Accelerator sulfenamide polysulfide

GradweU and McGill argued that sulfenamide decomposition upon heating formed various products such as MBTS, MBTP, MBT, sulfenamide polysulfides, and aminobenzothiazoles due to dissociation of S—N bond in the sulfenamide, and S—S or S—C bond in MBTS and its derivatives [183]. Typical sulfenamide accelerators are benzothiazole + sulphur + amine... 

In the absence of zinc oxide, cross-linking proceeds through an accelerator polysulfide. With TBSI (14) and other sulfenamides, the accelerator decomposes upon heating during the induction period (before cross-linking) as shown in Figure 2 (13). 

Thus, one theory for delayed action is the quenching of free radical crosslink precursors by monomeric polysulfides. It has been found that, if bisalkylpolysullides are mixed with uncured rubber stocks, more delay results. It is also been shown that the early reaction products formed by the interaction between accelerator and sulfur (Ac-S -Ac) are inhibitors of crosslink formation. The very substances that give rise to the formation of the crosslink precursor (rubber-Sjc-Ac) inhibit the formation of the crosslinks. We note that other mechanisms for delayed action have been proposed. In the case of acceleration by benzothiazolesulfenamides, the accelerator is depleted in an autocatalytic fashion with the formation of 2-mercaptobenzothiazole (MET). The rate of this depletion is about proportional to the amount of MET present. There is strong evidence, which indicates that the following reactions occur in sulfenamide-accelerated systems ... 

---