Silane coupling agent Silane coupling agent Si-69 chemistry is named double [gamma - (triethoxy silyl) propyl] four sulfide.It is often used to treat inorganic fillers such as carbon black and SiO 2. It not only has the function of activator and coupling agent, but also has the function of crosslinking agent, softener and reinforcing agent. It is used as reinforcing agent and vulcanizing agent in rubber industry.