Low-CTE polyimide / silicon-doped aerogel substrate and preparation method thereof

Abstract

The invention discloses a low-CTE polyimide / silicon-doped aerogel substrate and a preparation method thereof, and relates to a polyimide aerogel substrate and a preparation method thereof. The problem that an existing modification means of doping silicon into PI aerogel cannot meet the requirements for low dielectric constant, low CTE, high dimensional stability and moisture resistance at the same time is solved. The low CTE polyimide / silicon doped aerogel substrate is prepared from an anhydride-terminated rigid chain-containing polyamide acid salt solution, polyhedral oligomeric silsesquioxane and silicon dioxide particles, the preparation method comprises the following steps: 1, preparing an anhydride-terminated rigid chain-containing polyamide acid salt solution; 2, weighing; 3, blending; 4, carrying out POSS crosslinking; 5, freeze drying; and 6, carrying out a thermal imidization reaction. The invention is used for the low-CTE polyimide / silicon doped aerogel substrate and the preparation method of the low-CTE polyimide / silicon doped aerogel substrate.

Description

Technical Field

[0001] The invention relates to a polyimide aerogel substrate and a preparation method thereof. Background Art

[0002] With the rapid development of 5G communication technology, antenna substrate materials are facing unprecedented performance requirements. The ideal antenna substrate needs to meet the following key indicators simultaneously: (1) ultra-low dielectric constant to reduce signal delay; (2) low thermal expansion coefficient that matches that of substrates such as copper foil; (3) excellent dimensional stability; and (4) good resistance to moisture and heat. Currently, mainstream antenna substrate materials cannot meet all of the above requirements simultaneously. For example, while modified epoxy resins are inexpensive, their dielectric constant (Dk≈3.5-4.5) is relatively high, and their coefficient of thermal expansion (CTE=50ppm / k-70ppm / k) is mismatched with copper foil substrates. PTFE-based materials (such as the ROGERS series) have good dielectric properties (Dk≈2.2-3.0), but their CTE is relatively high (>20ppm / k). They are susceptible to thermal mismatch with metal patches (such as copper foil) under high temperatures or temperature cycling conditions, leading to antenna signal offset and even metal layer peeling. Furthermore, PTFE has a high moisture absorption rate, significantly deteriorating its dielectric properties in humid environments, affecting the long-term stability of the antenna. Ceramic materials such as alumina and aluminum nitride, while having low CTE, are brittle, have high dielectric constants (Dk>6), and are difficult to process into complex shapes. Therefore, there is an urgent need to develop a new substrate material that combines low dielectric constant, low CTE, high dimensional stability, and moisture resistance.

[0003] Polyimide (PI) aerogel, due to its unique nanoporous structure and excellent high-temperature resistance, is considered an ideal candidate for breaking through existing technological bottlenecks. However, conventional PI aerogels exhibit three key drawbacks in practical applications: First, insufficient dimensional stability. During drying and thermal imidization, due to the destruction of capillary forces during the sol-gel process and the shrinkage of the molecular chains during imidization, the PI aerogel experiences a volume shrinkage of up to 15%-20%, causing substrate warping and severely impacting antenna performance. Second, the coefficient of thermal expansion (CTE) of pure PI aerogel is relatively high. The CTE of pure PI aerogel is typically in the range of 25ppm / k to 40ppm / k, significantly different from that of metallic conductors (such as copper, with a CTE of ≈17ppm / k). This thermal mismatch can lead to interfacial stress during temperature cycling, causing metal patch delamination or substrate cracking. Third, poor moisture resistance: Water infiltration can degrade dielectric properties, disrupt dimensional stability, and reduce interfacial reliability. Therefore, effectively controlling the dimensional stability, CTE, and moisture resistance of polyimide is a key regulatory measure to enhance its use in antenna substrates.

[0004] SiO2 is a commonly used filler to improve the dielectric properties and thermal stability of polymer-based composites, but its application in antenna substrates still faces two major technical bottlenecks. First, inorganic filler doping makes it difficult to achieve both uniform dispersion and interfacial bonding strength. For example, when adding low-CTE fillers such as SiO2 and BN to PI aerogels to improve performance, the doped micron-sized fillers tend to settle and disperse unevenly. During storage or curing, the microspheres settle due to gravity or phase separation, resulting in uneven material properties and seriously affecting the dielectric consistency of the final product. Furthermore, poor interface compatibility between the filler and the matrix results in weak bonding. These interfacial defects can act as stress concentration points during thermal cycling, accelerating material failure. Second, a single chemical crosslinking method cannot balance low-temperature fluidity and high-temperature stability. These technical bottlenecks stem from the difficulty of a single modification method in meeting multi-dimensional performance requirements, collectively hindering performance breakthroughs in high-frequency antenna substrates. Therefore, multi-scale structural coordination and control of existing PI aerogels is necessary.

