Profluorescent nitroxide

Monitoring Free Radical Reactions in Degrading Polymers with a Profluorescent Nitroxide... 

Figure 3 shows the CL - time profile for samples of PP containing different concentrations of the profluorescent nitroxide TMDBIO. The CL curve for unstabilized PP shows that after a very short time, there is an exponential increase in CL corresponding to rapid oxidation and embrittlement of the polymer. The effect of the added nitroxide is not to decrease totally the CL from the PP, but rather to retard the emission so that there is a slower development of the CL emission intensity. There is thus an increase in the time taken to see the exponential increase in emission intensity, but the emission is not reduced to zero in this retardation period. In contrast, if a peroxy-radical scavenging, hindered phenol such as Irganox 1010 were to be added to the PP then the increase with time of the CL intensity would be totally suppressed and there would be an apparent induction period 8), This result may be interpreted within the framework of the free-radical reactions in Figures 1 and 2 above. 

The use of a profluorescent nitroxide, in this case the phenanthrene analog TMDBIO, offers the prospect of not only quantifying the alkyl radical scavenging efficiency in the earliest stages of polyolefin oxidation (in the retardation period) as demonstrated here, but also integration over time of the total alkyl radical population formed on oxidation. Future prospects include imaging of the zones of degradation by fluorescence microscopy. 

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