TWI891935B - A polyimide and its application in metal laminates - Google Patents

Abstract

This invention relates to a polyimide and its application in metal laminates. The polyimide prepared in this invention exhibits good regularity and ordered long chain structures such as biphenyl and terphenyl. While maintaining the polyimide's good heat resistance, it promotes the bonding of the C=O groups in the imide ring with the metal surface, effectively improving the adhesion between the polyimide and the metal layer. Furthermore, the introduction of a phenyl ester-containing monomer further reduces dielectric loss. The polyimide described in this invention can be directly coated onto a metal layer to form a flexible copper-clad laminate, eliminating the need for an adhesive layer. The resulting flexible copper-clad laminate exhibits excellent heat resistance, peel strength, and dielectric properties, making it suitable for use in flexible circuit substrates and communications applications.

Description

A polyimide and its application in metal laminates

This invention belongs to the field of polymer material technology, and specifically relates to a polyimide and its application in metal laminates.

With the rapid adoption of 5G communications, flexible copper-clad laminates (FCCLs) with high frequency and low dielectric loss are finding increasingly widespread application in the electronics and information technology sectors. FCLs that combine excellent heat resistance, dielectric properties, and superior adhesion have become a current research and development hotspot.

Flexible copper-clad laminate (FCCL) refers to a flexible, multilayered composite material formed by coating a polymer base film with copper foil. Due to its advantages such as lightness, high heat resistance, and flexibility, it is widely used in mobile phones, laptops, and wearable electronic products. Traditional FCCLs use a three-layer structure of polyimide/adhesive/copper foil. The adhesive is a low-Tg (glass transition temperature) adhesive such as acrylic, epoxy, or phenolic resin. Its heat resistance and dimensional stability are poor, and it is prone to problems such as debonding and warping at high temperatures.

New FCCLs developed in recent years no longer use adhesives, consisting solely of an insulating composite film layer and a metal layer. These adhesive-free FCCLs not only offer excellent heat resistance, but also greater dimensional stability and thinner thickness. They have found widespread application in advanced integrated circuits and high-frequency communications. CN101786354A discloses a method for manufacturing a two-layer, double-sided flexible copper-clad laminate. The resulting double-sided flexible copper-clad laminate exhibits excellent heat resistance and peel strength, is simple to manufacture, and has promising industrial applications. However, how to obtain polyamides, polyimides, and metal laminates made from them with excellent heat resistance, peeling properties, and dielectric properties has become a technical problem that needs to be solved urgently.

CN108699243A discloses a thermoplastic polyimide, and metal-clad laminates and circuit substrates made from it. The thermoplastic polyimide developed in this article exhibits excellent peel strength and dielectric loss. However, its Tg of less than 320°C limits its use to only as an adhesive layer between insulating and metal layers, preventing the polyimide from fully realizing its advantages as a substrate material. CN109843588A discloses a polyimide film and metal laminate for high-temperature metal lamination. The application of a high proportion of long-chain aromatic rings significantly improves the heat resistance of the polyimide. However, the film still suffers from excessive dielectric loss and reduced adhesion. It requires adhesion with a hot-melt polyimide resin to improve the peeling force, but the hot-melt adhesive layer further reduces its heat resistance and operating temperature.

In view of the above reasons, this invention is proposed.

To address the aforementioned issues with existing technologies, the present invention provides a polyimide and its application in metal laminates. The polyimide described in the present invention exhibits excellent heat resistance and possesses a regularly ordered long chain structure of biphenyl and terphenyl. While maintaining the polyimide's excellent heat resistance, it also promotes the bonding of the C=O groups in the imide rings with the metal surface, effectively improving the adhesion between the polyimide and the metal layer. The polyimide can be directly coated onto the metal layer to form a flexible copper-clad laminate. The copper-clad laminate exhibits excellent heat resistance, peel strength, and dielectric properties.

The first object of the present invention is to provide a polyimide, wherein the general structural formula of the polyimide is shown in formula (I): Wherein, A represents a tetravalent residue, and B represents a divalent residue; in formula (I), B includes chemical formulas B1 and B2, and the structural formulas of B1 and B2 are as follows: In B1, n1 is 0 or 1, and in B2, _X1 is independently selected from

wherein R ₁ , R ₂ and R ₃ are independently selected from one or more of hydrogen, a halogen atom, an alkane having 1 to 3 carbon atoms, and a halogenated alkane; wherein A in formula (I) includes chemical formulas A1 and A2, and the structural formulas of A1 and A2 are as follows:

wherein n2 in A1 is 0 or 1, _X2 is independently selected from _{one or more of} -CH3-, -O-, -C(O)-, -C(O)O-, -C( _CF3 ) _2- , -S-, -C( _CH3 ) _2- , -S(O)O-, and benzene, and _R4 is selected from one of hydrogen, a halogen atom, an alkane having 1 to 3 carbon atoms, or a halogenated alkane.

