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Polyimide
Polyimide
Polyimide
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Chemical structure of Kapton, a polyimide.

Polyimide (sometimes abbreviated PI) is a polymer containing imide groups belonging to the class of high-performance plastics. With their high heat-resistance, polyimides enjoy diverse applications in roles demanding rugged organic materials, such as high temperature fuel cells, displays, and various military roles. A classic polyimide is Kapton, which is produced by condensation of pyromellitic dianhydride and 4,4'-oxydianiline.[1]

History

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The first polyimide was discovered in 1908 by Bogart and Renshaw.[2] They found that 4-amino phthalic anhydride does not melt when heated but does release water upon the formation of a high molecular weight polyimide. The first semialiphatic polyimide was prepared by Edward and Robinson by melt fusion of diamines and tetra acids or diamines and diacids/diester.[3]

However, the first polyimide of significant commercial importance—Kapton—was pioneered in the 1950s by workers at DuPont who developed a successful route for synthesis of high molecular weight polyimide involving a soluble polymer precursor. Up to today this route continues being the primary route for the production of most polyimides. Polyimides have been in mass production since 1955. The field of polyimides is covered by various extensive books[4][5] and review articles.[6][7]

Classification

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According to the composition of their main chain, polyimides can be:

According to the type of interactions between the main chains, polyimides can be:

  • Thermoplastic: very often called pseudothermoplastic.
  • Thermosetting: commercially available as uncured resins, polyimide solutions, stock shapes, thin sheets, laminates and machined parts.

Synthesis

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Several methods are possible to prepare polyimides, among them:

The polymerization of a diamine and a dianhydride can be carried out by a two-step method in which a poly(amidocarboxylic acid) is prepared first, or directly by a one-step method. The two-step method is the most widely used procedure for polyimide synthesis. First a soluble poly(amidocarboxylic acid) (2) is prepared which is cyclized after further processing in a second step to the polyimide (3). A two-step process is necessary because the final polyimides are in most cases infusible and insoluble due to their aromatic structure.

Dianhydrides used as precursors to these materials include pyromellitic dianhydride, benzoquinonetetracarboxylic dianhydride and naphthalene tetracarboxylic dianhydride. Common diamine building blocks include 4,4'-diaminodiphenyl ether (DAPE), meta-phenylenediamine (MDA) and 3,3'-diaminodiphenylmethane.[1] Hundreds of diamines and dianhydrides have been examined to tune the physical and especially the processing properties of these materials. These materials tend to be insoluble and have high softening temperatures, arising from charge-transfer interactions between the planar subunits.[8]

Analysis

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The imidization reaction can be followed via IR spectroscopy. The IR spectrum is characterized during the reaction by the disappearance of absorption bands of the poly(amic acid) at 3400 to 2700 cm−1 (OH stretch), ~1720 and 1660 (amide C=O) and ~1535 cm−1 (C-N stretch). At the same time, the appearance of the characteristic imide bands can be observed, at ~1780 (C=O asymm), ~1720 (C=O symm), ~1360 (C-N stretch) and ~1160 and 745 cm−1 (imide ring deformation).[9]⁠　Detailed analyses of polyimide[10] and carbonized polyimide[10] and graphitized polyimide[11] have been reported.

Properties

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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 340 MPa (49,000 psi) and flexural moduli of 21,000 MPa (3,000,000 psi). Thermoset polymer matrix polyimides exhibit very low creep and high tensile strength. These properties are maintained during continuous use to temperatures of up to 232 °C (450 °F) and for short excursions, as high as 704 °C (1,299 °F).[12] Molded polyimide parts and laminates have very good heat resistance. Normal operating temperatures for such parts and laminates range from cryogenic to those exceeding 260 °C (500 °F). Polyimides are also inherently resistant to flame combustion and do not usually need to be mixed with flame retardants. Most carry a UL rating of VTM-0. Polyimide laminates have a flexural strength half life at 249 °C (480 °F) of 400 hours.

Typical polyimide parts are not affected by commonly used solvents and oils – including hydrocarbons, esters, ethers, alcohols and freons. They also resist weak acids but are not recommended for use in environments that contain alkalis or inorganic acids. Some polyimides, such as CP1 and CORIN XLS, are solvent-soluble and exhibit high optical clarity. The solubility properties lend them towards spray and low temperature cure applications.

Applications

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Thermally conductive pads made of Kapton foil, thickness approx. 0.05 mm
Roll of Kapton adhesive tape

Insulation and passivation films

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Polyimide materials are lightweight, flexible, resistant to heat and chemicals. Therefore, they are used in the electronics industry for flexible cables and as an insulating film on magnet wire. 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. Examples of polyimide films include Apical, Kapton, UPILEX, VTEC PI, Norton TH and Kaptrex.

Structure of poly-oxydiphenylene-pyromellitimide, "Kapton".

Polyimide is used to coat optical fibers for medical or high temperature applications.[13]

An additional use of polyimide resin is as an insulating and passivation[14] layer in the manufacture of Integrated circuits and MEMS chips. The polyimide layers have good mechanical elongation and tensile strength, which also helps the adhesion between the polyimide layers or between polyimide layer and deposited metal layer. The minimum interaction between the gold film and the polyimide film, coupled with high temperature stability of the polyimide film, results in a system that provides reliable insulation when subjected to various types of environmental stresses.[15][16] Polyimide is also used as a substrate for cellphone antennas.[17]

Multi-layer insulation used on spacecraft is usually made of polyimide coated with thin layers of aluminum, silver, gold, or germanium. The gold-colored material often seen on the outside of spacecraft is typically actually single aluminized polyimide, with the single layer of aluminum facing in.[18] The yellowish-brown polyimide gives the surface its gold-like color.

