Determination of peroxides and hydroperoxides with 2,2-diphenyl-1-picrylhydrazyl (DPPH). Application to ozonized ethylene vinyl acetate copolymers (EVA)

Abstract

The compound 2,2-diphenyl-1-picrylhydrazyl (DPPH) is a stable free radical often used to determine the quantity and the decomposition rate constant of macroinitiators such as ozonized polymers. In fact, DPPH induces the decomposition of hydroperoxides and has no effect on the decomposition of peroxides. Consequently, the hydroperoxides are the only species determined by the method described in the literature. Consequently, the decomposition rate of ozonized polymers measured with this method is wrong. It may be an explanation due to the low activation energy 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 acetate copolymer. They can initiate the polymerization of vinyl monomers. On the other hand, peroxides are in a minority and their decomposition simply carries away a slight degradation by chain scissions.