Products from hydroperoxide decomposing antioxidants

Secondary antioxidants react with hydroperoxides to produce non-radical products and are therefore often termed hydroperoxide decomposers . They differ from priniaiy phenols and amines in that they are decomposed by reaction with hydroperoxide, rather than containing it. They are particularly useful in synergistic combinati(His with primary antioxidants.Systems that do not contain a phenolic... 

Sulfur-based hydroperoxide decomposers, such as thioesters, suffer from the disadvantage that they may be malodorous or may yield compounds that are. This fact largely precludes their use in many products. For this reason, phosphorus-based compounds are the most widely used type of secondary antioxidants in polyethylene. 

The mechanism of secondary stabilization by antioxidants is demonstrated in Figure 15.5. TnT-nonylphenyl phosphites, derived from PCI3 and various alcohols, and thio-compounds are active as a secondary stabilizer [21], They are used to decompose peroxides into non-free-radical products, presumably by a polar mechanism. The secondary antioxidant is reacting with the hydroperoxide resulting in an oxidized antioxidant and an alcohol. The thio-compounds can react with two hydroperoxide molecules. 

Ultimately, production of lipid hydroperoxides, even by circuitous routes, becomes the major process driving the oxidation reaction forward. LOOK are the first stable products of lipid oxidation, accumulating in the absence of pro-oxidant heat, metals, hemes, ultraviolet light, peroxyl radicals, or antioxidant acids or nucleophiles. However, from a practical standpoint, one or more of these or other decomposing factors are nearly always present, so the low energy 0—0 and O—H bonds undergo a variety of scission reactions. Indeed, a large proportion of the... 

There are two ways in which stabilizers can function to retard autoxidation and the resultant degradation of polymers. Preventive antioxidants reduce the rate of initiation, e.g., by converting hydroperoxide to nonradical products. Chain-breaking antioxidants terminate the kinetic chain by reacting with the chain-propagating free radicals. Both mechanisms are discussed and illustrated. Current studies on the role of certain organic sulfur compounds as preventive antioxidants are also described. Sulfenic acids, RSOH, from the decomposition of sulfoxides have been reported to exhibit both prooxidant effects and chain-breaking antioxidant activity in addition to their preventive antioxidant activity as peroxide decomposers. 

We have thus established that sulfides, disulfides, and their initial oxidation products are not the actual preventive antioxidants. The active peroxide decomposers are the sulfenic acid from sulfoxide decomposition, the thiosulfoxylic acid from thiolsulfinate decomposition, and the acidic products formed when they react with hydroperoxides. The catalytic... 

Antioxidants are classified according to the mechanism of their effect on polymer oxidation. Those that interrupt the oxidation chain reaction by reacting with the active radicals are called primary antioxidants. Those that decompose hydroperoxides are called secondary antioxidants. It must be kept in mind that antioxidant efficiency is affected by active products derived from selfoxidation reactions of the basic polymer. It is possible to protect a highly oxidized polymer against further oxidation by the use of peroxide decomposers. Weak peroxide decomposers are effective only when they are added to the polymer prior to the thermo-oxidative reaction [13]. 

Alvinox P is utilized to protect polymers from thermal oxidation particularly during processing. It acts essentially as a decomposer of hydroperoxides. Optimum performance is obtained when the product is used in combination with antioxidants (hindered phenols and/or thioethers) which additionally protect the polymer against long-term heat degradation. 

The values of a catalytic factor v showed that the transformation products of one molecule of antioxidant, depending on the structure, are able to decompose from several hundred to several thousand CHP molecules. The value v increases directly proportional to the increase of the ratio of CHP and the initial antioxidant concentrations (Fig. 9.6). This indicates that the antioxidants studied are more efficient in the decomposition of hydroperoxides than other known organic compounds. 

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