PEROXY ACIDS IN PHOTOOXIDIZED POLYPROPYLENE

The presence of peracids among the peroxy species formed during the photo-oxidation of isotactic polypropylene (PP) has been proven both chemically and spectroscopically. The fast reaction of organic sulphides (dimethylsulphide in particular) with peracids has been employed to remove the latter selectively from the preoxidized PP. Thus treated PP exhibited spectral changes in the IR carbonyl region indicating the disappearance of peracids from the system. The ability of such PP samples to form stable 2,2,6,6-tetramethylpiperidine nitroxyls from the corresponding amine solutions is considerably lower than that of untreated polymer. The formation of nitroxyls in HALS stabilized systems is discussed in this connection. A mechanism of peracid genesis in oxidizing PP is put forward based on the assumption of methyl group attack by macroalkoxy-radicals with subsequent macroaldehyde/peracid formation.