The use of an accelerator based on diisopropyl xanthogen polysulfide (DIXP) to formulate bromobutyl elastomer (BIIR-DIXP) compositions for sealing medical devices was published in the Journal of Applied Polymer Science (Ohbi, D. S.; Pureval, T. S.; Shah, T.; Siores, E. 2007, 106, 526). In this publication, a reaction scheme for the DIXP accelerator in situ with BUR is proposed. It is based on the evolved volatile chemical species determined during the curing reaction of BIIR-DIXP composition, and is formulated in the light of generally accepted mechanism of crosslinking elastomers using sulfur-based accelerators. The volatile chemical species were determined using coupled thermogravimetric infrared analysis (TGA-IR) and head space gas chromatography mass spectroscopy (GC-MS) analysis. The main volatiles evolved during the curing reaction were carbonyl sulfide, carbon disulfide, and isopropyl bromide. These are considered to be associated with the formation of the active rubber-bound DIXP sulfurating species required for the crosslinking reaction. Analysis of the acetone extract of cured BIIR-DIXP also showed that the DIXP is totally consumed during the cure reaction, and the formulation is largely free of cure reaction byproducts. (C) 2007 Wiley Periodicals, Inc.