In this study, we have developed a facile and effective method for fabricating polyimide (PI)-based nanocomposites incorporating octadecylamine (ODA)-functionalized graphene oxide (ODA-fGO) nanosheets. ODA-fGO sheets exhibit superior dispersibility and compatibility with the PI matrix and are successfully obtained through a chemical reaction between graphene oxide (GO) and ODA. The PI-based composites of various loading content of ODA-fGO sheets were prepared via in situ polymerization and thermal imidization process. The mechanical and electrical properties of the PI/ ODA-fGO composites were significantly improved relative to pure PI because of the excellent dispersion of ODA-fGO and the adequate compatibility between fillers and the PI matrix. A 40.7% increase in tensile strength and a 95.5% improvement of Young's modulus were observed for the 3 wt% ODA-fGO (PI/3 wt% ODA-fGO) loading content composite. The electrical and thermal conductivity of PI/3 wt% ODA-fGO was 3.8 Â 10 À2 S m À1 and 0.468 W m À1 K À1 , respectively, which is more than 10 11 times and almost 3 times higher than that of pure PI. The reported approach provides an effective strategy for developing high-performance and multifunctional polymer-based composite materials.

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Graphene is a two-dimensional sheet of sp 2 hybridized carbon atoms, which can be viewed as an extra-large polycyclic aromatic molecule. It has stimulated research interest owing to its ultralarge surface area, excellent conductivity, high mechanical stiffness, chemical inertness 1-3 , good biocompatibility 4 and low manufacturing cost 5. These unique properties of graphene hold great promise for potential applications in various fields such as nanoelectronics 6,7 , nanocomposites 8,9 , supercapacitors 10,11 , electrochemical devices 12 , catalysis 13 , sensors 14 , batteries 15 and dye-sensitized solar cell 16 , etc. Graphene-based applications undoubtedly need low-cost, high quality and large-scale production of graphene. Up to now, some approaches have been developed to prepare graphene, such as: micromechanical exfoliation of graphite with Scotchtap 1 , chemical vapor deposition on metal substrates 17 , epitaxial growth on electrically insulating surface 18, 19 and the reduction of graphene oxide (GO) 20,21 , which can be prepared from natural graphite by the modified Hummers' method 22,23. Among these methods, the reduction from graphene oxide is the most realistic approach for low-cost and gram-level production of graphene. Especially, the electrochemical reduction of graphene oxide (EG) coated on glassy carbon electrode (GCE) surfaces is a promising route for preparing graphene-modified GCE because it is green, fast, low cost and more effective than chemical and