[0005] In summary, the core contradiction of polyimide aerogels currently suitable for antenna substrates is that the existing modification method of doping silicon into PI aerogels cannot simultaneously meet the problems of low dielectric constant, low CTE, high dimensional stability and moisture resistance. Summary of the Invention

[0006] The present invention aims to solve the problem that the existing modification method of doping silicon into PI aerogel cannot simultaneously meet the requirements of low dielectric constant, low CTE, high dimensional stability and moisture resistance, and further provides a low CTE polyimide / silicon-doped aerogel substrate and a preparation method thereof.

[0007] A low CTE polyimide / silicon-doped aerogel substrate, characterized in that it is prepared from 100 parts by mass of an anhydride-terminated rigid chain-containing polyamic acid salt solution, 5 to 15 parts by mass of polyhedral oligomeric silsesquioxane, and 5 to 30 parts by mass of silicon dioxide particles;

[0008] The anhydride-terminated rigid chain-containing polyamic acid salt solution is prepared from a catalyst tertiary amine, an aromatic diamine, an aromatic dianhydride, and a solvent; the molar ratio of the aromatic diamine to the aromatic dianhydride is 1:(1.00-1.02); the molar ratio of the aromatic diamine to the catalyst tertiary amine is 1:(0.05-2); and the mass ratio of the total mass of the aromatic diamine and the aromatic dianhydride to the solvent is 1:(2-10);

[0009] The structural formula of the repeating unit in the anhydride-terminated rigid chain-containing polyamic acid salt solution is n=10-90, R is a catalyst tertiary amine.

[0010] A method for preparing a low CTE polyimide / silicon-doped aerogel substrate is carried out according to the following steps:

[0011] 1. Preparation of anhydride-terminated rigid chain-containing polyamic acid salt solution:

[0012] ① Weighing a catalyst tertiary amine, an aromatic diamine, an aromatic dianhydride and a solvent; mixing the solvent and the catalyst tertiary amine to obtain a solvent / catalyst tertiary amine mixture;

[0013] The molar ratio of the aromatic diamine to the aromatic dianhydride is 1:(1.00-1.02); the molar ratio of the aromatic diamine to the catalyst tertiary amine is 1:(0.05-2); the mass ratio of the total mass of the aromatic diamine and the aromatic dianhydride to the solvent is 1:(2-10);

[0014] ② Under nitrogen atmosphere, room temperature and stirring conditions, the solvent / catalyst tertiary amine mixture and aromatic diamine are mixed for 0.5h to 1h to obtain a mixture, the reaction temperature is raised to 40°C to 65°C, and under nitrogen atmosphere, the temperature is 40°C to 65°C and stirring conditions, the aromatic dianhydride is added to the mixture in three portions and stirred for 2h to 5h. Finally, under nitrogen atmosphere, the reaction temperature is lowered from 40°C to 65°C to 25°C to 30°C, and the mixture is allowed to stand for 5h to 10h to obtain an anhydride-terminated rigid chain-containing polyamic acid salt solution;

[0015] 2. Weighing:

[0016] Weigh 100 parts by mass of an anhydride-terminated rigid chain-containing polyamic acid salt solution, 5 to 15 parts by mass of polyhedral oligomeric silsesquioxane, and 5 to 30 parts by mass of silica particles;

[0017] 3. Blending:

[0018] At a temperature of 80° C. to 100° C., under mechanical stirring and ultrasonic dispersion conditions, the weighed silica particles were added to a solution of anhydride-terminated polyamic acid salt containing rigid chains, and stirred for 1 h to 2 h to obtain a reaction system A;

[0019] 4. POSS cross-linking:

[0020] Under nitrogen atmosphere, temperature of 80°C to 100°C and stirring, the weighed polyhedral oligomeric silsesquioxane was added to reaction system A and reacted for 1 hour to 4 hours to obtain reaction system B;

[0021] 5. Freeze drying:

[0022] The reaction system B is placed in a mold, and then frozen in a freeze dryer at a freezing temperature of -50°C to -10°C for 10 hours to 15 hours, and finally freeze-dried at a temperature of -30°C to -10°C for 60 hours to 100 hours to obtain a polyimide precursor aerogel;

[0023] 6. Thermal imidization reaction:

[0024] The polyimide precursor aerogel is subjected to a thermal imidization reaction to obtain a low CTE polyimide / silicon doped aerogel substrate.

