New insights on the anti-skinning effect of methyl ethyl ketoxime in alkyd paints

Abstract

In order to shed light on the role of oxime additives as blocking agents of the cobalt-catalyzed autoxidative drying in alkyd paints, various techniques have been applied. Spectroscopic studies (Vis-NIR, ¹H NMR) of different model solutions show, together with investigations on the coordination chemistry of cobalt salts with oximes, that only weak interactions between cobalt and oximes can be evidenced; in several cases the residual water that is present is a stronger ligand than oximes for the cobalt ion. From CoCl₂ and methyl ethyl ketoxime (meko) the highly unstable complex [Co(meko)Cl₂]_n has been isolated. The polymerization inhibition properties of different oximes were studied by TR-FTIR and SEC techniques. From EPR and GC-MS model experiments, it has been established that the free radicals formed in the coating compositon may readily add to the CN double bond of the oxime, producing stable radical addition products that could inhibit further free radical chain reactions.