A new mechanism of benzophenone photoreduction in photoinitiated crosslinking of polyethylene and its model compounds
A new mechanism of benzophenone photoreduction in photoinitiated crosslinking of polyethylene and its model compounds
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DOI：
10.1002/(sici)1099-0518(20000315)38:6
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发表时间：
2000-03
期刊：
影响因子：
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通讯作者：
B. Qu;Yunhua Xu;L. Ding;B. Rånby
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文献类型：
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作者：
B. Qu;Yunhua Xu;L. Ding;B. Rånby
用荧光、ESR、~(13)C和~1H核磁共振研究了二苯甲酮(BP)作为光引发剂在聚乙烯(PE)及其模型化合物(MD)光交联反应中的光解产物和新的光还原机理。PE和MD体系的荧光光谱表明，BP(PPB)的主要光还原产物是由两个二苯基羟甲基(K·)自由基中间体复合而成的苯并品酚。MD/BP体系紫外光照射的ESR谱给出了K·自由基的积极证据。通过~(13)C和~1H核磁共振谱首次从MD系统中检测和鉴定了两个新的PPB产物：具有喹类结构的苯并品酚异构体、1-phenyl-hydroxymethylene-4-diphenyl-hydroxymethyl-2，5-cyclohexa-diene和三种α-烷基苯并氢化合物。后者可通过K·自由基与聚乙烯或其模型化合物中激发三重态3(BP)*的抽氢生成的烷基自由基反应而形成。这些结果为阐明BP在聚乙烯光引发交联反应中的光还原机理提供了新的实验证据。©2000 John Wiley&Sons，Inc.J Polym Sci A：Polym Chem 38：999-1005,2000
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, 13C and 1H 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 α-alkylbenzhydrols have been detected and identified for the first time by 13C and 1H 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. © 2000 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 38: 999–1005, 2000