ESR study of the effect of ferric chloride on the photodegradation of model compound for polypropylene

In our previous article on the photodegradation of polypropyle (PP), the effect of ferric chloride (FeCl₃) accelerating the formation of peroxy radical and depressing the formation of alkyl radical were reported. In the present article, the influence of FeCl₃ on model compounds of PP was examined using electron spin resonance (ESR) spectrometry. The following compounds were employed as models of PP, including its irregular structures: 2-methylpentane (2-MP), 2,4-dimethylpentane (2,4-DMP), 2-methyl-4-pentanone (2-M4P), 2,6-dimethyl-4-heptanone (2,6-DM4H), 2-methyl-1-pentene (2-M1P), and tert-butylhydroperoxide (t-BuO₂H). FeCl₃ accelerated the formation of alkyl radicals for 2-MP and 2,4-DMP, alkyl and acyl radicals for 2-M4P and 2,6-DM4H, and alkyl radicals for 2-M1P. As no definite effect of FeCl₃ was observed for n-pentane and 2-octanone, FeCl₃ was assumed to attack saturated hydrocarbons, ketones at a tertiary carbon-hydrogen bond, and hydrocabons at an allylic hydroge, leading to easier photodegradations. FeCl₃ was also effective for the photodegradation of t-BuO₂H using λ >300 nm, so that FeCl₃ is believed to contribute also to the photodegradation of PP under the same irradation conditions. The catalytic effect of FeCl₃ in photodegradation seems to origirate in a redox reaction.