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

摘要

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 coordiantion chemistry of cobalt salts with oximes, that only weak interactions between cobalt and oximes can be evidence; in several cases the residual water that is present is a stronger ligand than oximes for the cobalt ion. From CoCl_2 and methyl ethyl ketoxime (meko) the highly unstable complex [Co(meko)Cl_2]_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 composition may readily add to the C=N double bond of the oxime, producing stable radical addition products that could inhibit further free radical chain reactions.