The cross-linking reaction of ER and curing agent will form a polymer with a three-dimensional cross-linked network structure. Because of its excellent insulation and mechanical properties, it has been widely used in electrical and electronic, aerospace, transportation and other fields [[1], [2], [3]]. Among them, the cured product formed by ER and acid anhydride has higher dielectric properties and is widely used as an important electrical insulating material worldwide [4]. However, with the improvement of power supply requirements and the access of a large number of alternate energy generator sets, the voltage level of the transmission has been continuously improved, and the operating conditions of the insulation components have become quite involved, often dealing with high temperature and high mechanical stress environments [5,6]. The thermal and mechanical properties of traditional ER are gradually difficult to meet the increasingly severe operating environment, which leads to failure of insulating components, affecting the safety of equipment and the stability of power supply. Therefore, improving the heat resistance and mechanical properties of epoxy resins has become a key technical difficulty to be solved urgently in the energy and power industry.

Researchers have long proposed a variety of modification methods to improve the thermal and mechanical properties of ER. In actual production, the use of inorganic fillers for filling and modification, such as SiO2 and alumina, can effectively improve the mechanical and thermal properties of ER composites [7,8]. However, a higher filler doping amount will significantly increase the cost, and the filler is likely to cause agglomeration in the composite, causing regional differences in dielectric constant, resulting in local electric field distortion and inducing discharge failures. The use of organic polymer materials for blending modification is still the most commonly used method to improve the performance of ER [9]. Rubber elastomers, thermoplastic resins, liquid crystal polymers, etc. all have a certain improvement effect on the performance of blended ER. However, However, due to the differences in compatibility and thermal expansion coefficient between polymers, insulators are often cracked at high temperature. Therefore, developing epoxy resin matrix formulation system with high stability, high thermal and mechanical properties is a current research focus in the field of high-voltage insulation. In recent years, there have been reports on ER with high thermal and mechanical properties. Tian et al. [10] blended the trifunctional ER with the ER of rigid conjugated structure, and cured it with methyl hexahydro phthalic anhydride, which significantly improved the glass transition temperature (Tg) and tensile strength of the cured product. Andreas Hartwig et al. [11] introduced polytetrafluoroethylene into alicyclic resin for blending, and studied the variation of mechanical properties of the product. Harada et al. [12] synthesized a new tetrafunctional mesocrystalline epoxy monomer centered on cyclic siloxane chain, which improved the tensile modulus and elongation of the cured product. However, at present, the development progress of high-performance epoxy resin substrate for high-voltage insulation is relatively slow, and most of the research still focuses on experimental attempts, ignoring the combination of microstructure analysis and performance test of epoxy resin crosslinking network, resulting in the lack of reference significance for the research and development of specific scene materials.

The performance of cured ER are closely related to the molecular structure of epoxy resin and curing agent. The monomer molecule is the core unit in the cross-linked network, and its group composition determines the cross-linked form of the polymer. Zhang et al. [13] found through MD simulation that the change of the molecular structure of the cross-linked monomer has a significant effect on the performance of the epoxy resin cured system, and the molecular stiffness will significantly change the thermodynamic properties of the cross-linked network. In addition, intermolecular force and molecular chain structure are also key factors affecting the properties of cured products. Zhang et al. [13] found through MD simulation that the change of the molecular structure has a significant effect on the performance of the ER cured system, and the molecular stiffness will significantly change the thermal and mechanical properties of the cross-linked network. In addition, intermolecular force and chain structure are also key factors affecting the properties of cured products. Junsoo Kim [14] and others found that the polymer network with entangled structure contains more entanglement nodes, and these nodes make the tension transfer in the polymer chain, which makes it have higher toughness and strength. These researches provide important guidance for the design and synthesis of high-performance ER. Targeted selection of monomer components according to engineering application scenarios and design of cross-linked network structures with high strength are the key means to obtain ER for high-voltage insulation with excellent performance.

Cycloaliphatic epoxy resins have excellent thermal and insulating properties. Blending it with bisphenol A diglycidyl ether (DGEBA) can improve the Tg and mechanical strength of the crosslinked system. As a typical cycloaliphatic epoxy resin, Diglycidyl 4,5-epoxy-hexane-1,2-dicarboxylic acid (TDE-85) has excellent mechanical properties and heat resistance due to its special Y-type trifunctional structure [15,16]. However, due to the complex preparation process and high cost, the extensive application of TDE-85 is limited. At the same time, there are relatively few studies on the blending modification of alicyclic resin, bisphenol a resin and anhydride curing agent crosslinking system. The molecular mechanism of its performance variation is not clear, which limits its application in the field of high voltage insulation.

With the rapid development of computer simulation, the material simulation method represented by molecular dynamics shows obvious advantages in studying the microstructure and macro properties of composite polymer materials, and is widely used in research and development of new materials, polymer synthesis and other fields [17,18]. S. Masoumi et al. [19] constructed the molecular model of DGEBA/D-230 epoxy system with different crosslinking degrees based on the self-developed crosslinking algorithm, and analyzed the group changes of the resin during curing. Literature [20] used different methods to calculate the Tg and elastic modulus of ER, and discussed the relationship between the micro information and thermal and mechanical properties of the material. Yang et al. [21] used MD technology to calculate the torsional energy barrier and cohesive energy density of DDM/TDE-85 and DDS/TDE-85 blended ER. It was found that the monomer with stronger rigidity has relatively high cohesive energy density, and the cured product has higher Tg. Regarding the improvement of polymer properties, it can be effectively explained through the theory of free volume and mean square displacement. Li et al. [22] investigated the thermodynamic properties of DGEBA/OSC epoxy composites using molecular dynamics simulations. They discovered a highly consistent correlation between the decrease in the proportion of free volume and the low torsion values of crosslinks. Sridehar AS [23] compared the performance parameters of epoxy systems at different R values, and revealed a strong link between the free volume fraction and the thermodynamic properties of the material in high temperature environment. Zhang et al. [24] employed molecular dynamics simulations to demonstrate that grafting hyperbranched polyesters onto silica surfaces can efficiently reduce the system's FFV and MSD values, as well as enhance the bonding between silica and epoxy resin matrix, resulting in the best possible thermomechanical properties for the material. It can be seen that MD method shows great potential in understanding the behavior of materials and simulating the properties of new materials, which is expected to provide new ideas for the design and synthesis of high-performance ER.

In this paper, DGEBA and TDE-85 are used as ER matrix and methyl tetrahydrophthalic anhydride (MTHPA) is used as curing agent. The mixed system models with different proportions are constructed through simulation software. The torsional energy barrier and system compatibility of monomer molecules were analyzed, the thermal, mechanical properties and micro parameters of different formulation systems were calculated, and the influence of Y-nodes introduced by TDE-85 on the properties of crosslinked network was studied. The samples of the blend system were synthesized through experiments, and their Tg and mechanical strength were tested. It is expected to provide guidance for the design and synthesis of high-performance ER for high-voltage insulation.