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PI Polyimide

PI Polyimide

PI Polyimide is one of the best overall performance of organic polymer materials, high temperature of 400 ℃ or more, long-term use temperature range of -200 ~ 300 ℃, no clear melting point, high insulation properties, dielectric constant of 4.0 at 103 Hz, Dielectric loss is only 0.004 to 0.007, is F to H-class insulation.
According to the chemical structure of the repeating units of the PI polyimide can be divided into aliphatic, aromatic and semi-aromatic PI polyimide three. The thermal properties, can be divided into thermoplastic and thermoset polyimides [1].
Polyimide means a main chain imide ring (-CO-NH-CO-) of a class of polymers in which the polymer containing phthalimide structure is most important. Polyimide as a special engineering materials, it has been widely applied in the fields of aviation, aerospace, microelectronics, nano, LCD, separation membranes, laser. In the 1960s, countries in the PI polyimide in the research, development and utilization of the inclusion of engineering plastics in the 21st century one of the most promising. Polyimide, its outstanding performance characteristics and synthesis, whether as a structural material or as a functional material, its potential application has been fully recognized, known as a “problem solver” ( protion solver), and that “there would be no PI polyimide microelectronic technology today.”
A polymer having repeating units of the imide


Condensation type

Condensation-type aromatic PI polyimide is an aromatic diamine and an aromatic dianhydride, aromatic tetracarboxylic acid or aromatic tetracarboxylic acid dialkyl ester obtained by reacting. Since the condensation type PI polyimide synthesis reaction, such as dimethylformamide, N- methylpyrrolidone high-boiling aprotic solvent, and polyimide composites typically employ prepreg molding process These high-boiling aprotic solvent prepreg prepared in the past


Process difficult to evaporate, while the polyamic acid cyclization (imidization) period also release volatiles, which is prone to voids in the composite article, it is difficult to obtain high-quality, no porosity composites. Therefore condensation type polyimide composite material used has been less matrix resin, mainly used to manufacture PI polyimide films and coatings.
Polyaddition type
Since the condensation type PI polyimide has a disadvantage as described above, in order to overcome these shortcomings, we have developed an addition polymerization type polyimide. Widely used mainly poly bismaleimide and norbornene-terminated polyimide. These resins are typically ends with an unsaturated group of low molecular weight polyimide, and then through the unsaturated end groups polymerization applications.
① Poly Bismaleimide
Poly Bismaleimide by maleic anhydride and aromatic


Condensation from aromatic diamine. Compared with polyimide, the performance is not bad from top to bottom, but the synthesis process is simple, easy post-processing, low cost, can be easily made into a variety of composite materials products. But more brittle cured.
② norbornene-terminated PI polyimide resin
One of the most important is the development by the NASA Lewis Research Center, a class of PMR (for insitu polymerization of monomer reactants, monomer reactants in situ polymerization) PI polyimide resin. RMR polyimide resin is a monomeric dialkyl esters of aromatic tetracarboxylic acids, aromatic diamine, and 5-norbornene-2,3-dicarboxylic acid monoalkyl ester was dissolved in a Species taste alcohol (e.g., methanol or ethanol), can be used directly as solutions were used to impregnate fibers.
Polyimide is an aromatic heterocyclic polymer compound molecular structure containing imide group links, the English name Polyimide (abbreviated PI), can be divided into pyromellitic type PI, soluble PI, polyamide – imide (PAI) and polyetherimide (PEI) four categories.
1, wholly aromatic PI polyimide by thermal gravimetric analysis, it begins to decompose temperature is generally
At about 500 ℃. Biphenyl dianhydride and p-phenylenediamine synthetic polyimide, the thermal decomposition temperature of 600 ℃, is one of the highest in the thermal stability of the polymer species so far.
2, PI polyimide can withstand very low temperatures, such as liquid helium will not rattle in the -269 ℃.
3, PI polyimide has excellent mechanical properties, tensile strength unfilled plastics are more than 100Mpa, pyromellitic PI polyimide film (Kapton) is 170Mpa or more, Hangzhou Plastic AU special thermoplastic polyimide (TPI) impact strength up 261KJ / m2. The biphenyl type PI polyimide (Upilex S) reaches 400Mpa. As a plastic, elastic modulus usually 3-4Gpa, fiber can reach 200Gpa, according to theoretical calculations, pyromellitic dianhydride and p-phenylenediamine synthetic fiber up 500Gpa, second only to carbon fiber.
4, a number of varieties of PI polyimide is insoluble in organic solvents, acid stable, generally little hydrolysis varieties, this seemingly shortcoming performance while filling the PI polyimide is different from a lot of other high-performance polymers characteristics, i.e., the raw material can be recovered by alkaline hydrolysis dianhydride and a diamine, for example, Kapton film having a recovery of up to 80% -90%. Changing the structure can be obtained quite hydrolysis resistant varieties, such as withstand 120 ℃, 500 小时 boiled.
5, the thermal expansion coefficient of the polyimide in 2 × 10-5-3 × 10-5 ℃, Nanjing Yue-Chemical YZPI thermoplastic polyimide 3 × 10-5 ℃, biphenyl up 10-6 ℃, individual Variety of up to 10-7 ℃.
6, PI polyimide has a high resistance to radiation performance, the film after 5 × 109rad fast electron irradiation strength retention rate of 90%.
7, the PI polyimide having good dielectric properties, dielectric constant of about 3.4, the introduction of fluorine, or dispersed in a nano-sized air polyimide, the dielectric constant can be reduced to about 2.5. Dielectric loss 10-3, a dielectric strength of 100-300KV / mm, wide as the thermoplastic PI polyimide 300KV / mm, volume resistivity of 10∧17Ω · cm. These properties over a wide temperature range and frequency range can maintain at a high level.
8, polyimide polymer is self-extinguishing, fuming rate.
9, PI polyimide in a high vacuum gas rarely decentralized.
10, polyimide non-toxic, used to make cutlery and medical equipment, and can withstand thousands of sterilization. Some PI polyimide also has good biocompatibility, for example, in blood compatibility test non-hemolytic, non-toxic in vitro cytotoxicity experiments.

