Virtually all polymeric materials undergo oxidation reactions. Oxidation can occur at every stage of the life cycle of a polymer, i.e. during manufacturing and storage of the material or during processing and end-use.
Typical manifestations of oxidation of polymers can be change of viscosity during processing, appearance, and loss of mechanical properties such as elongation, impact strength, tensile strength, and flexibility. Antioxidants protect polymers against oxidation by controlling molecular weight changes that lead to a loss of physical, mechanical, and optical properties.
Among other factors heat, light and mechanical stress can result in the degradation of the polymer.
Antioxidants interrupt the degradation processes in different ways, depending on their structure. The two major classifications are: chain terminating primary antioxidants and hydroperoxide decomposing secondary antioxidants.
Primary antioxidants react rapidly with free radicals and are, therefore, called "Radical Scavengers". The majority of primary antioxidants for polymers are sterically hindered phenols.
Primary antioxidants: