Modelling light stabilizers as thermal antioxidants

The Cyasorb 2908 revealed weak antioxidant activity with a rate constant for the addition of cumylperoxy RO2 radicals to the functional group of the stabilizer k7 = 106.2±0.1 e−(3900±600)/RT, however, the inhibition index f (80 °C) is significantly higher than that of the commercial phenolic antioxidant Irganox 1076. Oxidation rate profiles in the presence of Cyasorb 3529 displayed a strong retarding activity by the stabilizer under conditions of the model experiments. The rates were found to depend linearly on the reciprocal square root of the concentration of the stabilizer over a sufficiently wide range thereby fitting the mechanism for the addition of cumylalkyl R radicals to the Cyasorb molecules. The rate constants for the addition of cumyl R radicals to the Cyasorb were determined to be k(333-353 K) = (2.0 ± 0.8) × 108 M−1 s−1. This value surpasses even the rate constants for other related HAS Chimassorb [Zeynalov EB, Allen NS. Effect of micron and nano-grade titanium dioxides on the efficiency of hindered piperidine stabilizers in a model oxidative reaction. Polym Degrad Stab 2006;91(4):931-9.] stabilizers and it follows that Cyasorb 3529 is a powerful retarder of thermal oxidation.