[0025] The beneficial effects of the present invention are:

[0026] The present invention uses a simple and green aqueous polycondensation reaction to prepare a polyimide / silicon-doped aerogel with good dispersibility. When micropores are introduced into the material, the pores of the aerogel reduce the overall polarization ability of the material, thereby significantly reducing the dielectric constant. The dielectric constant is further reduced by adding octa(aminophenyl)-T8-silsesquioxane, a cage-type silsesquioxane with a unique T8 cage structure (Si8O 12 ) has a nanoscale pore structure and a large free volume. This structure can effectively weaken the dipole interaction between polyimide (PI) molecular chains, thereby reducing the dielectric constant and dielectric loss of the material. Specifically, the cage structure of octa(aminophenyl)-T8-silsesquioxane forms nanoscale "cavities" in the PI matrix. These cavities restrict the orientation freedom of the dipoles of adjacent polar groups (such as C=O) under high-frequency electric fields, reducing the orientation polarization of the dipoles, so that the material still has excellent dielectric properties at high frequencies (8.2GHz to 12.4GHz). In addition, the introduction of octa(aminophenyl)-T8-silsesquioxane will also cause a dielectric confinement effect. Because the silicon-oxygen skeleton (Si-O-Si) of octa(aminophenyl)-T8-silsesquioxane has a low polarizability and its nanoscale dispersion characteristics can form a uniform organic-inorganic hybrid structure, this structure can restrict the polarization behavior of the PI molecular chains under the action of an electric field.

[0027] This invention proposes a groundbreaking dual silica modification strategy of "physical doping + chemical crosslinking." By introducing silica with an extremely low thermal expansion coefficient (≈0.5 ppm / k) as a filler into a polyamic acid solution, the thermal expansion coefficient of the material can be effectively reduced. Under mechanical stirring and ultrasonic dispersion conditions, smaller silica particles can be better dispersed in the matrix, forming more interfacial interactions and enhancing the inhibitory effect on thermal expansion. However, silica microspheres are prone to sedimentation due to gravity or phase separation, resulting in uneven material properties. The introduction of octa(aminophenyl)-T8-silsesquioxane chemically crosslinks with the chain segments. The POSS nodes in the crosslinked network "lock" the SiO2 microspheres (0.2μm to 1μm) through chemical bonds, restricting their free movement and making them difficult to settle even when the microsphere density exceeds that of the solvent. Moreover, the rigid cage-like structure of POSS significantly enhances the mechanical strength of the crosslinked network, inhibiting the displacement of the microspheres under external forces (such as shear and thermal stress). This chemically crosslinked network avoids the problem of microsphere reaggregation in traditional physical dispersions, maintaining uniformity even after long-term storage.

[0028] The present invention is to realize low shrinkage by the three-dimensional cross-linked network and the physical barrier effect of SiO2 microspheres constructed by octaaminophenyl POSS, thereby reducing dimensional change. During the freeze-drying process, the solvent sublimates from the gel, and the pore wall of traditional aerogels collapses inwards due to the effect of capillary force, causing significant shrinkage. The cage structure of POSS in the present invention has extremely high rigidity, and the three-dimensional network formed by its cross-linking provides nanoscale skeleton support when the solvent sublimes, resists capillary stress and suppresses the relaxation shrinkage of the chain segment due to solvent removal. SiO2 microspheres are uniformly dispersed in the gel network, and their high hardness, as an incompressible physical barrier during freeze-drying, hinders the collapse of the pore wall, because SiO2 microspheres are fixed by the chemical cross-linking formed by POSS, which can avoid stress concentration in the weak area of ​​the polymer, making the shrinkage force uniformly dispersed, and the overall deformation capacity is minimal. During the thermal imidization process, a closed-loop reaction occurs in the polymer precursor to generate polyimide (PI), with molecular chain shortening and volume shrinkage. The unique design of the present invention significantly inhibits this process. The amino groups of POSS react with the anhydride groups of the polymer chain to form a stable amide bond, which undergoes dehydration and cyclization at high temperatures to produce an imide ring, preventing the free shrinkage of the molecular chain during thermal imidization. The thermal decomposition temperature of the Si-O bond of POSS is >400°C, which is much higher than the imidization temperature (usually 250°C to 300°C), ensuring that the network does not degrade at high temperatures. The "interfacial effect" of the SiO2 microspheres can inhibit the thermal motion of the chain segments and reduce the driving force for contraction. Moreover, the SiO2 microspheres hardly expand when heated, forcing the surrounding polymer chain segments to remain in place.

