Atlas of Polymers

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The Engineering Polymers Era (1961-1979)

1975

Polyetherimide (PEI)

The Amber Guardian of the Electronics Age

thermoplastic·polyimide·Tohru Takekoshi, General Electric

In July 1975, an American Apollo capsule and a Soviet Soyuz spacecraft docked in Earth orbit, and for two days five men who had spent careers training to beat each other to the Moon shook hands through an open hatch instead. The hardware that made it possible was itself a small miracle of joining incompatible systems: American and Soviet docking mechanisms, electrical standards and life-support chemistries had to be redesigned from scratch so that two spacecraft built by rival superpowers could connect without killing anyone.

Plate I

Five men in flight suits pose for a formal portrait, three in tan NASA suits and two in olive Soviet suits, seated around a table holding a scale model of the docked Apollo and Soyuz spacecraft, flanked by American and Soviet flags.
The Apollo and Soyuz crews, photographed together ahead of the July 1975 docking mission that required American and Soviet hardware to be engineered to work as one system.Wikimedia Commons

A smaller, quieter act of joining two incompatible systems was going on that same year inside General Electric’s Corporate Research and Development Center in Schenectady, New York. Aromatic polyimides (the Kapton-style chemistry already a decade old by 1975) were superb insulators and could shrug off heat that would destroy an ordinary plastic, but they shared a stubborn family trait: once the imide rings closed, the polymer would not melt, which meant it could only be cast as a film or built up as a solution-processed coating, never simply injection-molded the way an ordinary thermoplastic could. Chemist Tohru Takekoshi, working with John Kochanowski, found a way around that limit: build the imide rings onto a backbone that also carried flexible ether linkages between them, breaking up the rigid stacking that made conventional polyimide so heat-tolerant and so unmeltable at the same time. Their process patent, describing what would become polyetherimide, was granted on 16 September 1975.

Plate II

A large early-twentieth-century brick research building with a rooftop sign reading GENERAL ELECTRIC beneath the company's script-lettered monogram, seen across a park-like lawn with mature trees.
General Electric's Research and Development Center in Schenectady, New York, where Tohru Takekoshi's team developed the ether-linked polyimide chemistry behind Ultem.Wikimedia Commons

The One That Melts

Every other imide-ring polymer in this atlas earns its place by refusing to soften: that refusal is precisely what makes Kapton film survive a spacecraft’s temperature swings and Torlon bearings survive friction that would melt an ordinary plastic. Polyetherimide’s whole reason for existing is that it breaks that rule just enough. The ether oxygen between imide-bearing segments gives the chain a hinge the fully rigid polyimides don’t have, so instead of decomposing before it ever reaches a melt, the polymer flows like glass above its softening point and can be injection molded, extruded, or 3D-printed on equipment built for ordinary engineering plastics, at higher temperatures than those plastics tolerate, but on the same machines. GE brought the result to market a few years later as Ultem, and the “meltable polyimide” description has stuck to it ever since as the trait that sets it apart from its more rigid relatives.

Plate III

Several rolls of amber, semi-transparent Kapton polyimide tape, still shrink-wrapped with barcode labels, stacked together.
Rolls of Kapton polyimide tape, the rigid, unmeltable chemistry that polyetherimide shares an imide ring with, but that it alone among this family can also melt and mold.Wikimedia Commons

What the Trade-Off Buys

Because it is fully amorphous rather than crystalline, Ultem is naturally transparent with a distinctive amber tint, clear enough to see fluid levels through a molded part. This is an unusual property for a polymer this heat-resistant, and one most of its imide relatives simply don’t have. It tolerates heat well above the point that softens ordinary engineering plastics without needing any additive to do so, and it self-extinguishes readily, producing little smoke when it does burn, which is precisely why it ended up in aircraft cabin interiors subject to strict fire, smoke and toxicity rules. Mechanically it is stiff and strong enough to substitute for metal in lightly loaded parts, though (like most of the rigid, aromatic polymers in this atlas) it does not stretch far before it breaks. It shrugs off acids, alkalis, oils and greases without much trouble, and holds up reasonably well against alcohols, esters and hydrocarbons too, a broader chemical tolerance than many high-heat plastics manage. Being amorphous does cost it a little in moisture uptake compared with the fully rigid polyimides, so parts are dried carefully before molding, but that is a small price for a resin that processes on an injection press rather than only as a cast film.

Plate IV

A close-up view inside an aircraft cabin showing two rows of blue upholstered economy seats beside oval windows, with white overhead panelling and ventilation nozzles visible above.
An aircraft cabin interior, the kind of environment where Ultem-family resins are chosen for panels and ducting precisely because they resist fire and produce little smoke.Wikimedia Commons

From Cockpit to Kitchen Drawer

Ultem’s aerospace career came first: aircraft interior panels, ducting and connectors that had to meet strict flammability rules while still being light enough to matter, and later structural components on the Boeing 787 substituting for metal parts to save weight aircraft-wide. But the same amber resin turned up somewhere far more ordinary: inside the sterilizable trays and surgical instrument handles that pass through a hospital autoclave hundreds of times without warping, and later as filament for high-temperature 3D printers, letting engineers print load-bearing prototypes in a material that would previously have needed a mold. A polymer developed to solve one very specific problem (melting a polyimide without breaking its heat resistance) ended up wherever that same combination of properties happened to matter.

