PHOTOOXIDATION OF UNSTABILIZED AND HALS-STABILIZED POLYPHASIC ETHYLENE-PROPYLENE POLYMERS

The oxidation photoproducts of a polyphasic polymer P-E/EPR have been identified by different methods of analysis. It has been shown that the oxidation photoproducts were those of the polypropylene phase, which is by far the most oxidizable. The formation of the oxidation products detected by IR analysis of the solid polymeric matrix or by analysis of the volatiles have been studied. It is shown that oxidation of the tertiary carbon atoms can account for the formation of alpha-methylated carboxylic acids. Oxidation of the tertiary carbons also explains the formation of acetone detected in the gas phase. The presence of stabilizers (HALS) gives evidence for the migration of low molecular weight oxidation photoproducts, such as alpha-methyl levulinic acid and acetic acid, which notably modifies the shape of the IR oxidation band in the carbonyl region. Moreover, the behavior of the HALS stabilized materials is largely dependent on the migrating possibilities of the additives, especially as far as thick samples are concerned. Analysis of the surface layers of thick samples stabilized with a migrating HALS show that a grafting reaction occurs by interaction of nitroxyl radicals and oxidized macroradicals.