Inverse Vulcanization of Vinyltriethoxysilane: A Novel Interfacial Coupling Agent for Silica-Filled Rubber Composites

Sulfur-containing silane coupling agents (SSCAs) are widely incorporated into silica-filled rubber composites to improve silica dispersion and enhance interfacial adhesion, maximizing the potential of silica. However, SSCA synthesis involves multistep procedures and requires organic solvents. In addition, modifying rubber composites with SSCAs has persistent issues, such as low coupling efficiency and uncontrollable structure. Herein, we report the facile synthesis of alkoxysilyl-functionalized polysulfides (SPVs) with a tunable molecular structure (sulfur rank and alkoxysilyl fraction) via inverse vulcanization of vinyltriethoxysilane (VTES) with a copolymer of sulfur and styrene. SPVs serve as interfacial modifiers in silica-filled rubber composites by separately reacting with the silica and rubber chains. In particular, the multiple alkoxysilyl sites in the SPV chain increase the probability of silanization, yielding high coupling efficiency in the rubber composite. Although the molar content of alkoxysilyl groups in SPV1 (the mass feed ratio of VTES and copolymer is 1) is half of that in the most widely used small-molecules SSCAs of bis(3-triethoxysilylpropyl)tetrasulfide, stronger interfacial adhesion and better silica dispersion are achieved in SPV1-modified composites, which consequently lead to more improvements on the composite properties. In addition, the advantages of SPV1 as an interfacial modifier in improving the "magic triangle" properties of a practical tread composite have been demonstrated. More importantly, the effects of the SPV molecular structure on silica dispersion and interfacial adhesion have been investigated, providing the fundamentals for unraveling the coupling mechanism and guiding composite property regulation.