Fifty Years of the Meltable Polyimide

Apollo-Soyuz was a one-time gesture, retired along with the hardware that made it possible. Polyetherimide’s trick, breaking the imide backbone’s stubborn refusal to flow, has aged rather better: five decades on, it is still the polyimide chemists reach for whenever the job calls for injection-molding, not casting.

values with [n] cite the numbered references·estimates are flagged·“not yet available” and “N/A” are honest states, not gaps

polyetherimide repeat unit N O O O O N O O n

Polyetherimide repeat unit

Abbreviation
PEI
Type
polymer family (hub)
CAS number
61128-46-9
Resin ID code
none assigned
Formula
(C37H24N2O6)nThe bisphenol A-based polyetherimide shown is the commercial archetype (Ultem). Each (CO)2 bridge is one fused five-membered imide ring, written open for readability; the ether links either side of the bisphenol A bridge are what make this polymer melt-processable, unlike the fully rigid polyimides.
Repeat unit (BigSMILES)
{[][>]N1C(=O)c2ccc(Oc3ccc(cc3)C(C)(C)c3ccc(cc3)Oc3ccc4C(=O)N(C(=O)c4c3)c3cccc(c3)[<])cc2C1=O[]}
IUPAC name
—
Synonyms
Ultem
Also known as
Ultem

Chemical family
polyimide
Backbone class
heterochain
Polymerization mechanism
step-growth-condensation
Constitutional monomer
Bisphenol A dianhydridem-Phenylenediamine
Polymer class
thermoplastic

Year of origin
1975
Era
The Engineering Polymers Era (1961-1979)
Key figures
Tohru Takekoshi · General Electric
Events referenced
Apollo-Soyuz Test Project docking (July 1975) · Takekoshi and Kochanowski's polyetherimide patent grant (16 September 1975)

Polymerization type
step-growth condensation (imidization)
Common monomers (feedstocks)
bisphenol A dianhydride, m-phenylenediamine
Catalysts
not yet available

Research by J.G. Wirth's team at General Electric in the early 1970s led to commercial introduction in 1982 under the trade name Ultem. Made via imidization of a flexible dianhydride with m-phenylenediamine.

Tacticity
not yet available
Crystal structure
not yet available
Typical crystallinity
0 %[2]Amorphous, which underlies its amber transparency.

Molecular weight

Number average (Mn)
10000–42000 g/mol[2]
Mass average (Mw)
30000–75000 g/mol[2]
Dispersity (Mw/Mn)
1.6[2]

Mark-Houwink constants

not yet available

Combines aromatic imide rigidity (heat/chemical resistance) with ether linkages that improve melt-processability relative to fully rigid polyimides like Kapton.

Density
1.27 (1.27–1.31) g/cm³[2]amorphous, unfilled
Melt flow index
14–18 g/10min[2]230 °C/3.8 kg
Refractive index
1.63–1.687[2]
Transmittance
58 %[2]
Haze
2 %[2]
Gloss
not yet available
Water absorption
0.65–1.75 %[2]equilibrium in water immersion, 23 °C; 0.65% at 24 h, 1.75% at 30 days
Dielectric constant
3.15[2]100 Hz-1 MHz; essentially frequency-independent (Wypych, Mark)
Dielectric strength
14–33 kV/mm[2]K20/P50 electrodes, d=0.6–0.8 mm (Wypych); Mark reports 33 kV/mm at 1.6 mm in air, dropping to 20 kV/mm at 3.2 mm in oil
Electrical conductivity
1 × 10⁻¹⁵–1 × 10⁻¹³ S/m[2]reciprocal of volume resistivity range (1×10¹³-1×10¹⁵ Ω·m)

Glass transition (Tg)
209–249 °C[2]commonly cited as ~217 °C; range reflects different test methods (torsion pendulum, DMA, dielectric measurement)
Melting temperature (Tm)
Not applicableAmorphous; no true melting point.
Crystallization (Tc)
Not applicable
Heat deflection (HDT)
190–235 °C[2]ASTM D6481.8 MPa; Mark reports 200 °C for Ultem 1000, unannealed, 6.4 mm
Decomposition onset
not yet available
Thermal conductivity
0.22 W/(m·K)[3]ASTM C177

