Polyimide as a special engineering material polyimide
<br has been widely used in the field of aviation, aerospace, microelectronics, nano, liquid crystals, membranes, lasers and so on. Recently, the country is polyimide research, development and utilization of engineering in the 21st century contains the most promising. Polyimide, with its outstanding performance properties and synthesis, either as structural or functional materials, its potential for application has been fully recognized, known as the "problem solver" (protion solver), and said: "There would be no polyimide in microelectronics today! ".
2 polyimide properties
1, all-aromatic polyimide by thermogravimetric analysis, it begins to decompose at a temperature usually about 500 ℃. Biphenyl tetracarboxylic dianhydride and p-phenylenediamine polyimide, the thermal decomposition temperature reaches 600 ° C, the substance is by far the polymer's highest thermal stability 1.
2, very low temperature resistance polyimide, such as not brittle cracking in liquid helium-269 ° C.
3, polyimide has excellent mechanical properties, tensile strength of unfilled plastics exceeds 100Mpa, benzene tetramethylene polyimide film (Kapton) for more than 170MPa, and polybiphenylimide (Upilex S) reaches 400MPa level. As a plastic, the modulus of elasticity is usually 3-4Gpa, fiber up to 200Gpa, according to theoretical calculations, benzene tetracarboxylic acid dianhydride and p-phenylenediamine synthesized fibers up to 500Gpa after the carbon fiber.
4, several varieties of polyimide is insoluble in organic solvents, acid stable, generally very little hydrolysis of species, this seemingly flawed performance but unlike other high-performance polyimide polymers, a great feature, it can be recovered through alkaline hydrolysis of the tetracarboxylic acid dianhydride and diamine raw materials, such as Kapton film, which is 80% -90% recovery rate. Structural changes can also be obtained in fairly hydrolyzed species, such as the ability to withstand 120°C and 500 hours of boiling.
5, the coefficient of thermal expansion of polyimide at 2 × 10-5-3 × 10-5 ° C, widely used as thermoplastic polyimide 3 × 10-5 ° C, up to 10-6 ° C biphenyl individual species can reach 10-7 ° C.
6, the polyimide is also available as a raw material, such as Kapton film, which is 80% -90% recycled.
6, polyimide has high radiation resistance, its film after 5 × 109rad fast electron irradiation intensity retention rate of 90%.
7, has good dielectric properties, about 3.4 dielectric constant, the introduction of fluorine, or dispersed in the nano-size air polyimide polyimide, the dielectric constant can be reduced to about 2.5. dielectric loss of 10-3, dielectric strength of 100-300KV/mm, Hiroari into a thermoplastic polyimide 300KV / mm, 1017Ω / cm volume resistivity. These properties in a wide range of temperatures and frequency range can be maintained at a high level.
8, polyimide polymer is self-extinguishing, fuming rate.
9, Polyimide gases in high vacuum put very little.
10, polyimide is non-toxic, used in the manufacture of tableware and medical equipment, withstood thousands of sterilization. Some polyimides also have good biocompatibility, for example, in a non-hemolytic, non-toxic in vitro cytotoxicity assay blood compatibility test.
Third, on multiple synthetic routes:
Polyimides come in a wide variety of forms, synthesized in a variety of different ways, which can be selected according to the purpose of the different applications, and the continuity of this variable is also difficult to have other synthetic polymers.
1, polyimide is mainly synthesized from dicarboxylic anhydride and diamine, as well as many other heterocyclic polymers of the two monomers, such as polybenzimidazole, polybenzoxazole dummy oxadiazole, polybenzothiazole polyquinoline, polyquinoline monomers, a relatively wide range of sources of raw materials, the present synthesis is very easy. Carboxylic acid dianhydride, diamine of various different properties of different combinations can be obtained from the polyimide.
2, polyimide carboxylic acid dianhydride and diamine in polar solvents such as DMF, DMAC, NMP or THE / methanol mixed solvents, the first low-temperature polycondensation of polyamidoic acid obtained by the water-soluble, film-forming or spinning after the mixture heated to about 300 ℃ dehydrated into cyclic imide; acetic anhydride, and also can be added to the tertiary amine catalyst for polyamidoic acid, chemical dehydrocyclization, to obtain polyimide solutions and cyclic. Polyimide solutions and powders are obtained. Diamines and dianhydrides, can also be in high boiling point solvents, such as in the thermal polycondensation process phenolic solvents, the polyimide obtained. In addition, also includes tetracarboxylic acid diesters obtained by the reaction of diamine and polyimide; polyamide acid can be converted to polyisocyanate, polyimide, and then converted to polyimide. These methods for ease of processing, the former is called PMR method can be obtained a low viscosity, low melt viscosity in the processing window there is a particularly suitable for the manufacture of composites in the high solids content of the solution, in the process of the latter increased solubility transformations do not release the low molecular weight compounds.
