Profluorescent nitroxide sensors for monitoring the natural aging of polymer materials

The utility of profluorescent nitroxides (PFNs) as sensitive probes to detect early stage photodegradation in a cyclic olefin copolymer, TOPAS®, during both natural aging and accelerated aging under laboratory conditions is reported. PFN additives in TOPAS® capture radicals to form fluorescent adducts as the material degrades. The levels of fluorescence detectable from the polymer reflect the degree of free-radical degradation in the material, with the PFN probes delivering enhanced sensitivity over traditional analytical methods for the detection of photodegradation of TOPAS®. The probes are able to highlight polymer degradation occurring within the oxidation “induction” period, where little change can be observed using infrared spectroscopy; however, their efficacy does not extend far beyond this period. The effective probe lifetime however can be significantly extended through the use of common additives such as the UV absorber (Tinuvin P) and a hindered amine stabiliser analogue (1,1,3,3-tetramethylisoindol-2-yloxyl, TMIO).