The mechanism of Zinc(II)-Mediated Vulcanization Uncovered; Theoretical and Experimental Evidence.

The mechanism of cross-link formation in sulfur vulcanization mediated by bis(dimethyldithiocarbamato)zinc(II), ZDMC, has been uncovered, utilizing a combination of Density-Functional calculations and model experiments. These studies have revealed that, in a three-stage process, ZDMC exhibits a unique combination of catalytic activity: (1) It mediates the reaction between sulfur and rubber. This is achieved by incorporating sulfur atoms in the zinc-dithiocarbamate ring and inducing their insertion into an allylic C-H bond via an ene-like reaction. This ene reaction yields a rubber-bound polythiothiol and is only slightly endothermic, even though an activation energy of ~90 kJ mo