Mechanical parts

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Polyimide powder can be used to produce parts and shapes by sintering technologies (hot compression molding, direct forming, and isostatic pressing). Because of their high mechanical stability even at elevated temperatures they are used as bushings, bearings, sockets or constructive parts in demanding applications. To improve tribological properties, compounds with solid lubricants like graphite, PTFE, or molybdenum sulfide are common. Polyimide parts and shapes include P84 NT, VTEC PI, Meldin, Vespel, and Plavis.

Filters

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In coal-fired power plants, waste incinerators, or cement plants, polyimide fibres are used to filter hot gases. In this application, a polyimide needle felt separates dust and particulate matter from the exhaust gas.

Polyimide is also the most common material used for the reverse osmotic film in purification of water, or the concentration of dilute materials from water, such as maple syrup production.[19][20]

Flexible circuits

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Main article: Flexible electronics

Polyimide is used as the core of flexible circuit boards and flat-flex cables. Flexible circuit boards are thin and can be placed in odd-shaped electronics.[21]

Other

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Polyimide is used for medical tubing, e.g. vascular catheters, for its burst pressure resistance combined with flexibility and chemical resistance.

The semiconductor industry uses polyimide as a high-temperature adhesive; it is also used as a mechanical stress buffer.

Some polyimide can be used like a photoresist; both "positive" and "negative" types of photoresist-like polyimide exist in the market.

The IKAROS solar sailing spacecraft uses polyimide resin sails to operate without rocket engines.[22]

See also

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References

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Further reading

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Revisions and contributorsEdit on WikipediaRead on Wikipedia

Polyimide

View on Grokipedia
from Grokipedia
Polyimide (PI) is a class of high-performance polymers characterized by the presence of groups in their backbone, offering exceptional thermal stability, mechanical strength, chemical resistance, and electrical insulation properties. These polymers are typically synthesized through a two-step process involving the reaction of dianhydrides and diamines to form polyamic acid intermediates, followed by thermal or chemical imidization to yield the final rigid, aromatic structure. First discovered in 1908 by Bogert and Renshaw, polyimides achieved commercial significance in 1955 with the development of aromatic variants via condensation , such as those using (PMDA) and oxydianiline (ODA). The defining attributes of polyimides stem from their stiff, aromatic backbones, which confer high temperatures (Tg) ranging from 181°C to over 300°C depending on selection, and thermal endurance up to approximately 500°C in inert environments while maintaining structural integrity down to -196°C. They exhibit superior mechanical properties, including tensile strengths often exceeding 100 MPa, low coefficients of , and resistance to , solvents, and atomic oxygen, making them infusible and insoluble in most common solvents without specialized processing. Polyimides can be tailored into or thermosetting forms, with variants like colorless polyimides (CPIs) addressing optical limitations through fluorination or bulky side groups to reduce charge-transfer complexes and enhance for advanced applications. Due to these robust characteristics, polyimides find extensive use across demanding industries, including for engine components, insulation, and structural composites; for flexible printed circuits, semiconductors, and high-frequency laminates in and IoT devices; and protective applications such as filtration media, foams, and garments exposed to extreme conditions. In emerging fields, they serve as substrates in flexible displays, gas separation membranes, sensors, and photocatalysts, often enhanced via nanocomposites with nanofillers like carbon nanotubes to boost conductivity and multifunctionality. In 2025, advancements include photosensitive polyimides enabling high-aspect-ratio fine patterning for . Ongoing focuses on molecular design strategies to improve processability, optical clarity, and , ensuring polyimides remain pivotal in high-tech innovations.

History

Early Discovery

The discovery of polyimides traces back to 1908, when American chemists Marston Taylor Bogert and Roemer Rex Renshaw reported the synthesis of the first known member of this polymer class. They heated 4-amino-o-phthalic anhydride at 200°C, observing dehydration and formation of a hard, infusible resinous product that did not melt even at high temperatures but released water vapor, indicating polycondensation via linkage formation. This material, derived from a single bifunctional capable of self-reaction, represented an early example of an aromatic polyimide, though its polymeric nature was not fully recognized at the time. Early characterization of this proved challenging due to its insolubility in common organic solvents and its exceptionally high , which rendered it infusible and difficult to process or analyze using contemporary techniques. These properties, while hinting at remarkable thermal stability, restricted initial investigations to basic observations of its physical form and reactivity, limiting potential applications to speculative uses in heat-resistant coatings or . The lack of also hindered molecular weight determination and structural elucidation, leaving the material largely overlooked for practical development in the ensuing decades. Research on imide linkages for heat-resistant materials gained momentum in the 1930s and 1940s, as chemists sought polymers capable of withstanding elevated temperatures for emerging industrial needs. Key efforts focused on synthesizing imide-containing compounds and exploring their condensation to form stable networks, with publications emphasizing the potential of aromatic imides to confer thermal endurance. In the late 1940s, significant advancements came through patents at E.I. du Pont de Nemours & Co., including Norman E. Searle's US Patent 2,444,536 (1948) for the synthesis of N-aryl maleimides via nucleophilic addition and cyclodehydration, providing monomers for subsequent polymerization. Similarly, US Patent 2,462,835 (1949) by H.W. Arnold and N.E. Searle detailed improved methods for preparing these maleimides, highlighting their utility in forming infusible resins with enhanced heat resistance through imide bond formation. These works laid foundational intellectual property for imide-based polymers, though full commercialization awaited scalable processes in the 1950s.

