Macromolecular coupling agents (MCA) containing epoxide and silanol functional groups were synthesized by radical copolymerization of glycidyl methacrylate (GMA) and γ-methacryloxypropyltrimethoxysilane (MPS), (F1–F3). The MCAs were successfully grafted on the surface of TiO2 nanoparticles via direct reaction, (TiO2-Fs). The homogeneous mixture of TiO2-Fs nanoparticles and epoxy resin was coated on the commercial grade mild steel (St-37) and cured using triethylenetetramine (TETA) as curing agent. The beneficial effects of homogeneous mixing and interfacial binding between TiO2-Fs nanoparticles and epoxy matrix on the long term anticorrosion performance on the steel were investigated by electrochemical impedance spectroscopy (EIS) before and after immersion in 3.5 wt% NaCl solution. The effect of interfacial binding was also investigated on the mechanical properties and water diffusion of the TiO2-Fs/epoxy resin nanocomposite samples. The highest tensile strength and modulus with the lowest water adsorption were observed for the coating samples prepared from MCA contained 50/50 mol ratio of GMA/MPS.