During the operation process, property deterioration of ethylene propylene diene monomer (EPDM) cable is often caused by multiple stresses. In order to explain the variation law and mechanism of dielectric properties of EPDM cable under the extrusion stress and thermal stress, we took EPDM for cable insulation of coal cutter as an object to study. The dielectric spectroscope of EPDM under the combined action of extrusion pressure and thermal stress was measured. The characteristic parameters of dielectric spectroscopy were obtained by simulating the dielectric spectroscopy according to the expression of complex permittivity from the single relaxation Cole-Cole model modified by DC conductivity. The change rule of the DC conductance and relaxation time constant was analyzed. The results show that temperature and extrusion pressure have obvious effects on the complex dielectric constant of EPDM. At a higher temperature, the increase of the real part of the complex permittivity at the lower frequency is obvious. Under the effect of DC conductivity and polarization, with the increase of extrusion pressure and temperature, the increase trend of real part of the complex permittivity at low frequencies slows down, while the real part decreases gradually at higher frequencies. Therefore, the change of DC conductance caused by extrusion stress and temperature is the key to the change of the complex dielectric constant of EPDM.

High-frequency copper-clad laminate is the core foundation to the development of 5G related industries, it has high technical threshold and broad market prospects. In order to clarify the development trend of high-frequency copper-clad laminate field, we comprehensively excavated and deeply studied the patent big data of high-frequency copper-clad laminate and its key technologies, including resin, fiber cloth, filler, and copper foil. The results show that the field of high-frequency copper-clad laminate is still in a period of rapid development, and the technology evolution of resin, fiber cloth, filler, and copper foil are aimed at achieving stable dielectric constant and low dielectric loss. Companies from the USA and Japan occupy the dominant position, the application amount of patent form Hitachi, Sumitomo, Panasonic, Mitsubishi and other Japanese companies are in the front rank. The research on high frequency copper-clad laminate in China starts late but develops rapidly, with two major research and development highlands formed in Guangdong and Jiangsu, and advantageous enterprises emerged such as Shengyi Technology and WAZAM New Materials. However, on the whole, patent technologies of China lack core competitiveness and face strong patent barriers. Accordingly, the countermeasures and suggestions for the high-quality development of high-frequency copper-clad laminate industry in China are put forward.

In order to guide the application of composite cross arms in heavy ice areas, we investigated the icing characteristics of glass fiber reinforced composite material and composite insulated crossarms in this paper. The results show that the icing amount and ice flashover voltage of blank sample under vertical suspension are better than that of horizontal suspension, and its icing amount is less than that of pure aluminum rod and Q345 steel rod with the corresponding hydrophilic. The icing amount of the composite material coated with PRTV coating is less than that of the blank sample, its flashover voltage increases sharply; the ice surface adhesion value is the least, which is 19% of ice surface adhesion value of pure aluminum rod, while the ice surface adhesion value of the blank sample is 78% of pure aluminum rod. The ice coating characteristics of the silicone rubber composite insulated crossarm are just the opposite of that of the composite material sample. Compared with vertical suspending the same composite insulator, when the insulators are horizontal suspending, the icing amount of composite insulated crossarm suspension reduces by 30%, and the flashover voltage increases by 51%.

With the development of electronics and microelectronics technology, thermally conductive polyimide (PI) film is facing new application requirements. The control of thermal conductivity and preparation of PI film have drawn much attention. However, there is a lack of systematic research on the analytical methods of its thermal conductivity. In this paper, the analytical methods of thermal conductivity for PI film at home and abroad were summarized. The basic principles, main features, and application scope of the transient methods, steady-state methods, and temperature wave analysis were introduced in detail. In addition, the comparison results of thermal conductivity along the out-of-plane direction and in-plane direction and thermal diffusivity of PI films tested by different methods were reviewed. The existing problems and future development trends of the thermal conductivity analytical methods for PI films were summarized and prospected.