Commercial Development

Following , significant advancements in polyimide production techniques emerged, driven by the need for high-performance materials in demanding applications. In the 1950s, pioneered key developments, culminating in a 1955 patent for polyimides derived from pyromellitic acid, which laid the groundwork for scalable synthesis methods. This work built upon earlier foundational discoveries, such as the 1908 synthesis of polyimide resins, to address processing challenges inherent to the material's insolubility. By leveraging soluble polyamic acid precursors, enabled the casting and thermal imidization of films, leading to the mass production of polyimide film in the early . , introduced commercially around 1961, offered exceptional thermal stability and mechanical strength, quickly finding use in electrical insulation and flexible circuitry. The 1960s marked the expansion of polyimides into industrial markets, particularly aerospace, through collaborations involving companies like and . contributed experimental polyimide insulations, such as HML, for high-temperature electrical applications during this period. adopted extensively for its programs, valuing the material's ability to withstand extreme temperatures from -269°C to +400°C in environments. Notably, polyimide tape and foil served as thermal protection and on Apollo missions, including in 1969, where it shielded the command module from radiative heat and micrometeoroids. These applications demonstrated polyimides' reliability in space, spurring further investment and adoption beyond laboratory settings. By the , polyimide processing evolved from batch lab-scale methods to lines, facilitating global and broader . This shift, enabled by refined precursor handling and automated techniques, reduced costs and increased output for films, varnishes, and molded parts. Companies worldwide, including those in and , integrated polyimides into products like wire enamels and composite structures, establishing the material as a cornerstone of high-performance .

Chemical Structure and Classification

Molecular Composition

Polyimides are characterized by their repeating backbone containing imide groups (-CO-NR-CO-), where R is typically an aromatic moiety, forming a five-membered heterocyclic ring that imparts thermal stability and rigidity. The general formula for aromatic polyimides can be represented as [-Ar-CO-NR'-CO-]n, where Ar is an aromatic dianhydride-derived unit and R' is an aromatic diamine-derived unit. These polymers are commonly synthesized from the condensation of aromatic dianhydrides, such as (PMDA), and aromatic diamines, like 4,4'-oxydianiline (ODA), via a two-step process: first forming a soluble poly(amic acid) precursor in a dipolar aprotic (e.g., N,N-dimethylacetamide), followed by thermal or chemical cyclodehydration to form the rings, releasing . The aromatic nature of the backbone enhances chain stiffness, leading to high temperatures (Tg) ranging from 181°C to over 300°C, superior mechanical strength, and resistance to thermal degradation up to 500°C in inert atmospheres, whereas aliphatic segments would reduce rigidity and lower Tg.

Types of Polyimides

Polyimides are broadly classified based on their processing behavior into and thermosetting types, as well as by structural variations such as fully aromatic, semi-aromatic, and fluorinated subclasses, all unified by the characteristic five-membered ring in their polymer backbone. polyimides feature linear, non-cross-linked polymer chains that enable melt processing at elevated temperatures, allowing for injection molding, , and other fabrication techniques. These materials exhibit good chain flexibility, which contributes to their processability while maintaining high thermal resistance. A representative example is (PEI), commercially available as Ultem, which incorporates flexible linkages between aromatic units to improve solubility in common solvents and facilitate processing without compromising inherent strength or heat stability up to 170–180°C. In contrast, thermosetting polyimides form highly cross-linked, three-dimensional networks during curing, resulting in infusible and insoluble materials with exceptional rigidity and dimensional stability under extreme conditions. This cross-linking enhances chain interconnectivity, reducing flexibility but providing superior resistance to creep and solvents. Bismaleimides (BMIs) exemplify this category, serving as resins for advanced composites in applications where they deliver balanced mechanical toughness and thermal performance exceeding 250°C. Structural subclasses further differentiate polyimides by the degree of and groups, influencing properties like and optical behavior. Fully aromatic polyimides, composed entirely of aromatic monomers, offer the highest thermal stability and mechanical strength due to their rigid, conjugated backbones; a classic instance is the PMDA-ODA polyimide, marketed as film, which withstands continuous use at 300°C. Semi-aromatic polyimides include aliphatic segments in one of the monomers ( or ), providing a compromise between the processability of aliphatic polymers and the durability of aromatic ones, often resulting in lower temperatures for easier handling. Fluorinated polyimides incorporate fluorine atoms, typically via monomers like 4,4'-(hexafluoroisopropylidene)diphthalic anhydride (6FDA), to achieve enhanced , optical transparency, low constants (around 2.5–3.0), and minimal water absorption (less than 1%), ideal for and optoelectronic devices.

