Effect of secondary structure on physical behaviour and performance of hindered phenolic antioxidants in polypropylene

摘要

The performances of five hindered phenolic antioxidants of molecular weights between 206 and It 78, all containing 2,6-di-tert-butylphenol functionalities (1), were studied from the view-point of long-term heat ageing (LTHA) and processing stabilities in isotactic polypropylene. In order to separate the chemical effect from physical interactions with the matrix, efficiencies of stabilizers were studied in equimolar 0.1% concentrations of (1) in the polymer. Under such conditions, the chemical reactions of all the compounds were expected to be equal and all the differences in performances were accounted for purely by the physical interactions between stabilizer and polymer. In the solid semi-crystalline polymer, the effect of physical loss was intense so far, that at molecular weights below 300-400 in LTHA tests at 130 and 150 degreesC, performances of stabilizers were considerably diminished. On the other hand, in processing tests, the contribution of secondary structure was found to be practically meaningless and the performances of stabilizers tested were controlled almost exclusively by the chemistry of the active moiety (1). (C) 2004 Elsevier Ltd. All rights reserved.