The photochemical surface grafting method based on the photochemistry of aryldiazonium, aryldiazo, and arylazido groups was explored. Five hydrophilic photoreactive copolymers containing these three photosensitive groups in their side chains were prepared by a one-pot procedure from two precursors, which were obtained by radical copolymerization of N,N-dimethylacrylamide and styrene derivatized with appropriate functional groups. The photoreactivity of the copolymers was verified by Fourier transform infrared (FT-IR) and ultraviolet (UV) spectroscopies. Upon coating of a photoreactive copolymer on poly(ethylene terephthalate) (PET) film as a model substrate and subsequent UV light irradiation, the surface became wettable by water irrespective of the type of copolymers. The photochemical fixation of the copolymers on PET surface was demonstrated by X-ray photoelectron spectroscopy analyses and water contact angle measurements. The potential application in the biomedical devices is discussed.