Effect of carboxylic acids on 2-bisbenzothiazole-2,2 '-disulfide- and tetramethylthiuram disulfide-accelerated sulfur vulcanization. II. Vulcanization of polyisoprene in the absence of ZnO

Polyisoprene was vulcanized by 2-bisbenzothiazole-2,2'-disulfide (MBTS)/sul fur and tetramethylthiuram disulfide (TMTD)/sulfur in the absence and prese nce of benzoic and stearic acids. It was found that the crosslink density o f MBTS vulcanizates is halved by the addition of carboxylic acids and this can be explained in terms of the attack of the acids on the accelerator pol ysulfides. TMTD polysulfides are more reactive toward polyisoprene than are MBTS polysulfides, and their addition to the polymer chain occurs before s ignificant attack by the carboxylic acids can reduce the polysulfide concen tration. Consequently, the acids have little effect on the crosslink densit y of TMTD vulcanizates. (C) 1999 John Wiley & Sons, Inc.