THE THERMAL-DECOMPOSITION OF SULFENAMIDE ACCELERATORS

The thermal decomposition of three sulfenamide accelerators N-cyclohexylbenzothiazole sulfenamide (CBS), 2- (4-morpholinothio) benzothiazole (MOR) and 2-t-butylaminobenzothiazole sulfenamide (TBBS) were investigated by differential scanning calorimetry. The sulfenamides decompose rapidly at 210-220-degrees-C, yielding a number of products, including reactive polysulfidic complexes. Thus, CBS gives N-cyclohexylamino-2-benzothiazole polysulfides (CBP), 2-bisbenzothiazole-2,2'-disulfide (MBTS), 2-bisbenzothiazole-2,2'-polysulfides (MBTP), 2-bisbenzothiazole-2,2'-monosulfide (MBTM), 2-mercaptobenzothiazole (MBT), and 2-N-cyclohexylaminobenzothiazole (CB). The polysulfides are unstable, and on prolonged heating, only MBT and CB remain. The amine fragment of the accelerator is present as the amine salt of MBT. At lower temperatures, the sulfenamides are relatively stable. MOR forms an analogous product spectrum. The decomposition of TBBS is endothermic, in contrast to the exothermic reaction observed with CBS and MOR, and the concentrations of the various polysulfides do not decrease on prolonged heating. Reaction mechanisms are proposed to account for the formation of the products. (C) 1994 John Wiley & Sons, Inc.