A Study of Phosphorus-Containing Antioxidants in Polyolefins

Abstract

Metal dithiophosphonates (Ni, Zn, Fe, Co, Cu) and the corresponding sulphide, TPS, were examined as potential antioxidants in polypropylene. All the dithiophosphonates were very good melt stabilisers when compared to commercial controls. Their effectiveness as thermal antioxidants varied considerably from CuDiBuPn which was poor to NiDiBuPn which was excellent and appears to be better than Irganox 1076, a commercial antioxidant. The photostabilising activity of these compounds also varied considerably. The NiDiBuPn was found to be the most outstanding photostabiliser when compared to the other phosphonates both on a molar and weight basis and its activity was found to be highly dependent on concentration, alkyl substituent and processing severity. NiDiBuPn and CuDiBuPn were both found to synergise effectively with the U.V. absorber HOBP and their effectiveness was found to increase when an excess of the U.V. absorber was used. The dithiophosphonates were shown to be effective radical traps (oxygen absorption) and peroxide decomposers (hydroperoxide decomposition). Mechanistic studies of NiDiBuPn also showed the complex to be highly stable to thermolysis and photolysis. The lp NMR studies of NiDiBuPn and TBH showed that the major transformation products are the corresponding sulphides, the acidic species, the phosphorus esters and some highly oxygenated inorganic species.