ESR as a Tool for the Study of Polymer Degradation

In this section we will illustrate the application of ESR methods in order to detect and identify polymer fragments, reactive intermediates, as well as reactive oxygen species that attack the polymer structure. Some examples are selected from studies of polymer degradation performed at the University of Detroit Mercy laboratory. 

1 Direct ESR detection of radicals formed during degradation 

Radicals can be detected by direct ESR if their concentration is stable and high enough during spectra acquisition. This condition is often fulfilled in the case of 

Simulation programs for the ESR line shapes of peroxy radicals for specific models of dynamics have been developed for the study of oxidative degradation of polymers due to ionizing radiation [66]. The motional mechanism of the peroxy radicals, ROO, was deduced by simulation of the temperature dependence of the spectra, and a correlation between dynamics and reactivity has been established. In general, peroxy radicals at the chain ends are less stable and more reactive. This approach has been extended to protiated polymers, for instance polyethylene and polypropylene (PP) [67], 

Ionomer membranes are used in fuel cells in order to separate the anode and cathode compartment and to allow the transport of protons from the anode to the cathode. The typical membrane is Nation , which consists of a perfluorinated backbone and side chains terminated by sulfonic groups. In the oxidizing environment of fuel cells, Nation , as well as other membranes, is attacked by reactive oxygen radicals, which reduce the membrane stability. Direct ESR was used recently in our laboratory to detect and identify oxygen radicals as well as radical intermediates formed in perfluorinated membranes upon exposure to oxygen radicals [73,74]. The three methods used to produce oxygen radicals in the laboratory and the corresponding main reactions are shown below. 

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