How it's made
PEI is synthesized through the polycondensation of aromatic bis(ether anhydrides) with diamines, such as meta-phenylene diamine (mPDA), at high temperatures and in aprotic solvents such as N-methylpyrrolidone (NMP). The initial step yields an amic acid intermediate, which, upon heating, cyclizes to form the imide ring characteristic of PEI. The synthesis is controlled to yield high molecular-weight polymers with superior mechanical properties.
PEI is processed using standard techniques: extrusion, injection/compression molding, thermoforming, or machining. It has good processability, as it can be machined with high precision and is compatible with additive manufacturing processes.
Strength
PEI has excellent mechanical properties, including high tensile strength, enabling the polymer to withstand heavy mechanical loads. It also has high stiffness. Moreover, PEI ensures long-term stability under sustained loads due to its high creep resistance.
Heat
PEI maintains its mechanical properties even with sustained exposure to temperatures as high as 170 °C. Its ability to maintain stability without softening is indicated by its high glass transition temperature of 217 °C (423 °F). This polymer has low thermal conductivity and exhibits a low coefficient of thermal expansion, maintaining dimensional stability under thermal cycling and high-temperature conditions. This high thermal resistance has enabled PEI’s widespread use in the healthcare sector, as it can withstand repeated autoclave conditions.
PEI is an excellent insulator, possessing high dielectric strength. Its electrical insulation properties can withstand a range of temperatures and frequencies, a critical characteristic in the electronics and electrical sectors. PEI exhibits a low dielectric constant, making it suitable for high-frequency communication devices.
Chemicals and water
PEI has excellent chemical resistance to most compounds, including weak acids and bases, organic solvents, hydrocarbons, and oils. However, it is susceptible to degradation by strong bases and strong acids with prolonged exposure. Additionally, PEI is prone to stress cracking in chlorinated solvents. While not hydrophobic, PEI exhibits low moisture absorption, allowing it to withstand humid conditions with minimal impact on its electrical and mechanical properties.
Wear and fire
PEI exhibits good wear resistance and low friction, making it widely used in applications involving sliding or rotational motion. It is also inherently flame-retardant, without the need for additional flame-retardant additives. It emits minimal smoke and toxic gases when exposed to flames, a desirable feature for aerospace and transportation applications where stringent fire safety standards must be met.
Sustainability
PEI’s manufacturing is energy-intensive due to the high temperatures required for processing, contributing to its carbon footprint. Furthermore, the polymer is non-biodegradable, persisting in the environment if improperly disposed of. However, as a high-performance polymer, its recycling remains limited.
History
Polyetherimide (PEI) is a high-performance thermoplastic polymer developed by General Electric Plastics (now part of SABIC) and introduced to the market under the tradename Ultem. PEI’s development was driven by the need for novel materials combining excellent mechanical and electrical properties with thermal and chemical resistance. Its target sectors included aerospace, automotive, and electronics, which require materials that can withstand extreme conditions.