CANCELLED: Insights Into the Sulfur Cure Chemistry of Bromobutyl Rubber Via Model Compound Studies

Sulfur vulcanization has been used for over 50 years in the tire industry for curing bromobutyl rubber (BIIR), and over 500,000 tonnes of BIIR are cured this way every year in the production of tires.  And yet after all these years, the fundamental chemical mechanism is still largely a mystery due to the difficulty in studying the reaction in the solid state.  To this end, the sulfur cure chemistry of  BIIR was studied using a model compound, brominated 2,2,4,8,8-pentamethyl-4-nonene (BPMN).  The reaction of BPMN with S₈ produced bisallylic polysulfides of various ranks, yielding sulfur bromide intermediates that likely contributed to the rapid oxidation of allylic sulfides into thiophenes.  Reductive cure reversion to pentamethylnonene was also observed in the latter stages of vulcanization.  The reaction of 2,2-dithiobisbenzothiazole with BIIR and BPMN produced a stable adduct that reduced the concentration of allylic bromide available for vulcanization.