Sequential surface derivatization of PET films

The present study describes the surface tailoring of a polymeric substrate by a multistep process using two consecutive plasma treatments, followed by derivatization reactions. The chemical concept of this approach is present ed in this paper, using a poly(ethylene terephthalate) (PET) substrate. In the first step, tetrafluoroethylene (TFE) was plasma polymerized, generatin g a highly cross-linked perfluoric surface layer. The next step introduced amine groups into the plasma polymer, by exposing the surface to plasma of ammonia. The reactive amine moieties were then used as anchoring sites for further derivatization. Finally, poly(ethylene glycol) (PEG) chains were gr afted onto the surface via a hexamethylene diisocyanate (HDI) spacer. The E SCA spectrum of treated PET revealed that the surface chemistry obtained af ter plasma polymerizing TFE was one clearly dominated by CF2 and CF moietie s, as demonstrated by the large peaks appearing at 291.1 and 289.5 eV, resp ectively. As expected, substantial amounts of nitrogen could be seen after exposing the surface to a plasma of ammonia, as revealed by the large N 1s peak at 402.0 eV. ESCA also demonstrated the presence of PEG chains bound t o the sur face. These findings were confirmed by FTIR spectroscopy and supp orted by water contact angle measurements. Special attention was given to t he absorption bands of the CF groups and ether bonds belonging to the fluor inated plasma polymer and the PEG chains, respectively, as well as to the c haracteristic N=C=O band (2272 cm(-1)). While the water contact angle of un treated PET was 76 degrees, it increased sharply after the fluorinated laye r was created (93 degrees), decreasing drastically (to less than 20 degrees ) once the highly hydrophilic PEG chains were grafted on the surface.