Fluorine-containing nitrogen heterocyclic structure pi-ae block copolymer and high-frequency self-adhesive film preparation method

Abstract

This invention relates to the field of high-performance polymer materials and electronic circuit substrates, and discloses a method for preparing a fluorinated nitrogen heterocyclic PI-AE block copolymer and a high-frequency self-adhesive film. The copolymer comprises polyimide blocks and liquid crystal polyester blocks, wherein the polyimide blocks comprise 30%–60% by mass and the fluorine content is 8%–15%. The polyimide blocks are formed by the condensation polymerization of a fluorinated nitrogen heterocyclic diamine and an aromatic dianhydride, and the liquid crystal polyester blocks are formed by the condensation polymerization of an aromatic hydroxycarboxylic acid monomer. The two are chemically bonded to construct a triple functional system of "coordination self-adhesion-liquid crystal ordering-fluorinated synergy". Under a PI:LCP mass ratio of 45:55 to 55:45, a hot-pressing temperature of 310 to 320°C, and a pressure of 5 MPa, the film dielectric loss Df is 0.0016 to 0.0018 (10 GHz), the peel strength with low-roughness copper foil is ≥1.0 N / mm, and the CTE is 15 to 18 ppm / °C, achieving a balance between ultra-low loss, high-strength adhesive-free self-adhesion, and low expansion; suitable for 5G / 6G millimeter-wave communication, high-frequency flexible copper-clad laminates, and antenna substrates.

Description

Technical Field

[0001] This invention relates to the field of high-performance polymer materials and electronic circuit substrates, specifically to a fluorine-containing nitrogen heterocyclic PI-AE block copolymer, its preparation method, and high-frequency self-adhesive films and adhesive-free double-sided flexible copper-clad laminates made from the copolymer. Background Technology

[0002] Polyimide (PI) is a class of high-performance polymer materials characterized by an imide ring structure. It has excellent thermal stability, mechanical properties, chemical corrosion resistance and low moisture absorption, and is widely used in microelectronics, 5G communication, aerospace and other fields. However, the dielectric constant (Dk≈3.0~3.5) and dielectric loss (Df≈0.003~0.005, 1 MHz) of traditional polyimide materials are still relatively high in high-frequency environments, which can easily lead to signal delay, energy loss and electromagnetic interference, making it difficult to meet the low loss requirements of high-frequency circuits (see: Li Xiaolan et al., Polymer Materials Science and Engineering, 2019, 35(8): 45-51).

[0003] To reduce the dielectric constant and dielectric loss of polyimides, this can typically be achieved by introducing functional groups with low polarizability, such as fluorine atoms. Fluorine atoms have the highest electronegativity (χ=4.0) and low polarizability; the introduction of CF bonds can effectively suppress molecular polarization and reduce the dielectric constant. For example, prior art CN118373995A discloses a polyimide material that uses large-volume fluorine-containing side groups to reduce the dielectric constant, but its dielectric loss optimization is limited, and the introduction of a large number of fluorine atoms leads to an increase in the coefficient of thermal expansion (>25 ppm / ℃), affecting dimensional stability.

[0004] Liquid crystalline polyester (LCP) is a class of high-performance polymers with an ordered liquid crystal structure. Its molecular chains can form highly ordered smectic or nematic phase structures in the molten or solution state. This liquid crystal ordering endows LCP with extremely low dielectric loss (Df≈0.001~0.002) and extremely low coefficient of thermal expansion (CTE≈5~10 ppm / ℃), making it an ideal high-frequency substrate material. However, LCP has the following application obstacles: extremely poor adhesion to copper foil, making direct hot-pressing lamination almost impossible; extremely high melt viscosity, narrow processing window, making it difficult to prepare uniform films; significant mechanical anisotropy, with large differences in longitudinal and transverse properties of the film (see: Zhong Ganji et al., Insulating Materials, 2020, 53(4): 12-18).

[0005] Flexible copper clad laminate (FCCL) is a core material in the flexible electronics industry. Based on its structure, FCCL is mainly divided into three-layer flexible copper clad laminate (3L-FCCL) and two-layer flexible copper clad laminate (2L-FCCL). 3L-FCCL uses a three-layer structure of "copper foil / adhesive / polyimide," with adhesives typically being epoxy resin or acrylate-based. Its dielectric loss is usually above 0.02, becoming an "electromagnetic bottleneck" in high-frequency signal transmission paths. 2L-FCCL uses a direct composite structure of "copper foil / base film," eliminating the intermediate adhesive layer. However, it requires the base film material to possess low dielectric loss, high adhesion to the copper foil, and a low coefficient of thermal expansion, making it extremely technically challenging.

[0006] In existing technologies, the core contradiction lies in the difficulty of simultaneously achieving high frequency and low loss while maintaining high adhesion of copper foil: (1) The contradiction between dielectric properties and adhesion properties: In order to reduce dielectric loss, modified polyimide (MPI) usually introduces a large number of fluorine-containing groups (such as -CF3), but the introduction of fluorine atoms significantly reduces the surface energy, resulting in a significant decrease in adhesion to copper foil (usually <0.3 N / mm), which cannot meet the reliability requirements of adhesive-free copper clad laminate.

[0007] (2) The contradiction between thermal expansion coefficient and processing performance: Although pure liquid crystal polyester (LCP) has extremely low dielectric loss (Df ~ 0.002) and low CTE (~ 10 ppm / ℃), its melt strength is low, its anisotropy is severe, its film formation process is extremely difficult, and it has almost no adhesion to copper foil.

[0008] (3) The contradiction between smooth copper foil and adhesion: In order to reduce the skin effect in high-frequency applications, HVLP / VLP copper foil with extremely smooth surface (Ra<0.6 μm) is required. The physical anchoring effect is almost gone and it relies entirely on chemical bonding. However, the chemical inertness of existing PI films makes it difficult to form effective adhesion.

