Photochemical behavior of isotactic-polypropylene irradiated in O-32(2)-O-36(2)

The photochemical oxidation of isotactic polypropylene (IPP) in an atmosphe re composed of a blend of O-32(2) and O-36(2) has been investigated using m ass spectroscopy (MS) and infra-red spectroscopy (IR). The samples were irr adiated with an artificial accelerated photoageing unit at 60 degreesC. MS analysis reveals the formation of several oxidation photoproducts previousl y identified, and unambiguously shows that photooxidation of iPP generates O-34(2). A possible interpretation is that, according to the results propos ed in the literature, a pseudo-termination reaction by recombination of per oxy radicals POO. occurs and undergoes a head-to-head reaction, which produ ces tetroxides. These intermediate species decompose to give molecular oxyg en and two alkoxy macroradicals. On a kinetic point of view, two successive stages are observed. In the first, at low levels of oxygen incorporation, recombinations of POO. are not favoured and peroxy radicals mostly generate hydroperoxides. In the second phase, the local concentrations of peroxy ra dicals are high enough to favour recombination. (C) 2000 Elsevier Science L td. All rights reserved.