Assessment of the photodegradation tendency of coatings and components by ESR spectroscopy

 
The earliest possible messengers of onset of photodegradation are radicals. If it is possible to quantify the tendency of light-induced radical formation in coatings or in their components, conclusions can be drawn on the photodegradation resistance of these systems in the early weathering stages. ESR spectroscopy is a highly sensitive method for the detection of paramagnetic compounds, including radicals. This method has been used mainly in basic research and required a high expenditure on equipment. Meanwhile, there are also cost-effective spectrometers that can be operated with moderate effort. The present work describes the possibilities and limitations of a new method by which coatings or their components can be quantitatively characterized by ESR spectroscopy with respect to their tendency to radical formation under light exposure. This method essentially involves a suitable sample preparation, the insertion of an internal standard as well as an in situ irradiation under temperature control. "