Influence of functionalized S–SBR on silica–filled rubber compound properties

Styrene–butadiene–Rubber, SBR, is most often used in tread compounds in order to improve the Rolling Resistance (RR). The functionalized SBRs are used to increase the polymer–filler interaction in the compound to improve RR. In this study, the effect of different types of functional groups in SBR was investigated. Several types of functionalized S–SBR’s were synthesized by anionic polymerization: (i) SBR with an amine group at one end of the polymer chain, (ii) SBR with an alkoxy silane group at one end (iii) SBR with an amine group at one end and an alkoxy silane group at the other end of the polymer chain. A model reaction of silanization was conducted in a solvent to estimate how the amine functional group affects the silanization. Silica filled compounds were prepared with these SBR types. Payne effect and bound rubber measurement were done. The model silanization reaction of TESPT (Bis(triethoxysilylpropyl)tetrasulfide) with silica in the presence of amine shows that a higher amount of ethanol (EtOH) is released from TESPT compared to the amine free system. This result indicates that the silanization reaction can be accelerated by the presence of an amine functional group at the SBR polymer chain used in silica–filled compounds. The amine functionalized SBR and the alkoxy silane functionalized SBR show less Payne effect of the compounds which indicates that both functional groups can decrease the filler–filler interaction. More chemical bound rubber was obtained in branched SBRs compared to the corresponding linear SBRs. A branched polymer chain has a higher molecular weight compared to the linear type. Therefore, when one branched polymer chain reacts with silica or creates a silica–silane–polymer bond, more bound rubber can be obtained for the branched than for the linear type. The compound of the SBR with the alkoxy–silane functional group shows lower tan δ compared to the non–functionalized SBR and the amine functionalized SBR compounds. The influence of the type of functionalization of the SBR on tan δ at 70 °C was more significant in branched SBRs than in linear SBRs, due to the before–mentioned effect of the functional group on silanization and bound rubber.