In order to improve the biocompatibility of graphene oxide (GO) and enhance its application in preparing biomaterials

four-arm star polyethylene glycol (sPEG) was used to modify GO under the assistance of toluene-2

4-diisocyanate (TDI).Polyethylene glycol-modified graphene oxide (GO-TDI-sPEG) obtained by this facile method possesses high sPEG grafting density

which could be stably suspended in aqueous solutions.Fourier transform infrared spectroscopy (FTIR)

Raman spectroscopy (Raman)

X-ray diffraction (XRD)

atomic force microscopy (AFM)

transmission electron microscopy (TEM) and thermogravimetric analysis (TGA) were used to characterize the resultant material.The appearance of the characteristic absorptions at 2861 and 1093 cm-1 in FTIR spectrum

as well as the AFM and TEM micrographs indicated that sPEG was successfully grafted onto GO.No diffraction peak could be found in XRD figure of GO-TDI-sPEG

which indicated that the layers of GO-TDI-sPEG were fully exfoliated after modification.The TGA test results showed that the thermal stability of the modified GO had been greatly increased and the grafting degree of sPEG in GO-TDI-sPEG was about 12.1 wt%.