3, as long as the purity of the anhydride (or tetra acid) and diamine is qualified regardless of the polycondensation process, it is easy to obtain a sufficiently high molecular weight amine in the addition of cellular or cellular anhydride can easily adjust the molecular weight.
4, with tetracarboxylic acid dianhydride (or tetraacid) and diamine polycondensation, as long as the equimolar ratio is reached, heat treatment in a vacuum, the solid can be a low molecular weight prepolymer, greatly increasing the molecular weight, and thus the convenience of processing and powder.
5, it is easy to introduce the formation of reactive groups in the chain or side chain of the active oligomer, thus making heat-curing polyimide.
6, the use of esterification or salting of polyimide carboxyl groups, photosensitive introduction of long-chain alkyl groups or polymers to parents, or photoresists can be used to prepare LB films.
07 of the general synthesis process does not produce salts of polyimide, the preparation of insulating materials is particularly advantageous.
08 Dianhydride and diamine monomers sublimate easily under high vacuum, and it is easy polyimide film vaporization method to form on the workpiece, especially in the use of the device surface irregularities.
Fourth, the application of polyimide:
Because of the performance and synthetic chemical properties of polyimide, in many polymers such as polyimide, it is difficult to find with such a wide range of applications, but also in terms of performance in each exhibition very prominent.
1, Film: It was one of the first commodity polyimides used in slot insulation for electric motors and cable packaging materials. The main products are DuPont Kapton, the Upilex series of UBE Kogyo and Jongbuchi Heart Tip. A transparent polyimide film can be used as a flexible backing for solar cells.
2 Coatings: Coatings are used as insulating wires, or as high temperature resistant coatings.
3 Advanced Composites: Used in aerospace, aircraft and rocket components. One of the highest temperature structural materials. U.S. supersonic aircraft, such as the speed plan aims to be 2.4M, when flying 177 ° C surface temperature, the required service life of 60,000H, it is reported that the structure of the thermoplastic material is determined 50% is polyimide resin carbon fiber reinforced composites, the amount of each aircraft for about 30 tons.
4 Fibers: Carbon fiber for media and high temperature filtration materials and radioactive materials bulletproof, fireproof fabrics after the modulus of elasticity.
5 Foam: used as a high temperature insulation material.
6 Plastics: thermoset also thermoplastic, thermoplastic molding, also used for injection molding or transfer molding. The main lubrication, sealing, insulation and self-structuring materials. Guangcheng polyimide materials have been used in rotary lobe compressors, piston rings and special pump seals and other mechanical parts.
7 Adhesives: for high temperature resistant structural adhesives. A wide range of electronic components bonding polyimide high insulation encapsulation materials have been produced.
8 Membrane: Used for various gases such as hydrogen/nitrogen separation, nitrogen/oxygen, carbon dioxide/nitrogen or methane, hydrocarbon feedstock gases and alcohols from air to remove moisture. Osmotic vaporization membranes can be used as ultrafiltration membranes. Due to the heat and organic solvent resistance of polyimide, it is of particular importance in the separation of organic gases and liquids.
9 Resistance: There are negative and positive rubberized adhesives that can be used with sub-micron resolution. With pigments or dyes available with color filters can greatly simplify processing operations.
10 applications in microelectronics: as an insulating layer between dielectric layers, the buffer layer can reduce stress and improve yield. As a protective layer to reduce the environmental impact of the device when the particles can also be used as a shielding layer to reduce or eliminate soft errors (soft error) devices.
11 Liquid crystal orientation agent arrangement: polyimide in the TN-LCD, SHN-LCD, TFT-CD and ferroelectric liquid crystal display material orientation agent of the future occupies a very important position.
12 - Optical materials: materials used in passive or active optical waveguides, such as switches, fluorinated polyimide in the wavelength range of said communication is transparent polyimide as chromophores to improve the stability of the matrix material.
In summary, it is easy to see why from polyimides in the 1960s, a large number of aromatic heterocyclic polymers appeared in the 1970s to stand out and eventually led to an important category of polymer materials.
Polyimide polymers are molecular structures containing aromatic heterocyclic imide groups linked by the English name polyimide (abbreviated PI), which can be divided into two types of benzene-type PI, soluble PI, polyamine - imide (PAI) and polyetherimide (PEI) 4.
PI is one of the best heat-resistant varieties of plastics, and some varieties can withstand high temperatures of 290 ° C for a long time and a short time. Withstand high temperatures of 490 ℃, while other mechanical properties, fatigue resistance, flame retardancy, dimensional stability, electrical properties are good, low molding shrinkage, oil, acid and general organic solvents, not alkali resistant, excellent resistance to wear and abrasion, wear resistance
Pi electrical and electronic aspects of the electronics industry has been applied to do electronic industry circuit boards printing, insulating materials, thermal - fire resistant cables, terminals, sockets and other fields.