I. Overview Polyimide, as a special engineering material, has been widely used in aviation, aerospace, microelectronics, nanotechnology, liquid crystals, separation membranes, lasers and other fields. Recently, all countries have included the research, development and utilization of polyimides as one of the most promising engineering plastics in the 21st century. Polyimide, because of its prominent characteristics in performance and synthesis, whether it is used as a structural material or as a functional material, its great application prospect has been fully recognized and is known as “a problem-solving expert†( Protion solver) and believe that "without polyimide, there will be no microelectronic technology today."
Second, the performance of polyimide 1, fully aromatic polyimide by thermogravimetric analysis, the initial decomposition temperature is generally about 500 °C. The polyimide synthesized from biphenyl dianhydride and p-phenylenediamine has a thermal decomposition temperature of 600°C. It is one of the highest thermal stability polymers in the polymer so far.
2, polyimide can withstand extremely low temperature, such as -269 °C liquid helium will not be brittle.
3, polyimide has excellent mechanical properties, the tensile strength of unfilled plastics are all above 100Mpa, the film of benzene type polyimide (Kapton) is more than 170Mpa, and biphenyl type polyimide ( Upilex S) reaches 400Mpa. As engineering plastics, the amount of elastic film is usually 3-4Gpa, and the fiber can reach 200Gpa. According to theoretical calculation, the synthetic fiber of phthalic anhydride and p-phenylenediamine can reach 500Gpa, second only to carbon fiber.
4, some polyimide varieties are insoluble in organic solvents, stable to dilute acid, the general variety is not resistant to hydrolysis, this seemingly disadvantageous performance makes polyimide different from other high-performance polymer The characteristic is that the raw material dianhydride and diamine can be recovered by alkaline hydrolysis, for example, the recovery rate of Kapton film can reach 80%-90%. Changing the structure can also result in a fairly hydrolysis-resistant variety, such as a boiled water at 120°C for 500 hours.
5, the thermal expansion coefficient of polyimide is 2×10-5-3×10-5°C, Guangcheng thermoplastic polyimide is 3×10-5°C, biphenyl type is up to 10-6°C. Up to 10-7 °C.
6, polyimide has a very high resistance to radiation, the film after 5 × 109rad fast electron irradiation intensity retention rate was 90%.
7, polyimide has good dielectric properties, the dielectric constant of about 3.4, the introduction of fluorine, or the air nano-size dispersed in polyimide, the dielectric constant can be reduced to about 2.5. The dielectric loss is 10-3, the dielectric strength is 100-300KV/mm, Guangcheng Thermoplastic Polyimide is 300KV/mm, and the volume resistance is 1017Ω/cm. These properties can still be maintained at a high level over a wide temperature range and frequency range.
8, polyimide is a self-extinguishing polymer, low smoke rate.
9. Polyimide emits very little air under very high vacuum.
10, polyimide non-toxic, can be used to make cutlery and medical appliances, and withstand thousands of times disinfection. Some polyimides also have good biocompatibility, for example, non-hemolytic in blood compatibility experiments and non-toxic in vitro cytotoxicity experiments.
Third, the synthesis of a variety of ways:
Polyimide has a wide range of products in various forms, and has a variety of synthetic routes. Therefore, it can be selected according to various application purposes. This kind of synthetic flexibility is also difficult for other polymers.
1. Polyimides are mainly synthesized from dibasic anhydrides and diamines, these two monomers and numerous other heterocyclic polymers such as polybenzimidazoles, polybenzoxazoles, polybenzothiazoles, and polyquinoquinones. Compared with other monomers such as quinoline and polyquinoline, raw materials are widely available and the synthesis is also easier. There are a wide variety of dianhydrides and diamines, and different combinations can yield polyimides with different properties.
2. Polyimide can be polycondensed firstly in a polar solvent such as DMF, DMAC, NMP or a mixed solvent of methanol to obtain soluble polyamic acid. After filming or spinning The mixture is dehydrated by heating to about 300 DEG C. and then converted into polyimide. It is also possible to add acetic anhydride and a tertiary amine catalyst to the polyamic acid to perform chemical dehydration cyclization to obtain a polyimide solution and a powder. Diamines and dianhydrides can also be heat-polycondensed in a high-boiling solvent, such as a phenolic solvent, to obtain a polyimide in one step. In addition, polyimides can also be obtained from the reaction of dibasic acid dibasic esters and dibasic amines; polyamic acid can also be converted into polyisoimide first and then converted into polyimide. All of these methods are convenient for processing. The former is called PMR method and can obtain low-viscosity, high-solid solutions. When processing, there is a window with low melt viscosity, which is particularly suitable for the manufacture of composite materials; the latter increase. Solubility does not release low-molecular compounds during the conversion process.
