DETERMINATION OF HYDROPEROXIDE CONCENTRATIONS IN CROSS-LINKED POLYMER-COATINGS CONTAINING HINDERED AMINE LIGHT STABILIZERS

A procedure for measuring hydroperoxide concentrations in unstabilized , cross-linked polymer coatings as a function of weathering time has b een extended for use on coatings containing hindered amine light stabi lizers (HALS). The modification involves electron spin resonance spect roscopic measurements of the nitroxide concentration in HALS stabilize d coatings. Hydroperoxide concentrations are determined by correcting iodometric titration values for the contribution from nitroxide reduct ion by I-. The correction is usually small. This procedure has been us ed to compare hydroperoxide concentrations formed during weathering of unstabilized and HALS stabilized acrylic melamine and urethane cross- linked coatings. The reduction in hydroperoxide level with the additio n of HALS is consistent with longer-term infrared spectroscopic measur ements of carbonyl growth in these coatings. The results strongly sugg est that measurements of hydroperoxides formed during controlled 'outd oor-like' exposures can be used for the rapid evaluation of stabilized coating weatherability and the selection of effective HALS additives.