Preparation Of Graphene Derivatives Andits Polyimide Nanocomposites

For the unique2D-dimensional honeycomb structure, graphene and itsderivatives exhibits excellent physical and chemical properties, such as excellentmechanical properties, high transmittance, huge specific surface area and barrierproperties, etc. These excellent properties make graphene and its derivatives have awide range of applications in many fields, and the usage of graphenen and itsderivatives in fabrication of polymer composites with high performance andmulti-function is one of the important researches in recent years. Graphene fluorideand graphene oxide are the most concerned grahene derivatives. However, preparationof graphene fluoride by a low cost and high efficiency method, and the application ofgraphene fluoride in polymer nanocomposites are needed further study. Furthermore,the basic research, organic functionalization and application researches on thegraphene oxide still have a large research space. On the field of the modifiedpolyimide by nano-inorganic materials, the application of graphene and its derivativeshas become a research hotspot. Based on the above research background, we carriedout some research work, including preparation of graphene fluoride, graphene oxideand its organic functional products. Meantime, the graphene derivatives above wereused in preparation of polyimide nanocomposite films, and the properties of polymercomposites, including mechanical properties, thermal stability, dielectric propertiesand water absorption rate, were studied in details.In this paper, we had explored the simple, low cost and efficient methods topreparation graphene fluoride. The graphite fluoride with the F/C atomic ratio of o.6and1.08was used as stating materials (denoted as GIF-L and GIF-H, respetively).The GIF-L and GIF-H were both firstly modified by improved Hummers methods andNaOH solution with high concentration, respectively, and then the correspondingproducts were liquid-phase exfoliation into graphene fluoroxide by ultrasonication.Compared to alkali modification–exfoliation process, the oxidation-exfoliationprocess offered more advantages in preparing graphene fluoride, because the later method could obtain graphene fluoride with F content ramainning, better dispersion inorganic solvents and fewer layers (layers1-5). This result is due to the more effectiveto introduce oxygen-containing groups in the GIF-L configuration by the oxidation-exfoliation process,which led to enhencing the interface interaction between modifiedgraphene fluoride and polar organic solvents.Graphene oxide was preparation through the processes of oxidization andexfoliation by using three particle sizes of graphite as the raw materials. The effects offactors on the lateral size and lateral size distribution of GO were studied in details,and the factors included the particle size of graphite, ultrasonication conditions(power, time and solvents). The results shown that the lateral size of GO decreasedwith increasing the ultrasonication power, time and decreasing the particle size of theraw materials, but when the ultrasonication time was up to60min, the average oflateral size of GO was similar and less than1μm. The changes of lateral size of GOobtained by ultrasonication in NMP was similar to in water, whereas, the yield of GOin NMP is smaller than in water.The sebacic acid and1,5-bis(4-aminophenyl)-1,4-pentadiene-3-ketone (DAPD)were used as organic modifiers, and two type of organic functional GO (MGO-1andMGO-2) were preparation by the reaction between the modifiers and GO. Introducingthe organic molecules onto the GO flakes lead to the increasing the solubility offunctional GO in organic solvents. The DAPD molecules endowed MGO-2a goodphotosensitivity. The [2+2] photocycloaddition reaction between the C=C from theα,β-unsaturated ketone structure in the DAPD occurred under the ultraviolet (UV)light irradiation, and when the irradiation time was338s, the equilibrium extent ofphotocycloaddition reached up to41%We had explored the effects of the fillers, modified graphene fluoride (GFO) andfunctional graphene oxide (MGO-1), on the properties of polyimide composite films.The polyimide/modified graphene fluoride (PI/GFO) and polyimide/functionalgraphene oxide (PI/MGO) composite films were preparation by in situpolymerization, in which the4,4’-diaminodiphenyl ether (ODA) and pyromelliticanhydride (PMDA) were used as monomers. The study demonstrated that the fillers could be uniformly dispersed in the PI matrix when the filler content was low (≤2wt%), and there existed strong interface interaction (hydrogen bonding and covalentbonding) between the filler and PI matrix.Therefore, the over performance includingmechanical properties, glass-transition temperature and water absorption of PIcomposite films were effectively improved. However, adding fillers content resultedin agglomeration of fillers and weakening the interface interaction between thefillers and matrix, and finally led to decreasing the overall performance of PIcomposite films. There were big differences in dielectric properties and thermalexpansion properties between these two types of PI composite films. The presence ofC-F bonds, which possess the properties of low polarizability and susceptible tothermal motion, caused reduction of dielectric constant (only for the low GFOcontent) but giving rise to the increasing line expansion coefficient (CTE) of thePI/GFO composite films. For PI/MGO composite films, because of being affected bythe following factors, the more polar groups existing in MGO-1structure, theagglomeration of partially reduction of MGO-1resulting from thethermalimidization and the limitation of MGO-1for the thermal motion of PI molecules, sothe dielectric constant and CTE of PI/MGO composite films obviously increased anddecreased, respectively.