A variety of copolymers composed of polysiloxane and phosphate esters were synthesized. The copolymers with two kinds of pendent groups (oxy-organic and amino) were coated on the porous PVDF substrates and then cured to form composite membranes. An interfacial layer was deposited on the surface of the PVDF substrate prior to the composite membrane formation by plasma-induced polymerization of trimethoxyvinylsilane to enhance the adhesion of the silicone and PVDF layers. The composite membranes were applied to the separation of ethanol from water in pervaporation separation processes. The experimental results showed that these inherently hydrophobic composite membranes were highly ethanol-permselective, especially when the ethanol concentration in the feed was low. The permeation rate was affected by the attached pendent groups on the copolymers and decreased in the order: 1-butylamino > diethylamino > ethoxy > phenoxy. The separation factor followed a reversed order. Phenoxy composite membrane was found to exhibit the best performance with the separation factor of 4.6 and the permeation rate of 2.85 kg/m(2)h at a feed concentration of 10 wt% ethanol.