Early stages of p-phenylenediamine antiozonants reaction with ozone: Radical cation and nitroxyl radical formation
Early stages of p-phenylenediamine antiozonants reaction with ozone: Radical cation and nitroxyl radical formation
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DOI：
10.1016/j.polymdegradstab.2017.11.020
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发表时间：
2018-01-01
影响因子：
5.9
通讯作者：
Cataldo, Franco
中科院分区：
文献类型：
--
作者：
Cataldo, Franco
物理-化学考虑表明，N，N '-取代的对苯二胺（PPD）抗臭氧剂（AOZ）对二烯橡胶烯属双键的保护是由于它们的电离电位与烯属双键的电离电位相比非常低。因此，由PPD AOZ施加的臭氧清除作用是由于从PPD到臭氧分子的一个电子转移以及PPD自由基阳离子的形成。此外，一系列芳香胺（还包括N，N '-取代的PPD）与臭氧的反应速率的Hammett型曲线表明，臭氧氧化的结果是形成PPD自由基阳离子。本研究以三氯甲烷和邻二氯苯为溶剂，用臭氧氧化一系列常用的N，N '-取代PPD作为AOZ，并用电子自旋共振（ESR）研究了它们的氧化反应。收集了关于自由基阳离子的形成和随后作为PPDs自由基阳离子与臭氧自由基阴离子反应的结果的几乎定量的PPDs硝酰基自由基的形成的实验证据，并在实验上支持物理化学前提。在向PPD的硝酰基自由基溶液中加入三氯乙酸后，观察到硝酰基自由基的立即分解和稳定的PPD自由基阳离子的形成。
Physical-chemical considerations suggest that the diene rubber olefinic double bonds protection by N,N'-substituted p-phenylenediamines (PPDs) antiozonants (AOZs) is due to their very low ionization potential in comparison to the ionization potential of the olefinic double bonds. Thus, the ozone scavenging action exerted by PPDs AOZs is due to one electron transfer from the PPDs to the ozone molecule with the formation of the PPDs radical cation. Furthermore, Hammett-type plot of the reaction rate with ozone of a series of aromatic amines including also N,N'-substituted PPDs suggests that the result of ozone oxidation is the formation of PPDs radical cations. In the present study, a series of common N,N'-substituted PPDs used as AOZs in rubber compounds were oxidized with ozone in trichloromethane and/or o-dichlorobenzene solutions and studied with Electron Spin Resonance (ESR). Experimental evidences about the radical cation formation and the subsequent almost quantitative PPDs nitroxyl radical formation as a result of the reaction of PPDs radical cation with ozone radical anion were collected and support experimentally the physical-chemical premises. Upon addition of trichloroacetic acid to the PPDs nitroxyl radical solutions, the immediate decomposition of the nitroxyl radical and the formation of stabilized PPDs radical cation was observed.