Role of additives in cobalt-mediated oxidative crosslinking of alkyd resins

Spectroscopic and chromatographic studies have been carried out to investigate the interaction between bis(acetylacetonato)cobalt(II) and pyrazole ligands as possible anti-skinning additives, and their role in the oxidative crosslinking reactions has been tested. From experimental results (UV-Vis, TR-FTIR, SEC) it has been concluded that Co(acac)(2) can be used as drier promoter for alkyd paints and its catalytic activity is similar to that of the actual commercial drier (Co Nuodex). The presence of pyrazole ligands as anti-skinning additives precludes association of Co(acac)2 that usually occurs in nonpolar media and it facilitates the formation of stable coordinated ROO. radicals, that inhibit the radical chain reaction. From EPR results it has been established that the stability of the [Co-III(acac)(2)(ROO.)L](+) complex radicals is highly dependent of the molar ratio between the cobalt catalyst and the organic additive L. The dependence of anti-skinning activity on the concentration of the pyrazole additives has been studied and a mechanism of inhibiting properties of azoles on the oxidative crosslinking reactions has been proposed. (C) 2003 Elsevier B.V. All rights reserved.