Kinetic factors as well as physical parameters such as volatility are often considered in explaining the different antioxidant efficiencies of monophenols and polyphenols. The objective of this work is to examine these factors in comparing the behavior of different sterically hindered phenols in processing stabilization and long term heat aging. For this purpose, mainly data relative to phenols of the 3,5-di-tert.butyl-4-hydroxyphenyl propionate type in polypropylene are examined. It is found that the stabilizing efficiency of phenolic antioxidants of the propionate type in processing of polypropylene is a function of the concentration of phenolic groups, regardless of the number of phenolic groups attached to a single molecule.
To explain the superiority of the polyphenols over the monophenol in long term heat aging, a reaction model involving chemical as well as physical aspects is proposed.
The kinetics of stabilization are applied to the interpretation of oven aging data. For this purpose, two concepts are considered, the well-known critical antioxidant concentration and another one, the critical oxidation level. It is found that the results are best accounted for by the latter.