Quality Index

Appearance light yellow powder
Flexural strength (20 ℃) ​​≥170MPa
Density 1.38 ~ 1.43g / cm3
Impact strength (unnotched) ≥28kJ / m2
Tensile strength ≥100 MPa
Vicat softening point> 270 ℃
Water absorption (25 ℃, 24h)
Elongation> 120%

Polyimide variety, in various forms, in the synthesis of a variety of ways, so you can

To be selected according to various application purposes, this synthetic variable continuity on other polymers are also difficult to have. Synthesis described as follows:
1, the PI polyimide is mainly of a dibasic acid anhydride and diamine synthesis, the two monomers with numerous other heterocyclic polymers, such as polybenzimidazole, polybenzoxazole dumb yl, polybenzothiazoles, polyquinoline dumb Compare morpholino and poly quinoline monomer, wide source of raw materials, synthesis is also easier. Dianhydride, diamine wide variety of different combinations of different properties can be obtained a polyimide.
2, may be formed of a PI polyimide dianhydride and a diamine in a polar solvent, such as DMF, DMAC, NMP, or THE / methanol mixed solvent of low temperature polycondensation to obtain a polyamic acid soluble, film-forming or spinning It was heated to about 300 ℃ dehydration ring-converted to a polyimide; may also be added acetic anhydride and the tertiary amine catalyst to the polyamic acid, the chemical dehydration cyclization to obtain a polyimide solution and a powder. Diamines and dianhydrides can also be in a high boiling solvent, such as phenolic solvent was heated polycondensation step to obtain a polyimide. In addition, it can by a four yuan acid dibasic esters and diamine reaction to obtain a polyimide; PI polyamide acid can also be made into a poly isoimide first, and then converted to a PI polyimide. These methods are easy to process brings, the former is called PMR method, you can obtain a low viscosity, high solid content solution, a low melt viscosity during processing window has a has, especially for the manufacture of composite materials in; the latter increase solubility, in the process of transformation does not release low molecular weight compounds.
3, as long as two anhydride (or four acid) and diamine purity qualified Regardless of the condensation method, are easy to obtain a sufficiently high molecular weight, added anhydride unit or units can be easily amine molecular weight regulation.
4, with the dianhydride (or tetracarboxylic acid) and a diamine polycondensation, as long as to reach an equimolar ratio, in a vacuum heat treatment, the solid low molecular weight prepolymer greatly increased molecular weight, and thus to the processing into powder with to facilitate.
5, it is easy to introducing a reactive group at the chain end or chain to form an active oligomers to obtain a thermosetting polyimide.
6, the use of polyimide carboxy, esterified or salified, or introducing a photosensitive group to give a long-chain alkyl amphiphilic polymer, photoresist or can be used for the preparation of LB films.
7, the general synthetic process does not produce polyimide inorganic salts, for the preparation of an insulating material is particularly advantageous.
8, as the dianhydride and diamine monomer is easily sublimated under high vacuum, it is easy to polyimide film vapor deposition method is formed on the workpiece, in particular the use of the uneven surface of the device.


