Characteristics And Applications Of Polyimide (PI)

November 04, 2024

Polyimide (Polyimide, abbreviated as PI) refers to a class of polymers containing an imide ring (-CO-NR-CO-) on the main chain, is one of the best overall performance of organic polymer materials. Its high temperature resistance of more than 400 ° C, long-term use of the temperature range -200 ~ 300 ° C, part of the melting point is not obvious, high insulation properties, 103 Hz dielectric constant 4.0, dielectric loss of only 0.004 ~ 0.007, is F to H class insulation.

HONY Plastic can provide super high temperature resistant special engineering plastics - polyimide profiles, such as rods, sheets, pipes and injection molding, machining finished products according to the customer's specific needs, with temperature resistance grades of 220 ℃, 260 ℃, 300 ℃, 350 ℃ and above respectively. Polyimide can be compounded with molybdenum disulfide, graphite, carbon fiber, polytetrafluoroethylene, etc., which can greatly change the mechanical strength of the material and self-lubricating wear-resistant properties.

Polyimide PI has high and low temperature resistance (-269~400℃), high friction resistance, self-lubricating, high strength, high insulation, radiation resistance, corrosion resistance, small coefficient of thermal expansion, resistance to organic solvents, self-extinguishing, non-toxic, etc. PI part of the category of long-term working temperature of more than 350 ℃, short-term up to 450 ℃, the current engineering plastics in the temperature of engineering plastics is better, and its comprehensive performance is unmatched by other special engineering plastics. Its comprehensive performance is also incomparable to other special.

Polyimide's rich variety of main varieties are homophthalic polyimide, ether anhydride polyimide, polyamide imide and maleic anhydride polyimide. Among them, homopolymer polyimide is the representative of polycondensation polyimide. However, it is insoluble and fusible, and is difficult to process. Usually can only use powder metallurgy method by molding powder pressed plastic products, or the use of impregnation or casting method into a film. For example, glass cloth impregnated with a polyamide acid solution is hot-pressed to produce sheets. In contrast, monoether anhydride type polyimide as a fusible polyimide, molding processing performance has improved greatly. It can not only molding processing, but also through the injection, extrusion and other methods of molding, can also be impregnated and cast method to manufacture film.

Classification

Polycondensation

Condensation type aromatic polyimides are produced by reacting aromatic diamines with aromatic dianhydrides, aromatic tetracarboxylic acids, or aromatic tetracarboxylic acid dialkyl esters. Since the synthesis of polycondensed polyimide is carried out in high boiling point non proton polar solvents such as dimethylformamide, N-methylpyrrolidone, etc., and polyimide composites are usually molded by prepreg, these high boiling point non proton polar solvents are difficult to evaporate cleanly during prepreg preparation, and there are volatiles released during cyclization of the polyamides, which easily create pores in the composite products. This makes it easy to produce pores in the composite products, and it is difficult to obtain high-quality composite materials without pores. Therefore, polycondensation polyimide has been less used as the matrix resin of composite materials, mainly used to manufacture polyimide films and coatings.

Polymerization

As polycondensation polyimide has the disadvantages mentioned above, in order to overcome these shortcomings, have developed a polymerization polyimide. The main ones that have been widely used are polybismaleimide and norbornene-based end-capped polyimides. Usually these resins are low relative molecular mass polyimides with unsaturated groups at the ends, and then polymerized by unsaturated end groups when applied.

(1) Polybismaleimide

Polybismaleimide is made by polycondensation of maleic anhydride and aromatic diamine. It is compared with polyimide, the performance is not bad, but the synthesis process is simple, easy post-processing, low cost, can be easily made into a variety of composite products. But the cured material is more brittle.

(2) Buckminsterfullerene-based end-capped polyimide resins

One of the most important is a class of PMR (for insitu polymerization of monomer reactants, monomer reactants in situ polymerization) type polyimide resins developed by NASA Lewis Research Center. PMR-type polyimide resins is a combination of aromatic tetracarboxylic acid dialkyl esters, aromatic diamines and 5-norbornene-2, 3-dicarboxylic acid monoalkyl esters, aromatic diamines and 5-norbornene-2, 3-dicarboxylic acid monoalkyl esters, aromatic diamines and 5-norbornene-2, 3-dicarboxylic acid monoalkyl esters. 3-dicarboxylic acid monomers such as alkyl esters of aromatic tetracarboxylic acids, aromatic diamines, and monoalkyl esters of 5-norbornene-2, 3-dicarboxylic acid are dissolved in an alkyl alcohol (e.g., methanol or ethanol) to produce a solution that can be used directly to impregnate fibers.

Subclasses

Polyimides can be divided into four categories: homophenylene PI, soluble PI, polyamide-imide (PAI) and polyetherimide (PEI).

