Details
Material hierarchy: Polymer - Engineering Thermoplastic
These linear, aromatic polymers are prized for their high-temperature performance. While nominally thermoplastic, polyimides will degrade at temperatures below their softening point and thus have to be processed in precursor form. Material is supplied in powder form for compression molding and cold forming, and some injection molding grrades are being offered.
The outstanding physical properties of the polyimides make them valuable in applications involving severe environments such as high temperature and radiation, heavy load, and high rubbing velocities. In terms of heat resisttance, the continuous service of polyimide in air is on the order of 500°F. At elevated temperatures, polyimide parts retain an unusually high degree of strength and stiffness, but prolonged exposure at high temperatures can cause a gradual reduction in tensile strength.
Polyimides are resistant to most dilute or weak acids and organic solvents; they are not attacked by aliphatic or aromatic solvents, ethers, esters, alcohols, and most hydraulic fluids. However, they are attacked by bases such as strong alkali and aqueous ammonia solutions; and the resin is not suitable for prolonged exposure to hydrazine, nitrogen dioxide, or primary or secondary amine components. Parts fabricated from unfilled polyimide resin have unusual resistance to ionizing radiation and good electrical properties.
Polyimides are used to mold high-performance bearings for jet aircraft, compressors, and appliances. In film form, the material is used for electric motor insulation and in flexible wiring. Polyimides also are used in making printed circuit boards.