Degradation processes, electron spin resonance

Electron paramagnetic resonance spectroscopy (EPR) (also called electron spin resonance spectroscopy, ESR) has been scarcely applied in the field of art and art conservation. Some work can be found in which EPR is used as complementary technique to SEM-EDX, NMR, and mass spectrometry (MS) for studying free radicals occurring in polymerization, pyrolytic, oxidative, and other radical degradative processes in artwork, as well as in the characterization of varnishes and oleoresinous media [42]. 

In the photodegradation process of PVC, the involvement of free radicals has been extensively documented. The applications of electron spin resonance, ESR, spectroscopy have revealed some details in the degradation mechanism (5, 6). However, the potential applications of ESR spectroscopy in this area are far from being exhaustively exploited. For instance, in the initial step of the photodegradation of PVC, one would expect "Radical I" to be a predominant radical (8) ... 

Characterization of the chemical structure of highly cross-linked polymers, and of the chemical changes that accompany degradation processes, relies on spectroscopic methods. Solid-state nuclear magnetic resonance techniques have the potential to allow a more detailed characterization than before possible of the chemical environment and structure of chemical crosslinks in elastomers and thermoset epoxies. Degradation processes in cross-linked systems have been studied by using infrared spectroscopy, solid-state NMR, and electron spin resonance. 

The oxidative degradation of isotactic PP in the presence of air (as well as the postradiation oxidation) takes place frequently in industrial irradiation processes. The estimation of peroxy radicals, formed as a direct product of radiolytic oxidation reactions between oxygen and carbon-centred free radicals, is very useful in understanding the oxidation process. The application of electron spin resonance (ESR) is a practical method to follow the quantitative effect of this process [2],... 

Id and 2d Electron Spin Resonance Imaging (ESRI) of Transport and Degradation Processes in Polymers... 

Electron spin resonance is a powerful tool for free radical studies. Applications of ESR spectroscopy to polymers are specific and often almost exclusive in various sectors of the physico-chemical characterisation of polymers and processes (Table 1.36). ESR spectroscopy offers a unique technique to study the role of radical species as intermediates in both polymerisation and polymer degradation processes. In particular, ESR spectroscopy enables measurement of radical concentrations [781] and is therefore... 

Electron spin resonance spectroscopy offers a unique technique to study the role of radical species as intermediates in both polymerization and polymer degradation processes. The technique has been developed significantly since its introduction to chemical applications in the 1950s [1], with major advances in the stability of the magnetic field, in the sensitivity to low radical concentrations— and hence the limit of detection and measurement—and in data collection and manipulation. ESR spectrometry enables both the identification of radicals and the measurement of their concentration. It is a non-destructive technique and spectra can be recorded both during polymerization, and, in suitable circumstances, during degradation of polymers [2]. 

Schlick, S. and Motyakin, M.V. (2004) ID and 2D electron spin resonance imaging (ESRI) of transport and degradation processes in polymers, in Instrumental Methods in Electron Magnetic Resonance. Biolcgical Magnetic Resonance, vol. 21 (eds... 

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