A new mechanism of benzophenone photoreduction in photoinitiated crosslinking of polyethylene and its model compounds
✍ Scribed by Baojun Qu; Yunhua Xu; Lunhan Ding; Bengt Rånby
- Publisher
- John Wiley and Sons
- Year
- 2000
- Tongue
- English
- Weight
- 174 KB
- Volume
- 38
- Category
- Article
- ISSN
- 0887-624X
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✦ Synopsis
The photolytic products and a new photoreduction mechanism of benzophenone (BP) as a photoinitiator in the photocrosslinking of polyethylene (PE) and its model compounds (MD) have been studied by means of fluorescence, ESR, 13 C and 1 H NMR spectroscopy. The fluorescence spectra from the PE and MD systems demonstrate that the main photoreduction product of BP (PPB) is benzpinacol formed by the recombination of two diphenylhydroxymethyl (K • ) radical intermediates. The ESR spectrum obtained from the UV irradiation of the MD/BP system gives positive evidence of K • radicals. Two new PPB products: an isomer of benzpinacol with quinoid structure, 1-phenyl-hydroxymethylene-4-diphenyl-hydroxymethyl-2,5-cyclohexa-diene and three kinds of ␣-alkylbenzhydrols have been detected and identified for the first time by 13 C and 1 H NMR spectroscopy from the MD systems. The latter could be formed by the reactions of K • radicals with alkyl radicals produced by hydrogen abstraction of the excited triplet state 3 (BP)* from polyethylene or its model compounds. These results provide new experimental evidence for elucidating the photoreduction mechanism of BP in the photoinitiated crosslinking of polyethylene.