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

Abstract

AbstractIn 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.