Synthesis

Monomer Selection and Preparation

The synthesis of polyimides begins with the careful selection of dianhydride and diamine monomers, which form the foundational building blocks for the backbone. Among the most commonly used dianhydrides are (PMDA) and 3,3',4,4'-benzophenone tetracarboxylic dianhydride (BTDA), valued for their ability to produce polyimides with exceptional thermal stability and mechanical integrity. PMDA, derived from the dehydration of pyromellitic acid, is typically prepared industrially through the oxidation of 1,2,4,5-tetramethylbenzene (durene) to the corresponding tetraacid, followed by thermal or chemical dehydration, often using in laboratory settings. Similarly, BTDA is obtained by dehydrating 3,3',4,4'-benzophenone tetracarboxylic acid, which itself results from the oxidation of precursors like 3,3',4,4'-tetramethylbenzophenone, ensuring the rigid aromatic structure essential for high-performance applications. Diamines such as 4,4'-oxydianiline (ODA) and m-phenylenediamine (MPDA) are frequently selected to complement these dianhydrides, balancing in polymerization solvents with controlled reactivity to facilitate uniform growth. ODA, with its linkage, introduces flexibility and enhances processability in aprotic solvents like N,N-dimethylacetamide, making it ideal for forming soluble poly(amic acid) precursors without excessive brittleness in the final polymer. MPDA, featuring a meta-substituted ring, provides improved compared to its para-isomer while maintaining sufficient nucleophilicity for efficient reaction with dianhydrides; this configuration helps mitigate risks of premature gelation by moderating the rate of imidization during synthesis. The choice of these diamines ensures a stoichiometric balance that promotes linear over branching, critical for achieving desired molecular architectures. Purification of these monomers is paramount to attaining high molecular weight polyimides, as even trace impurities can disrupt chain propagation and introduce defects. Dianhydrides like PMDA and BTDA are commonly purified by recrystallization from solvents such as or , followed by vacuum drying to remove residual moisture and achieve purities exceeding 99%. Diamines, including ODA and MPDA, undergo under reduced pressure or recrystallization from or to eliminate volatile contaminants and ensure stoichiometric precision. Such high-purity levels (>99%) are essential in polymerization, where deviations can limit and compromise the thermal and mechanical properties of the resulting polyimides.

Polymerization and Imidization

The synthesis of polyimides is predominantly achieved through a two-step process that first forms a polyamic acid precursor via , followed by cyclization through imidization. This method, developed in the mid-20th century, allows for the production of high-molecular-weight polymers with controlled and processability. In the initial step, a tetracarboxylic dianhydride undergoes nucleophilic ring-opening reaction with a diamine in a polar aprotic solvent, such as N,N-dimethylacetamide (DMAc) or N-methyl-2-pyrrolidone (NMP), typically at ambient or mildly elevated temperatures. This exothermic reaction proceeds via nucleophilic attack of the amine groups on the anhydride carbonyls, yielding a soluble polyamic acid (PAA) with amide linkages and pendant carboxylic acid groups. The process can be represented by the general equation: n \ce(O=)2C−Ar−C(=O)2+n \ceH2N−Ar′−NH2→[−\ce(O=)C−Ar−C(=O)−NH−Ar′−NH−CO−Ar−COOH−]nn \ \ce{(O=)2C-Ar-C(=O)2} + n \ \ce{H2N-Ar'-NH2} \rightarrow \left[ -\ce{(O=)C-Ar-C(=O)-NH-Ar'-NH-CO-Ar-COOH-} \right]_n where Ar and Ar' denote the aromatic segments from the dianhydride and diamine, respectively. For example, pyromellitic dianhydride (PMDA) and 4,4'-oxydianiline (ODA) are commonly employed monomers in this step to produce precursors for commercial polyimides like Kapton. The second step involves imidization of the PAA, where thermal or chemical treatment induces dehydration and ring closure to form the characteristic five-membered imide rings along the polymer backbone. Thermal imidization is most common, conducted progressively at temperatures ranging from 200°C to 400°C under inert atmosphere to prevent oxidation, releasing water as a byproduct. This cyclization enhances thermal stability but renders the polymer insoluble. The reaction is summarized as: [−\ce(O=)C−Ar−C(=O)−NH−Ar′−NH−]n+n \ceH2O→[−\ce(O=)C−Ar−C(=O)−N−Ar′−N−]n+n \ceH2O\left[ -\ce{(O=)C-Ar-C(=O)-NH-Ar'-NH-} \right]_n + n \ \ce{H2O} \rightarrow \left[ -\ce{(O=)C-Ar-C(=O)-N-Ar'-N-} \right]_n + n \ \ce{H2O} The degree of imidization is typically monitored to ensure complete conversion, often achieving over 95% cyclization for optimal properties. Chemical imidization using dehydrating agents like acetic anhydride with tertiary amines can be an alternative for lower-temperature processing. An alternative one-step method involves direct high-temperature polycondensation of the dianhydride and in a high-boiling , such as , at 180–220°C, where and imidization occur simultaneously. This approach, pioneered in the , avoids the PAA intermediate but is less widely adopted due to challenges like volatility, side reactions, and poorer molecular weight control.