Tensile modulus
3000–3700 MPa[2]Wypych 3,420–3,700 MPa; Mark reports 3,000 MPa for Ultem 1000 (ASTM D638)
Yield strength
96–105 MPa[2]tensile stress at yield; Wypych 96–103 MPa, Mark 105 MPa for Ultem 1000 (ASTM D638)
Tensile strength at break
53–124 MPa[2]unqualified 'tensile strength' row, distinct from tensile stress at yield above
Elongation at break
14–60 %[2]Wypych 14–50%; Mark reports 60% ultimate elongation at break for Ultem 1000 (ASTM D638)
Impact strength (Izod)
27–69 J/m[2]notched, 23 °C; Mark reports 50 J/m for Ultem 1000 (ASTM D256)
Impact strength (Charpy)
21 kJ/m²[2]notched, 23 °C
Hardness
127 Rockwell R[2]Mark separately reports 109 for Ultem 1000, scale not specified in source (ASTM D785)
Flexural modulus
3040–3810 MPa[2]Mark reports 3,300 MPa for Ultem 1000 (ASTM D790)
Poisson's ratio
0.36[2]
Coefficient of friction
0.15–0.7[2]against steel; varies with sliding speed and applied pressure

Solvent: dilute acids
very good[2]
Solvent: concentrated acids
very good[2]
Solvent: alcohols
good[2]
Solvent: alkalis
very good[2]
Solvent: aliphatic hydrocarbons
good[2]
Solvent: aromatic hydrocarbons
good[2]
Solvent: esters
good[2]
Solvent: greases & oils
very good[2]
Solvent: halogenated hydrocarbons
very good[2]
Solvent: ketones
good[2]
Weathering / UV
not yet available
Hydrolysis resistance
not yet available
Flammability (UL94)
V-0[2]V-0 achieved at 0.41 mm thickness; 5VA rating achieved at 1.9 mm (Mark, Ultem 1000)
Limiting oxygen index
45–47 %[2]
Solubility parameter (δ)
19.8 MPa^0.5[2]

Gas permeability

O₂
3.75 × 10⁻¹⁴ cm³(STP)·cm/(cm²·s·Pa)[2]25 °C; converted from 0.5 barrer
N₂
5.25 × 10⁻¹⁵ cm³(STP)·cm/(cm²·s·Pa)[2]25 °C; converted from 0.07 barrer
CO₂
9.975 × 10⁻¹⁴ cm³(STP)·cm/(cm²·s·Pa)[3]35 °C, 10 atm; converted from 1.33 barrer (Ultem 1000)

Polymer-solvent interaction parameter (χ)

not yet available

Processing methods
injection moldingextrusion3D printing (build plates/filament)
Drying required
Yes
Processing temperature
260–320 °C[2]molding
Shrinkage rate
0.5–1.2 %[2]Mark reports 0.7% mold shrinkage for Ultem 1000

  • Aerospaceaircraft interior components
  • Medicalsterilizable devices
  • Electronicscomponents requiring stable electrical properties across frequencies · 3D printer build plates

Recyclable
Yes
Biodegradable
No
Degradation pathway
not yet available

LD50 (oral, rat)
5000 mg/kg[2]reported as >5,000 mg/kg
NFPA health
0[2]HMIS rating, 0–4 scale
NFPA flammability
1[2]HMIS rating, 0–4 scale
NFPA reactivity
0[2]HMIS rating, 0–4 scale
Carcinogenic classification
not listed by ACGIH, NIOSH, NTP[2]

Thermal/photooxidative degradation products include acetophenone, phenylacetic acid, phenols, benzoic acid, and phthalic anhydride/acid chain-end groups.

  1. [1]PolyetherimideWikipediaAccessed 2026-07-14https://en.wikipedia.org/wiki/Polyetherimide[wiki-pei]
  2. [2]Handbook of PolymersChemTec Publishinghttps://www.worldcat.org/isbn/9781895198928[handbook-wypych-2016]
  3. [3]Polymer Data HandbookOxford University Presshttps://search.worldcat.org/search?q=Polymer+Data+Handbook+Mark+1999[handbook-mark-1999]

Illustrations

  1. Plate IThe Apollo and Soyuz crews, photographed together ahead of the July 1975 docking mission that required American and Soviet hardware to be engineered to work as one system.Adam Cuerden · Public domainWikimedia Commons
  2. Plate IIGeneral Electric's Research and Development Center in Schenectady, New York, where Tohru Takekoshi's team developed the ether-linked polyimide chemistry behind Ultem.Andre Carrotflower · CC BY-SA 4.0Wikimedia Commons
  3. Plate IIIRolls of Kapton polyimide tape, the rigid, unmeltable chemistry that polyetherimide shares an imide ring with, but that it alone among this family can also melt and mold.Dsimic · CC BY-SA 3.0Wikimedia Commons
  4. Plate IVAn aircraft cabin interior, the kind of environment where Ultem-family resins are chosen for panels and ducting precisely because they resist fire and produce little smoke.FDV · CC BY-SA 4.0Wikimedia Commons