Photochemical behavior of isotactic-polypropylene irradiated in ~32O_2--~36O_2

摘要

The photochemical oxidation of isotactic polypropylene (iPP) in an atmosphere composed of a blend of ~32O_2 and ~36O_2 has been investigated using mass spectroscopy (MS) and infra-red spectroscopy (IR). The samples were irradiated with an artificial acceler- ated photoageing unit at 60℃. MS analysis reveals the formation of several oxidation photoproducts previously identified, and unambiguously shows that photooxidation of iPP generates ~34O_2. A possible interpretation is that, according to the results pro- posed in the literature, a pseudo-termination reaction by recombination of peroxy radicals POO' occurs and undergoes a head-to- head reaction, which produces tetroxides. These intermediate species decompose to give molecular oxygen and two alkoxy macro- radicals. On a kinetic point of view, two successive stages are observed. In the first, at low levels of oxygen incorporation, recom- binations of POO' are not favoured and peroxy radicals mostly generate hydroperoxides. In the second phase, the local concentrations of peroxy radicals are high enough to favour recombination.