Phenolic antioxidant activity substrates used

Besides the reactions between phenols and peroxidic bodies, other factors can influence the activity of antioxidants—e.g., compatibility with substrate and volatility. The results show that under the conditions used the influence of the antioxidant structure is dramatic. In this connection we note agreement of the general conclusions dealing with the influences of pyrocatechol antioxidant structure on the activity in polypropylene at 180°C. and those influences found in Tetralin (28) at 80 °C. Despite great differences in experimental conditions, the sequences of the activities of pyrocatechol antioxidants I-VI were in agreement. Great similarities were also found within each particular group of antioxidants. 

This second phase of the inhibition mechanism, which is proved by the isolation of a similar peroxide with quinol structure from monohydric phenols (13,15) is unfavorably affected by steric influence of the present substituent R however, even physical factors will probably influence the activity—e.g., the change in the solubility of the antioxidant in the substrate caused by substitution. The possible resonance of radical VUIb is also illustrated in the scheme. In this case the second radical R OO may be fixed in position 5 (IXb). The reaction may be used to help... 

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