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

✍ Scribed by B. Morgan; W. J. McGill

• Publisher: John Wiley and Sons
• Year: 2000
• Tongue: English
• Weight: 178 KB
• Volume: 76
• Category: Article
• ISSN: 0021-8995
• DOI: 10.1002/(sici)1097-4628(20000531)76:9<1386::aid-app3>3.0.co;2-9

✦ Synopsis

2,3-Dimethyl-2-butene (TME) was used as a model compound for polyisoprene in 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°C for various times and the reaction intermediates and products analyzed by HPLC. In the absence of sulfur, even though MBT and ZnO react to form bis(2-mercaptobenzothiazole)zinc(II) [Zn(mbt) 2 ], no crosslinking resulted. On addition of sulfur, the (incomplete) conversion of MBT and ZnO to Zn(mbt) 2 permitted vulcanization from the outset. Benzothiazole-terminated pendent groups were not detected, and crosslinking is proposed to occur via pendent groups that incorporate zinc. It is proposed that polysulfidic Zn(mbt) 2 reacts with TME to form zinc-containing pendent groups and MBT. These zinc-containing pendent groups are highly reactive and react with TME to form crosslinked products and MBT. The reaction was more rapid and the induction period prior to crosslinking 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 zinccontaining pendent groups. MBT released during Zn(mbt) 2 -initiated crosslinking would, in part, contribute to crosslinking via TME-S x H.