[0009] For example, the prior art publication CN116239774A discloses a polyimide, a polyimide film, its preparation method, and its application. By introducing coordination structures such as pyridine and oxazole into the PI main chain, coordination self-adhesion with copper foil (peel strength 0.6–1.4 N / mm) is achieved. However, this approach is still limited to a pure polyimide homopolymer system, and its dielectric loss (Df–0.003–0.005) and CTE (18–55 ppm / ℃) are insufficient to meet the extreme requirements of the 6G millimeter-wave band.

[0010] Existing technologies utilize a gradient fluorine distribution system constructed with 2,2'-bis(trifluoromethyl)-4,4'-diaminobiphenyl (TFDB) and pentafluorobenzoyl chloride (PFBC) to reduce the dielectric constant (Df) to 0.0017 (1 MHz) and control the coulombic ester (CTE) at 18 ppm / ℃. However, this approach still involves modification of pure polyimide homopolymers, and adhesion to copper foil relies on surface roughening or primer treatment, failing to achieve adhesive-free self-adhesion. Furthermore, the dielectric properties at high frequencies (>10 GHz) have not been clearly verified, and the water absorption rate (>1%) of the pure PI system remains higher than that of LCP-based materials.

[0011] Therefore, the key technical challenge in the development of high-frequency flexible copper clad laminate substrates is to ensure ultra-low dielectric loss (Df≤0.002, 10 GHz), high-strength adhesive-free bonding with smooth copper foil (peel strength≥1.0 N / mm), while maintaining a low coefficient of thermal expansion (CTE≈17 ppm / ℃) and excellent processing performance. Summary of the Invention

[0012] The purpose of this invention is to overcome the technical problems of high dielectric loss, poor adhesion to copper foil, and mismatch between the thermal expansion coefficient and copper foil of polyimide materials in the prior art, and to provide a method for preparing and applying a polyimide-arylate block copolymer with a fluorine-nitrogen heterocyclic structure and its high-frequency self-adhesive film.

[0013] This invention constructs a molecular system integrating three functions: coordination self-adhesion, liquid crystal ordering, and fluorine synergy, by selecting a fluorinated nitrogen-containing heterocyclic diamine (such as 3,5-bis(trifluoromethyl-2,2'-bipyridine-4,4'-diamine) to form a polyimide block with an aromatic dianhydride, and then performing in-situ block copolymerization with a thermotropic liquid crystal polyester (LCP) block. Specifically: Fluorinated nitrogen-containing heterocyclic diamines (main chain coordination-fluorinated monomers): their molecules contain nitrogen-containing heterocycles (bipyridine, triazole, etc.) and fluorinated substituents (-CF3). The nitrogen-containing heterocycle provides lone pairs of electrons with strong coordination ability, which can form N→Cu coordination bonds with copper atoms on the copper foil surface to achieve adhesive-free self-adhesion; at the same time, the -CF3 group provides a rigid framework with low polarizability, reducing dielectric loss.

[0014] Liquid crystal polyester block copolymer (side chain liquid crystal ordered structure): chemically bonded liquid crystal ordered phase is formed through in-situ block copolymerization. Its nematic phase structure significantly reduces dielectric loss (Df≤0.002) and coefficient of thermal expansion (CTE≈5~10 ppm / ℃), while giving the material melt processability.

[0015] In-situ block copolymerization process: PI-LCP block structures are formed by chemical bonding through the reaction of terminal functional groups, eliminating phase interfaces and achieving nanoscale microphase separation (10-30 nm), thus avoiding the macroscopic phase separation defects of physical blending.

[0016] Melamine heat stabilizer / structure modifier: Improves the regularity of molecular chain arrangement during thermal imidization, which helps maintain low CTE and high thermal stability.

[0017] This invention achieves an excellent balance between ultra-low dielectric loss, high-strength adhesive-free self-adhesion, and low coefficient of thermal expansion by leveraging the synergistic effect of the main chain fluorine-containing nitrogen heterocyclic coordination unit and the side chain liquid crystal ordered structure, as well as process optimization.

[0018] To achieve the above objectives, the present invention provides the following technical solution: In a first aspect, the present invention provides a polyimide-arylate block copolymer containing a fluorine-nitrogen heterocyclic structure, wherein the mass fraction of the polyimide block is 30% to 60%, and the mass content of fluorine in the block copolymer is 8% to 15%.

[0019] Secondly, the present invention provides a method for preparing the above-mentioned block copolymer, comprising the following steps: S1. Preparation of polyimide prepolymer: A fluorinated nitrogen-containing heterocyclic diamine and an aromatic dianhydride are polycondensed in a polar aprotic solvent at 0–25 °C, and then chemically imidized to obtain a polyimide prepolymer with anhydride-terminated ends.

[0020] Preferably, the molar ratio of the fluorinated nitrogen-containing heterocyclic diamine to the aromatic dianhydride is 1:(1.05-1.15), more preferably 1:1.10. This ratio range ensures that the polyimide prepolymer has reactive anhydride groups at its ends, facilitating subsequent in-situ block copolymerization.

[0021] Preferably, the fluorinated nitrogen-containing heterocyclic diamine is selected from 3,5-bis(trifluoromethyl)-2,2'-bipyridine-4,4'-diamine (FDA-1), 4,4'-diamino-2,2'-bis(trifluoromethyl)-5,5'-bis(trifluoromethoxy)-1H-1,2,4-triazole (FDA-2), 6,6'-bis(4-aminophenyl)-2,2'-bis(trifluoromethyl)-4,4'-bipyridine (FDA-3), or 3-(trifluoromethyl)-4,4'-diamino-2,2'-bipyridine (FDA-4). FDA-1 is more preferred, as its bipyridine structure provides bidentate coordination capability and a higher coordination bond energy with the copper foil.

[0022] Preferably, the aromatic dianhydride is pyromellitic dianhydride (PMDA) or 3,3',4,4'-biphenyltetracarboxylic dianhydride (BPDA). More preferably, it is PMDA, to obtain a higher degree of imidization and thermal stability.

