Free Radical Reactions in Poly(methyl methacrylate) Films Monitored Using a Prefluorescent Quinoline−TEMPO Sensor
2003; American Chemical Society; Volume: 36; Issue: 10 Linguagem: Inglês
10.1021/ma0212994
ISSN1520-5835
AutoresAlexis Aspée, Olga Garcı́a, Luca Maretti, R. Sastre, J. C. Scaiano,
Tópico(s)Advanced Polymer Synthesis and Characterization
ResumoThe photochemical and photophysical properties of 4-(3-hydroxy-2-methyl-4-quinolinoyloxy)-2,2,6,6-tetramethylpiperidine-1-oxyl free radical (QT) have been studied as a prefluorescent probe to monitor free radical processes in polymer films. This methodology takes advantage of the efficient intramolecular quenching of the fluorescence of quinoline by the paramagnetic nitroxide, which is disabled when TEMPO reacts with carbon-centered radicals. The fluorescence intensity−time profile observed in the thermal decomposition of 2,2'-azobis(isobutyronitrile) (AIBN) in poly(methyl methacrylate) (PMMA) films showed initial increments in the fluorescence with time, according to the trapping of carbon-centered radicals by QT in the polymer films. Comparison of data under nitrogen and oxygen saturation conditions suggests that oxygen trapping of the carbon-centered radicals at 90 °C is about 20 times faster than reaction with nitroxides. The activation energy for AIBN decomposition in PMMA was measured as 34.1 kcal/mol. Analysis of the fluorescence lifetime distribution establishes the involvement of both static and dynamic fluorescence quenching of the diamagnetic reaction product by AIBN.
Referência(s)