Polyimide

Polyimide is a class of polymers that contain imide linkages in the polymer backbone. Most polyimides are highly aromatic, which contributes to exceptional thermal stability, mechanical strength, and chemical resistance. They are commonly synthesized by the condensation of a dianhydride with a diamine to form a poly(amic acid), which is then converted to the imide polymer by thermal or chemical imidization.

There are two main formats of polyimides: thermoset polyimide resins and thermoplastic polyimides (TPIs). Thermoset resins cure to form a crosslinked network, while TPIs are melt-processable and can be formed into films, fibers, coatings, and other shapes.

Key properties include high glass transition and decomposition temperatures, high modulus and creep resistance, and excellent dielectric properties and chemical resistance. Many aromatic polyimides are inherently insoluble and infusible, complicating processing, though soluble or melt-processable variants have been developed through backbone modification or end-capping.

Common applications span electrical insulation for motors and cables, flexible printed circuit boards, high-temperature coatings, aerospace and industrial membranes, and lightweight structural composites. Kapton is a well-known polyimide film derived from pyromellitic dianhydride and 4,4'-oxydianiline (PMDA-ODA).

Synthesis notes: imidization can be achieved thermally or chemically; processing often involves poly(amic acid) intermediates and, in solvent-based routes, specific solvents and curing conditions.