Research And Preparation Of Linear Polymer Dielectric Materials

Energy storage dielectric capacitors with high energy density and low loss are widely used in modern electronic equipment,power systems,defense weapons and equipment.As the key material of capacitors,dielectric materials have far-reaching significance for the preparation and research of high-performance dielectric materials.Polymer film capacitors are of great interest compared to ceramic dielectric capacitors because they are not only inexpensive,but also have high breakdown strength and high energy density.As for linear polymer dielectric materials,polymers with polar groups have larger dipole moments,tend to have smaller losses and higher breakdown strength,while linear polymer materials have better charge and discharge efficiencies than other polymers.In this paper,linear polymer dielectric materials with polar groups,such as polyimide,polyurea and polythiourea were selected as the main research objects.The main research contents and conclusions are as follows:?1?The dielectric properties of three linear polymer materials,polyimide?PI?,polyurea?PU?and polythiourea?PTU?,were calculated by functional density functional theory?DFT?.Since the dielectric constant and the forbidden band width can determine the dielectric properties of the dielectric material,Fourier transform infrared spectroscopy?FTIR?and X-ray diffraction?XRD?can analyze the molecular model and crystal structure of the dielectric material,so the calculated data is dielectric constant,band gap,FTIR and XRD of the three dielectric materials.The results show that the dielectric constant of PI is 4.5,the forbidden band width is 3.621 eV,and the FTIR has a characteristic peak of imide ring?-CO-NH-CO-?at 1252 cm^-1;the dielectric constant of PU is 5.2.The forbidden band width is 3.236 eV,and the FTIR has a characteristic peak of urea group?-HN-CO-NH-?at 1496 cm^-1;the dielectric constant of PTU is 5.7,the forbidden band width is 2.647 eV,and the FTIR has a characteristic peak of thiourea group?-HN-CS-NH-?at 1270 cm^-1.No significant peaks of the three dielectric materials in XRD spectrum indicates that PI,PU and PTU are all amorphous structures.?2?Polyurea and polythiourea dielectric materials were synthesized by polyaddition reaction and related dielectric films were prepared by casting method.The dielectric properties of the films were studied.The results show that the synthesized polyurea has a dielectric constant of 3.5,a breakdown field strength of 5120 kV/cm and a storage density of 4.06 J/cc was achieved;Moreover,the polythiourea dielectric shows a dielectric constant of 5.508,and a breakdown field strength of 5920 kV/cm,and the energy storage density is about 8.54 J/cc.The energy storage densities of the two linear polymeric media materials are much higher than that of the currently commercial biaxially oriented polypropylene?BOPP?films??2.2 J/cc?.Further research shows that the dielectric properties of the two materials are close to those of the?DFT?simulation calculation,indicating that the molecular structure design is correct,which provides an experimental basis for the design of high performance linear dielectric polymer materials.?3?In order to further improve the dielectric constant of the material and film-forming properties of the polythiourea material,a combination of magnetic stirring and ultrasonic dispersion method was used to prepare vinylidene fluoride-trifluoroethylene-chlorofluoroethylene P?VDF-TrFE-CFE?/polythiourea composite dielectric material.The investigation of dielectric properties shows that the dielectric constant of the composite is 37.74,the breakdown field strength is 4000 kV/cm,and the dielectric loss is0.0362.The good synergistic effect between P?VDF-TrFE-CFE?and polythiourea results in the high storage density of the composite dielectric about 25.79 J/cc,which is 11.7times above the storage density of BOPP film.The effective compounding of high electric material with linear polymer dielectric materials provides an effective way for the preparation of new polymer dielectric materials.