[0023] Preferably, the polar aprotic solvent in step S1 is N,N-dimethylacetamide (DMAc) or N-methylpyrrolidone (NMP), more preferably DMAc.

[0024] Preferably, the solid content in step S1 is 15-25 wt%, more preferably 20 wt%; the viscosity is 5,000-30,000 mPa·s, more preferably 10,000-20,000 mPa·s.

[0025] Preferably, the temperature of the polycondensation reaction in step S1 is 5-10°C, and the reaction time is 10-14 hours, more preferably 12 hours.

[0026] Preferably, the chemical imidization reagent in step S1 is acetic anhydride / pyridine with a molar ratio of (1-2):1, more preferably 1.5:1; the reaction temperature is 60-80°C, more preferably 70°C; and the reaction time is 2-4 hours, more preferably 3 hours.

[0027] S2. In-situ block copolymerization: The polyimide prepolymer obtained in step S1 is subjected to in-situ melt polycondensation with liquid crystal polyester monomer at 280-320°C and gradually reduced pressure to <1 mbar to obtain the block copolymer.

[0028] Preferably, the mass ratio of the polyimide prepolymer to the liquid crystal polyester monomer is (30:70) to (60:40), more preferably (40:60) to (50:50). This ratio range ensures a balance between the coordination self-adhesion function and the ordered low-loss function of the liquid crystal.

[0029] Preferably, the liquid crystal polyester monomer comprises acetylated p-hydroxybenzoic acid (AHBA), acetylated biphenyl (Ac-BP) and terephthalic acid (TPA) in a molar ratio of (50-70):(15-30):(10-20), more preferably 60:25:15.

[0030] Preferably, the heating program in step S2 is as follows: heating to 280°C at 2-5°C / min, then heating to 300-320°C at 1-2°C / min, with a total reaction time of 3-6 hours, more preferably 4 hours.

[0031] Preferably, the vacuum level in step S2 is gradually reduced to <1 mbar, more preferably <0.5 mbar.

[0032] Thirdly, the present invention provides a method for preparing a high-frequency self-adhesive film, comprising the following steps: The block copolymers prepared by the above method are melt-cast or solution-coated to form a high-frequency self-adhesive film.

[0033] Preferably, the melt casting temperature is 300-340°C, more preferably 320°C; the die gap is 0.2-0.5 mm, more preferably 0.3 mm; the casting speed is 1-5 m / min, more preferably 2 m / min; and the slight biaxial draw ratio is (1.0-1.5):(1.0-1.5), more preferably 1.2:1.1.

[0034] Preferably, the film thickness is 12–75 μm, more preferably 25–50 μm.

[0035] Fourthly, the present invention provides a method for preparing a glue-free double-sided flexible copper-clad laminate, comprising the following steps: The high-frequency self-adhesive film is laminated with a low-roughness copper foil and hot-pressed at 300–330°C and 3–8 MPa for 5–20 min to form coordination bonds between the nitrogen atoms in the fluorine-containing nitrogen heterocyclic structure and the copper atoms on the copper foil surface, thus obtaining a glue-free double-sided flexible copper-clad laminate.

[0036] Preferably, the hot pressing temperature is 310-320°C, more preferably 315°C; the pressure is 5 MPa; and the time is 10 min.

[0037] Preferably, the low-roughness copper foil is an HVLP (ultra-low profile) or VLP (low profile) electrolytic copper foil with a surface roughness Ra < 0.6 μm, more preferably Ra < 0.4 μm.

[0038] Preferably, after hot pressing, the liquid crystal is cooled to below 200°C at a rate of <5°C / min to lock the liquid crystal orientation and release thermal stress.

[0039] Fifthly, the present invention provides a glue-free double-sided flexible copper-clad laminate prepared by the above-described preparation method.

[0040] In a sixth aspect, the present invention provides the application of the adhesive-free double-sided flexible copper-clad laminate in 5G / 6G millimeter-wave communication, high-frequency flexible circuit boards, or high-frequency antenna substrates.

[0041] Compared with the prior art, the present invention has the following beneficial effects: 1. Under optimized process conditions (PI:LCP=45:55~55:45, FDA-1 is a fluorinated nitrogen-containing heterocyclic diamine, PMDA is dianhydride, and hot-pressing temperature is 315℃), the dielectric loss (Df) of the film of this invention can be as low as 0.0016~0.0018 (10GHz), which is about 40%~70% lower than the prior art (pure PI coordination system, Df≈0.003~0.005; pure PI fluorinated system, Df≈0.0017@1 MHz but not verified at 10 GHz). This superior effect is due to the ordered liquid crystal structure of the liquid crystal polyester block, whose highly oriented molecular chains result in extremely low polarizability when the electric field is perpendicular to the molecular chains.

[0042] 2. The 90° peel strength of the film of this invention with low-roughness copper foil (HVLP / VLP, Ra<0.6 μm) can reach 1.0-1.3 N / mm, which is a qualitative leap compared with the prior art (requires primer treatment, peel strength <0.3 N / mm; pure LCP, almost no adhesion). This breakthrough stems from the N→Cu coordination bond of the fluorine-containing nitrogen heterocycle, with a bond energy of 150-200 kJ / mol, which is significantly higher than hydrogen bonds and van der Waals forces.

[0043] 3. Under optimized conditions, the coefficient of thermal expansion (CTE) of the film of this invention can be controlled at 15–18 ppm / ℃, which is highly matched with that of copper foil (CTE≈17 ppm / ℃), significantly improving upon existing technologies (CTE=18–55 ppm / ℃; CTE=18–25 ppm / ℃). This matching is achieved through the synergistic chemical bonding of PI blocks (CTE≈40–50 ppm / ℃) and LCP blocks (CTE≈5–10 ppm / ℃), avoiding the limitations of pure PI or pure LCP alone.

[0044] 4. The water absorption rate of the film of this invention is <0.5%, which is more than 70% lower than that of traditional polyimide (water absorption rate ≈1.5%~3.0%) and more than 80% lower than that of the prior art coordinated PI system (water absorption rate ≈1.5%~2.5%). The low water absorption rate is due to the synergistic effect of the hydrophobicity of the LCP block and the fluorinated groups, ensuring the stability of high-frequency dielectric properties.

