Polyimide (sometimes abbreviated PI) is a polymer of imide monomers. Polyimides have been in mass production since 1955. With their high heat-resistance, polyimides enjoy diverse applications in roles demanding rugged organic materials, e.g. high temperature fuel cells, displays, and various military roles. According to the composition of their main chain, polyimides can be:
- Aliphatic (linear polyimides),
- Aromatic: these are the most used polyimides because of their thermo stability.
According to the type of interactions between the main chains, polyimides can be:
- Thermoplastic: very often called pseudo thermoplastic.
- Thermosetting: commercially available as uncured resins, polyimide solutions, stock shapes, thin sheets, laminates and machined parts.
Thermosetting polyimides are known for thermal stability, good chemical resistance, excellent mechanical properties, and characteristic orange/yellow color. Polyimides compounded with graphite or glass fiber reinforcements have flexural strengths of up to 50,000 psi (340 MPa) and flexural moduli of 3,000,000 psi (21,000 MPa).Polyimide materials are lightweight, flexible, and resistant to heat and chemicals. Therefore, they are used in the electronics industry for flexible cables, as an insulating film on magnet wire and for medical tubing. For example, in a laptop computer, the cable that connects the main logic board to the display (which must flex every time the laptop is opened or closed) is often a polyimide base with copper conductors.