Types of Redox Initiators

Peroxides in combination with a reducing agent are a common source of radicals for example, the reaction of hydrogen peroxide with ferrous ion 

Ferrous ion also promotes the decomposition of a variety of other compounds including various types of organic peroxides [Bamford, 1988], 

The combination of a variety of inorganic reductants and inorganic oxidants initiates radical polymerization, for example 

Other redox systems include reductants such as HSO3, SO2-, S202-, and SjOg- in combination with oxidants such as Ag+, Cu2+, Fe3+, CIO3, and H2O2. 

Organic-inorganic redox pairs initiate polymerization, usually but not always by oxidation of the organic component, for example, the oxidation of an alcohol by Ce4+, 

Ferrous ion also promotes the decomposition of a variety of other compounds including 

---

Today it is possible to distinguish four types of redox initiators ... 

Batch polymerisation runs, intended to establish a starting recipe for continuous operation, were carried out with 15% rubber and 85% copolymer. Monomer composition was azeotropic.The reaction was carried out at 70°C and 20% total solids, using standard types of redox initiator, chain-... 

Two types of redox systems (Fig. 7) are used for batteries [14]. The standard potential (E°) of MnO 2 should be a good representation of the total energy of the oxide. For two-phase systems such as Pb02, Ag20, HgO, etc., the initial potential (E ) and middle potential (Em ) are equal to E°, from which we can calculate AF (-nFE°). For MnOz, a one-phase system, as shown in Fig. 7(A), the E (initial potential) cannot be used as E°. Ko-zawa proposed the middle potential (Em) of the S-shaped curve to be used as the E°... 

The titration is represented in Fig. 2.22 by plotting the Pt electrode potential versus the titration parameter k. BB is the voltage curve for titration of Fe2+ with Ce4+ and B B that for titration of Ce4+ with Fe2+ they correspond exactly to the pH curves BB and B B in Fig. 2.18, with the exception that the initial point in Fig. 2.22 would theoretically have an infinitely negative and an infinitely positive potential, respectively. In practice this is impossible, because even in the absence of any other type of redox potential there will be always a trace of Fe3+ in addition to Fe2+ and of Ce3+ in addition to Ce4+ present. Further, half way through the oxidation or reduction the voltage corresponds to the standard reduction potentials of the respective redox couples it also follows that the equivalence point is represented by the mean value of both standard potentials ... 

At one time, benzoyl peroxide (BPO) was the favoured initiator for radical polymerizations in non-aqueous media. It is still widely used and it is also important as a component of redox initiating systems it is discussed in some detail in this section. BPO is an example of a diaroyl peroxide and there are many other types of organic peroxides used as initiators of polymerizations, giving end-groups of various types extensive lists are available, e.g. the catalogues and pamphlets issued by AKZO and by the Nippon Oil and Fats Company. 

Random copolymer—Distribution of the monomer units does not follow any definite sequence. These are produced in bulk, aqueous, suspension, or emulsion using free radical initiators of the peroxide type or redox systems. 

The initiator in radical polymerization is often regarded simply as a source of radicals. Little attention is paid to the various pathways available for radical generation or to the side reactions that may accompany initiation. The preceding discussion (see 3.2) demonstrated that in selecting initiators (whether thermal, photochemical, redox, etc.) for polymerization, they must be considered in terms of the types of radicals formed, their suitability for use with the particular monomers, solvent, and the other agents present in the polymerization medium, and for the properties they convey to the polymer produced. 

General. A mathematical model has been developed in the previous section, which can now be employed to describe the dynamic behaviour of latex reactors and processes and to simulate present industrial and novel modes of reactor operation. The model has been developed in a general way, thus being readily expandable to include additional mechanisms (e.g. redox initiation (59)) or to relax any of the underlying assumptions, if necessary. It is very flexible and can cover various reactor types, modes of operation and comonomer systems. It will be shown in the following that a model is not only a useful... 

Several groups have recently shown (36,42,43,44) that photoanode materials can be protected from pRotoano3ic corrosion by an anodically formed film of "polypyrrole".(45) The work has been extended (46) to photoanode surfaces first"Treated with reagent that covalently anchors initiation sites for the formation of polypyrrole. The result is a more adherent polypyrrole film that better protects n-type Si from photocorrosion. Unlike the material derived from polymerization of I, the anodically formed polypyrrole 1s an electronic conductor.(45) This may prove ultimately important in that the rate of ionTransport of redox polymers may prove to be too slow... 

---