1, all aromatic polyimide by thermal gravimetric analysis, the temperature at which it begins to decompose generally polyimide at about 500 ℃. Polyimide, synthesized from pyromellitic dianhydride and p-phenylenediamine, has a thermal decomposition temperature of 600 ° C and is by far one of the most thermally stable polymers.
2, polyimide can withstand very low temperatures, such as -269 ℃ liquid helium will not be brittle.
3, polyimide has excellent mechanical properties, the tensile strength of unfilled plastic are above 100Mpa, polyimide film thickness (Kapton) is above 170Mpa, thermoplastic polyimide (TPI) Impact strength up to 261KJ / m2. The biphenyl polyimide (Upilex S) reached 400Mpa. As engineering plastics, the amount of elastic film is usually 3-4Gpa, fiber can reach 200Gpa, according to theoretical calculations, pyromellitic dianhydride and para-phenylenediamine synthetic fibers up to 500Gpa, second only to carbon fiber.
4, some polyimide species do not dissolve in organic solvents, stable to dilute acid, the general varieties are not resistant to hydrolysis, this seemingly flawed performance makes the polyimide is different from other high-performance polymer is a very large The feature is that alkaline dianhydride can be used to recover the starting dianhydride and diamine, for example, Kapton membrane, the recovery rate of up to 80% -90%. Change the structure can also be quite resistant to hydrolysis varieties, such as withstand 120 ℃, 500 hours boiled.
5, the thermal expansion coefficient of polyimide in 2 × 10-5-3 × 10-5 ℃, thermoplastic polyimide 3 × 10-5 ℃, biphenyl type up to 10-6 ℃, individual species up to 10 -7 ° C.
6, polyimide has high resistance to radiation, the film after 5 × 109rad fast electron irradiation intensity retention rate of 90%.
7, polyimide has good dielectric properties, the dielectric constant of about 3.4, the introduction of fluorine, or air nano-size dispersed in the polyimide, the dielectric constant can be reduced to 2.5 or so. Dielectric loss is 10-3, dielectric strength is 100-300KV / mm, thermoplastic polyimide is 300KV / mm, volume resistivity is 10Λ17Ω · cm. These features remain high at a wide temperature range and frequency range.
8, polyimide is a self-extinguishing polymer, low smoke rate.
9, Polyimide in a very high vacuum deflated little.
10, polyimide non-toxic, can be used to make tableware and medical appliances, and can withstand thousands of disinfection. Some polyimides also have good biocompatibility, for example, non-hemolytic in blood compatibility experiments, and in vitro cytotoxicity experiments are non-toxic.
Due to the properties and synthetic chemistry of the above-mentioned polyimides, polyimides find it difficult to find a wide range of applications such as polyimides among a wide range of polymers, and in every respect Extremely outstanding performance.
1, film: polyimide is one of the earliest products for motor slot insulation and cable wrapping materials.
2 paint: as insulating paint for the magnet wire, or as a high temperature paint use.
3. Advanced composite materials: for aerospace, aircraft and rocket components. Is one of the most high temperature structural materials. For example, the United States plans for the supersonic airliner designed speed of 2.4M, flight surface temperature of 177 ℃, life expectancy of 60000h, it has been reported that 50% of the structural material has been identified as thermoplastic polyimide matrix resin Of carbon fiber reinforced composites, the amount of each aircraft is about 30t.
4. Fiber: elastic modulus second only to carbon fiber, as a high temperature medium and radioactive materials and bullet-proof filter material, fire-resistant fabric.
Foam: used as a high temperature insulation material.
6. Engineering Plastics: There are thermosetting thermoplastic, thermoplastic molding can also be used injection molding or transfer molding. Mainly used for self-lubricating, sealing, insulation and structural materials. Polyimide materials have been used in compressor rotary vanes, piston rings and special pump seals and other mechanical components.
To sum up, it is not difficult to see that the reason that polyimide can stand out from the numerous aromatic heterocyclic polymers that appeared in the 60s and 70s eventually becomes an important class of polymer materials.