Preparation and properties of thermostable well-functionalized graphene oxide/polyimide composite films with high dielectric constant, low dielectric loss and high strength via in situ polymerization

This study proposes a novel and facile method to synthesize high-quality NH2-functionalized and carboxyl-functionalized graphene oxide (PPD–CFGO)/polyimide (PI) composite films with high dielectric constant (ε), low dielectric loss, high-temperature resistance and outstanding mechanical properties by in situ polymerization. In addition to the partial carboxyl groups located at the edges, the ample hydroxyl and epoxy groups bonded on the basal plane of graphene sheets were exploited to covalently bond to the amines. GO was modified by oxalic acid to obtain carboxyl-functionalized GO (CFGO) before amidation. NH2-functionalized CFGO (PPD–CFGO), dispersing well in dimethylacetamide (DMAc), was the initial platform for polymer grafting to improve the CFGO dispersion in the polymer matrix. Partially reduced graphene nanosheets are formed during the imidization process. The PPD–CFGO/PI composite films exhibit high tensile strength (up to 848 MPa) and Young's modulus (18.5 GPa). The thermogravimetric analysis results indicate that the PPD–CFGO/PI composites have good thermal stability below 500 °C. The dielectric constant increases up to 36.9 with an increasing amount of PPD–CFGO, higher than that of the pure PI polymer by a factor of 12.5, while the dielectric loss is only 0.0075 and the breakdown strength still remains at a high level (132.5 ± 9.3 MV m−1).