Structural Analysis

Structural analysis of polyimides is essential to confirm the successful completion of the imidization step following polymerization of polyamic acid (PAA) precursors. Techniques such as spectroscopy, thermal analysis, and viscometry provide detailed insights into the molecular architecture, degree of cyclization, and chain characteristics, ensuring the material's integrity for high-performance applications. Spectroscopic methods are widely employed to verify the presence of imide functionalities and overall chain structure. Fourier-transform infrared (FTIR) spectroscopy identifies characteristic absorption peaks for the imide carbonyl groups, with symmetric and asymmetric stretching vibrations typically appearing at approximately 1780 cm⁻¹ and 1720 cm⁻¹, respectively, confirming the formation of the five-membered imide ring. These peaks are distinct from the amide carbonyl absorptions in PAA precursors, which shift upon thermal or chemical imidization. Nuclear magnetic resonance (NMR) spectroscopy, particularly ¹H and ¹³C NMR, further elucidates the polymer chain conformation and substitution patterns. In ¹H NMR spectra of polyimides, aromatic protons resonate in the 7.0–8.5 ppm range, while ¹³C NMR distinguishes imide carbonyl carbons around 165–170 ppm and monitors structural changes from PAA to the fully imidized form, aiding in the assignment of local chain motions and end-group analysis. Thermal analysis techniques assess the degree of imidization and thermal stability of the polymer backbone. (DSC) detects the endothermic peak associated with imidization, typically shifting or disappearing as the reaction progresses toward completion, with full imidization often indicated by the absence of a peak below 200°C and the emergence of a temperature (Tg) above 250°C. (TGA) evaluates the decomposition onset, where fully imidized polyimides exhibit high thermal stability with initial above 500°C in inert atmospheres, contrasting with PAA precursors that decompose earlier due to incomplete cyclization. These methods collectively quantify imidization degrees, often exceeding 90% in optimized processes, by correlating or heat flow data with structural integrity. Molecular weight determination is crucial for understanding chain length and polydispersity, influencing processability and performance. (GPC), performed on soluble PAA precursors in solvents like N-methyl-2-pyrrolidone, measures number-average (Mn) and weight-average (Mw) molecular weights relative to standards, with high-molecular-weight polyimides often achieving Mw values above 100,000 g/mol for robust . Inherent measurements, conducted on dilute PAA solutions (e.g., 0.5 g/dL in ), provide a rapid indicator of molecular weight, where values typically range from 0.5 to 2.0 dL/g for processable polyimides, correlating with chain entanglement and solution . These techniques are often combined to validate synthesis outcomes, ensuring consistent structural parameters across batches.

Properties

Thermal and Chemical Stability

Polyimides are renowned for their superior thermal stability, which stems from their rigid aromatic backbone and enables applications in demanding high-temperature environments. The glass transition temperature (Tg) for aromatic polyimides typically ranges from 250 to 400°C, allowing continuous operation up to 232°C without significant degradation in mechanical or physical properties. This elevated Tg reflects the material's ability to maintain structural integrity under prolonged heat exposure, far surpassing many conventional polymers. Thermal decomposition of polyimides begins above 500°C in an inert atmosphere, demonstrating remarkable resistance to oxidative breakdown. indicates that these materials experience only 5% weight loss at around 550°C, highlighting their suitability for extreme conditions such as components where short-term excursions can reach higher temperatures. The aromatic structure contributes to this rigidity, limiting chain mobility and enhancing overall heat endurance. In addition to thermal resilience, polyimides exhibit strong chemical inertness, resisting degradation from a wide array of substances including acids, bases, and hydrocarbons. They maintain dimensional stability in aggressive environments, showing low swelling in polar solvents like (DMF), which ensures minimal absorption or structural compromise. Furthermore, polyimides demonstrate excellent resistance to , with no significant degradation observed up to high doses in applications like space insulation, underscoring their robustness in radiative conditions.

Mechanical and Electrical Characteristics

Polyimides exhibit robust mechanical properties, characterized by tensile strengths typically ranging from 70 to 150 MPa, depending on the specific formulation and processing conditions. For instance, HN polyimide film demonstrates an of 231 MPa at , which decreases to 139 MPa at 200°C, reflecting its ability to maintain structural integrity under varying loads. Elongation at break further highlights their flexibility, spanning 7% to 80%, with values such as 72% at 23°C and up to 83% at elevated temperatures for standard films. The reaches up to 3.5 GPa in certain variants, enabling resistance to bending and deformation in demanding structural roles. Electrically, polyimides serve as exceptional insulators, with constants of 3.0 to 3.5 measured at 1 kHz, providing low in high-frequency applications. Volume resistivity exceeds 10¹⁷ Ω·cm, often reaching 1.0 to 1.5 × 10¹⁷ Ω·cm, which minimizes leakage currents under sustained . surpasses 200 kV/mm, as evidenced by films achieving 205 kV/mm for 75 μm thickness, ensuring reliability in high-voltage environments. Under prolonged stress, polyimides demonstrate superior creep resistance and fatigue endurance compared to many engineering plastics, such as polyetheretherketone or , due to their rigid aromatic backbone that limits viscoelastic deformation. This performance is particularly notable at elevated temperatures, where thermal stability supports sustained mechanical loading without significant strain accumulation.

