Structural and mechanical properties of styrene–butadiene rubber/silica composites with an interface modified in-situ using a novel hindered phenol antioxidant and its samarium complex

In this study, a novel hindered phenol antioxidant with thioether and carboxy groups (GMMP) and its samarium complex (Sm-GMMP) were employed as an interfacial modifier for styrene-butadiene rubber/silica (SBR/SiO2) composites. The curing properties, filler dispersion, rubber–filler interfacial interaction, and mechanical properties of the SBR/SiO2 composites modified in-situ by GMMP and Sm-GMMP were studied in detail. The model compounds showed that the chemical interaction between GMMP and SiO2 consisted only of hydrogen bonding, whereas that of Sm-GMMP toward SiO2 included not only hydrogen bonding but also coordination bonding owing to the introduction of rare-earth ions, which could effectively promote the homogeneous dispersion of SiO2 particles into the SBR matrix and strengthen the rubber–filler interfacial interaction. Consequently, the mechanical properties of the SBR/SiO2 composites modified in-situ by the GMMP or Sm-GMMP were remarkably improved and better than those of the unmodified SBR/SiO2 composites with corresponding filler content. Moreover, the SBR/SiO2 composites modified by Sm-GMMP showed a better filler dispersion, tougher rubber–filler interfacial bonding, and stronger mechanical properties than those modified with the same dosage of GMMP. Based on the crosslink density and immobilized polymer layer results, the possible microstructure and reinforcing mechanism of the SBR/SiO2 composites modified in-situ by GMMP or Sm-GMMP were proposed, and these could effectively account for the experimental observations.