Preparation of a new polymeric antioxidant for polypropylene based on phenylmalonic acid

Abstract

Stabilization of polypropylene (PP) against thermal oxidation, due to the susceptibility of this commodity polymer to oxidation, is of great importance from both scientific and industrial points of view. The present work aimed at preparing a new polymeric antioxidant for polypropylene, which has no tendency toward migration from the polymer. Accordingly, a diacid (phenylmalonic acid), which has a labile hydrogen atom and can act as a hydrogen donor antioxidant, was polymerized with 1,4-phenylenediamine to render a polyamide. Occurrence of the reaction was confirmed by FT-IR spectroscopy, differential scanning calorimetry (DSC), gel permeation chromatography and thermogravimetric analysis (TGA). The synthesized polyamide was melt-mixed with PP and its uniform distribution in the matrix was verified by the yellowness index measurements. Oxidation onset temperature and oxidative induction time of the samples using DSC proved that the additive enhances stability of the polymer remarkably in melt state. However, its stabilization efficiency is not as outstanding as that of SONGNOX 1010; a conventional antioxidant for PP. But oven ageing experiments followed by FT-IR spectroscopy revealed that the synthesized antioxidant amends thermo-oxidative stability of the polymer in solid state with an eminent efficiency which is even better than that of SONGNOX 1010. Furthermore, its remarkable stabilization activity was proved by DPPH method. Finally, the synthesized polyamide's potential, as an efficient antioxidant for PP, especially in the long-term stabilization, was assigned to the presence of the two different hydrogen donor groups, i.e. allylic and amine hydrogen atoms, in the molecular structure of the new antioxidant.