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Chinese electric high-speed locomotive and multiple unit train have made rapid progress in recent years, and high-power traction electrical machine is the key component of them. Polyimide (PI) enamel can be used in large motor as insulating enamel of conductive wire, coil impregnating varnish, and anticorona varnish. When electrical machine is operating, large amount of heat is generated associating with current and voltage. It will result in insulation aging and destruction. PI paint films possess excellent properties such as heat-resistance, high-strength, flexibility, aging-resistance and radiation-resistance, and show better dielectric property even thinner than other insulating materials, which is favorable towards the miniaturization and light-weight of electronic machine.The project is mainly including four parts:(1) synthesis and characterization of polyimide monomers. (2) preparation and performance study of polyimide resin with maleimide side groups. (3) molecular structure design and synthesis study of heat-resistant enamel. (4) manufacture and performance research of heat-resistant enamel and its wire.In this paper, a novel tetramine monomer called 2,2-bis[4-(2,4-diaminophenoxy)phenyl] propane (BDAPPP) was designed. It was prepared through the reducing reaction of 2,2-bis[4-(2,4-dinitrophenoxy)phenyl]propane(BDNPPP) in the system of Pd/C hydrazine hydrate. The compound of BDNPPP was obtained by the condensation reaction between bisphenol A and 2,4-dinitrochlorobenzene in the mixture solvents of N,N-dimethylformamide(DMF) and tolune in the presence of potassium carbonate. Subsequently the monomer of BDAPPP was partly amidated by maleic anhydride first, and then together with 4,4’-diaminodiphenylether(ODA) as amino-compounds polymerized with aromatic dianhydrides including pyromelitic dianhydride (PMDA),3,3’,4,4’-diphenylether dianhydride(ODPA),3,3’,4,4’-benzophenone tetracarboxylic dianhydride (BTDA) and biphenyl dianhydride (BPDA) respectively to obtain corresponding polyamic acid resin with maleimide side groups.To adopt this branched structure, viscosity is decreased sharply. Then a series of polyimide film were manufactured by thermal imidization, and the properties of them were researched, including FT-IR, mechanical performance, dielectric loss, light transparency, surface energy and water absorption.A diamine with phenolic hydroxyl group called 4,4’-diamino-4"-hydroxytriphenyl methane (DAHTM) was synthetized through the condensation reaction between phydroxy benzaldehyde and aniline in the presence of aniline hydrochloride as catalyst. Then it was used to polymerize together with other monomers to obtain a kind of excellent polyimide enamel with high temperature resistance.The effect of film molecular structure on properties was also studied.By optimizing, a kind of heat-resistant polyimide enamel polymerized by DAHTM, BAPP,4,4’-ODA, BTDA and PMDA was selected at last. Its proper viscosity and surface tension make it easy to be coated. The enamel wire has excellent heat resistance with 293℃of glass transition temperature (Tg), and the cut-through temperature and breakdown voltage are obviously higher than the national standard of 240 class round aromatic polyimide enamel copper-wire.
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