In terms of modification, polyimide has a variety of ways. Through the enhancement of modification, glass fibers, boron fibers, carbon fibers and metal whiskers can be added. This reinforcement can effectively reduce the coefficient of linear expansion of polyimide, improve its strength, while reducing costs. For example, in the manufacture of high-strength structural components, after the enhancement of the modified polyimide can withstand greater loads.

Filler modification, on the other hand, utilizes inorganic fillers, graphite, molybdenum disulfide, or polytetrafluoroethylene as fillers, which improves its self-lubricating effect and reduces costs. Co-mingling gold is also an important modification method, polyimide can be co-mingled with epoxy resins, polyurethane, polytetrafluoroethylene and polyether ether ketone, etc., to form a material with more excellent performance.

Performance

1, All-aromatic polyimide analyzed by thermogravimetric analysis, the beginning of its decomposition temperature is generally around 500 ℃. Polyimide synthesized by homophthalic acid dianhydride and p-phenylenediamine, the thermal decomposition temperature of 600 ℃, is so far one of the polymers with the highest thermal stability of the species.

2, Polyimide can withstand extremely low temperatures, such as -269 ℃ in the liquid helium will not be brittle.

3, Polyimide has excellent mechanical properties, unfilled plastic tensile strength are more than 100MPa, homobenzene-type polyimide film (Kapton) for more than 170MPa, thermoplastic polyimide (TPI) impact strength as high as 261kJ/m2. and biphenylene-type polyimide (Upilex S) reaches 400MPa. as engineering plastics. Modulus of elasticity is usually 3-4GPa, the fiber can reach 200GPa, according to theoretical calculations, benzene tetracarboxylic acid dianhydride and p-phenylenediamine synthesized fibers up to 500GPa, second only to carbon fiber.

4, Some varieties of polyimide insoluble in organic solvents, dilute acid stability, general varieties are not very resistant to hydrolysis, this seems to be a disadvantage of the performance of the polyimide is different from other high-performance polymers, a very big feature, that is, alkaline hydrolysis can be used to recover raw materials, such as dianhydride and diamine, such as for the Kapton film, the recovery rate of up to 80% -90%. Change the structure can also get quite resistant to hydrolysis varieties, such as withstand 120 ℃, 500 hours of boiling.

5, Polyimide has a wide solubility spectrum, according to the structure of the different, some varieties are almost insoluble in all organic solvents, and others can be soluble in common solvents, such as tetrahydrofuran, acetone, chloroform and even toluene and methanol.

6, The coefficient of thermal expansion of polyimide in 2 × 10-5-3 × 10-5 / ℃, thermoplastic polyimide 3 × 10-5 / ℃, biphenyl type up to 10-6 / ℃, individual varieties up to 10-7 / ℃.

7, Polyimide has a high resistance to irradiation, its film in 5 × 109rad fast electron irradiation strength retention rate of 90%.

8, Polyimide has good dielectric properties, dielectric constant of 3.4 or so, the introduction of fluorine, or air nanometer size dispersed in polyimide, the dielectric constant can be reduced to about 2.5. Dielectric loss of 10-3, dielectric strength of 100-300kV/mm, volume resistance of 1017Ω-cm. These properties in a wide range of temperatures and frequency range can still be maintained at a high level.

9, Polyimide is a self-extinguishing polymer, low smoke rate.

10, Polyimide in a very high vacuum under very little outgassing.

11, Polyimide non-toxic, can be used to manufacture tableware and medical instruments, and withstand thousands of times sterilization. Some polyimide also has good biocompatibility, for example, in the blood compatibility test for non-hemolytic, in vitro cytotoxicity test for non-toxic.

Typical applications include:

(1) Parts with low friction coefficient and wear resistance under high speed and high pressure;

(2) Parts with excellent resistance to creep or plastic deformation;

(3) Excellent self-lubricating or oil lubrication performance parts;

(4) High temperature and pressure under the liquid sealing parts;

(5) High resistance to bending, stretching and high impact resistance parts;

(6) Corrosion-resistant, radiation-resistant, rust-resistant parts;

(7) Long-term use of temperature exceeding 300 ℃ or more, short-term up to 400 ~ 450 ℃ parts;

(8) High temperature (more than 260 ℃) structural adhesives (modified epoxy resins, modified phenolic resins, modified silicone adhesives and other temperature resistance does not exceed 260 ℃ occasions);

(9) Microelectronic packaging, stress buffer protective coating, multi-layer interconnection structure of the interlayer insulation, dielectric film, chip surface passivation, etc..

Author:

Ms. Tina

E-mail:

sales@honyplastic.com

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+86 18680371609