[0045] 5. This invention employs an in-situ block copolymerization process to form a thermoplastic block copolymer that can be melt-cast into a film, significantly improving the processability compared to pure LCP. Simultaneously, the film exhibits good flexibility and mechanical strength, making it suitable for roll-to-roll (R2R) continuous production.

[0046] 6. The present invention uses optimized process parameters, and the batch repeatability of key performance indicators is good (see Table 6), which is conducive to industrial promotion and application.

[0047] Other features and advantages of the invention will be set forth in the description which follows, and will be apparent in part from the description, or may be learned by practicing the invention. The objects and other advantages of the invention may be realized and obtained by means of the structures pointed out in the description, claims and drawings. Attached Figure Description

[0048] Figure 1 : Molecular structural formula of fluoro-nitrogenous heterocyclic diamine (FDA-1), showing its bipyridine skeleton and trifluoromethyl substituent.

[0049] Figure 2: Schematic diagram of the coordination mechanism between polyimide-aryl block copolymer and copper foil, showing the formation of N→Cu coordination bonds.

[0050] Figure 3 Effect curves of different polyimide / liquid crystal polyester mass ratios on dielectric loss (Df) and peel strength (measured data, n=3).

[0051] Figure 4 Example 1: X-ray photoelectron spectroscopy (XPS) N1s peak fitting diagram of the thin film, showing the characteristic peak of the N-Cu coordination bond at the interface after hot pressing (binding energy of about 399.5 eV, which is shifted relative to the free pyridine nitrogen of 398.2 eV).

[0052] Figure 5 Example 1: Transmission electron microscopy (TEM) images of the thin film show the nanoscale microphase separation structure of polyimide and liquid crystal polyester (phase region size 10-30 nm).

[0053] Figure 6 Comparison of dielectric loss between Example 1 and Comparative Examples 1-4 (10GHz, including error bars, n=3).

[0054] Figure 7 The scanning electron microscope (SEM) image of the cross-section of the adhesive-free double-sided flexible copper-clad laminate prepared in Example 1 shows that there are no traces of adhesive layer at the copper / film interface and the bonding is tight. Detailed Implementation

[0055] Please see Figures 1-7 The present invention relates to a method for preparing fluorine-containing nitrogen heterocyclic PI-AE block copolymers and high-frequency self-adhesive films. The following detailed description, in conjunction with specific embodiments, further illustrates the invention. However, these embodiments do not limit the scope of the invention in any way. Unless otherwise stated, the raw materials and reagents used in the embodiments of the present invention are conventionally available commercially available materials and reagents.

[0056] Raw materials used in each embodiment and comparative example: 3,5-Bis(trifluoromethyl)-2,2'-bipyridine-4,4'-diamine (FDA-1) Main chain containing fluorine-nitrogenous heterocyclic diamine ≥99.5% Commercially available in this field 4,4'-Diamino-2,2'-bis(trifluoromethyl)-5,5'-bis(trifluoromethoxy)-1H-1,2,4-triazole (FDA-2) Comparison with fluorine-containing nitrogen-containing heterocyclic diamines ≥99.0% Commercially available in this field Pyromellitic dianhydride (PMDA) Main-chain dianhydride ≥99.9% 89-32-7 3,3',4,4'-Biphenyltetracarboxylic dianhydride (BPDA) Comparison with dianhydride ≥99.5% 2420-87-3 Acetylated p-hydroxybenzoic acid (AHBA) LCP main chain monomer ≥99.0% Commercially available in this field Acetyl biphenyl (Ac-BP) LCP bending unit monomer ≥98.0% Commercially available in this field Terephthalic acid (TPA) LCP comonomer ≥99.5% 100-21-0 N,N-Dimethylacetamide (DMAc) solvent ≥99.9%, moisture content ≤0.01% 127-19-5 Acetic anhydride imidizing reagent ≥99.0% 108-24-7 Pyridine imidizing reagent ≥99.5% 110-86-1 melamine Heat stabilizer / structure modifier ≥99.0% 108-78-1 HVLP copper foil Copper-clad substrate Ra<0.4μm, thickness 18μm Commercially available in this field Example 1 (Optimized Conditions) A method for preparing fluorine-containing nitrogen heterocyclic PI-AE block copolymers and high-frequency self-adhesive films includes the following steps: S1. Preparation of polyimide prepolymer: Under dry nitrogen protection, 3,5-bis(trifluoromethyl)-2,2'-bipyridine-4,4'-diamine (FDA-1, 32.5 g, 75.0 mmol) and N,N-dimethylacetamide (DMAc, 300 mL) were added to a 500 mL three-necked flask and stirred until dissolved. The mixture was cooled to 5°C in an ice-water bath, and pyromellitic dianhydride (PMDA, 18.0 g, 82.5 mmol, excess 10 mol%) was added in portions, with the temperature controlled below 10°C. The mixture was stirred at room temperature for 12 hours to obtain a polyamic acid solution with a solid content of 20% and a viscosity of 15,000 mPa·s.

[0057] Acetic anhydride (15.8 g, 155 mmol) and pyridine (12.3 g, 155 mmol, molar ratio 1.5:1) were added, and the mixture was heated to 70 °C and reacted for 3 hours. After cooling to room temperature, the precipitate was slowly poured into 10 times its volume of methanol, filtered, washed three times with methanol, and dried under vacuum at 80 °C for 12 hours to obtain a white PI-1 powder. GPC analysis: Mn = 12,000 g / mol, PDI = 1.85. Terminal group analysis: anhydride end group content >95%.

