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Stabilizers are essential in the processing and molding of polymeric materials, as well as for the maintenance of the polymer properties for a long time. Among them, phenolic antioxidants as radical scavengers and hindered amine light stabilizer (HALS) called multifunctional stabilizers are widely used in various polymeric materials. These two kinds of stabilizers are often used together, and sometimes show apparent antagonism, although synergism is also observed. However, the mechanism of antagonism generally accepted at present does not describe all of observed antagonisms. We have previously proposed a new antagonism1). Hydroperoxide decomposition by HALS is a very important process, and consists of two phases: slow decomposition in the induction period, and fast decomposition which proceeds homolytically. The induction period of decomposition is remarkably shortened by the presence of an acidic compound including a phenolic antioxidant, such as 3,5-di-t-butyl-4-hydroxytoluene (BHT), and so promotes the homolytic decomposition of a hydroperoxide, such as cumene hydroperoxide (CHP), resulting in the initiation of autoxidation and deterioration of the polymeric materials. We previously reported that a HALS nitrosonium species is formed as the active species or precursor of a highly active catalytic hydroperoxide decomposer, regardless of the presence or absence of a phenol2). The present study investigated the formation mechanism of the HALS nitrosonium salt.

journal of the japan petroleum institute

New Antagonism of Hindered Amine Light Stabilizers with Acidic Compounds Including Phenolic Antioxidants (Part 2) Formation Mechanism of Active Species of Peroxide Decomposition Reaction