In order to improve the weak dispersion of two-dimensional nanosheets in polymer matrix and improve the electrical performance of composite materials, a two-dimensional micron expanded layer molybdenum disulfide (E-MoS₂) was prepared by hydrothermal method, and then polyimide (PI) based super-large lattice molybdenum disulfide nanosheets (PI/E-MoS₂) composite films were prepared by in-situ polymerization method. The surface/cross section structure of the composite films was observed by scanning electron microscopy (SEM), the molecular valence bond composition of the composite film was analyzed by Fourier infrared spectroscopy (FTIR), and the phase structure of the composite film was analyzed by X-ray diffraction (XRD). Furthermore, the dielectric constant, DC electrical conductivity, and dielectric loss factor of the composite films were tested, and the effect mechanism of extended lattice on the breakdown and polarization behavior of composite films was studied. The results show that when a small amount of E-MoS₂ nanosheets is added into PI film, there is little agglomeration phenomenon on the surface of PI/E-MoS₂ films, and there is little obvious holes and a small number of structural defects on the cross section, which indicates a good compatibility between fillers and matrix. The incorporation of E-MoS₂ nanosheets can enhance the interfacial polarization of the composite films, improve both the dielectric constant and electric field strength, and decrease the dielectric loss.

The insulation status of the cable intermediate joint plays an important role in the safe and stable operation of cable. In view of the immaturity of terahertz imaging technology and the limitation of finite element analysis method, an ultrasonic signal characterization method for typical internal defects of silicone rubber in cable accessories was proposed in this paper. At first, different types of typical defect in silicone rubber were designed by simulation. Then the time-domain characteristic quantity and correlation analysis were carried out on the reflected echoes received in the ultrasonic detection simulation, and the correlation coefficient between the time-domain waveform characteristic quantity and the size and angle of defects was obtained. Finally, an ultrasonic test platform was built on the basis of pulse echo method to carry out ultrasonic test on the flat silicone rubber samples with defects. The results show that the size and angle of the internal defects of silicone rubber have a good correlation with the amplitude peak of the first echo, and the detection results of crack defects are more affected by the angle than that of bubble defects, and the amplitude peaks of defects at different angles are significantly different. It is concluded that the ultrasonic signal can effectively characterize the typical internal defects of silicone rubber in cable accessories.

A series of fluorinated polythioetherimide films were synthesized by copolymerization using 4,4′-diaminodiphenyl sulfide (SDA) and 2,2-bis[4-(4-aminophenoxy)phenyl]hexafluoropropane (HFBAPP) as diamine monomers, and 4,4′-biphenylene ether dianhydride (ODPA) as dianhydride monomer. The thermal, electrical, optical properties, and water absorption of the PI films were tested. The results show that the PI films have good thermal, dielectric properties and optical transparency. The glass transition temperature of the film is in the range of 240.7-251.6℃, the 5% and 10% heat loss temperature is above 480℃ and 514℃, respectively, and the residual carbon rate reaches 50% at 800℃. Under the frequency of 1 MHz, the dielectric constant of the PI films are 2.27-2.99, the dielectric loss factors are 0.004 7-0.005 6. The highest transmittance of the films reaches 88.75% in the range of visible light, and the water absorption rate is 0.95%-2.26%.

Photosensitive polyimide (PSPI) is a kind of high-performance polyimide with special structures, which is widely used in semiconductor packaging, integrated circuits, optical display, and other fields due to its excellent heat resistance, mechanical properties, insulating properties, and lithographic processability. In this paper, the PSPI patents applied in China were taken as object, the overall situation of these patents, including changes in the number of patent applications, applicants, and their source countries was analyzed systematically. Especially, the patent applicants inside and outside China and the patent subject distribution since 2011 were discussed. The difference of patent technology and protection priorities of enterprise applicants inside and outside China was compared in detail. The patent technology characteristics and development trends of PSPI were explored.

Three fluoro-containing polyimide (PI) resins (PI-II_a, PI-II_b, and PI-II_c) were prepared by two-step chemical imidization procedure using a fluoro-containing dianhydride 9,9-bis(trifluoromethyl)xanthene-2,3,6,7-tetracarboxylic dianhydride (6FCDA, II) and three kinds of aromatic diamines, including 2,2ʹ-bis(trifluoromethyl)-4,4ʹ-diaminodiphenylether (6FODA, a), 1,4-bis[(4-amino-2-trifluoromethyl)phenoxy]benzene (6FAPB, b) and 2,2-bis[(4-aminophenoxy) benzene]propane (BAPP, c), respectively. For comparison, the referenced PI resins (PI-I_a, PI-I_b, and PI-I_c) were prepared with the same procedure except that 6FCDA was replaced by 4,4ʹ-(hexafluoroisopropylidene)diphthalic anhydride (6FDA). And then six kinds of PI films were prepared by high temperature curing process, and their properties were studied. The results show that the solubility of PI-II_a, PI-II_b, and PI-II_c resins in organic solvents is lower than that of PI-I_a, PI-I_b, and PI-I_c resins. Compared with PI-I_a, PI-I_b, and PI-I_c films, PI-II_a, PI-II_b, and PI-II_c films show higher glass transition temperature (T_g), lower linear coefficient of thermal expansion (CTE), little lower optical transparency, and relatively higher dielectric constant (D_k). The PI-II_a film has the optimal comprehensive properties, its T_g and CTE is 362.5℃ and 39.6×10^-6 K^-1, respectively, its optical transmittances at the wavelength of 450 nm (T₄₅₀) is 83.9%, and the D_k at the frequency of 10 GHz is 3.00.

