Zinc accelerator complexes.: Versatile homogeneous catalysts in sulfur vulcanization Original Research Article

This paper reviews homogeneous catalysis during the sulfur vulcanization of rubber by zinc dithiocarbamates and zinc mercaptobenzothiazolates. By means of quantumchemical calculations and model studies, individual reaction steps of the vulcanization reaction sequence have been studied in detail. This has revealed that zinc accelerator complexes, such as the zinc dithiocarbamates and mercaptobenzothiazolates homogeneously catalyze a multitude of reactions during sulfur vulcanization. Among these are the formation, desulfuration, but also the degradation, of sulfur cross-links. In addition it could be shown that under oxidative conditions these zinc complexes catalyze the formation of diene and triene structures in the rubber. The zinc complexes are able to effect these reactions by (a) their ability to incorporate and activate sulfur atoms and (b) their Lewis acidity, which enhances the reactivity of sulfur vulcanization intermediates.