Electron Paramagnetic Resonance (EPR) is a spectroscopic technique sensitive and selective to paramagnetic compounds. Since a large number of depolymerization processes occurs through radicalic mechanisms, detection of intermediate radical species through EPR is particularly important for elucidating the depolymerization mechanism. The radical intermediates formed during the process are often short-lived and cannot be directly observed on a typical EPR time scale. In this case spin traps can be used, consisting in molecules highly reactive towards radical species, which give rise to stable EPR-detectable radicals. The hyperfine splitting patterns allow to identify the trapped radicals. The lineshape analysis of the signals provides information about radical mobility, related to the viscosity of the polymeric medium. Our in-situ setup, including a home-built EPR resonator, allows to monitor the reactions at high temperatures, control the reaction atmosphere and is therefore of crucial importance for obtaining information relevant for the operational reaction conditions.
This overview covers several examples of EPR studies on depolymerization in which our group is involved, including thermally, chemically and optically induced depolymerization for such diverse applications as, for instance, visible light-induced recycling of commercial polymethacrylates [1] and oxidative degradation of aromatic hydrocarbon-based proton-exchange fuel cell membranes. [2]
EPR has proven to be a powerful method for gaining valuable mechanistic and structural insights into depolymerization processes.
1. H. S. Wang et al., Science 387, 874.
2. T. Nemeth et al., J. Phys. Chem. C 2022, 126, 37, 15606–15616.