Furthermore, B1 accounts for 40-90% of the total diamine, B2 accounts for 10-60% of the total diamine, and the sum of B1 and B2 accounts for 90% or more of the total diamine; A1 accounts for 50-100% of the total dianhydride, and A2 accounts for 0-50% of the total dianhydride.

Furthermore, B1 is independently selected from one or more of the following chemical formulas: B2 is independently selected from one or more of the following chemical formulas:

Furthermore, A1 is independently selected from one or both of the following chemical formulas: A2 is composed of one or more of 2,2'3,3'-biphenyltetracarboxylic dianhydride, 2,3,3'4-biphenyltetracarboxylic dianhydride, 3,3'4,4'-diphenyl sulfide tetracarboxylic dianhydride, 3,3'4,4'-diphenyl ether tetracarboxylic dianhydride, 2,3,3'4-diphenyl ether tetracarboxylic dianhydride, 2,2'3,3'-diphenyl ether tetracarboxylic dianhydride, 2,2'-bis(3,4-dicarboxylic)hexafluoropropane dianhydride, biphenyl diether dianhydride, 4,4'-terephthalic anhydride, 3,3'-isophthalic anhydride, and 3,3',4,4'-benzophenone tetracarboxylic dianhydride.

Furthermore, the polyimide also includes a total amount of diamine 10% of the following diamines: one or more of 4,4'-diaminodiphenyl ether, 4,4'-diaminodiphenylmethane, 1,3-bis(3-aminophenoxy)benzene, 1,4-bis(3-aminophenoxy)benzene, 1,4-bis(4-aminophenoxy)benzene, 2,2'-bis(trifluoromethyl)-4,4'-diaminophenyl ether, 2,2'-bis[4-(4-aminophenoxyphenyl)]propane, 2,2-bis[4-(4-aminophenoxy)phenyl]-1,1,1,3,3,3-hexafluoropropane, and 1,4-bis(4-amino-2-trifluoromethylphenoxy)benzene.

Furthermore, the polyimide is a thermosetting polyimide, and Tg 360℃.

The polyimide described in the present invention is obtained by reacting a dianhydride and a diamine in a solvent. The solvent used is not limited and may include N,N-dimethylformamide, N,N-dimethylacetamide, N,N-diethylacetamide, N-methylpyrrolidone, N-ethylpyrrolidone, N-methyl-2-pyrrolidone, and γ-butyrolactone. N,N-dimethylacetamide is preferred. The solid content of the polyimide is not particularly limited and may range from 5% to 30%. The viscosity is not particularly limited and can be adjusted according to actual needs, preferably between 1,000 and 200,000 cp. The resin reaction temperature may be kept within the range of 10°C to 100°C, with stirring for 1 to 24 hours to polymerize the obtained polyimide.

The synthesized polyamine can be diluted or the solvent replaced as needed. Film formation can be performed using conventional methods, such as direct heating at 80-400°C. Alternatively, conventional dehydrating agents and promoters can be added, such as one or more of acetic anhydride, propionic anhydride, and benzoic anhydride (dehydrating agents). Alternatively, one or more of pyridine, picoline, isoquinoline, and triethylamine (promoting agents).

The second purpose of the present invention is to provide an application of the polyimide in a metal laminate, wherein the polyimide is coated on the surface of the metal layer and has a peeling strength. 0.8N/mm, 50-200℃, thermal expansion coefficient 35ppm, dielectric constant Dk 3.4, Df 0.005.

Furthermore, the metal laminate is used in high-frequency flexible circuit substrates or high-frequency communications fields.