Applications

Electronics and Insulation

Polyimides serve as critical passivation layers in semiconductor devices, providing robust protection for metallization films against environmental degradation while maintaining high dielectric strength and thermal stability. In microelectronics and power electronics, these layers prevent moisture ingress and mechanical stress, ensuring long-term reliability in integrated circuits and MEMS devices. For instance, a 2 μm thick polyimide layer has been effectively employed as a passivation coating in MEMS fabrication processes. Additionally, spin-coated polyimide films are favored for SiC-based power devices due to their ability to withstand high operating temperatures exceeding 200°C without compromising insulation integrity. Kapton polyimide films, a prominent commercial variant, are widely used for wire insulation in electrical applications, offering continuous operation up to 260°C with excellent chemical resistance and low . This temperature rating supports their deployment in high-reliability wiring for and automotive sensors, where wires must endure cycling without dielectric breakdown. The film's inherent balance of physical and electrical enables it to serve as a primary insulator in magnet wire constructions, achieving a index of 220-240°C under UL standards. Polyimides also exhibit high resistivity, typically exceeding 10^16 Ω·cm, which minimizes leakage currents in insulated components. In flexible printed circuits, polyimide-based substrates enable compact, bendable , such as those integrated into smartphones for displays, cameras, and batteries in confined spaces. These polyimide PCBs, often found in devices like the Z Fold series, support repeated flexing with minimum bend radii below 1 mm, facilitating innovative form factors like foldable screens without signal degradation. The material's flexibility stems from its thin-film structure, typically 25-50 μm thick, allowing dynamic bending in consumer gadgets while preserving trace integrity. For high-frequency applications, polyimides demonstrate low , with dissipation factors (tan δ) below 0.003 across frequencies up to 60 GHz, making them ideal substrates for antennas and millimeter-wave circuits. This ultralow loss reduces signal attenuation in RF modules, enhancing data transmission efficiency in next-generation wireless infrastructure. Specialized variants like DuPont's Pyralux AP exemplify this performance, supporting the miniaturization of components while maintaining thermal and mechanical robustness.

Mechanical and Aerospace Components

Polyimides are widely utilized in mechanical and aerospace components due to their exceptional ability to withstand high stresses and temperatures while maintaining structural integrity. In jet engines, Vespel®, a polyimide developed by DuPont, is commonly employed for bearings, seals, and bushings, such as pivot bushings on unison rings and bellcrank bushings, as well as engine duct seals. These components benefit from Vespel's low coefficient of friction, typically ranging from 0.12 to 0.29 depending on the grade and conditions, enabling values below 0.2 in unlubricated environments for smooth operation and reduced wear. This lubricity, combined with high service temperatures up to 260°C continuous and low creep, allows Vespel parts to endure the demanding vibrational and thermal loads in turbine environments without frequent maintenance. In aircraft structures, polyimide-based composites, particularly those using PMR-15 resin developed by , serve as lightweight alternatives to metals in load-bearing applications like engine ducts, fairings, and flaps. For instance, PMR-15 reinforced with or has been implemented in components such as the JT8D reverser stang fairing, achieving up to 40% weight reduction compared to metallic counterparts, and the T700 swirl frame, offering potential savings of 30%. These composites maintain structural integrity at temperatures exceeding 300°C, with excellent retention of mechanical properties after prolonged exposure, facilitating overall aircraft weight reductions of 20-30% in targeted high-temperature sections. PMR-15's processability via prepregs and molding ensures void-free parts suitable for hybrid metal-composite designs in engines like the F404 and F101. Polyimides also demonstrate superior wear resistance in automotive and industrial applications, particularly for piston rings and valve components in compressors and pumps that operate under cyclic thermal stresses up to 300°C. These parts leverage polyimides' high strength, dimensional stability, and low abrasion to extend in high-friction zones, reducing wear rates even without . For example, graphite-filled polyimide formulations provide robust performance in piston rings, enduring repeated heating and cooling cycles while minimizing material degradation and maintaining tight tolerances. This durability contributes to improved efficiency and longevity in high-performance systems.

Filtration and Membranes

Polyimides are widely utilized in microporous configurations for gas separation processes, particularly in the purification of streams by selectively removing from . These membranes are typically fabricated using the phase inversion casting method, where a polyimide solution is cast into a or hollow fiber and then immersed in a non-solvent bath to induce , forming an asymmetric structure with a microporous support layer and a selective . For instance, hollow fiber and flat sheet polyimide membranes prepared via this technique have demonstrated high mixture CO₂/CH₄ selectivity values exceeding 20, with one example achieving 57 at 10% v/v CO₂ concentration, enabling efficient separation under industrial conditions. This selectivity arises from the polymer's rigid backbone and polar groups, which favor CO₂ solubility and over CH₄. In high-temperature filtration applications, polyimides serve as durable materials for filters in power plants, where they capture particulate matter from hot flue gases generated during or other thermal processes. P84® polyimide fibers, known for their multilobal cross-section that enhances efficiency, are needle-punched into felts capable of continuous operation up to 260°C, with short-term surges to 280°C, while maintaining structural integrity and low . These filters are particularly effective in retrofits or dedusting systems, removing fine dust particles down to submicron sizes without significant degradation, thus complying with stringent emission standards in energy production facilities. The inherent of polyimides to acidic and oxidative environments in these gases further supports their in harsh operational settings. For liquid separation, polyimide-based modules are employed in systems to remove , colloids, and macromolecules from industrial effluents or municipal . These membranes, often made from variants, provide robust performance in compact modules, contributing to scalable treatment processes that achieve high recovery rates while minimizing .