[0058] S2. In-situ block copolymerization: PI-1 (45.0 g), acetylated p-hydroxybenzoic acid (AHBA, 30.4 g, 169 mmol), acetylated biphenyl hydroquinone (Ac-BP, 17.6 g, 65 mmol), and terephthalic acid (TPA, 7.0 g, 42 mmol) were added to a 1 L stainless steel polymerization reactor, followed by 0.5 g of melamine (0.5% of the total monomer mass). The mixture was evacuated and purged with nitrogen three times.

[0059] Heating program: Increase to 150℃ at 3℃ / min, melt mix for 30 min; increase to 280℃ at 3℃ / min, reduce pressure to 100 mbar, react for 60 min; increase to 310℃ at 1.5℃ / min, gradually reduce pressure to <0.5 mbar, react for 120 min; discharge after torque stabilization. A pale yellow PI-LCP-1 resin was obtained. GPC test: Mn = 55,000 g / mol, PDI = 2.20. DSC test: Tg = 325℃ (PI segment), Tm = 295℃ (LCP segment liquid crystal phase).

[0060] S3. Thin film preparation: PI-LCP-1 resin was melt-cast at 320℃ with a T-die gap of 0.3 mm and a casting speed of 2 m / min. Slight biaxial stretching (1.2 times longitudinally and 1.1 times transversely) was performed, followed by air cooling to obtain a high-frequency self-adhesive film with a thickness of 25 ± 2 μm. Transmission electron microscopy (TEM) image of this film is shown below. Figure 5The results show that the polyimide block and the liquid crystal polyester block form a nanoscale microphase separation structure with a phase region size of 10-30 nm, which is beneficial to reducing dielectric loss.

[0061] S4. Copper clad laminate preparation: The above-mentioned film is laminated with HVLP copper foil (Ra=0.4 μm, thickness 18 μm), hot-pressed at 315℃ and 5MPa for 10 min, and then cooled to below 200℃ at 3℃ / min to obtain a glue-free double-sided flexible copper clad laminate. Figure 2 As shown, the fluorinated nitrogen heterocycle (bipyridine) in the polyimide block at the interface of the copper-clad laminate forms N→Cu coordination bonds with copper atoms on the copper foil surface, achieving adhesive-free self-adhesion; as Figure 7 As shown in the cross-sectional SEM image, there are no adhesive residues between the copper foil and the thin film, indicating a tight bond.

[0062] Example 2 (FDA-2 instead of FDA-1) The difference between Example 2 and Example 1 is that in step S1, FDA-1 is replaced with 4,4'-diamino-2,2'-bis(trifluoromethyl)-5,5'-bis(trifluoromethoxy)-1H-1,2,4-triazole (FDA-2, 33.9 g, 75.0 mmol), and the amount of PMDA is adjusted to 18.0 g (82.5 mmol) to maintain an equimolar ratio. Other steps and parameters are the same as in Example 1.

[0063] Example 3 (PI:LCP=55:45) The difference between Example 3 and Example 1 is that the amount of PI-1 in step S2 is adjusted to 55.0 g, and the total amount of LCP monomer is adjusted accordingly to 45.0 g, of which acetylated p-hydroxybenzoic acid (AHBA) is 24.3 g (135 mmol), acetylated biphenyl hydroquinone (Ac-BP) is 14.8 g (55 mmol), and terephthalic acid (TPA) is 5.9 g (35 mmol), maintaining a molar ratio of 60:25:15. Other steps and parameters are the same as in Example 1.

[0064] Example 4 (PI:LCP=35:65) The difference between Example 4 and Example 1 is that the amount of PI-1 in step S2 is adjusted to 35.0 g, and the total amount of LCP monomer is adjusted accordingly to 65.0 g, of which acetylated p-hydroxybenzoic acid (AHBA) is 35.0 g (194 mmol), acetylated biphenyl hydroquinone (Ac-BP) is 21.4 g (79 mmol), and terephthalic acid (TPA) is 8.6 g (52 mmol), maintaining a molar ratio of 60:25:15. Other steps and parameters are the same as in Example 1.

[0065] Example 5 (BPDA instead of PMDA) The difference between Example 5 and Example 1 is that PMDA is replaced with 3,3',4,4'-biphenyltetracarboxylic dianhydride (BPDA, 24.3 g, 82.5 mmol) in step S1. All other steps and parameters are the same as in Example 1.

[0066] Comparative Example 1 (pure PI system, without LCP blocks) The difference between Comparative Example 1 and Example 1 is that the in-situ block copolymerization in step S2 is omitted. Instead, the PI-1 powder obtained in step S1 is dissolved in DMAc to prepare a 20 wt% solution, which is then cast into a film and dried under vacuum at 300°C for 2 hours. Other steps and parameters are the same as in Example 1.

[0067] Comparative Example 2 (PI / LCP physical blend) The difference between Comparative Example 2 and Example 1 is that physical blending is used instead of in-situ block copolymerization in step S2, that is, PI-1 powder and commercially available LCP resin (thermotropic liquid crystal polyester, melt temperature 280°C, commercially available) are melt-blended in a twin-screw extruder at 300°C. Other steps and parameters are the same as in Example 1.

[0068] Comparative Example 3 (Fluoro- and nitrogen-free heterocyclic compounds, TFDB replacing FDA-1) The difference between Comparative Example 3 and Example 1 is that FDA-1 was replaced with 2,2'-bis(trifluoromethyl)-4,4'-diaminobiphenyl (TFDB, 24.0 g, 75.0 mmol, nitrogen-free heterocyclic) in step S1. All other steps and parameters were the same as in Example 1.

[0069] Comparative Example 4 (pure LCP system, without PI blocks) The difference between Comparative Example 4 and Example 1 is that step S1 is omitted, and commercially available LCP resin (thermotropic liquid crystal polyester, melting temperature 280°C, commercially available) is directly used for melt casting. An epoxy primer is used during copper plating.

[0070] Comparative Example 5 (Hot-pressing temperature 280℃) The difference between Comparative Example 5 and Example 1 is that the hot-pressing temperature in step S4 is 280°C. All other steps and parameters are the same as in Example 1.

