Vulcanization Chemistry. Sulfur, Nt-Butyl-2-Benzothiazole Sulfenamide Formulations Studied by High Performance Liquid Chromatography

Abstract

Abstract The paper reports on the sulfur vulcanization chemistry of cis-polyisoprene formulations accelerated with N-t-butyl-2-benzothiazole sulfenamide. High Performance Liquid Chromatography (HPLC) is utilized to examine the kinetics of accelerator—sulfur disappearance and the formation—disappearance profiles of extra-network cure intermediates across the vulcanization process. Cure profile measurements are reported on three formulations covering a wide range of sulfur—accelerator ratios. Also unique aspects of the analytical methodology are highlighted. The observed cure-intermediate concentration profiles reinforce earlier theories about the chemical details of sulfurization and subsequent crosslinking. On all formulations, benzothiazole polysulfides (S1−S4) reach a maximum concentration at the scorch midpoint coincident with slope changes in reactant and product profiles. Although pendant-accelerator crosslink precursors are not measured directly, their presence is implied from material balance calculations. Also, the formation of a small amount of benzothiazole early in the scorch period is a new observation in sulfenamide acceleration. It suggests that accelerator hydrolysis is a competitive side reaction early in the vulcanization process.