Polyetherimide (PEI) forms, together with polyeythersulfone (PS) and polysulfone (PSU), a trio of amorphous, aromatic high-temperature polymers. They are difficult to deform when cold, they are excellently resistant to numerous chemicals and they are inherently flame-extinguishing. In terms of specifications and prices, PEI and PES are largely equivalent and therefore exhibit a considerable overlap in their fields of application. Overall, PES provides slightly better chemical resistance, high resistance to hydrolysis, a 5 to 10° higher thermal load limit and a lighter basic colour. PEI scores better on chemical properties, UV resistance and smoke emission.
PEI is frequently used in the automotive industry and in connectors for electrical or optical fibre connections. The thermal properties and tight tolerances make the material suitable for size-critical parts that must be capable of withstanding high temperatures. Thanks to the material’s considerable flame-extinguishing capability and low smoke emission, manufacturers of transport vehicles and aircraft like to use PEI.
PEI’s moisture absorption is low, i.e. 0.7% at 23°C/50% RH and 1.25% when saturated. The glass transition temperature is 215°C, enabling a continuous usage temperature up to 180°C. The UV resistance is reasonable. To a high degree PEI is resistant to watery mineral acids and alkaline and saline solutions, detergents and oils. The material swells or dissolves on contact with polar organic solvents like ketones and halogenated or aromatic hydrocarbons. PEI is not resistant to concentrated acids and alkaline substances.
At room temperature PEI is one of the most rigid thermoplastics. Cold deformation is extremely low at temperatures up to 170°C, while this can be improved still further by adding glass fibre. PEI possesses high-quality dielectric properties across a wide frequency range and temperature range, thus enabling its use in equipment like microwave ovens.