3. As long as the purity of the dianhydride (or tetraacid) and the diamine is satisfactory, it is easy to obtain a sufficiently high molecular weight no matter which polycondensation method is used, and addition of a unit anhydride or a unit amine can also easily regulate the molecular weight.
4. Polycondensation of dianhydride (or tetraacid) and diamine, as long as it reaches an equimolar ratio and heat treatment in vacuum, can greatly increase the molecular weight of the solid low-molecular-weight prepolymer, thus giving processing and powder ribbons. It is convenient.
5. It is easy to introduce reactive groups to form reactive oligomers at the ends of the chains or chains to obtain thermosetting polyimides.
6. The use of carboxyl groups in polyimides for esterification or salt formation, introduction of photoactive groups or long chain alkyl groups to obtain amphiphilic polymers, and the possibility to obtain photoresists or for the preparation of LB films.
7. The process of synthesizing polyimides generally does not produce inorganic salts, which is particularly advantageous for the preparation of insulating materials.
8. Diamides and diamines as monomers are easily sublimated under high vacuum, so it is easy to use a vapor deposition method to form a polyimide film on a workpiece, particularly a surface uneven device.
Fourth, the application of polyimide:
Because of the performance and synthetic chemistry of the above-mentioned polyimides, it is difficult to find such a wide range of applications as polyimides among a large number of polymers, and shows outstanding performance in every respect. .
1. Film: It is one of the earliest commercial products of polyimide. It is used for slot insulation and cable wrapping materials for motors. The main products are DuPont Kapton, Ube's Upilex series and Chungchi Apical. Transparent polyimide film can be used as a soft solar cell master.
2. Coating: Use as an insulating varnish for magnet wire, or as a high temperature resistant coating.
3. Advanced composite materials: for aerospace, aircraft and rocket components. It is one of the most high-temperature structural materials. For example, the U.S. supersonic airliner plan has a design speed of 2.4M, a surface temperature of 177°C during flight and a service life of 60,000h. It has been reported that 50% of the structural material has been determined to be a thermoplastic polyimide matrix resin. The carbon fiber reinforced composite material, the amount of each aircraft is about 30t.
4. Fiber: The modulus of elasticity is second only to carbon fiber, as a filter material for high-temperature media and radioactive materials, and **, fire-retardant fabrics.
5. Foam: Used as a high-temperature insulation material.
6. Engineering plastics: Thermosetting and thermoplastic. Thermoplastics can be molded or injection molded or transfer molded. Mainly used for self-lubricating, sealing, insulation and structural materials. Guangcheng Polyimide Materials has been applied to mechanical components such as compressor rotary vanes, piston rings and special pump seals.
7. Adhesives: Used as high temperature structural adhesives. Guangcheng Polyimide adhesive has been produced as a high-insulation potting material for electronic components.
8. Separation membrane: For the separation of various gas pairs, such as hydrogen/nitrogen, nitrogen/oxygen, carbon dioxide/nitrogen or methane, remove moisture from air hydrocarbon feed gas and alcohols. It can also be used as a pervaporation membrane and an ultrafiltration membrane. Due to the heat resistance and resistance to organic solvents of polyimides, it is of particular importance for the separation of organic gases and liquids.
9. Photoresist: Negative and positive adhesives with sub-micron resolution. With pigments or dyes can be used for color filter film, can greatly simplify the processing process.
10. Applications in microelectronic devices: Use as a dielectric layer for interlayer insulation, as a buffer layer to reduce stress and improve yield. As a protective layer, the influence of the environment on the device can be reduced, and a-particles can also be shielded to reduce or eliminate the soft error of the device.
11. Alignment Aligners for Liquid Crystal Displays: Polyimides occupy an important position in TN-LCD, SHN-LCD, TFT-CD, and future orientation materials for ferroelectric liquid crystal displays.
12. Electro-optic materials: used as passive or active waveguide materials, optical switch materials, etc., fluorine-containing polyimide is transparent in the communication wavelength range, polyimide can be used as the matrix of the chromophore to improve the material. Stability.
