Profluorescent nitroxides: Sensors and stabilizers of radical-mediated oxidative damage |
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Authors: | James P Blinco Tim Wade Graeme A George |
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Institution: | a ARC Centre of Excellence for Free Radical Chemistry and Biotechnology, Queensland University of Technology, GPO Box 2434, Brisbane Q4001, Australia b BlueScope Steel Research, PO Box 202, Port Kembla, NSW 2505, Australia |
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Abstract: | In this study, three profluorescent nitroxides 1,1,3,3-tetramethyldibenzoe,g]isoindolin-2-yloxyl (TMDBIO), 1,1,3,3-tetramethyl-2,3-dihydro-2-azaphenalene-2-yloxyl (TMAO) and 5-2-(4-methoxycarbonyl-phenyl)-ethenyl]1,1,3,3-tetramethylisoindoline-2-yloxyl (MeCSTMIO) were tested as probes for radical-mediated damage in polypropylene arising from both UV and thermally initiated sources. These nitroxides possess a very low fluorescence quantum yield due to quenching by the nitroxide group; however, when the free-radical moiety is removed by reaction with alkyl radicals (to give an alkoxyamine), strong fluorescence is observed. The results obtained from this profluorescent nitroxide trapping technique compare favourably with other methods of monitoring degradation, provided the appropriate probe is chosen for the conditions of oxidation, signalling an indication of damage well before other techniques show any response. The technique was also applied to the monitoring of crosslinked polyester coating resins. Differentiation in the oxidative stability of the resins was evident after as little as 200 min where other monitoring techniques require up to 300 h of accelerated degradation. This highlights the sensitivity of this method as well as demonstrating the scope of this technique to assess polymer stability. |
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Keywords: | Profluorescent nitroxide Fluorescence Polypropylene Crosslinked polyester Thermal oxidation Photo-oxidation |
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