Intramolecular synergism

The product study272) and the kinetic study261) form the experimental basis for the discussion of complex transformations of thiobisphenolic antioxidants. Their retardation effect in polypropylene after the induction period and the mechanism of formation of intermediates or products catalytically active in ROOH decomposition indicate the reactivity of both different centres in molecule and provide partial data for the discussion of intramolecular synergism of thiobisphenols5 57,258,26 ). 

The phosphite efficiency in hydroperoxide reduction decreases in the order phosphites > alkyl phosphites > aryl phosphites > hindered aryl phosphites. Hindered aryl phosphites can also act as chain breaking primary antioxidants when substituted by alkoxy radicals but their activity is lower than that of hindered phenols but in oxidizing media at high temperatures the hydrolysis of aryl phosph(on)ites takes place and produces hydrogen phosph(on)ites and phenols which are effective chain-breaking antioxidants. Multifunctional stabilizers such as those containing HAS-phosph(on)ites moieties show a superior efficiency due to the intramolecular synergism—Table 6 [49]. 

The antimony oxide/organohalogen synergism in flame retardant additives has been the subject of considerable research and discussion over the past twenty-five years (1-17). In addition to antimony oxide, a variety of bismuth compounds and molybdenum oxide have been the subject of similar studies (18-20). Despite this intensive investigation, relatively little has been conclusively established about the solid state chemical mechanisms of the metal component volatilization, except in those cases where the organohalogen component is capable of undergoing extensive intramolecular dehydrohalogenation. 

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