The metal laminate of the present invention is prepared by directly coating polyamide resin on one side of the metal plate, then drying and imidizing it to form a single-sided copper-clad plate. Alternatively, polyamide resin is coated on one side of two metal plates, pre-dried to form a gel film, and then the two plates coated with polyimide resin are hot-pressed to form a double-sided copper-clad plate. The resin film thickness can be adjusted as needed, preferably within the range of 5-100 μm. The hot-pressing temperature and pressure can be adjusted according to actual needs, ranging from 150°C to 380°C and 3 MPa to 7 MPa. High-temperature hot-pressing requires an oxygen-free environment. The metal plates are not particularly limited, but copper foil is preferred. The surface roughness of the surface in contact with the resin layer is preferably within a ten-point average roughness Rz of 2.0 μm.

During the synthesis of the polyimide of the present invention, a small amount of inorganic or organic additives is added according to actual needs. Specifically, one or more of silicon dioxide, aluminum oxide, calcium oxide, calcium fluoride (inorganic), or vinyltrimethoxysilane, hexamethyldisiloxane, 3-aminopropyltrimethoxysilane, aminopropylmethyldiethoxysilane (organic) are added.

Compared with existing technologies, the present invention has the following advantages: the polyimide prepared by the present invention has good regularity and ordered long chain structures such as biphenyl and terphenyl. While maintaining the good heat resistance of the polyimide, it promotes the bonding of the C=O groups in the imide ring with the metal surface, thereby effectively improving the adhesion between the polyimide and the metal layer. Furthermore, the introduction of a phenyl ester-containing monomer further reduces dielectric loss. The polyimide described in the present invention can be directly coated on the metal layer to form a flexible copper-clad laminate, without the need for an adhesive layer. The resulting flexible copper-clad laminate has excellent heat resistance, peel strength, and dielectric properties, making it suitable for use in flexible circuit substrates and the communications field.

To further clarify the purpose, technical solutions, and advantages of the present invention, the technical solutions of the present invention are described in detail below. Obviously, the embodiments described herein are only a portion of the present invention, and not all of the present invention. All other implementations derived by persons of ordinary skill in the art based on the embodiments of the present invention without inventive effort are also within the scope of protection of the present invention.

The present invention provides a polyimide and its application in metal laminates. The polyimide described in the present invention has excellent heat resistance and possesses a regular and ordered long chain structure of biphenyl and terphenyl. While maintaining the good heat resistance of the polyimide, it promotes the bonding of the C=O groups in the imide ring with the metal surface, thereby effectively improving the adhesion between the polyimide and the metal layer. The polyimide can be directly coated on the metal layer to form a flexible copper-clad laminate. The copper-clad laminate has excellent heat resistance, peel strength, and dielectric properties.

The general structural formula of the polyimide is shown in formula (I): Wherein, A represents a tetravalent residue, and B represents a divalent residue; in formula (I), B includes chemical formulas B1 and B2, and the structural formulas of B1 and B2 are as follows: In B1, n1 is 0 or 1, and in B2, _X1 is independently selected from

wherein R ₁ , R ₂ and R ₃ are independently selected from one or more of hydrogen, a halogen atom, an alkane having 1 to 3 carbon atoms, and a halogenated alkane; wherein A in formula (I) includes chemical formulas A1 and A2, and the structural formulas of A1 and A2 are as follows:

wherein n2 in A1 is 0 or 1, _X2 is independently selected from _{one or more of} -CH3-, -O-, -C(O)-, -C(O)O-, -C( _CF3 ) _2- , -S-, -C( _CH3 ) _2- , -S(O)O-, and benzene, and _R4 is selected from one of hydrogen, a halogen atom, an alkane having 1 to 3 carbon atoms, or a halogenated alkane.

Furthermore, B1 accounts for 40-90% of the total diamine, B2 accounts for 10-60% of the total diamine, and the sum of B1 and B2 accounts for 90% or more of the total diamine; A1 accounts for 50-100% of the total dianhydride, and A2 accounts for 0-50% of the total dianhydride.

Furthermore, B1 is independently selected from one or more of the following chemical formulas: B2 is independently selected from one or more of the following chemical formulas:

Furthermore, A1 is independently selected from one or both of the following chemical formulas: A2 is composed of one or more of 2,2'3,3'-biphenyltetracarboxylic dianhydride, 2,3,3'4-biphenyltetracarboxylic dianhydride, 3,3'4,4'-diphenyl sulfide tetracarboxylic dianhydride, 3,3'4,4'-diphenyl ether tetracarboxylic dianhydride, 2,3,3'4-diphenyl ether tetracarboxylic dianhydride, 2,2'3,3'-diphenyl ether tetracarboxylic dianhydride, 2,2'-bis(3,4-dicarboxylic)hexafluoropropane dianhydride, biphenyl diether dianhydride, 4,4'-terephthalic anhydride, 3,3'-isophthalic anhydride, and 3,3',4,4'-benzophenone tetracarboxylic dianhydride.

