Polyetherimide (PEI): A Comprehensive Review

Characterized by a combination of outstanding thermal, mechanical and electrical properties, Polyetherimide (PEI) has made its place in high performance applications like automotive, aerospace, industrial and many more.

Explore Polyetherimide in detail along with its key properties like mechanical, thermal, electrical, etc. and understand what makes it an ideal choice in high-end engineering applications. Also, learn about its production process and conditions to process this polymer material. Let’s first start by understanding basic characteristics of PEI…

Polyetherimide Features and Applications

Polyimides are a relatively new class of specialty plastic materials that are characterized by:

  • High strength-to-weight ratio
  • Thermo-oxidative stability
  • Excellent mechanical properties
  • High temperatures resistance and more…

The characteristic group of polyimides is the imide or –C=ONC=O- group.

Polyetherimides have been developed to overcome challenges associated with polyimides i.e. this polymer family is not readily melt processable, and finished parts tend to be rather expensive.

Key Properties and Benefits of Polyetherimide (PEI)

Incorporating the proper ether linkages into the polyimide molecular chain provides sufficient flexibility to allow good melt processibility yet retains aromatic imide characteristics of excellent mechanical and thermal properties.

  • Imides impart high temperature performance
  • Ether groups allow melt processing

Polyetherimide was first developed in 1982 by General Electric Company (now known as SABIC) under the trade name ULTEM resin.

Molecular Structure of Polyetherimide (PEI)
Molecular Structure of Polyetherimide (PEI)

Today, PEI is available from several suppliers such as: SABIC, RTP Company, Lehmann & Voss, Quadrant, PolyOne etc.

Polyetherimide (PEI) is an amorphous engineering thermoplastic known to exhibit high temperature resistance, outstanding mechanical and electrical properties.

  • Molecular Formula: [C37H24O6N2]
  • Molecular weight: 592.61 g/g-mol

This high-performance polymer also exhibits high tensile strength, good flame resistance and low smoke emission making it an ideal material of choice in automotive, electrical, medical and other industrial applications.

The high-temperature resistance of Polyetherimide competes with polyketones, polysulfones, and polyphenylene sulfide.

» View All Commercially Available PEI Grades & Suppliers in Omnexus Plastics Database

This plastic database is available to all, free of charge. You can filter down your options by property (mechanical, electrical…), applications, conversion mode and many more dimensions.

Key Properties of PEI

The basic characteristics and key features of Polyetherimide are already discussed. Apart from them, there are various other properties that need to be considered before choosing a particular thermoplastic for a required end-use application.

  • PEI is an amorphous thermoplastic resin with amber transparency

  • The resin is characterized by high deflection temperature (200°C at 264 psi), high tensile strength and flexural modulus (480,000 psi), and very good retention of mechanical properties at elevated temperatures

  • It has unique combination of high specific strength, rigidity, flexibility, exceptional dimensional strength etc.

  • In addition, the resin exhibits good electrical properties, which remain stable over a wide range of temperature and frequencies (including microwave)

  • It has good UV-light resistance and weatherability

  • PEI is inherently flame resistance without the use of additives

  • It has a high limiting oxygen index of 47, combined with NBS smoke chamber results which show the lowest specific optical density of any unfilled thermoplastic

  • Polyetherimide is resistant to alcohols, acids, and hydrocarbon solvent but dissolves in partially halogenated solvents

  • PEI also displays good hydrolytic stability

  • Most of the PEI grades has a UL94 flame resistance rating of VTM-0, is FDA compliant, EU Food Contact Compliant, and ISO10993 compliant in natural color

Polyetherimide resin is available in an unreinforced grade for general-purpose processing methods as a transparent resin and in standard and custom colors.

It is also available in:

Glass reinforcement provides even greater rigidity and dimensional stability while maintaining many of the useful characteristics of basic PEI. The glass reinforcement yields a product with an exception strength-to-weight ratio and increased tensile strength.

» Compare Properties of Unfilled PEI and 30% Glass-fiber Reinforced PEI

Limitations Associated with PEI

  • Very high cost. Applicable for highly demanding applications
  • Low colorability
  • Attacked by polar chlorinated solvents leading to stress cracking
  • A long drying before processing is necessary
  • Hot mold during injection molding

Popular Applications of Polyetherimide (PEI)

PEI’s unique combination of properties makes it the choice of material for a variety of applications. Let’s discuss some of the applications in detail.

Automotive and Aerospace Market

PEI in Automotive Applications Polyetherimide applications in automotive have been increasing due to its replacement with metal, thermosets and bulk molding compounds (BMC). Electrical and lighting systems are the largest application areas for PEI in the automotive market followed by under-the-hood applications.

Polyetherimide is used in applications that require high heat resistance, high strength and modulus and broad chemical resistance.

The principal automotive applications of Polyetherimide include:

  • Transmission components
  • Throttle bodies,
  • Ignition components
  • Thermostat housings,
  • Bezels
  • Reflectors
  • Lamp sockets, and
  • Electromechanical systems such as fuses, gears, bearings, solenoid bodies, ignition switches and oil pump drives

Polyetherimide is also widely used in automotive lighting applications such as headlight reflectors, fog light reflectors, bezels and light bulb sockets. In these applications PEI is selected for its high heat resistance (up to 200°C), ability to be metalized without a primer, and its competitive systems cost versus thermosets.

» Review All Polyetherimide Grades for Automotive Application!

