Determination of active HALS in weathered automotive paint systems I. Development of ESR based analytical techniques

Two analytical techniques based on electron spin resonance spectroscopy hav e been developed to estimate the longevity of hindered amine light stabiliz er (HALS) additives in clearcoat/basecoat paint systems at long exposure ti mes. The first technique is based on determination of the steady-state conc entration of nitroxyl radical in weathered clearcoats. The second one is ba sed on determination of the concentration of clearcoat HALS transformations products that can be oxidized to nitroxyl radical by p-nitroperbenzoic aci d in methylene chloride at 20 degrees C. The two techniques provide complim entary information. Both techniques are used to estimate HALS longevity in four weathered clearcoat/basecoat/primer/electrocoat automotive paint syste ms. (C) 2000 Elsevier Science Ltd. All rights reserved.