Furthermore, the polyimide also includes a total amount of diamine 10% of the following diamines: one or more of 4,4'-diaminodiphenyl ether, 4,4'-diaminodiphenylmethane, 1,3-bis(3-aminophenoxy)benzene, 1,4-bis(3-aminophenoxy)benzene, 1,4-bis(4-aminophenoxy)benzene, 2,2'-bis(trifluoromethyl)-4,4'-diaminophenyl ether, 2,2'-bis[4-(4-aminophenoxyphenyl)]propane, 2,2-bis[4-(4-aminophenoxy)phenyl]-1,1,1,3,3,3-hexafluoropropane, and 1,4-bis(4-amino-2-trifluoromethylphenoxy)benzene.

Furthermore, the polyimide is a thermosetting polyimide, and Tg 360℃.

The polyimide described in the present invention is obtained by reacting a dianhydride and a diamine in a solvent. The solvent used is not limited and includes, for example, N,N-dimethylformamide, N,N-dimethylacetamide, N,N-diethylacetamide, N-methylpyrrolidone, N-ethylpyrrolidone, N-methyl-2-pyrrolidone, and γ-butyrolactone. N,N-dimethylacetamide is preferred. The solid content of the polyimide is not particularly limited and can be between 5% and 30%. The viscosity is not particularly limited and can be adjusted according to actual needs, preferably between 1,000 and 200,000 cp. The resin reaction temperature can be kept between 10°C and 100°C, with stirring for 1 to 24 hours to polymerize the obtained polyimide.

The synthesized polyamine can be diluted or the solvent replaced as needed. Film formation can be performed using conventional methods, such as direct heating at 80-400°C. Alternatively, conventional dehydrating agents and promoters can be added, such as one or more of acetic anhydride, propionic anhydride, and benzoic anhydride (dehydrating agents). Alternatively, one or more of pyridine, picoline, isoquinoline, and triethylamine (promoting agents).

The polyimide of the present invention is used in metal laminates. The polyimide is coated on the surface of the metal layer to improve the peeling strength. 0.8N/mm, 50-200℃, thermal expansion coefficient 35ppm, dielectric constant Dk 3.4, Df 0.005.

Furthermore, the metal laminate is used in high-frequency flexible circuit substrates or high-frequency communications fields.

The metal laminate of the present invention is prepared by directly coating polyamide resin on one side of the metal plate, then drying and imidizing it to form a single-sided copper-clad plate. Alternatively, polyamide resin is coated on one side of two metal plates, pre-dried to form a gel film, and then the two plates coated with polyimide resin are hot-pressed to form a double-sided copper-clad plate. The resin film thickness can be adjusted as needed, preferably within the range of 5-100 μm. The hot-pressing temperature and pressure can be adjusted according to actual needs, ranging from 150°C to 380°C and 3 MPa to 7 MPa. High-temperature hot-pressing requires an oxygen-free environment. The metal plates are not particularly limited, but copper foil is preferred. The surface roughness of the surface in contact with the resin layer is preferably within a ten-point average roughness Rz of 2.0 μm.

During the synthesis of the polyimide of the present invention, a small amount of inorganic or organic additives is added according to actual needs. Specifically, one or more of silicon dioxide, aluminum oxide, calcium oxide, calcium fluoride (inorganic), or vinyltrimethoxysilane, hexamethyldisiloxane, 3-aminopropyltrimethoxysilane, aminopropylmethyldiethoxysilane (organic) are added.

Compared with existing technologies, the present invention has the following advantages: the polyimide prepared by the present invention has good regularity and ordered long chain structures such as biphenyl and terphenyl. While maintaining the good heat resistance of the polyimide, it promotes the bonding of the C=O groups in the imide ring with the metal surface, thereby effectively improving the adhesion between the polyimide and the metal layer. Furthermore, the introduction of a phenyl ester-containing monomer further reduces dielectric loss. The polyimide described in the present invention can be directly coated on the metal layer to form a flexible copper-clad laminate, without the need for an adhesive layer. The resulting flexible copper-clad laminate has excellent heat resistance, peel strength, and dielectric properties, making it suitable for use in flexible circuit substrates and the communications field.

