Graphene oxide (GO) sheets were first synthesized through oxidation of natural graphite by a modified Hummers method

and then their homogeneous and stable dispersion in N

N'-dimethylformamide (DMF) was obtained.Stable and homogeneous solution mixtures of GO and PAA (polyamic acid) in DMF at different mass ratios of GO/PAA were readily prepared.Uniform composite films of GO-PAA were subsequently prepared by solution casting.PAA was turned to polyimides (PI) and GO reduced in situ to graphene (GS) at the same time by a subsequent thermal imidization of GO-PAA films

leading to composite films of GS-PI.Electrical resistivity

thermal stability and mechanical property of GS-PI films were studied.The results indicate that the surface resistivity of GS-PI films was significantly decreased with the increase in GS content

lowered to about 106

the standard of the anti-static electricity film

in the film prepared with 1.0 wt% of GO in GO-PAA.The tensile strength and the elongation at break of GS-PI composite films were both increased with increase in GS content

reached their maxima in the film prepared with 0.6 wt% of GO in GO-PAA

followed by regular decreases with further increase in GS.Different from the tensile strength and the elongation at break

the tensile modulus of GS-PI was in constant increase with GS content in the film.An increase of 37% was detected in GS-PI film prepared with 3.0 wt% of GO.Moreover

the ductility and the thermal stability of GS-PI were well kept in all the composite films regardless of its GS content.