Benzothiazole-accelerated sulfur vulcanization. I. 2-Mercaptobenzothiazole as accelerator for 2,3-dimethyl-2-butene

2,3-Dimethyl-2-butene (TME) was used as a model compound for polyisoprene in a study of 2-mercaptobenzothiazole (MBT)-accelerated sulfur vulcanization. Mixes that contained curatives only were heated in a DSC to various temperatures, while those that also contained TME were heated isothermally at 150°C in evacuated, sealed glass ampules. Heated mixtures were analyzed for residual curatives, intermediates, and reaction products by HPLC. It is proposed that MBT forms polysulfidic species (BtSxH) in the presence of sulfur and that these react with TME via a concerted, substitutive reaction pathway to form polysulfidic hydrogen-terminated pendent groups of varying sulfur rank (TME–SxH). MBT is released as a by-product of this reaction. Crosslinking occurs slowly as a result of the interaction of polythiol pendent groups, the rate being dependent on the pendent group concentration. H2S is released on crosslinking. 2,3-Dimethyl-2-butene–1-thiol was synthesized and reacted in the presence of sulfur to confirm the formation of crosslinked products (TME–Sx–TME). Benzothiazole-terminated pendent groups (TME–SxBt) were not observed.