Preparation And Properties Of Functionalized Graphene Oxide And Its Polyimide Composites

For the unique two-dimensional nanoscale structure,graphene exhibits excellent mechanical,electrical and thermal properties.And due to the good enhancement effect on the polymer matrix,its polymer composites have been receiving widespread attention and research.Polyimide,as an important high-temperature resistant polymer,has been widely applied in many fields such as aerospace,electronics,chemical industry,medical treatment and so on.With the advancement of science and technology,the demand for high performance materials is getting higher.The traditional polyimide products have been unable to meet the needs of people.The modification of polyimide has become a hot spot of research,and polyimide/graphene composite is one of the most important directions.In this paper,the highly active molecule TCTHDM was synthesized by the reaction of cyanuric chloride(TCT)and hexanediamine(HDM).Its structure was characterized by~1H-NMR and FT-IR spectra.Then the TCTHDM was grafted onto the surface of graphene oxide(GO)and the functional product TGO was obtained.Many instruments such as FT-IR,X-ray diffraction,Raman spectroscopy,TG,SEM and AFM were used to study the structure of TGO.The results showed that TCTHDM was successfully grafted onto the surface of GO,and the thermal stability of TGO was greatly improved.The char yield of TGO at 800℃was45.6%,which was 3%higher than that of GO.The carboxyl groups on GO surface were activated by thionyl chloride.Then the 2,6-dibromo-4-nitroaniline was grafted onto the surface of GO,and the amino functionalized graphene MGO was obtained by reducing the nitro group on the surface.The successful synthesis of MGO was proved by XPS detection and FT-IR spectra.With the further characterization of MGO,it was found that due to the removal of some oxygen-containing functional groups in the synthesis process,the interlayer distance of MGO reduced,the degree of disorder increased and the thermal stability enhanced which were compared with GO.With 4,4’-diaminodiphenyl ether(ODA)and pyromellitic anhydride(PMDA)used as monomers,two groups of polyimide composite films(PI/TGO and PI/MGO)were prepared by in-situ polymerization,in which the functionalized graphene oxide TGO and MGO were respectively added.The research indicated that after adding a certain amount of functionalized graphene oxide,the mechanical properties,thermal expansion and water absorption properties of the composite films were improved.When the amount of TGO was 0.5wt%,the tensile strength of PI/TGO composite film increased by 21MPa,and its glass transition temperature was 384.9℃,which was increased by 12.6℃.When the addition amount of MGO was0.1wt%,the tensile strength of the PI/MGO composite film increased by 17.1%,while the glass transition temperature was 382.7℃,which was 10.4℃higher than that of pure PI.In addition,when the content was increased to 2wt%,the dielectric constant of PI/TGO composite film increased by 60.2%at 1MHz,and the conductivity of PI/MGO composite film increased by 4 orders of magnitude.