In recent years, flexible electronic devices have developed rapidly. As a flexible substrate material and dielectric insulating material, polyimide (PI) film has been widely used in the preparation of flexible electronic devices and flexible circuit boards. However, its high thermal expansion coefficient reduces its dimensional stability in the process of variable temperature processing. Therefore, it is necessary to adjust its thermal expansion coefficient to match with other materials of electronic devices. In this paper, the patent status of low expansion polyimide films at home and abroad, the preparation and application research progress of low expansion polyimide composite films were introduced, and the general trend of synthesis, modification and application research of low expansion PI was forecasted.

Dielectric polymer materials with high breakdown, low loss, high flexibility, and low cost play an important role in film capacitor industry. However, low energy storage density and poor thermal stability limit its applications in high-temperature working environments. In this paper, the polyimide-based dielectric energy storage materials and the research methods to improve energy storage property were introduced emphatically, including the influences of the structure and morphology of inorganic fillers with high dielectric constant and high insulation properties or multifunctional composite fillers on the performance of composite films, and the studies on the property of interface micro-area. The future research direction of interface design for high-temperature medium energy storage composite materials was discussed.

As a special engineering plastic, polyimide is widely used in electrical insulation, electronics, and other fields because of its excellent dielectric properties, mechanical properties, and thermal stability. The polyimide films with excellent thermal stability and dielectric properties can be obtained by adjusting the molecular chain structure of polyimide through molecular structure design and monomer optimization. In this paper, the molecular structure design strategies for adjusting the dielectric properties of polyimide and the influencing mechanism of polyimide structure on its dielectric properties were reviewed, and the research direction of dielectric properties adjusting was prospected.

Since the American DuPont company improved the polyimide (PI) synthesis technology to produce membrane material and applied it to industry for the first time in 1960, PI had shined in the information age, and its related research had been developed by leaps and bounds. In the fields of gas separation industry and new energy, cross-linking modification is an effective way to improve the performance of PI membranes. In this paper, the latest research progress in the PI cross-linking modification for membranes in recent years was reviewed, which included thermal cross-linking, ultraviolet cross-linking, and chemical cross-linking, and the future research direction of cross-linked PI membranes was prospected.

According to the application requirements of low thermal expansion (low-CTE) for colorless and transparent polyimide (CPI) films, the structural design and synthesis of methyl-substituted aromatic diamine monomers containing rigid amide bonds in the main chain, including 2-methyl-4,4′-diaminobenzanilide (MeDABA) and 2,3′-dimethyl-4,4′-diaminobenzanilide (MMDABA), were performed. Firstly, the dinitro compounds were prepared by the amide reactions using the methyl-substituted p-nitrobenzoic acid or methyl-substituted p-nitroaniline as raw material. Then, a series of new diamine compounds were obtained by the reduction of hydrazine hydrate under the catalysis of Pd/C. The chemical structures of the diamine monomers were characterized by differential scanning calorimetric analysis (DSC), Fourier infrared spectroscopy (FT-IR), nuclear magnetic resonance (NMR), mass spectrometry (MS), and elemental analysis (EA). The results show that the aromatic diamine monomers with expected structure are prepared successfully.

Two novel diamines contained N-phenyl substituted benzimidazole were synthesized, and their difference was that the ortho-position of N-phenyl was substituted by methyl and fluorine atom, respectively. The novel diamines and commercially available dianhydrides 4,4′-(hexafluoroisopropylidene) diphthalic anhydride (6FDA) and 4,4′-oxydiphthalic anhydride (ODPA) were used to prepare poly(benzimidazole-imide) (PBII) films by two-step thermal imidization. The properties of new diamine monomer and PBII films were tested and characterized. The results show that the PBII films exhibit good thermal properties (glass transition temperature T_g=341-381℃) and mechanical properties (σ=95-135 MPa). The N-phenyl groups with different ortho units destroy the effective molecular packing, which improves the solubility and optical transmittance of the PBII films.