Antioxidant effectiveness determining factors

Three factors determine the effectiveness of antioxidants in polymers, namely (i) intrinsic molar activity (ii) substantivity in the polymer and (iii) solubility in the polymer. Multifunctional AOs combine multiple functions in one molecule. Sterically hindered amine stabilisers (HAS), such as Chimassorb 944, Tinuvin 622 and Tinuvin 783 are prime examples. 

Consequently, the retarder may be consumed slowly while oxygen uptake is only reduced slightly, but the effect occurs well past the time at which two peroxyl radicals have been generated from the initiator for every molecule of retarder. Under these conditions, a retarder may appear to react with more than two peroxyl radicals. This situation is quite often observed and causes misinterpretation of results concerning inhibition efficiency, unless a reliable method is used to determine the stoichiometric factor and antioxidant activity (See Section II.A.)... 

Factors Determining the Effectiveness of Antioxidants. It was for many years a source of puzzlement to polymer chemists that the rating of antioxidants in polymers and in model hydrocarbons appeared to be very different. The widely used antioxidant BHT (I) is one of the most "efficient" antioxidants known for liquid hydrocarbons as measured by oxygen absorption but is virtually ineffective in rubbers... 

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