Sulfur vulcanization of polyisoprene accelerated by benzothiazole derivatives. I. Comparison of sulfur and 2‐mercaptobenzothiazole accelerated reactions

Polyisoprene compounds with sulfur and with sulfur and 2‐mercaptobenzothiazole (MBT) were vulcanized by heating in a differential scanning calorimeter (DSC) at a programmed rate. The reaction was stopped at various temperatures along the thermogram and the product analyzed by determining the crosslink density and crosslink type, and by determining the amount of extractable curatives and soluble reaction products by high‐performance liquid chromatography. DSC cure curves and plots of crosslink density and extractable sulfur vs. temperature for the unaccelerated and MBT accelerated compounds can be made to coincide by shifting them along the temperature axis. It is suggested that MBT accelerated sulfur vulcanization occurs by the same mechanism as unaccelerated sulfur vulcanization, with SH + ions from MBT adding across the carbon–carbon double bond, thus increasing the rate at which the reaction is initiated.