Wikipedia
Bis(triethoxysilylpropyl)tetrasulfide
Bis(triethoxysilylpropyl)tetrasulfide is an organosulfur compound with the formula S[CHSi(OEt)] ( Et = CH). The molecule consists of two trialkoxysilyl propyl groups linked with a polysulfide. It is often sold as a mixture with the trisulfide. The compound is a colorless viscous liquid that is soluble in ordinary organic solvents such as toluene. Commercial samples often are yellowish. The compound is added to rubber compositions that contain silica filler.