Sulfenamides, vulcanization agents

For halobutyl rubbers, zinc oxide is used as the vulcanizing agent with low levels of sulfur stearic acid and sulfenamide accelerators. Bromobutyl rubber shows higher cure reactivity than chlorobutyl rubber. Both CIIR and BUR will cure with zinc oxide, but only BUR will cure with sulfur alone, no zinc oxide or accelerator being necessary. Bromobutyl rubber can be cured with 0.5 phr of sulfur and 1.3 phr of dibenzothiazyl disulfide accelerator, 3 phr of zinc oxide and 1 phr of stearic acid. Levels of sulfur as low as 0.5 phr will give a rapid and reasonable degree of cure. Zinc diethyl dithiocarbomate (ZDC) accelerator can be used in small quantities (0.25-0.75 phr) with zinc oxide for heat resistant products, and to improve compression set. 

The filler/silane intermediate can now react with the allyl position of unsaturated sites on the polymer chain. The vulcanization of rubber is known to proceed via reaction of an accelerator, such as a sulfenamide, with sulfur, zinc oxide, and stearic acid, to generate a sulfurating agent (Bateman et al., 1963). 

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