Vulcanization of isobutylene/isoprene copolymer (butyl rubber) using sulfur and organic accelerators is facilitated by the presence of the carbon-carbon double bond in the polymer isoprenyl unit. The low degree of unsaturation, usually in the order of 2%, necessitates use of ultra-fast accelerators such as tetramethyl thiuram disulfide (TMTD) or zinc dimethyldithiocarbamate (ZMDC). However, such accelerators can potentially form nitrosamines which may be undesirable. Due to the absence of a nitrogen atom in the xanthate structure such as in zinc diisopropylxanthate, nitrosamines cannot be formed during vulcanization. Furthermore, cure systems containing xanthates enable vulcanization over a broader range of temperatures not possible with some thiuram or thiourea containing cure systems. Many low temperature cure systems contain xanthates such as zinc diisopropyl xanthate (ZIX) or isopropylxanthate tetrasulfide (IXS_4). When xanthates are used in combination with sulfur and benzothiazyl disulfide (MBTS), compounds with satisfactory states of cure may be achieved. The desired physical properties which can be obtained by use of such accelerators, without loss on butyl rubber performance parameters such as impermeability, are discussed.
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