Biomedical and Emerging Uses

Polyimides have gained prominence in biomedical applications due to their , flexibility, and thermal stability, which enable long-term implantation without significant tissue . In neural probes, polyimide coatings provide mechanical compliance that soft tissue, reducing and improving chronic recording stability; for instance, flexible polyimide-based microelectrode arrays have demonstrated minimal in sheep implants over 28 days, with low verified across multiple cell lines per ISO standards. These probes support applications like treatment, where FDA-cleared clinical trials utilize polyimide substrates for subdural (ECoG) arrays that remain functional for months , as seen in rabbit eye and mouse cortex studies lasting up to 180 days. Additionally, polyimide tubing facilitates controlled , such as in subcutaneous implants for mice that maintain stability over months, and in intracranial or systems for targeted release, leveraging the material's chemical inertness to minimize adverse reactions. In , fluorescent polyimides serve as substrates for organic light-emitting diodes (), benefiting from their high thermal and mechanical robustness alongside enhanced . Side-chain modifications, such as incorporating bulky triarylamine or tetraphenylethylene units, disrupt charge transfer complexes and promote aggregation-induced emission, achieving quantum yields up to 50%—for example, a diphenylamine-pyrene modified polyimide reached 49% in solution, while a triarylamine-based variant hit 53% in solution and 61% in film. These adaptations loosen molecular packing, suppress non-radiative decay, and improve , enabling efficient OLED performance with stable emission under operational stresses. Emerging uses of polyimides extend to lightweight foams for and acoustic insulation, where copolymerized variants exhibit densities as low as 0.03 g/cm³, superior heat resistance up to 300°C, and , making them suitable for advanced and automotive components without adding significant weight. has accelerated design optimization in the , using models like graph convolutional neural networks on datasets of over 1,400 polyimides to predict and tune temperatures (Tg) with R² accuracies exceeding 0.85; for instance, predictions guided the incorporation of rigid substructures to elevate Tg to ~590 K in validated designs, enhancing stability for high-performance applications. However, sustainable remains challenging due to polyimides' rigid aromatic heterocyclic structures, which resist degradation and limit mechanical reprocessing; recent advances include acid-assisted to recover monomers for high-value , though scalability and energy efficiency pose ongoing hurdles in achieving closed-loop systems.

Market and Commercial Significance

In 2025, the Asia-Pacific region dominated the global polyimide film market, holding approximately 44-45% of the market share. Coherent Market Insights estimates the region's share at 44%, while Fortune Business Insights reports 45%. This dominance is primarily driven by strong demand from the electronics manufacturing sector in countries such as China, Japan, South Korea, and Taiwan, which aligns with the applications of polyimide films in flexible printed circuits, semiconductors, displays, and related electronic components. Key players in the market include DuPont, Kaneka Corporation, Toray Industries, and PI Advanced Materials.