In summary, it is not difficult to see that polyimides can stand out from the numerous aromatic heterocyclic polymers that emerged in the 1960s and 1970s, and eventually become a type of important polymer material.
Second, the performance of polyimide 1, fully aromatic polyimide by thermogravimetric analysis, the initial decomposition temperature is generally about 500 °C. The polyimide synthesized from biphenyl dianhydride and p-phenylenediamine has a thermal decomposition temperature of 600°C. It is one of the highest thermal stability polymers in the polymer so far.
2, polyimide can withstand extremely low temperature, such as -269 °C liquid helium will not be brittle.
3, polyimide has excellent mechanical properties, the tensile strength of unfilled plastics are all above 100Mpa, the film of benzene type polyimide (Kapton) is more than 170Mpa, and biphenyl type polyimide ( Upilex S) reaches 400Mpa. As engineering plastics, the amount of elastic film is usually 3-4Gpa, and the fiber can reach 200Gpa. According to theoretical calculation, the synthetic fiber of phthalic anhydride and p-phenylenediamine can reach 500Gpa, second only to carbon fiber.
4, some polyimide varieties are insoluble in organic solvents, stable to dilute acid, the general variety is not resistant to hydrolysis, this seemingly disadvantageous performance makes polyimide different from other high-performance polymer The characteristic is that the raw material dianhydride and diamine can be recovered by alkaline hydrolysis, for example, the recovery rate of Kapton film can reach 80%-90%. Changing the structure can also result in a fairly hydrolysis-resistant variety, such as a boiled water at 120°C for 500 hours.
5, the thermal expansion coefficient of polyimide is 2×10-5-3×10-5°C, Guangcheng thermoplastic polyimide is 3×10-5°C, biphenyl type is up to 10-6°C. Up to 10-7 °C.
6, polyimide has a very high resistance to radiation, the film after 5 × 109rad fast electron irradiation intensity retention rate was 90%.
7, polyimide has good dielectric properties, the dielectric constant of about 3.4, the introduction of fluorine, or the air nano-size dispersed in polyimide, the dielectric constant can be reduced to about 2.5. The dielectric loss is 10-3, the dielectric strength is 100-300KV/mm, Guangcheng Thermoplastic Polyimide is 300KV/mm, and the volume resistance is 1017Ω/cm. These properties can still be maintained at a high level over a wide temperature range and frequency range.
8, polyimide is a self-extinguishing polymer, low smoke rate.
9. Polyimide emits very little air under very high vacuum.
10, polyimide non-toxic, can be used to make cutlery and medical appliances, and withstand thousands of times disinfection. Some polyimides also have good biocompatibility, for example, non-hemolytic in blood compatibility experiments and non-toxic in vitro cytotoxicity experiments.
Third, the synthesis of a variety of ways:
Polyimide has a wide range of products in various forms, and has a variety of synthetic routes. Therefore, it can be selected according to various application purposes. This kind of synthetic flexibility is also difficult for other polymers.
1. Polyimides are mainly synthesized from dibasic anhydrides and diamines, these two monomers and numerous other heterocyclic polymers such as polybenzimidazoles, polybenzoxazoles, polybenzothiazoles, and polyquinoquinones. Compared with other monomers such as quinoline and polyquinoline, raw materials are widely available and the synthesis is also easier. There are a wide variety of dianhydrides and diamines, and different combinations can yield polyimides with different properties.
2. Polyimide can be polycondensed firstly in a polar solvent such as DMF, DMAC, NMP or a mixed solvent of methanol to obtain soluble polyamic acid. After filming or spinning The mixture is dehydrated by heating to about 300 DEG C. and then converted into polyimide. It is also possible to add acetic anhydride and a tertiary amine catalyst to the polyamic acid to perform chemical dehydration cyclization to obtain a polyimide solution and a powder. Diamines and dianhydrides can also be heat-polycondensed in a high-boiling solvent, such as a phenolic solvent, to obtain a polyimide in one step. In addition, polyimides can also be obtained from the reaction of dibasic acid dibasic esters and dibasic amines; polyamic acid can also be converted into polyisoimide first and then converted into polyimide. All of these methods are convenient for processing. The former is called PMR method and can obtain low-viscosity, high-solid solutions. When processing, there is a window with low melt viscosity, which is particularly suitable for the manufacture of composite materials; the latter increase. Solubility does not release low-molecular compounds during the conversion process.
