Surface modification of poly(ethylene terephthalate) to prepare surfaces with silica-like reactivity

Reactions of semicrystalline poly(ethylene terephthalate) (PET) film with 3-aminopropyltrialkoxysilanes at the film-solution interface and subsequent hydrolysis render silanol (Si-OH) functionality that is attached to the PET surface by amide linkages (PET-CONH(CH2)(3)Si(OH)(3)). Toluene was found to be the preferred solvent for the initial amidation reaction, rendering a higher surface concentration of silanol groups than that for other solvents. Polycondensation of tetraethyl orthosilicate on the surface of PET-CONH(CH2)(3)Si(OH)(3) produces thin silica films, the thickness of which can be controlled with reaction time. The surface of this composite film (PET-(SiO2)(x)-OH) also contains reactive silanol groups. These two reactive surfaces were further modified using other reactive silanes to introduce alkyl, perfluoroalkyl, bromoalkyl, and aminoalkyl functionality to the PET film surface. The surface density of attached groups was assessed by X-ray photoelectron spectroscopy, and wettability of the surfaces was determined using contact angle analysis. The reactivity of these surfaces was compared to that of oxidized silicon wafers, and we conclude that these PET modification procedures (amidation with 3-aminopropyltrialkoxysilanes and polycondensation of tetraethyl orthosilicate) produce surfaces that react with the versatility of oxidized silicon wafers.