Benzothiazole-accelerated sulfur vulcanization. II. 2-mercaptobenzothiazole/zinc oxide and bis(2-mercaptobenzothiazole)zinc(II) as accelerators for 2,3-dimethyl-2-butene

2,3-Dimethyl-2-butene (TME) was used as a model compound for polyisoprene i n a study of 2-mercaptobenzotiazole (MBT)-accelerated sulfur vulcanization in the presence of ZnO. Mixes of curatives and TME were heated isothermally in evacuated sealed glass ampules at 150 degrees C for various times and t he reaction intermediates and products analyzed by HPLC. In the absence of sulfur, even though MBT and ZnO react to form bis(2-mercaptobenzothiazole)z inc(II) [Zn(mbt)(2)], no crosslinking resulted. On addition of sulfur, the (incomplete) conversion of MBT and ZnO to Zn(mbt)(2) permitted vulcanizatio n from the outset. Benzothiazole-terminated pendent groups were not detecte d, and crosslinking is proposed to occur via pendent groups that incorporat e zinc. It is proposed that polysulfidic Zn(mbt)(2) reacts with TME to form zinc-containing pendent groups and MET. These zinc-containing pendent grou ps are highly reactive and react with TME to form crosslinked products and MET. The reaction was more rapid and the induction period prior to crosslin king was removed on increasing the MBT concentration in the system. This is ascribed to an exchange reaction between Zn(mbt)(2) and MBT polysulfides, formed by the interaction of MBT with sulfur, leading more rapidly to high concentrations of polysulfidic Zn(mbt)(2) and, hence, to zinc-containing pe ndent groups. MBT released during Zn(mbt)(2)-initiated crosslinking would, in part, contribute to crosslinking via TME-SxH. (C) 2000 John Wiley & Sons , Inc. J Appl Polym Sci 76: 1386-1394, 2000.