Polyimide films are mainly divided into homophenyl polyimide films and biphenyl polyimide films.

Polyimide film is one of the best film insulating materials in the world. Widely used in liquid crystal display, microelectronics, aerospace and military industry, rail transit and other industries. Polyimide film is called "gold film" because of its high price, high technical barriers and excellent performance. For a long time, high-performance polyimide films have been monopolized by foreign giants and tightly blocked by technology. It is one of the key polymer material bottlenecks restricting the development of my country's high-tech industry.

Polyimide film was one of the first polyimide products and was used for slot insulation in motor and cable wrapping materials. The main products are the upilex series produced by DuPont Kapton, Yubuxing and Zhongyuan Top. Transparent polyimide films can be used as flexible solar cell substrates. Ikaros sails are made of polyimide film and fibers. In the thermal power generation sector, polyimide fibers can be used for hot air filtration, and polyimide yarns can separate dust and special chemicals from exhaust gases.

Polyimide film is an insulating material for high temperature motors and electrical appliances, which is yellow and transparent. Mainly divided into homophenyl polyimide film and biphenyl polyimide film. It has outstanding high temperature resistance, radiation resistance, chemical corrosion resistance and electrical insulation properties, and can be used for a long time in the air at 250 ~ 280 ℃.

Polyimide is chemically stable. Polyimide prevents combustion without adding flame retardants. Generally polyimides are resistant to chemical solvents such as hydrocarbons, esters, ethers, alcohols and halothanes. They are also resistant to weak acids, but are not recommended for use in strong bases and mineral acid environments. Some polyimides such as CP1 and Corin XLS are solvent soluble, which helps develop their applications in spray coating and low temperature crosslinking.

1. According to thermogravimetric analysis, the initial decomposition temperature of fully aromatic polyimide is generally around 500 °C. The polyimide synthesized from biphthalic anhydride and p-phenylenediamine has a thermal decomposition temperature of 600°C, which is one of the polymers with high thermal stability so far.

2. Polyimide can withstand extremely low temperature, such as not embrittlement in liquid helium at -269℃.

3. Polyimide has excellent mechanical properties. The tensile strength of unfilled plastic is greater than 100MPa, that of homophenyl polyimide (Kapton) film is greater than 170MPa, and that of biphenyl polyimide (upilex s) is 400MPa. As an engineering plastic, the amount of elastic film is usually 3-4gpa, and the fiber can reach 200GPa. According to theoretical calculation, the fiber synthesized by phthalic anhydride and p-phenylenediamine can reach 500gpa, second only to carbon fiber.

In recent years, polymer foams have been widely used in aviation, aerospace, transportation and construction industries due to their advantages of light weight, high specific strength, high specific stiffness, heat absorption and sound absorption. With the further improvement of high and low temperature resistance, insulation, smoke-free, non-toxic, easy processing and other properties of foamed plastics and polymer foamed plastics (such as polyolefin foam, polystyrene foam, polyurethane foam, polyvinyl chloride foam, phenolic foam) Augmentation does not meet the requirements. Therefore, the research and development of high-performance polymer foams has become a new research focus and direction.

Polyimide has excellent comprehensive properties. It can be used continuously at high temperature of 250°C, and the tensile strength at room temperature can reach 200MPa; it has good creep resistance, good flame retardancy, self-extinguishing, secondary chemical resistance, resistance to most chemicals and good resistance to radioactive. The processing methods of polyimide include injection molding, extrusion, casting, molding and so on. Polyimide can be processed into complex static parts with light weight and high specific strength. It can replace metal to manufacture aircraft structural parts and shells. It can also be used to manufacture films, laminates, gears, bearings, waveguide materials, engine parts, etc.