In order to improve the solubility and meltability of polyimide (PI), a series of addition thermosetting fluorinated poly(imide-siloxane) copolymer resins (ABIS) were prepared from two kinds of synthesized trifluoromethyl-containing aromatic diamine monomers and 3,3′,4,4′-benzophenone tetracarboxylic acid dianhydride (BTDA), besides, aminopropyl-terminated polydimethylsiloxane (APPS) was chosen as flexible segment, and 3-aminophenyl acetylene (APA) was used as reactive end-capping agent. The structure of ABISs were characterized by proton nuclear magnetic resonance spectroscopy (¹H NMR) and Fourier transformation infrared spectroscopy (FTIR). The solubility, rheological behavior of ABIS and the thermal stability of the cured ABIS were further studied. Moreover, ABIS films were prepared by solution filming, and their physical properties were studied. ABIS resin matrix composites (T300CF/ABIS) were prepared by hot pressing using T300 carbon cloth as reinforcement, and their mechanical properties were also tested. The results show that the introduction of siloxane segment and trifluoromethyl group can significantly increase the flowability and solubility of PI resin systems. The introduction of fluorinated diamine decreases the 5% weight loss temperature (T_d5) of the cured ABIS, but its T_d5 is still higher than 425℃. At the same time, the residual yield at 800℃ (Y_r800℃) of ABIS resins reach 26%. The tensile strength and elongation at break of ABIS films are as high as 15.8 MPa and 65.3%, respectively. In the frequency range of 40 Hz-10⁷ Hz, the dielectric constant (ε) and dielectric loss factor (tanδ) of the PI films are 3.21 and 0.01, respectively, which keep unchanged basically. The contact angle of water on the cured ABIS film is 94°. The flexural strength and interlaminar shear strength (ILSS) of T300CF/ABIS composites can be 137.6 MPa and 16.6 MPa, respectively. The synthesized ABIS resin has promising applications in microelectronic devices and flexible heat-protective composites.

Firstly, a Y-shape diamine monomer 4-(4′-tertbutyl)phenyl-2,6-di(4′-aminophenyl)pyridine (TPAPP) containing pyridine ring structure and tertbutyl group was synthesized. Then, it was polymerized with 2,2-bis(3-amino-4-hydroxyphenyl)hexafluoropropane (6FAP) and 4,4′-(4,4′-isopropyldiphenyloxy)bis(phthalic anhydride) (BPADA), and a series of copolyimide (PI) films were prepared by thermal imidization. The structure and optical, mechanical, and thermal properties as well as solubility of the PI films were investigated by infrared spectroscopy, X-ray diffraction, UV visible spectra, tensile tests, dynamic thermo-mechanical analysis, thermogravimetric analysis, and solubility tests. The results show that as the molar ratio of TPAPP increases, the optical transparency and glass transition temperature of the copolyimide films exhibit an increasing trend. When the molar ratio of diamine and dianhydride is 5:5, the copolyimide film shows the best mechanical properties, with the tensile strength of 144.9 MPa, the Young's modulus of 3.4 GPa, and the elongation at break of 9.3%. In addition, these copolyimides demonstrate good solubility in aprotic polar solvents.

With the constant updating of flexible display devices, the researches on colorless transparent polyimide (CPI) films as substrate materials have attracted considerable attention. In order to solve the inherent contradictions among optical performance, high-temperature resistance, dimensional stability, and mechanical properties of CPI, we synthesized a series of semi-aromatic CIP films with side chains containing benzimidazole by copolymerization using cyclobutanetetracarboxylic dianhydride (CBDA) as the dianhydride monomer, 2,2′-bis(trifluoromethyl)-4-diaminobiphenyl (TFMB) and 2-(3,5-diaminophenyl)-benzimidazole (BBIA) as diamine monomers. The influence of hydrogen bonding, free volume, and main chain structure on the properties of films was systematically investigated by the Materials Studio software simulation and experimental results. The results show that the prepared CPI films have excellent optical transparency, thermal resistance, and mechanical properties. The average transmittance of CPI films in wave length of 380-780 nm is higher than 85%, the glass transition temperature (T_g) is above 400℃, the linear coefficient of thermal expansion (CTE) is 15×10^-6-17×10^-6 K^-1, the maximum tensile strength is 165 MPa, and the modulus is in the range of 3.7-5.2 GPa.

Photosensitive polyimide (PSPI) is widely used in electronics, microelectronics, optical display, and other fields. Foreign companies attach great importance to the patent protection of PSPI material formulas and applications. In this paper, the PSPI patents applied by Toray Industries Inc. in China were taken into research, and the changes in the number of patent applications, legal status, technical subject distribution, and other key information were analyzed in detail. Through combining with Toray's representative PSPI products and their applications, the technical development, patent protection strategy, key points of patent technology of Toray were clarified. Based on the above analysis, the technology development trends and application direction of PSPI materials were explored and presented.

Air discharge results from the interaction between electric field and atmospheric environment, therefore the air gap switching impulse discharge voltage is affected by the interelectrode electric field distribution and the atmospheric parameters. In order to calculate the discharge voltage of rod-plane long air gaps at high altitude areas, we construct an insulation prediction model based on k-nearest neighbor (KNN) algorithm with air pressure, temperature, humidity, altitude, and electric field characteristic parameters as feature set. The KNN algorithm was trained by the test data in the altitude range of 55-4 300 m to establish the mapping relationship between air gap features and the insulation strength, and then discharge voltage prediction of rod-plane air gaps at the high altitude of 5 000 m with different gap distances was realized. The maximum relative error and the mean absolute percentage error are 8.58% and 3.78%, respectively, which verifies the effectiveness of the proposed method. When the model was extrapolated to the rod-plane air gaps in plain area under different atmospheric parameters, the predicted discharge voltages also had good agreement with the experimental values. This study results can provide references for the calculation of air gap insulation strength in different atmospheric environment.