GRAFTING OF WATER-SOLUBLE CHAINS ONTO A POLYMER SURFACE

To prepare a polymer surface with grafted chains, graft polymerization of poly(ethylene glycol) methacrylate was performed on the surface of poly(ethylene terephthalate) (PET) film with a simultaneous UV irradiation method at different monomer concentrations. This combination of graft polymerization was chosen because of the wide solubility of the monomer in hydrophilic and hydrophobic solvents and excellent physical stability of the PET substrate. The UV-induced graft polymerization could be performed without using any photosensitizer and degassing process. The surface structure of grafted films was characterized by contact angle, dye staining, attenuated total reflection (ATR)-FTIR, and zeta potential measurements. The grafted PET films had highly hydrophilic surfaces with low water contact angles even after UV irradiation with 2.5 wt % aqueous solution of the monomer for 1 h. The larger the degree of polymerization of poly(ethylene glycol) (PEG) in the monomer, the lower was its contact angle. The ATR-FTIR spectra and cross-section of the grafted films indicated that graft polymerization took place not merely on the outermost surface, but also within the thin surface region of the PET film without any change in the bulk properties. The depth profile of the grafted surface region was studied using the technique of ATR. The grafted surface exhibited zeta potentials of nearly zero over the wide pH range, indicating that water-soluble chains were tethered to the grafted film covering the outermost surface.