In this paper, the research process of alicyclic polyimides (Al-PIs) at home and abroad in recent years was reviewed, and the synthesis of typical monomers and polymers were described from the historical evolution perspective mainly. The applications of alicyclic polyimides in transparent flexible display, gas separation membrane, photosensitive material, and liquid crystal orientation membrane were discussed, and the development trend and application prospect of alicyclic polyimides were prospected.

The dielectric constant (D_k) and dielectric loss factor (D_f) of polyimide under high frequency can be reduced by changing the polarity of polymer and introducing pore structure in summary. In this paper, the research progress of the two modification methods at home and abroad in recent years was summarized. It is indicated that the properties of polyimide can be optimized by adding pore structure on the basis of introducing polar macromolecules. At the same time, the shortcomings of properties characterization in literature were pointed out, and the suggestions were proposed.

The research progresses of different polymers (polyimide, perfluorocyclobutyl-based polymer, benzoxazinyl polymer, benzocyclobutene resin, etc.) with low dielectric constant and low dielectric loss factor in recent five years were reviewed. The influence of different design strategies of polymer structures (chemical composition, molecular structure, pore structure, etc.) on their properties (dielectric properties, water absorption, thermal stability, mechanical properties, etc.) was discussed mainly, and the influencing mechanisms were analyzed briefly. At last, the four common methods (reducing molecular polarity, increasing the free volume of molecular, introducing porous structure, and introducing cross-linking structures) for the design of different low dielectric polymers were summarized, and the development direction of low dielectric polymers in future was prospected.

A nano organic silicone oxide sol was prepared by the hydrolysis and polymerization of methyl triethoxysilane and tetraethyl orthosilicate, which was converted into SiO₂ equivalent to mixed with polyamide-imide (PAI) resin through high-speed shearing, and then organic silicone oxide hybrid PAI composite films were prepared through film spreading and thermal curing. The composite films were characterized by infrared spectroscopy, X-ray diffraction, and SEM, and their dielectric spectra, electric strength, and corona resistance lifetime at high temperature (155℃) were tested. The results show that the nano organic silicone oxides disperse uniformly in an amorphous state in the resin matrix. With the increase of the nano organic silicone oxide content, the dielectric constant and dielectric loss factor of the hybrid PAI composite films increase gradually, the electric strength decreases gradually, and the corona resistance life increases at first and then decreases. When the mass fraction of the nano organic silicon oxide is 15% of SiO₂ equivalent, the corona resistance life of the hybrid PAI composite film at high temperature is 3.1 times longer than that of pure PAI film.

Three kinds of organic ultraviolet absorbers with the same concentration were added to polyethylene terephthalate (PET) films, and the properties of PET films before and after UV ageing were tested, and then the effects of ultraviolet absorbers on the UV ageing properties of PET films were studied. The results show that the UV ageing properties of PET films are related to the structure of ultraviolet absorber. Compared with triazine and benzotriazole ultraviolet absorbers, oxazinone ultraviolet absorber exhibits red shift of UV absorption wavelength, wider UV absorption range, and stronger UV absorption intensity because of its hyperconjugated structure. With the increase of ultraviolet radiation energy, the mechanical properties and glossiness of the three kinds of UV resistant transparent films decrease gradually, and the yellow index increases gradually. When the ultraviolet radiation energy is higher than 120 kWh/m², the property differences of the three kinds of UV resistant transparent films before and after ageing are obvious. The property difference of the film containing oxazinone hyperconjugated structure ultraviolet absorber before and after UV ageing is the smallest, and the ageing resistance is the best.

An epoxy insulating material with high moisture resistance was prepared by grafting the hydroxyl terminated polydimethylsiloxane on o-cresol epoxy resin, and its properties were analyzed from the perspective of theoretical calculation and experiment. The results show that when the mass fraction of hydroxyl terminated polydimethylsiloxane is 10%, the modulus and toughness of the modified epoxy resin are higher, the volume change rate at high temperature is smaller. In the layer model of modified epoxy resin and water, the water molecules diffuse away from the epoxy resin. The water absorption of modified epoxy resin is decreased by 13.74% compared with the unmodified epoxy resin. After water absorption, both the volume resistivity and surface resistivity of the modified epoxy resin sample are higher than those of the unmodified epoxy resin, and its electric strength increases by 1.1 kV/mm compared with the unmodified epoxy resin.

Taking urea and hexagonal boron nitride as raw materials, we prepared an amino modified boron nitride nanosheets (BNNS) by ball milling method, and then prepared a BNNS/epoxy composite by mixing the BNNS before and after modification with epoxy resin. The effect of amino modified BNNS on the surface insulating properties of epoxy resin was studied. The results show that the amino group is grafted on the surface of BNNS successfully by ball milling method, which improves the dispersion of fillers in epoxy composites. When the mass fraction of the modified BNNS is 0.5%, the flashover voltage of the BNNS/epoxy composite increases by 26.9% compared with the pure epoxy resin. In addition, the amino modification reduces the trap energy level on material surface and accelerates the space charge dissipation rate. The dielectric constant and dielectric loss factor of the composites filled with amino modified BNNS increase slightly. The flashover voltage of the composites can be improved by balancing the effects of space charge dissipation and polarization relaxation.

Three kinds of solvent-free vacuum pressure impregnated (VPI) insulating varnishes for wind turbine generator were introduced, and their chemical composition and properties were compared with those of the current solvent-containing insulating varnishes. The results show that the solvent-free insulating varnishes have the advantages of low volatilization, environmental protection, and good process applicability, which can meet the technical requirements of current insulating varnish.

Dodecylbenzene (DDB) is a kind of weak polar dielectric material widely used in self-contained high voltage oil filling cable and its accessories. A domestic dodecylbenzene insulating oil was selected as research object, and its physical and chemical properties, and electrical properties were tested. A test system for simulating different types of electrical faults in oil was established, and the gas production characteristics of the dodecylbenzene under two electrical faults of power frequency breakdown in oil and flashover along the oil-paper surface were studied. The results show that the dodecylbenzene insulating oil has excellent physical and chemical properties, and electrical properties. H₂ and C₂H₂ are the characteristic gases under two electrical faults. According to the dissolved gases analysis (DGA) technology of mineral oil, the three ratio method of IEC is suitable for the fault type diagnosis of dodecylbenzene insulating oil, while the Dewey triangle method is not suitable.

The free acid value and PH₃ release amount of PA66 prepared by red phosphorus flame-retardant with different coating process were compared, and the morphology and contact resistance of the corresponding contact element after surface contamination were tested. The effects of housing using different red phosphorus flame-retardant PA66 on the electrical performance of AC contactor were analyzed, and the experiment of simulating the actual application environment was conducted. The results show that the red phosphorus flame-retardant PA66 using multi-layer coating process has low free acid value and PH₃ release amount, which has little effect on the electrical performance of AC contactors and can be used as one of the alternative materials for AC contactor housing.