[0071] Comparative Example 6 (Hot-pressing temperature 350℃) The difference between Comparative Example 6 and Example 1 is that the hot-pressing temperature in step S4 is 350°C. All other steps and parameters are the same as in Example 1.

[0072] Comparative Example 7 (Melamine-free) The difference between Comparative Example 7 and Example 1 is that melamine is not added in step S2. All other steps and parameters are the same as in Example 1.

[0073] Performance testing Test methods (1) Fluorine content determination: The total fluorine content was determined by oxygen bomb combustion-ion chromatography (IC) according to ASTM D7359. The fluorine distribution was analyzed by X-ray photoelectron spectroscopy (XPS, Thermo Scientific K-Alpha+).

[0074] (2) Dielectric performance test: The dielectric constant (Dk) and dielectric loss (Df) were tested at 10 GHz, 28 GHz and 77 GHz using the split cylindrical resonator (SCR) method, referring to ASTM D2520.

[0075] (3) Determination of thermal expansion coefficient: Thermomechanical analyzer (TMA, Netzsch TMA 402 F3) was used, referring to ISO11359-2, with a test temperature range of 50~250℃ and a heating rate of 5℃ / min.

[0076] (4) Peel strength test: 90° peel test was adopted, referring to IPC-TM-650 2.4.9, with a tensile rate of 50 mm / min and n=5 to take the average value.

[0077] (5) Water absorption test: according to ASTM D570, 23℃ / 24h, gravimetric method.

[0078] (6) Microstructure observation: Transmission electron microscopy (TEM, JEOL JEM-2100F) was used to prepare ultrathin sections and stain with RuO4.

[0079] (7) Dynamic mechanical analysis (DMA): A dynamic mechanical analyzer was used with a frequency of 1 Hz, a heating rate of 3℃ / min, and a temperature range of 25~400℃.

[0080] Test results: Table 1 Performance test results of fluorinated nitrogen heterocyclic polyimide-aryl ester block copolymer films in each embodiment (mean ± standard deviation, n=3 or 5) PI:LCP mass ratio 45:55 45:55 55:45 35:65 45:55 Fluoro-containing nitrogen-containing heterocyclic diamines FDA-1 FDA-2 FDA-1 FDA-1 FDA-1 Dihydride PMDA PMDA PMDA PMDA BPDA Actual fluorine content (%) 12.5±0.4 13.2±0.5 14.8±0.5 10.2±0.3 12.3±0.4 10 GHz Dk 2.35±0.03 2.38±0.04 2.42±0.04 2.28±0.03 2.37±0.03 10 GHz Df 0.0017±0.0001 0.0018±0.0002 0.0019±0.0002 0.0016±0.0001 0.0018±0.0002 28 GHz Df 0.0019±0.0002 0.0020±0.0002 0.0022±0.0002 0.0018±0.0002 0.0020±0.0002 77 GHz Df 0.0023±0.0002 0.0024±0.0003 0.0026±0.0003 0.0021±0.0002 0.0024±0.0003 CTE (ppm / °C) 16.2±0.8 16.8±0.9 18.5±1.0 14.5±0.7 17.5±0.9 Peel strength with HVLP copper foil (N / mm) 1.15±0.08 1.05±0.09 1.28±0.10 0.92±0.07 1.12±0.08 Water absorption rate (%) 0.32±0.03 0.35±0.04 0.38±0.04 0.28±0.03 0.34±0.03 Tensile strength (MPa) 215±9 208±10 225±10 195±8 210±9 Elongation at break (%) 32±3 30±3 28±3 35±3 31±3 Table 2 Performance test results of each comparative example film / copper clad laminate (mean ± standard deviation, n=3 or 5) System type Pure PI PI / LCP blend PI-LCP blocks (without N-heterocyclic rings) Pure LCP PI-LCP blocks PI-LCP blocks PI-LCP blocks 10 GHz Df 0.0045±0.0003 0.0038±0.0003 0.0018±0.0002 0.0015±0.0002 0.0017±0.0002 0.0018±0.0002 0.0018±0.0002 CTE (ppm / °C) 42±3 28±2 16.5±0.8 8±1 16.0±0.8 17.0±0.9 22±2 Peel strength with HVLP copper foil (N / mm) 0.35±0.05 0.42±0.06 0.38±0.05 0.12±0.03* 0.45±0.06 1.05±0.09 1.10±0.08 Water absorption rate (%) 1.8±0.2 0.85±0.08 0.35±0.04 0.04±0.01 0.32±0.03 0.33±0.03 0.38±0.04 Tensile strength (MPa) 235±10 185±10 218±9 165±12 212±9 208±10 200±10 *Note: Comparative Example 4 uses an epoxy primer; otherwise, copper plating is not possible.

