Effect of DPG on Silanization Chemistry of Silica in Rubber Processing

Silane chemistry plays an important role in reinforcement of silica filled rubbers. It is well known that the silanization reaction is accelerated by an amine compound, in particular 1,3-diphenyl-guanidine (DPG). In the present study the effect of DPG on the kinetic parameters is investigated by model experiments in presence of n-decane. The reaction rate constant of Bis(tri-ethoxysilyl-propyl)tetrasulfide (TESPT) with silica increases by a factor of six and the activation energy Ea decreases till one third in the presence of DPG. The influence of DPG on the reactions between TESPT and two unsaturated model-olefins: 2,3-dimethyl-2-butene(TME) and 3-methyl-1-pentene(3-m-1-p), and between TESPT and DPG in absence of silica is also investigated using model experiments and subsequent analysis with LC-MS. Even without free elemental sulfur present, the amount of cross-linked products between the model olefins significantly increases in the presence of DPG. The tri-sulfide isomer of TESPT significantly increases in the presence of DPG, which contributes to a sulfur-donor

effect of TESPT. Additionally, the LC-MS experiments demonstrate that the presence of DPG accelerates the silane/model olefins coupling, and that DPG itself also reacts with TESPT during processing. Therefore, a significant amount of DPG could be consumed during regular rubber processing due to this mutual TESPT-DPG reaction.