Homogeneous zinc(II) catalysis in accelerated vulcanization I. Reaction-stage modeling and cross-link formation

This paper reports a never approach for the study of the mechanism of accel erated vulcanization, namely, Reaction-Stage Modeling (RSM). By carefully s tudying the reactivity of relevant model compounds under selected condition s, detailed knowledge about a particular reaction stage of vulcanization ca n be obtained. Background, experimental details and synthesis of model comp ounds are described. An RSM study after cross-link formation in the thiuram- and dithiocarbamate type vulcanization has been performed, and the role of zinc compounds here in was investigated. In contrast to earlier studies, it has appeared that a t 140 degrees C, cross-links form from cross-link precursors solely via dis proportionation. Allylic substitution was not observed. Zinc compounds act as catalysts for disproportionation, but especially ZDMC can be regarded as an efficient, soluble molecular turntable for sulfur atoms.