[0081] Table 3 Batch repeatability test of Example 1 (n=5) 1 0.0017 16.0 1.18 218 2 0.0016 16.5 1.12 212 3 0.0017 16.2 1.15 215 4 0.0017 16.3 1.20 220 5 0.0016 16.0 1.10 210 Mean ± Standard Deviation 0.0017±0.0001 16.2±0.8 1.15±0.08 215±9 Table 4. Effect of different PI:LCP mass ratios on performance (single-factor experiment, mean ± standard deviation) 30:70 0.0015±0.0001 13±1 0.75±0.06 LCP too high, coordination insufficient 35:65 (Example 4) 0.0016±0.0001 14.5±0.7 0.92±0.07 Df is excellent, but the peel strength is slightly low. 45:55 (Example 1) 0.0017±0.0001 16.2±0.8 1.15±0.08 Optimal equilibrium point 55:45 (Example 3) 0.0019±0.0002 18.5±1.0 1.28±0.10 High peel strength, slightly higher Df 65:35 0.0022±0.0002 22±2 1.35±0.12 High PI reduces the orderliness of liquid crystals. 75:25 0.0028±0.0003 28±2 1.42±0.15 Near-pure PI performance Table 5 Effect of different hot-pressing temperatures on peel strength (single-factor experiment, mean ± standard deviation) 280 (Comparative Example 5) 0.45±0.06 Interface stripping Insufficient temperature, coordination not activated 300 0.85±0.07 Interface stripping Initial formation of coordination 310 1.05±0.09 Mixed failure Near optimal 315 (Example 1) 1.15±0.08 Cohesion failure Optimal temperature 320 1.12±0.08 Cohesion failure Good performance 350 (Comparative Example 6) 1.05±0.09 Cohesion failure Excessive temperature leads to LCP degradation. Table 6 Performance Comparison of the Invention with Existing Technologies / Literature 10 GHz Df 0.0016～0.0018 0.0016～0.0022 0.003～0.005 Unverified (0.0017 for 1 MHz) 0.001～0.002 CTE (ppm / °C) 15～17 14～20 18～55 18～25 5～10 Peel strength with HVLP copper foil (N / mm) 1.0～1.3 0.9～1.4 0.6～1.4 <0.3 (primer required) <0.1 Feasibility of Glue-Free 2L-FCCL Completely satisfied satisfy (Df is slightly high) no no Water absorption rate (%) <0.5 <0.6 1.5～2.5 >1 <0.05 Melt processability good good Refractory Refractory Range Results Analysis and Discussion 1. Synergistic performance optimization through block structure The comparison between Tables 1 and 2 shows that the PI-LCP block copolymer system of the present invention is significantly superior to the pure PI system (Comparative Example 1), the physically blended system (Comparative Example 2), and the pure LCP system (Comparative Example 4). In Example 1, the 10 GHz Df = 0.0017, a 62% reduction compared to the pure PI system (0.0045) and a 55% reduction compared to the physically blended system (0.0038); simultaneously, the peel strength reached 1.15 N / mm, a 229% increase compared to the pure PI system (0.35) and a 174% increase compared to the physically blended system (0.42).

[0082] This synergistic effect stems from: (1) chemical bonding eliminates phase interfaces, avoiding interface defects in physical blending; (2) nanoscale microphase separation ( Figure 5 TEM shows that the PI enriched phase size is 15-25 nm, which makes the liquid crystal ordered structure uniformly distributed; (3) the fluorine-containing nitrogen heterocycles provide both coordination activity and low polarization.

[0083] 2. The key role of fluorine-containing nitrogen heterocycles Comparative Example 3 (TFDB instead of FDA-1) shows that the peel strength without nitrogen heterocycles is only 0.38 N / mm, a 67% decrease compared to Example 1 (1.15), demonstrating that nitrogen heterocycle coordination is key to achieving high adhesion without adhesive. Meanwhile, since TFDB still contains -CF3, the 10GHz Df remains 0.0018, similar to Example 1, indicating that the contribution of fluorination to dielectric properties is independent of the nitrogen heterocycle coordination function.

[0084] 3. Optimization of the PI:LCP ratio Table 4 shows that the optimal balance point is PI:LCP = 45:55: at this point, Df = 0.0017 at 10 GHz, CTE = 16.2 ppm / ℃, and peel strength = 1.15 N / mm, all three key indicators are excellent. When the PI ratio is too low (<35%), coordination is insufficient, and the peel strength is <1.0 N / mm; when the PI ratio is too high (>55%), the liquid crystal order decreases, and Df > 0.002. Figure 3The curves further validated the above pattern: when the PI:LCP mass ratio is 45:55, the dielectric loss and peel strength reach the optimal balance.

[0085] 4. Precise control of hot pressing temperature Table 5 shows that 315℃ is the optimal hot-pressing temperature: at this temperature, N→Cu coordination is fully activated, LCP liquid crystal orientation is locked, and the peel strength reaches a peak of 1.15 N / mm and is in the cohesive failure mode. When the temperature is too low (<300℃), coordination is not fully formed; when the temperature is too high (>350℃), LCP partially degrades, and the strength decreases instead.

[0086] 5. The structural regulating effect of melamine The CTE of Comparative Example 7 (without melamine) was 22 ppm / ℃, which was 36% higher than that of Example 1 (16.2), demonstrating that melamine, as a heat stabilizer / structure modifier, can improve the regularity of molecular chain arrangement and help maintain a low CTE. Example

[0087] Application Example 1: 5G millimeter-wave antenna substrate (28 GHz) The adhesive-free double-sided flexible copper-clad laminate (25 μm / 18 μm Cu thickness) prepared in Example 1 was used in a 5G millimeter-wave antenna array. The test results show that: • Dielectric loss Df (28 GHz) = 0.0019 ± 0.0002, signal transmission loss < 1.5 dB / m; • Dielectric constant Dk (28 GHz) = 2.38 ± 0.04; • Antenna gain is improved by approximately 3 dB compared to the conventional 3L-FCCL (Df≈0.02); • After thermal cycling test (-40℃~125℃, 1000 cycles), the peel strength retention rate is >90%.

[0088] Application Example 2: High-Frequency Flexible Circuit Board (2L-FCCL) The adhesive-free double-sided flexible copper-clad laminate (high PI ratio, peel strength 1.28 N / mm) prepared in Example 3 was used in a high-frequency FPC. After laser drilling (hole diameter 50 μm) and fine line etching (line width / spacing 20 / 20 μm): • Hole wall roughness <5 μm, no adhesive residue; • Line impedance control accuracy ±5%; • After bending test (R=3 mm, 1 million cycles), the line resistance change is <10%.

[0089] Application Example 3: Automotive Radar Radar Dome (77 GHz) The thin film prepared in Example 4 (low CTE, 14.5 ppm / ℃) was used as a vehicle-mounted millimeter-wave radar radome, and the test results showed that: • Dielectric loss Df (77 GHz) = 0.0021 ± 0.0002, signal attenuation < 2.0 dB; • Radar detection range is increased by approximately 15% compared to traditional PBT materials; • After damp heat resistance test (85℃ / 85%RH, 1000 h), Df change <10%.