References

  1. https://www.azom.com/article.aspx?ArticleID=19119
  2. https://pmc.ncbi.nlm.nih.gov/articles/PMC9961415/
  3. https://vtechworks.lib.vt.edu/bitstream/handle/10919/27771/polyimide1.pdf
  4. https://www.mdpi.com/2073-4360/16/16/2315
  5. https://www.toray.com/news/article.html?contentId=cxgnq2oa
  6. https://pubs.acs.org/doi/10.1021/ja01949a012
  7. https://link.springer.com/chapter/10.1007/978-94-011-7073-4_31
  8. https://patents.google.com/patent/US2444536A/en
  9. https://apps.dtic.mil/sti/tr/pdf/AD0475505.pdf
  10. https://ntrs.nasa.gov/api/citations/19740007423/downloads/19740007423.pdf
  11. https://www.sciencedirect.com/topics/materials-science/polyimide
  12. https://www.sabic.com/en/products/specialties/ultem-resin-family-of-high-heat-solutions/ultem-resin
  13. https://www.sciencedirect.com/topics/engineering/polyetherimide
  14. https://dl.asminternational.org/handbooks/edited-volume/60/chapter/701154/Bismaleimide-Resins
  15. https://polymerinnovationblog.com/beyond-epoxy-high-performance-thermosets-part-one/
  16. https://ntrs.nasa.gov/api/citations/20010092697/downloads/20010092697.pdf
  17. https://www.specialchem.com/plastics/guide/polyimide-pi-plastic
  18. https://www.sciencedirect.com/topics/engineering/fluorinated-polyimides
  19. https://www.researchgate.net/publication/272748278_Fluorinated_Polyimides_Synthesis_Properties_and_Applications
  20. https://www.chemicalbook.com/article/what-is-pyromellitic-dianhydride-.htm
  21. https://www.sciencedirect.com/science/article/abs/pii/004060319187245R
  22. https://www.sciencedirect.com/science/article/abs/pii/S007967000700010X
  23. https://ntrs.nasa.gov/api/citations/19900016813/downloads/19900016813.pdf
  24. https://www.sciencedirect.com/science/article/pii/S277282342500048X
  25. https://www.sciencedirect.com/science/article/abs/pii/S0141391006001698
  26. https://www.mdpi.com/2673-706X/4/3/17
  27. https://onlinelibrary.wiley.com/doi/abs/10.1002/macp.1996.021970220
  28. https://pmc.ncbi.nlm.nih.gov/articles/PMC4764896/
  29. https://www.researchgate.net/publication/286888081_Comparison_of_different_methods_for_determining_the_imidization_degree_of_polyimide_fibers
  30. https://www.sciencedirect.com/science/article/abs/pii/S0032386116311247
  31. https://www.sciencedirect.com/science/article/abs/pii/S0032386122008576
  32. https://lectromec.com/test/inherent-viscosity-of-polyimide/
  33. https://www.sciencedirect.com/science/article/pii/S2211715625005582
  34. https://vtechworks.lib.vt.edu/bitstream/handle/10919/27771/polyimide5.pdf
  35. https://www.professionalplastics.com/Polyimide_RodPlateFilmTube
  36. https://onlinelibrary.wiley.com/doi/10.1002/app.41412
  37. https://www.equilibar.com/support/polyimide-diaphragms/
  38. https://www.rsc.org/binaries/LOC/2009/Pdf/084-M13C.pdf
  39. https://ntrs.nasa.gov/api/citations/20010049269/downloads/20010049269.pdf
  40. https://www.dupont.com/content/dam/electronics/amer/us/en/electronics/public/documents/en/EI-10142_Kapton-Summary-of-Properties.pdf
  41. http://mu2e.phy.duke.edu/cw/misc/0404_kapton_properties.cfm.htm
  42. https://www.dupont.com/electronics-industrial/kapton-hn.html
  43. https://pmc.ncbi.nlm.nih.gov/articles/PMC7503409/
  44. https://pmc.ncbi.nlm.nih.gov/articles/PMC3691908/
  45. https://www.dupont.com/content/dam/electronics/amer/us/en/electronics/public/documents/en/EI-10150-Kapton-PST-Data-Sheet.pdf
  46. https://www.dupont.com/content/dam/dupont/amer/us/en/vespel/public/documents/en/DuPont%2520Vespel%25C2%25AE%2520S%2520Line%2520Design%2520Handbook.pdf
  47. https://www-eng.lbl.gov/~shuman/NEXT/CURRENT_DESIGN/EP/ULTEMProductBrochure.pdf
  48. https://ntrs.nasa.gov/api/citations/19960045294/downloads/19960045294.pdf
  49. https://ntrs.nasa.gov/api/citations/20070018345/downloads/20070018345.pdf
  50. https://searchit.libraries.wsu.edu/discovery/fulldisplay?docid=cdi_crossref_primary_10_1016_j_apsusc_2024_160719&context=PC&vid=01ALLIANCE_WSU:WSU&lang=en&search_scope=WSU_everything&adaptor=Primo%2520Central&tab=default_tab&query=creator%252Cexact%252C%2520Arena%252C%2520Giuseppe%2520&facet=creator%252Cexact%252C%2520Arena%252C%2520Giuseppe%2520&offset=0
  51. https://www.dupont.com/content/dam/electronics/amer/us/en/electronics/public/documents/en/EI-10139-Kapton-Motor-and-Magnet-Wire-Technical-Bulletin.pdf
  52. https://www.dupont.com/content/dam/electronics/amer/us/en/electronics/public/documents/en/EI-10206-Kapton-HN-Data-Sheet.pdf
  53. https://www.protoexpress.com/blog/why-polyimide-pcb-material-right-choice-for-flex-designs/
  54. https://www.pcbelec.com/blog/industry-applications/flexible-pcb-applications.html
  55. https://www.jlcpcb.com/blog/the-ultimate-guide-to-flexible-pcb/
  56. https://www.dupont.com/blogs/advanced-polyimides-flexible-high-speed-5G-networks.html
  57. https://www.curbellplastics.com/wp-content/uploads/2022/11/DuPont-Vespel-for-Jet-Engine-Applications.pdf
  58. https://www.dupont.com/products/vespel-sp-21.html
  59. https://www.bearingworks.com/uploaded-assets/pdfs/retainers/vespel-sp3-datasheet.pdf
  60. https://ntrs.nasa.gov/api/citations/19820016466/downloads/19820016466.pdf
  61. https://www.hsjuxin-pi.com/plasma-cutting/
  62. https://www.ensingerplastics.com/en-us/direct-forming
  63. https://www.sciencedirect.com/science/article/pii/S2772421223000211
  64. https://www.researchgate.net/publication/267522734_Polyimide_hollow_fiber_membranes_for_CO2_separation_from_wet_gas_mixtures
  65. https://www.p84.com/en/high-temperature-filtration
  66. https://www.p84.com/en/high-temperature-filtration/attachment/140700?rev=28822da91c011a1b8a1a6e08cde8cf29
  67. https://www.sciencedirect.com/science/article/abs/pii/S1381514823001773
  68. https://www.researchgate.net/publication/271558100_Preparation_of_PEI_Ultrafiltration_Membrane_with_Excellent_Thermal_Resistance
  69. https://pubs.rsc.org/en/content/articlehtml/2024/na/d4na00292j
  70. https://pmc.ncbi.nlm.nih.gov/articles/PMC11397098/
  71. https://publications.aston.ac.uk/id/eprint/46452/1/Accepted_Manuscript_polyimide_foams.pdf
  72. https://pubs.rsc.org/en/content/articlehtml/2024/dd/d3dd00256j
  73. https://www.coherentmarketinsights.com/market-insight/polyimide-films-market-5387
  74. https://www.fortunebusinessinsights.com/polyimide-film-market-103055
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