## 1 Introduction  
Graphene, a honeycomb quasi-two-dimensional material formed by sp\({}^{2}\) hybrid carbon atoms, was firstly obtained by [PERSON] in 2004 [1]. Since then, graphene (G) has drawn more and more attention in the applications of electrode material [2], biological composite material [3], liquid crystal materials [4; 5], supercapacitor [6; 7], polymer nanocomposites [8] as well as solar cells [9]. This is entirely based on its excellent properties such as good thermal and electrical conductivities, large theoretical specific surface area, flexibility, high intrinsic mobility and chemistry stability [10; 11]. To produce graphene sheets, there already exist various effective methods, for example, mechanical exfoliation [1], chemical vapor deposition (CVD) [12; 13; 14; 15], oxidation-reduction method [16; 17], unzipping of carbon nanotubes [18; 19; 20], electrochemical method [21; 22] and crystal epitaxial growth method [23; 24] and so on. It is its many intriguing properties that attract plenty of researchers to study graphene and make graphene polymer nanocomposites a hotspot in composite materials field. However, the strong intermolecular force between graphene sheets restricts the homogeneous dispersion within the polymer matrix. To avoid agglomeration of graphene sheets in a polymer matrix, modifications of graphene are urgently needed as essential methods. Covalent and noncovalent modifications are two approaches to modify and functionalize graphene [25]. Covalent modification is able to make modified graphene and polymer matrix connected through covalent bond, resulting in powerful capacity to bear mechanical load. However, the covalent bond may destroy the integrality of sp\({}^{2}\) hybridization in the microstructure of graphene so that the electrical and thermal conductivities may decrease. Given that via noncovalent modification the interactions between graphene and the modifier substances are weak which is unbenefited for load transfer, covalent modification is obviously a better choice. In a typical oxidation-reduction method, GO is obtained from graphite via oxidation by a strong oxidant like concentrated sulfuric acid and grafted with hydrophilic functional groups, such as -OH, epoxide, -COOH. Then GO is reduced to graphene by hydrazine hydrate, hydroquinone, NaBH\({}_{4}\) or other reductants with organic or inorganic functional groups [26; 27]. The functional groups remain on reduced graphene render larger interlayer space and strong interfacial interaction with the polymer matrix is demanded for mechanical stress transfer [28]. [PERSON] et al. systematically explored the implication of long-chain alkylamine functionalization of GO on electric conductivity and dispersion of GO in organic solvents. Through [PERSON]'s method and addition of alkylamine and hydrazine hydrate, octylamine functionalized GO exhibited optimal electric conductivity up to 180 S/m [29]. [PERSON] et al. obtained highly soluble functionalized GO and reduced graphene oxide (rGO) both in inorganic and organic solvents by polyetheramine (PEA) due to the amphipachicity of PEA [30]. [PERSON] et al. synthesized covalently modified graphene with high compressive strength from GO and triethyl phosphite in the presence of LiBr. The graphene and lithium phosphate oligomers were connected through covalent phosphonate linkages and the mechanical properties could be controlled through altering the variety of metal halide [31]. [PERSON] et al. compounded graphene/polyurethane nanocomposites with better thermal stability than pure matrix. The key point was that p-aminobenzoic acid functionalized GO acted as the pseudo-crosslinker for composites [32]. [PERSON] et al. applied polyetheramine to modify and reduce GO at the same time. Except for the solubility mentioned above, polyetheramine could enhance conductivity and mechanical performance of rGO/epoxy composites as well [33]. [PERSON] et al. firstly reduced and modified GO by tea polyphenol and the material had good dispersion in both water and some organic solvents.