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It might have been expected that the AO would not be able to change a fundamental parameter such as Po that is linked to the residual catalyst concentration and other oxidation-initiating centers. However, this may be considered in the light of the mechanisms of hindered phenol antioxidant action in which aggregation of antioxidant at sites containing polar groups may occur. Also, at the reaction temperature, the diffusion coefficient of the AO may be 10-7 to 10-8 cm2s-1 (42) so that migration to active sites may occur. There will, however, be a small number

of sites where AO is not present to inhibit effectively, or it may not mechanistically function at that site for chemical reasons. As the AO is consumed at the active site, the oxidation will spread and the role of the AO in the bulk of the resin is to limit that spreading. As shown in Table 2, the spreading coefficient b, continues to decrease with increased concentration of AO.