In Aerospace applications, PEI is recommended for its light-weight and electrically conductive properties suitable for EMI shielding, elevated thermal resistance, exception mechanical strength etc. It is used in jet engine components and sheeting of aircraft interiors.

Electrical and Electronical Market

Electrical / electronic is the second most important market for Polyetherimide. In the telecommunications market, there is an increasing need for high heat resistant materials, especially for high-end connectors in the fiber optics segment. PEI resin offers high heat resistance as well as great flow for thin wall design.

Polyetherimide  Other applications of Polyetherimide include:

  • Electrical switches and controls
  • Electrical motor parts
  • Printed circuit boards, and
  • Connectors

Polyetherimide is also used in so-called molded interconnect devices (MID). This is because of its unique plating capabilities. PEI allows the combination of electrical functions with the advantages of injection molded 3-D mechanical components.
The key trend influencing further use of polyetherimide in electrical / electronic applications is new product development. To meet the ongoing needs for miniaturization in the electronics sector, (increased packing densities and more lightweight carrier materials) ceramic-filled polyetherimide grades have been developed. These grades have excellent electrical and processing properties, and can also be easily metalized. They are suitable for applications such as:

  • Circuit boards operating in the microwave range as well as internal aerials
  • Electronic chips, and
  • Capacitors

» Check Out All Available Polyetherimide Grades For Electrical Applications!

Disposable & Re-Usable Medical Applications

Medical Uses of PEI There are a few significant applications of Polyetherimide in the medical sector. PEI resins are suitable for both disposable and re-usable medical devices and for medical monitor probe housing. They possess good combination of properties:

  1. They are autoclavable, both chemical and lipid resistant
  2. They are available in both clear and opaque grades

Polyetherimide also withstands dry heat sterilization at 180°C, ethylene oxide gas and gamma radiation.

PEI finds extensive use in membrane applications due to its separation, permeance, blood and tissue biocompatibility properties. Typical application include membranes for biohybrid applications. Other medical applications of PEI are surgical instrument handles and enclosures, non-implant prostheses etc.

» Explore All Polyetherimide Grades for Medical Applications!

Metal Replacing Property for Industrial Applications & Appliances

Polyetherimide is very often used as a metal replacement material. Industrial applications of Polyetherimide mainly consist of:

  • HVAC equipment and fluid handling systems
  • Manufacture of institutional kitchenware

In household and domestic appliances, PEI is widely used in:

  • Microwave cookware
  • Steam and curling irons
  • Dual-ovenable trays for food packaging that meets FDA food packaging requirements

Synthesis of Polyetherimide (PEI)

PEI is produced via the polycondensation reaction between bisphenol-A dianhydride such as tetracarboxylic dianhydride (produced from the reaction of bisphenol A and phthalic anhydride) and a diamine such as m-phenylene diamine.

 Monomer of Polyetherimide (PEI)
Tetracarboxylic Dianhydride (PEI Monomer)
Plus   m-Phenylene Diamine
m-Phenylene Diamine
Polymerization of PET
Molecular Structure of Polyetherimide (PEI)
Polyetherimide (PEI)

How to Process PEI?

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Suitable Conversion Mode

PEI Conversion Mode

Unlike most other polyimides, PEI is suitable for processing by typical methods such as:

  • Injection Molding
  • Extrusion
  • Thermoforming
  • Compression molding

Polyetherimides can be melt processed because of the ether linkages present in the backbone of the polymer. However, it still maintains high-temperature properties similar to the polyimides. The polymer should be dried at 140-150°C for 4 to 6 hours before processing for a maximum moisture content of 0.01% to 0.02%.

  • Processing temperature: 370 to 400°C
  • Purging of the barrel is necessary when changing material (PC or HDPE at 370-400°)
  • Mold Temperature 65 to 180°C
  • Suitable for injection of very small parts with tight dimensional tolerances

The polymer can be easily machined with conventional metalworking tools, painted, hot stamped, printed, or metallized.

PEI films are made via melt-extrusion and solvent casting processes and PEI fibers are made via melt-extrusion and spinning.

Bonding of PEI is carried out typically via:

  • Fuse bonding
  • Ultrasonic bonding
  • Solvent bonding
  • Adhesive bonding

Additionally, PEI is nowadays widely used resin material to create functional prototypes and production parts for high-strength, FST-rated and certified applications using 3D Printing. Check out this interesting video on PEI 3D Printing...

Commercially Available PEI (Polyetherimide) Compounds

This plastic database is available to all, free of charge. You can filter down your options by property (mechanical, electrical…), applications, conversion mode and many more dimensions.

Polymer Properties Compare Properties of Unfilled & Glass-filled PEI Polymer Application Check Latest News About PEI

3 Comments on "Polyetherimide (PEI): A Comprehensive Review"
Gabrie H Jan 11, 2018
Nanda, than pls change the structure of the polymer as well ;) The N atoms should be in the meta position. The structure you have written down, is ULTEM CRS, another great Polyetherimide with improved chemical resistance as main feature.
PAYAL A Jan 10, 2018
Thanks Nanda for sharing your comments. We've made the updates.
Nanda Kumar N Jan 7, 2018
In Synthesis of Polyetherimide (PEI), the structure of: m-Phenylene Diamine is incorrect. The Carbon on the fifth position of the phenyl ring consists of 5 chemical bonds as against four chemical bonds as per the valency of the Carbon atom. Please verify and comment. Thank you Nanda Kumar N

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