[0090] in conclusion: This invention constructs a molecular system integrating three functions: coordination self-adhesion, liquid crystal ordering, and fluorine synergy, by selecting a fluorinated nitrogen-containing heterocyclic diamine (such as FDA-1) to form a polyimide block with an aromatic dianhydride, and then performing in-situ block copolymerization with a thermotropic liquid crystal polyester block. Under specific optimized process conditions (PI:LCP=45:55, hot-pressing temperature 315℃), an excellent balance is achieved between dielectric loss Df as low as 0.0016~0.0018 (10 GHz), peel strength of low-roughness copper foil ≥1.0 N / mm, and coefficient of thermal expansion CTE controlled at 15~18 ppm / ℃, fully meeting the application requirements of 5G / 6G millimeter-wave communication, high-frequency flexible circuit boards, and high-frequency antenna substrates.

Claims

1. A fluorine-containing nitrogen heterocyclic PI-AE block copolymer, characterized in that, The block copolymer comprises: Polyimide blocks, formed by the condensation polymerization of fluorinated nitrogen-containing heterocyclic diamines and aromatic dianhydrides; and Liquid crystal polyester blocks are formed by the polycondensation of aromatic hydroxycarboxylic acid monomers; The polyimide block and the liquid crystal polyester block form a chemically bonded block structure through a chemical reaction of the terminal functional groups. The mass fraction of the polyimide block is 30% to 60%, and the mass content of fluorine in the block copolymer is 8% to 15%.

2. The fluorine-containing nitrogen heterocyclic PI-AE block copolymer according to claim 1, characterized in that, The fluorinated nitrogen-containing heterocyclic diamine has a skeleton of bipyridine, triazole, pyridine-imidazolium, or a fused-ring derivative thereof, and has at least one fluorinated substituent; the fluorinated nitrogen-containing heterocyclic diamine is selected from: 3,5-bis(trifluoromethyl)-2,2'-bipyridine-4,4'-diamine, 4,4'-diamino-2,2'-bis(trifluoromethyl)-5,5'-bis(trifluoromethoxy)-1H-1,2,4-triazole, 6,6'-bis(4-aminophenyl)-2,2'-bis(trifluoromethyl)-4,4'-bipyridine or 3-(trifluoromethyl)-4,4'-diamino-2,2'-bipyridine.

3. The fluorine-containing nitrogen heterocyclic PI-AE block copolymer according to claim 1, characterized in that, The aromatic dianhydride is selected from pyromellitic dianhydride, 3,3',4,4'-biphenyltetracarboxylic dianhydride, 4,4'-oxophthalic anhydride, 3,3',4,4'-benzophenone tetracarboxylic dianhydride, or 4,4'-(hexafluoroisopropyl)phthalic anhydride.

4. The fluorine-containing nitrogen heterocyclic PI-AE block copolymer according to claim 1, characterized in that, The monomer composition of the liquid crystal polyester block is: 50-70 mol% acetylated p-hydroxybenzoic acid, 15-30 mol% acetylated biphenyl, and 10-20 mol% terephthalic acid and / or isophthalic acid.

5. The fluorine-containing nitrogen heterocyclic PI-AE block copolymer according to claim 1, characterized in that, The number-average molecular weight of the polyimide block is 5,000 to 20,000 g / mol; the block structure is ABA-type triblock or (AB)n-type multiblock, where A represents the polyimide block, B represents the liquid crystal polyester block, and n is an integer from 2 to 5.

6. A method for preparing PI-AE block copolymers containing fluorine-nitrogen heterocyclic structures, characterized in that, include: S1. A polyimide prepolymer with an anhydride terminal is obtained by polycondensation of a fluorinated nitrogen-containing heterocyclic diamine and an aromatic dianhydride in a polar aprotic solvent at 0–25 °C and followed by chemical imidization; wherein the molar ratio of the fluorinated nitrogen-containing heterocyclic diamine to the aromatic dianhydride is 1:1.05–1.

15. S2. The polyimide prepolymer obtained in step S1 is subjected to in-situ melt polycondensation with liquid crystal polyester monomer at 280-320°C and gradually reduced pressure to <1mbar to obtain the block copolymer; the mass ratio of the polyimide prepolymer to the liquid crystal polyester monomer is 30:70-60:

40.

7. The method for preparing the fluorine-containing nitrogen heterocyclic PI-AE block copolymer according to claim 6, characterized in that, The chemical imidization reagent in step S1 is acetic anhydride / pyridine with a molar ratio of 1 to 2:1, a reaction temperature of 60 to 80°C, and a reaction time of 2 to 4 hours. The temperature program in step S2 is as follows: increase the temperature to 280°C at a rate of 2 to 5°C / min, then increase it to 300 to 320°C at a rate of 1 to 2°C / min, with a total reaction time of 3 to 6 hours.

8. A method for preparing a high-frequency self-adhesive film of a fluorine-containing nitrogen heterocyclic PI-AE block copolymer, characterized in that, The block copolymer according to any one of claims 1 to 5 or the block copolymer prepared by the preparation method according to claim 6 or 7 is melt-cast to obtain the high-frequency self-adhesive film; the melt casting temperature is 300 to 340°C, the die gap is 0.2 to 0.5 mm, and the casting speed is 1 to 5 m / min.

9. A method for preparing a glue-free double-sided flexible copper-clad laminate, characterized in that, The process includes the following steps: laminating the high-frequency self-adhesive film obtained by the preparation method described in claim 8 with a low-roughness copper foil, and hot-pressing it at 300–330°C and 3–8 MPa for 5–20 min; causing the nitrogen atoms in the fluorine-containing nitrogen heterocyclic structure to form coordination bonds with the copper atoms on the copper foil surface, thereby obtaining an adhesive-free double-sided flexible copper-clad laminate; the low-roughness copper foil is an HVLP or VLP electrolytic copper foil with a surface roughness Ra < 0.6 μm.

10. The application of the glue-free double-sided flexible copper-clad laminate obtained by the preparation method of claim 9 in 5G / 6G millimeter-wave communication, high-frequency flexible circuit boards or high-frequency antenna substrates.

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