Because of the characteristics of the polyimide in performance and synthetic chemistry, in many polymer,

Hard to find such as polyimide having such a wide range of applications, but also in every aspect of the show a very outstanding performance.
1 film: polyimide is one of the first commodity, for motor slot insulation and cable wrapping material. The main products are DuPont Kapton, Ube of Upilex series and Kaneka Apical. A transparent polyimide film can be used as flexible solar cell substrate.
2. Paint: as an insulating paint for magnet wire, or as a high-temperature coatings.
3. Advanced Composites: for the aerospace, aircraft and rocket parts. It is one of the most high-temperature structural materials. E.g., U.S. supersonic aircraft speed plan is designed 2.4M, flight surface temperature of 177 ℃, requires the service life of 60000h, is reported to have been determined as 50% of the structural material to a thermoplastic polyimide matrix resin Carbon fiber reinforced composite material, the amount of each aircraft is about 30t.
4. Fiber: elastic modulus after the carbon fiber as the medium and high-temperature filter material and radioactive substances bulletproof, fireproof fabric.
5. Foam: as high temperature insulation material.
6. Engineering Plastics: thermosetting also thermoplastic, thermoplastic molding can also be used for injection molding or transfer molding. The main lubrication, sealing, insulation and construction materials for the self. Wide polyimide materials have begun to use the rotary vane compressor, piston rings and special pump seals and other mechanical parts.
7. Adhesive: as high temperature structural adhesive. Wide polyimide adhesives as electronic components insulation potting material has high production.
8. membranes: for a variety of gases, such as the separation of hydrogen / nitrogen, nitrogen / oxygen, carbon dioxide / nitrogen or methane, etc., to remove moisture from the air the hydrocarbon feed gas and alcohols. But also as a pervaporation membrane ultrafiltration. Since the polyimide heat resistance and organic solvent properties, has a special significance in the separation of organic gases and liquids.
9. photoresist: negative and positive rubber glue, with sub-micron resolution. And pigments or dyes can be used with a color filter film, which can greatly simplify processing operations.
10. In the microelectronic device applications: used as an interlayer dielectric layer insulation, as a buffer layer can reduce stress and improve yield. As the protective layer can reduce the impact of the environment on the device, it can also a- particles from the shielding effect, reducing or eliminating soft error (soft error) devices.
-oriented Agent 11. The LCD used: polyimide in TN-LCD, STN-LCD, TFT-CD aligning agent material and future aspects of ferroelectric liquid crystal display occupies a very important position.
12. – The light material: material used for passive or active waveguide optical switch materials, fluorine-containing polyimide in the communication wavelength range of transparent polyimide as a chromophore base material can be improved stability.
13. Humidity: The use of hygroscopic linear expansion of its principle can be used to make a humidity sensor.
In summary, it is easy to see many of the aromatic heterocyclic polyimide polymer can reason from the 1960s, 1970s stand out, eventually become reasons for an important class of polymer materials.


As promising polyimide polymer material has been fully recognized in the insulating material and the material aspects of the application structure is constantly expanding. In terms of functional materials being brought on their potential is still excavations. But after 40 years of development has not yet become an even greater variety, the main reason is that compared with other polymers, the cost is still too high. Therefore, one of the main directions of future research should continue to be a polyimide on the monomer synthesis and polymerization process to find ways to reduce costs.
Synthesis of monomer
Polyimide monomer is a dianhydride (D acid) and diamine. Diamine synthesis method is relatively mature, there are many diamine commercially available. Dianhydride monomer is rather special, in addition to use as epoxy curing agent are mainly used in polyimide synthesis. Pyromellitic dianhydride and trimellitic anhydride, refined petroleum products by the heavy aromatic oils extracted durene and partial three toluene vapor and liquid phase oxidation step to obtain. Other important dianhydride, benzophenone dianhydride, biphenyl dianhydride, diphenyl ether dianhydride, hexafluoro dianhydride synthesized by various methods, but the cost is very expensive, such as hexafluoro dianhydride per kilogram to achieve the million. Changchun Institute of Applied Chemistry developed by the o-xylene chlorination, oxidation and then the isomerization separation can be obtained high purity 4-chloro-3-chloro anhydride and phthalic anhydride, with these two compounds can be synthesized as a raw material Series dianhydride, its great potential for cost reduction is a valuable synthetic route. If foreign polyimide DuPont in production, domestic as well as Changzhou Plastics Co., Ltd. and Changzhou Jianbang Yongbang plastic industry in the production.

PI Polymerization Process

Mainstream two-step synthesis, one-step condensation processes are using a high-boiling solvent, the higher the price of an aprotic polar solvent, it is difficult divisible, eventually requires high temperature processing. PMR method using cheap alcohol solvent. The thermoplastic polyimide can also use dianhydride and diamine polymerized directly in an extruder granulation, the solvent is no longer needed, it can greatly improve efficiency. Anhydride without using chlorinated dianhydride, and the diamine, bisphenol, sodium sulfide or elemental sulfur directly polymerized polyimide is the most economical synthetic route.


The application of polyimide surface is so wide, the processing is also a wide variety of requirements, such as high uniformity of deposition, spinning, vapor deposition, submicron lithography, etching depth straight wall, a large area , bulky shape, ion implantation, laser precision machining, nano-hybrid technology, and so are the application of polyimide open vast world. With the significant reduction in synthesis technology to further improve the processing technology and cost, but also has excellent mechanical properties, electrical insulation properties, thermoplastic polyimide will show its more prominent role in the field of future materials. The thermoplastic polyimide and its good workability and more promising.
Polyimide profile processing
Carbide knife, while cooled with cooling water to prevent the stress and deformation.