3. As long as the purity of the dianhydride (or tetraacid) and the diamine is satisfactory, it is easy to obtain a sufficiently high molecular weight no matter which polycondensation method is used, and addition of a unit anhydride or a unit amine can also easily regulate the molecular weight.
4. Polycondensation of dianhydride (or tetraacid) and diamine, as long as it reaches an equimolar ratio and heat treatment in vacuum, can greatly increase the molecular weight of the solid low-molecular-weight prepolymer, thus giving processing and powder ribbons. It is convenient.
5. It is easy to introduce reactive groups to form reactive oligomers at the ends of the chains or chains to obtain thermosetting polyimides.
6. The use of carboxyl groups in polyimides for esterification or salt formation, introduction of photoactive groups or long chain alkyl groups to obtain amphiphilic polymers, and the possibility to obtain photoresists or for the preparation of LB films.
7. The process of synthesizing polyimides generally does not produce inorganic salts, which is particularly advantageous for the preparation of insulating materials.
8. Diamides and diamines as monomers are easily sublimated under high vacuum, so it is easy to use a vapor deposition method to form a polyimide film on a workpiece, particularly a surface uneven device.
Fourth, the application of polyimide:
Because of the performance and synthetic chemistry of the above-mentioned polyimides, it is difficult to find such a wide range of applications as polyimides among a large number of polymers, and shows outstanding performance in every respect. .
1. Film: It is one of the earliest commercial products of polyimide. It is used for slot insulation and cable wrapping materials for motors. The main products are DuPont Kapton, Ube's Upilex series and Chungchi Apical. Transparent polyimide film can be used as a soft solar cell master.
2. Coating: Use as an insulating varnish for magnet wire, or as a high temperature resistant coating.
3. Advanced composite materials: for aerospace, aircraft and rocket components. It is one of the most high-temperature structural materials. For example, the U.S. supersonic airliner plan has a design speed of 2.4M, a surface temperature of 177°C during flight and a service life of 60,000h. It has been reported that 50% of the structural material has been determined to be a thermoplastic polyimide matrix resin. The carbon fiber reinforced composite material, the amount of each aircraft is about 30t.
4. Fiber: The modulus of elasticity is second only to carbon fiber, as a filter material for high-temperature media and radioactive materials, and **, fire-retardant fabrics.
5. Foam: Used as a high-temperature insulation material.
6. Engineering plastics: Thermosetting and thermoplastic. Thermoplastics can be molded or injection molded or transfer molded. Mainly used for self-lubricating, sealing, insulation and structural materials. Guangcheng Polyimide Materials has been applied to mechanical components such as compressor rotary vanes, piston rings and special pump seals.
7. Adhesives: Used as high temperature structural adhesives. Guangcheng Polyimide adhesive has been produced as a high-insulation potting material for electronic components.
8. Separation membrane: For the separation of various gas pairs, such as hydrogen/nitrogen, nitrogen/oxygen, carbon dioxide/nitrogen or methane, remove moisture from air hydrocarbon feed gas and alcohols. It can also be used as a pervaporation membrane and an ultrafiltration membrane. Due to the heat resistance and resistance to organic solvents of polyimides, it is of particular importance for the separation of organic gases and liquids.
9. Photoresist: Negative and positive adhesives with sub-micron resolution. With pigments or dyes can be used for color filter film, can greatly simplify the processing process.
10. Applications in microelectronic devices: Use as a dielectric layer for interlayer insulation, as a buffer layer to reduce stress and improve yield. As a protective layer, the influence of the environment on the device can be reduced, and a-particles can also be shielded to reduce or eliminate the soft error of the device.
11. Alignment Aligners for Liquid Crystal Displays: Polyimides occupy an important position in TN-LCD, SHN-LCD, TFT-CD, and future orientation materials for ferroelectric liquid crystal displays.
12. Electro-optic materials: used as passive or active waveguide materials, optical switch materials, etc., fluorine-containing polyimide is transparent in the communication wavelength range, polyimide can be used as the matrix of the chromophore to improve the material. Stability.
In summary, it is not difficult to see that polyimides can stand out from the numerous aromatic heterocyclic polymers that emerged in the 1960s and 1970s, and eventually become a type of important polymer material.