RedoxInitiatoren

Redox initiators are chemical systems used to start radical reactions through a rapid redox reaction between an oxidant and a reductant. In polymer chemistry, they generate free radicals at ambient or mildly elevated temperatures, enabling polymerization in aqueous or solvent-based media without the need for heat alone. The redox reaction produces radical species, commonly sulfate radicals or related reactive species, which initiate the polymerization of vinyl monomers.

Typical redox systems include combinations of persulfates (such as ammonium persulfate or potassium persulfate) with reductants like sulfites or bisulfites; hydrogen peroxide paired with a reducing agent such as ascorbate or glucose; and metal-based pairs such as ferrous/ferric ions with persulfate or copper complexes with reductants. The exact radical species depends on the system, but sulfate radical anions (SO4•−) are a common initiating species in persulfate-based processes.

Advantages of redox initiators include fast initiation at room temperature, good compatibility with aqueous and multi-component formulations, and high initiation efficiency, which can be beneficial for rapid curing of coatings, adhesives, and certain resins. They are especially useful for heat-sensitive monomers or processes where external heating is undesirable.

Limitations involve sensitivity to dissolved oxygen and impurities, potential residual oxidants or reductants that can affect product properties, and the need for careful control of pH and concentrations. Safety considerations are important due to the strong oxidizing nature of the components and the reactive radicals they generate.

Applications span emulsion and solution polymerizations, coatings, adhesives, and dental resins, where mild conditions and rapid curing are advantageous.