DETERMINATION OF PEROXIDES AND HYDROPEROXIDES WITH 2,2-DIPHENYL-1-PICRYLHYDRAZYL (DPPH) - APPLICATION TO OZONIZED ETHYLENE-VINYL ACETATE COPOLYMERS (EVA)

The compound 2,2-diphenyl-1-picrylhydrazyl (DPPH) is a stable free rad ical often used to determine the quantity and the decomposition rate c onstant of macroinitiators such as ozonized polymers. In fact, DPPH in duces the decomposition of hydroperoxides and has no effect on the dec omposition of peroxides. Consequently, the hydroperoxides are the only species determined by the method described in the literature. Consequ ently, the decomposition rate of ozonized polymers measured with this method is wrong. It may be an explanation due to the low activation en ergy and rapid decomposition rate always found by this method of assay . Using the selective deactivation of hydroperoxides we show that the hydroperoxides are the more numerous initiators in an ethylene vinyl a cetate copolymer. They can initiate the polymerization of vinyl monome rs. On the other hand, peroxides are in a minority and their decomposi tion simply carries away a slight degradation by chain scissions.