Polystyrene-graft-poly(ethylene glycol) copolymers (PS-g-PEG) were successfully synthesized using the "grafting-through" method. The graft copolymers and the surface properties of their coats were characterized by 1H-NMR, gel permeation chromatography (GPC), differential scanning calorimetry (DSC), transmission electron microscopy (TEM), X-ray photoelectron spectroscopy (XPS), static contact angle measurement, and atomic force microscopy (AFM). Both DSC and TEM indicated that the graft copolymers had a microphase separated structure. AFM showed the microphase separated structure also occurred at the coat surface, especially at high PEG content, which could also be indirectly confirmed by the XPS and contact angle results. The formation mechanism of the microphase separated structure was discussed. 2006 Wiley Periodicals, Inc. J Appl Polym Sci 103: 1458-1465, 2007