The specific names of the substances in this invention are as follows:

PDA: p-phenylenediamine

1,3,3-APB: 1,3-bis(4'-aminophenoxy)benzene

BAPP: 2,2-bis(4-(4-aminophenoxy)phenyl)propane

TFMB: 2,2'-bis(trifluoromethyl)-4,4'-diaminobenzidine

m-TB: 2,2'-dimethyl-4,4'-diaminobenzidine

DATP: 4,4'-diamino-p-terphenyl

APAB: p-aminophenyl para-aminobenzoate

BPBT: 1,4-phenylene bis(4-aminobenzoate)

ABHQ: di-p-aminophenyl terephthalate

s-BPDA: 3,3’,4,4’-biphenyltetracarboxylic dianhydride

ODPA: 4,4'-Oxydiphthalic anhydride

PMDA: Pyromellitic Dianhydride

TPDA: 5-[4-(1,3-dioxo-2-benzofuran-5-yl)phenyl]-2-benzofuran-1,3-dione

The specific method of performance testing is as follows:

(1) Coefficient of linear thermal expansion (CTE)

The thermal expansion coefficient of the polyimide film was measured using a thermomechanical analyzer (TA Instruments, Model Q400) using the following conditions: specimen size: 8 mm × 3-5 mm, atmosphere: nitrogen; temperature: heating rate: 10°C/min, scanning range: 50°C to 300°C; tensile force: 0.05 N, range: 50°C to 200°C.

(2) Glass transition temperature (Tg)

Measured using a thermomechanical analyzer (TA Instruments, Model Q400). Atmosphere: Nitrogen; Temperature: Heating rate: 10°C/min; Tensile force: 0.05N; Sample size: 8mm x 3-5mm.

(3)Dk&Df

The test was conducted using a Keysight N5224B vector network analyzer (cavity resonator method) at a test frequency of 10 GHz, with sample sizes of 6 x 6 cm.

(4) Peeling strength

Test samples were etched using an aqueous solution of ferric chloride from copper foil on the single-sided cast-resin side or the double-sided cast-resin hot-press bonded side. Testing was performed in accordance with IPC-TM-650 2.4.9 using a Shimadzu EZ-LX 500N test machine.

Example 1

Heat the reaction vessel to dryness and replace the atmosphere with nitrogen. After 30 minutes, add 150g of N,N-dimethylacetamide solvent, followed by 11.763g of DATP and 6.7457g of BPBT. Stir at 25°C until dissolved. Then, add 18.9913g of BPDA and stir at room temperature for 12 hours to obtain a 20% polyimide solution.

Example 2-9 and Reference Example 1-6

Refer to the polyimide method of Example 1, replace the diamine and dianhydride with the raw materials shown in Table 1, and the addition ratio is shown in Table 1.

Test Example 1

The polyimide solution prepared in Example 1 was cured and applied to a 25 μm thickness on copper foil. The film was then heated at 120°C to remove some of the solvent, forming a gel film. The film was then heat treated at temperatures ranging from 120°C to 360°C in a nitrogen atmosphere. The resulting metal laminate was used to prepare test samples. Excess copper foil was etched away using an aqueous ferric chloride solution, and various performance tests were performed. The results are shown in Table 2.

Test Examples 2-9 and Comparative Examples 1-6

Following the method of Experimental Example 1, the polyimide prepared in Examples 2-9 and Reference Examples 1-6 was used. The results are shown in Table 2.

Table 2 shows the properties of the copper-clad single-layer boards formed from the test examples and comparative examples. Comparison of the test examples and comparative examples reveals that the use of biphenyl and terphenyl monomers, as in Comparative Examples 1 and 2, outside the scope of this patent application, results in significantly lower peel strength. While sufficient peel strength is achieved in Comparative Examples 3 and 6, using flexible monomer ratios not specified in this patent application, the Tg is significantly too low, impacting the heat resistance and thermal dimensional stability of the copper-clad boards. Furthermore, insufficient or excessive phenyl ester monomer ratios can lead to reduced dielectric properties and insufficient peeling performance.

