Reactions in silica/silane compounds with functionalized SBRs

Functionalized SBR are widely used for modern passenger car tire tread compounds. The functional groups are introduced in a silica / silane-filled SSBR to enhance the polymer-filler interactions, however, what kind of reactions take place compound in the presence of the functionalized SBR were not clarified yet. In this study, the different possible interaction / coupling reactions in a silica/silane compound with functionalized SBRs were investigated. 3 types of SBRs (non-functionalized SBR as reference and two types of functionalized SBRs) were prepared for this study. These SBRs were mixed with non-sulfur silanes and sulfur containing silanes in the tread compound formulation. The Payne effect measurement and the bound rubber measurement were performed to investigate the polymer-filler interactions in each uncured compound. The Payne effect is much lower in the presence of the sulfur containing silanes for the non-functionalized SBR compared to the compound with nonsulfur silanes. However, this strong tendency was not observed for the functionalized SBRs. This result indicates that the functional groups in SBR can react with the alkoxy silyl groups in silanes and already create a covalent bond which can increase the polymer-filler interactions. For the functionalized SBRs, the amount of chemical bound rubber was higher in the non-sulfur silane filled compound compared to the compound without silane. This phenomenon was not observed in the non-functionalized SBR compounds. These results indicate that there is a reaction between the alkoxy silyl group in silane on the surface of silica and the alkoxy silyl group in functionalized SBR. The chemical bound rubber increased further in the presence of the sulfur containing silanes. The presence of sulfur in silanes increased the bound rubber content further due to the reaction between polymer and sulfur in silanes. The higher tensile modulus in the non-sulfur silane filled compound with functionalized SBR compared to that of the non-functionalized SBR implies the increased polymer-filler interactions caused by the reaction between the functionalized SBR and silanes.