UNDERSTANDING THE CHEMISTRY OF THE RUBBER/SILANE REACTION FOR SILICA REINFORCEMENT, USING MODEL OLEFINS

摘要

Although bifunctional organosilanes, particularly bis-(triethoxy-silyl-propyl) tetrasulfide (TESPT), are very efficient silica-rubber coupling agents, a high level is required to realize an optimum balance of processing as well as other performance characteristics. As to the functionality of TESPT in silica stocks, till today there remain numerous speculations rather than a clear understanding. An investigation has been carried out to understand the mechanism of the coupling of TESPT with rubber using a model olefin 2,3-dimethyl-2-butene (TME). Reverse Phase High Performance Liquid Chromatography in combination with Mass Spectroscopy shows that when pure TESPT is heated at 140℃, the concentration of higher S-ranks in TESPT decreases, but in the presence of S{sub}8 the concentration of higher S-ranks increases. Treating TME with TESPT at 140℃ yields a mixture of crosslink products differing in the length of the sulfur-link. A mechanistic model for the reaction of TESPT with rubber is proposed, where TESPT donates activated sulfur-radicals, which can react with the rubber or model compound without the need for additional accelerators or vulcanizing agents. As ZnO plays no role in this mechanism, the TESPT merely acts as a sulfur-donor, not in the sense of an accelerator.