Triethoxysilane HSi(OEt)(3) was used a; coupling agent to graft a poly( organophosphazene) (POPZ) containing allylic functions to the surface of poly(vinyl alcohol) or poly( ethylene- cc-vinyl alcohol) films. Hydrolyzed HSi(OEt)3, which contained both inorganic (Si-OH) and organic (Si-H) reactivities, acted at the interface between the hydroxylated substrates (via a condensation reaction) and the allylic functions in POPZ (via a hydrosilylation reaction). Starting materials and grafting surfaces were studied by ATR-IR and XPS spectroscopies and contact angle measurements. Data obtained indicated that different POPZ layers were produced, depending on whether the functionalization of materials with silane, and the grafting reaction were separately or simultaneously made. The POPZ layer thickness was higher when the grafting reaction was preceded by the POPZ functionalization. In each cases, the modified surfaces showed marked increases in hydrophobicity character.