The first stage of pre-polymerization, can be carried out at lower temperatures, the conversion rate is controlled at 10% to 30%, generally before the self-accelerating, when the system viscosity is low, heat dissipation is easy, polymerization can be carried out in a larger kettle.

The second stage continues to polymerization, in a thin layer or plate reactor, or the use of segmented polymerization, gradually increase the temperature, increase the conversion rate. The molecular weight distribution of the product is wide because it is difficult to control the reaction temperature at a constant level during the native polymerization process.

The post-processing of the polymerization is mainly to eliminate the residual monomer in the polymer. Commonly used method is to melt the polymer in a vacuum to remove monomers and volatiles, the equipment used for the screw or vacuum degasser. Foam degassing is also used, the polymer is heated under pressure to melt, and then suddenly depressurized so that the polymer is in the form of foam, which is conducive to the escape of monomers.

Solution polymerization process using solvents, the system monomer concentration is low, the polymerization rate is slow, the equipment production capacity and utilization rate decreased. If the production of solid products, it is necessary to carry out post-processing, solvent recovery costs are high, increasing production costs. Therefore, industrial solution polymerization is mostly used for polymer solution directly used occasions, such as coatings, adhesives, impregnating agents, dispersants, thickening agents.

Baidu Encyclopedia - Free Radical Polymerization