Abstract The chemical microstructural changes of an accelerated sulfur cure of IIR with TMTD/ ZnO/sulfur have been elucidated. No reaction occurs in the isobutylene units. Isomerization occurs at the initial stages of vulcanization and reaches an equilibrium at 30–35 min. Sulfurization initially results in III and VI and is polysulfidic in nature. At cure times greater than 75 min, desulfurization of III and VI occurs and mono- and poly-sulfidic sulfurization giving IV and VII occurs. The reaction rate of III and VI is much greater than that of IV and VII. Equilibrium swelling measurements have been shown to correlate with rheometry measurements for this system and have shown that polysulfldic III and VI correlate with an increase in properties, while mono- and poly-sulfldic IV and VII correlate with reversion. No migration of the double bond, saturation, internal cyclization, or sulfurization resulting in V and VIII were observed.