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81.
2,6-Di-tert-butyl-4-methylphenol (1) , a polyolefin processing stabilizer, is transformed during the stabilization process primarily into 2,6-di-tert-butyl-4-methyl-phenoxyl (2) . The important consecutive transformation pathway of 2 involves irreversible C? C coupling giving 4,4′-ethylenebis(2,6-di-tert-butylphenol) (8) and reversible C? C coupling accounting for formation of 2,6-di-tert-butyl-4-methyl-4-(3,5-di-tert-butyl-4-hydroxybenzyl)-2,5-cyclohexadiene-1-one (9) . The stepwise transformation of 9 into the parent phenol 1 , the stable dimer 8 and a variety of other products was found in EPR and chromatographic studies of free radical and molecular products generated from 9 in oxidative environment. It follows that compounds 1, 8 and 9 are stepwise transformed into coloured quinoide and quinonemethinoide compounds in the ultimate phase, and the antioxidant chain-breaking character of 1 is thus lost. It is considered that most of the free radical species formed transiently during transformation of 1 and/or of derived phenolic coupling products disappear from the system via disproportionation and alkylperoxy radicals (RO2) or oxygen trapping. Labile, cross-conjugated, peroxidic species generated by the latter process contribute to the fragmentation of coupling products. 相似文献
82.
Ralf Peter Edith Mder Manfred Rtzsch Jana Kovova Jitka Rotschov Jan Pospíil 《大分子材料与工程》1991,184(1):167-181
For the purpose of being compounded with glass fibres, homopolymers and polypropylene chemically functionalized in different ways were characterized with regard to their thermooxidative and photooxidative stabilities, after having been subject of different manners of stabilization. Consequently, in the basic state and after short ageing times, the compounds stabilized with 0.10% BHT, 0.30% DSTP, 0.05% Irganox 1010, and 0.25% Tinuvin 770 exhibit the best thermooxidative and mechanical stabilities. This effect is lost with increasing periods of ageing. Concerning the modifier it can be said that the samples functionalized with a mixture of acrylic acid and maleic anhydride in 5 : 1 ratio show the best thermooxidative and mechanical behaviour; on the other hand, the photooxidative behaviour is the worst. Pure maleic anhydride modifier leads to a significant worsening of the thermooxidative and mechanical properties, the UV stability is not changed against the unmodified samples. Glass fibres cause a significant improvement of the compound properties — particularly when applying a modifier —, a considerable retardation of the thermooxidation period as well as a decrease of the photostability. The latter influence is, however, not completely clear. 相似文献
83.
Li ZH Velisek J Zlabek V Grabic R Machova J Kolarova J Li P Randak T 《Journal of hazardous materials》2011,185(2-3):870-880
In this study, the toxic effects of verapamil (VRP) were studied on juvenile rainbow trout, Oncorhynchus mykiss, by chronic semi-static bioassay. Fish were exposed to sublethal concentrations of VRP (0.5, 27 and 270 μg/L) for 0, 21 and 42 d. Multiple biomarkers were measured, including morphological indices, hematological parameters and antioxidant responses of different tissues (brain, gill, liver, muscle and intestine). Based on the results, there was no significant change in all parameters measured in fish exposed to VRP at environmental related concentration, but VRP-induced stress in fish exposed to higher concentrations reflected the significant changes of physiological and biochemical responses. Through principal component analysis and integrated biomarker response assessment, effects induced by VRP-stress in each test group were distinguished. Additionally, all parameters measured in this study displayed various dependent patterns to VRP concentrations and exposure time using two-way ANOVA statistic analysis. In short, the multiple responses in fish indicated that VRP induced physiological stress and could be used as potential biomarkers for monitoring residual VRP in aquatic environment; but molecular and genetic mechanisms of these physiological responses in fish are not clear and need to be further studied. 相似文献
84.
Holzer Jakub Husťák Miroslav Hegrová Jitka Gröger Roman 《Metallurgical and Materials Transactions A》2023,54(2):439-449
Metallurgical and Materials Transactions A - Experimental studies on single crystals of pure metals are essential for understanding the mechanisms governing their plastic deformation as well as for... 相似文献