Polyimiden

Polyimiden, commonly referred to in English as polyimide, is a class of high-temperature polymers characterized by imide groups in the backbone. The repeating units typically contain one or more imide linkages between aromatic rings, which contribute to their thermal stability and chemical resistance. Polyimides are usually prepared by condensation of dianhydrides with diamines to form polyimide chains, often via a poly(amic acid) precursor that is converted to the imide through dehydration (thermal or chemical imidization).

Polyimides can be classified as thermoset or thermoplastic. Thermosetting polyimides form resin matrices upon curing, while thermoplastic polyimides (TPIs) can be melted and re-shaped, enabling melt processing for certain formulations. Films such as Kapton are well-known polyimide-based materials and are widely used in electronics and aerospace. Processing options include film casting, coatings, varnishes, fibers, and molding resins, with methods adapted to the specific formulation.

Key properties include high glass transition temperatures, often well above room temperature, and high thermal decomposition temperatures. They offer excellent mechanical strength at elevated temperatures, very good dielectric and insulating properties, chemical resistance, and low creep. Many polyimides also exhibit low outgassing, important for space applications. Processing can be challenging due to limited solubility and the tendency to be infusible, which generally requires specialized solvents for solutions or high-temperature methods for melt processing.

Applications encompass electronics (flexible circuits, insulating films, dielectric layers), aerospace (thermal insulation), coatings and adhesives, membranes for gas separation, and high-temperature engineering plastics. Safety and environmental considerations focus on handling of monomers and solvents used in manufacture, with emphasis on proper ventilation and waste treatment due to irritants and potentially hazardous precursors.