Test Example 10

The polyimide solution prepared in Example 1 was applied to two copper foils to a cured thickness of 12.5 μm. The films were heated at 120°C to remove some of the solvent and form a gel film. The two foils, with their resin-coated surfaces facing each other, were then brought into contact and hot-pressed at a temperature of 120°C to 360°C in a nitrogen atmosphere. The resulting double-sided metal laminates were then stacked to prepare test samples. Excess copper foil was etched away using an aqueous ferric chloride solution. The peel strengths 1 between the metal layer and the resin, and 2 between the resins, were tested. Specific properties are shown in Table 3.

Test Example 11-13

Double-sided copper-clad plates were prepared using the polyimide resin prepared in Examples 2-4, with all other conditions being the same as in Experimental Example 10. The properties are shown in Table 3.

Comparative Example 7

Double-sided copper-clad plates were prepared using the polyimide resin prepared in Reference Example 1, with all other conditions being the same as in Test Example 10. The properties are shown in Table 3.

As shown in Table 3, the double-sided copper-clad laminates produced by hot-pressing single-sided copper-clad laminates prepared using the polyimide of the present invention exhibit peel strengths exceeding 0.8 N/mm, significantly higher than that of Comparative Example 7. Therefore, metal laminates produced using the polyimide of the present invention are suitable for use in high-frequency flexible circuit substrates or high-frequency communications applications.

The above description is merely a specific embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any modifications or substitutions that a person skilled in the art can easily conceive within the technical scope disclosed herein should be included within the scope of protection of the present invention. Therefore, the scope of protection of the present invention shall be based on the scope of protection of the claims.

Claims (4)

A polyimide is used in a metal laminate, wherein the polyimide has a general structural formula as shown in formula (I): ; wherein A represents a tetravalent residue, and B represents a divalent residue; in formula (I), B includes chemical formulas B1 and B2; wherein B1 is independently selected from one or more of the following chemical formulas: ; B2 is independently selected from one or more of the following chemical formulas: ; In formula (I), A includes chemical formulas A1 and A2; wherein A1 is independently selected from one or two of the following chemical formulas: A2 is composed of one or more of 2,2'3,3'-biphenyltetracarboxylic dianhydride, 2,3,3'4-biphenyltetracarboxylic dianhydride, 3,3'4,4'-diphenyl sulfide tetracarboxylic dianhydride, 3,3'4,4'-diphenyl ether tetracarboxylic dianhydride, 2,3,3'4-diphenyl ether tetracarboxylic dianhydride, 2,2'3,3'-diphenyl ether tetracarboxylic dianhydride, 2,2'-bis(3,4-dicarboxylic acid)hexafluoropropane dianhydride, biphenyl diether dianhydride, 4,4'-terephthalic anhydride, 3,3'-isophthalic anhydride, and 3,3',4,4'-benzophenone tetracarboxylic dianhydride; wherein the polyacrylic acid An amine is coated on the metal surface of a sheet having a metal surface to form a flexible sheet, or the flexible sheet is butt-bonded with the polyimide by heat pressing. The polyimide coated on the surface of the metal layer has a peel strength of ≥0.8 N/mm, a thermal expansion coefficient of ≤35 ppm at 50-200° C., a dielectric constant Dk of ≤3.4, and a dielectric constant Df of ≤0.005. B1 accounts for 40-90% of the total diamine, B2 accounts for 10-60% of the total diamine, and the sum of B1 and B2 accounts for 90% or more of the total diamine. A1 accounts for 50-100% of the total dianhydride, and A2 accounts for 0-50% of the total dianhydride. The use of the polyimide in a metal laminate as described in claim 1, wherein the polyimide further comprises one or more of the following diamines, accounting for ≤10% of the total diamine amount: 4,4'-diaminodiphenyl ether, 4,4'-diaminodiphenylmethane, 1,3-bis(3-aminophenoxy)benzene, 1,4-bis(3-aminophenoxy)benzene, 1,4-bis(4-aminophenoxy)benzene, 2,2'-bis(trifluoromethyl)-4,4'-diaminophenyl ether, 2,2'-bis[4-(4-aminophenoxyphenyl)]propane, 2,2-bis[4-(4-aminophenoxy)phenyl]-1,1,1,3,3,3-hexafluoropropane, and 1,4-bis(4-amino-2-trifluoromethylphenoxy)benzene. The use of polyimide in a metal laminate as described in claim 1, wherein the polyimide is a thermosetting polyimide with a Tg of ≥ 360°C. An application of the polyimide according to any one of claims 1 to 3 in a metal laminate is disclosed, wherein the application is in the field of high-frequency flexible circuit substrates or high-frequency communications.