[0029] The hydrophobic Si-O-Si core of POSS in the present invention can increase the contact angle of aerogel surface and water, reduce the permeability of water to aerogel, and SiO2 microspheres inhibit swelling, making the material have extremely strong hydrophobicity. After POSS is cross-linked with polymer chains, its hydrophobic core is exposed to the material internal pore wall and surface, significantly reducing the water molecule permeability. The high-density POSS network forms a "molecular barrier", hinders the water molecule diffusion path, and reduces moisture absorption rate. SiO2 microspheres play its physical barrier effect, increase the tortuosity of water molecule diffusion and extend the permeation path. Low hygroscopicity and high contact angle water can make dielectric properties and aerogel size more stable. BRIEF DESCRIPTION OF THE DRAWINGS

[0030] Figure 1 This is a photo of a low-CTE polyimide / silicon-doped aerogel substrate prepared after the reaction system B prepared in step 4 of Example 1 was allowed to stand for 72 hours;

[0031] Figure 2 This is a photo of a low-CTE polyimide / silicon-doped aerogel substrate prepared by allowing reaction system B prepared in step 4 of comparative example 3 to stand for 24 hours;

[0032] Figure 3This is a scanning electron microscope image of the low CTE polyimide / silicon-doped aerogel substrate prepared in Example 2;

[0033] Figure 4 This is a contact angle diagram of the low CTE polyimide / silicon-doped aerogel substrate prepared in Example 3;

[0034] Figure 5 This is an infrared image of the low CTE polyimide / silicon-doped aerogel substrate prepared in Example 3. DETAILED DESCRIPTION

[0035] Specific embodiment 1: A low CTE polyimide / silicon-doped aerogel substrate of this embodiment is prepared by 100 parts by mass of an anhydride-terminated polyamic acid salt solution containing rigid chains, 5 to 15 parts by mass of polyhedral oligomeric silsesquioxane, and 5 to 30 parts by mass of silica particles;

[0036] The anhydride-terminated rigid chain-containing polyamic acid salt solution is prepared from a catalyst tertiary amine, an aromatic diamine, an aromatic dianhydride, and a solvent; the molar ratio of the aromatic diamine to the aromatic dianhydride is 1:(1.00-1.02); the molar ratio of the aromatic diamine to the catalyst tertiary amine is 1:(0.05-2); and the mass ratio of the total mass of the aromatic diamine and the aromatic dianhydride to the solvent is 1:(2-10);

[0037] The structural formula of the repeating unit in the anhydride-terminated rigid chain-containing polyamic acid salt solution is n=10-90, R is a catalyst tertiary amine.

[0038] The polyhedral oligomeric silsesquioxane is octa(aminophenyl)-T8-silsesquioxane, and the structural formula is as follows:

[0039] in for

[0040] The beneficial effects of this specific embodiment are:

[0041] This specific embodiment uses a simple and green aqueous polycondensation reaction to prepare a polyimide / silicon-doped aerogel with good dispersibility. When micropores are introduced into the material, the pores of the aerogel reduce the overall polarization ability of the material, thereby significantly reducing the dielectric constant. The addition of octa(aminophenyl)-T8-silsesquioxane further reduces the dielectric constant. Octa(aminophenyl)-T8-silsesquioxane is a cage-type silsesquioxane with a unique T8 cage structure (Si8O 12) has a nanoscale pore structure and a large free volume. This structure can effectively weaken the dipole interaction between polyimide (PI) molecular chains, thereby reducing the dielectric constant and dielectric loss of the material. Specifically, the cage structure of octa(aminophenyl)-T8-silsesquioxane forms nanoscale "cavities" in the PI matrix. These cavities limit the orientation freedom of the dipoles of adjacent polar groups (such as C=O) under high-frequency electric fields, reducing the orientation polarization of the dipoles, so that the material still has excellent dielectric properties at high frequencies. In addition, the introduction of octa(aminophenyl)-T8-silsesquioxane will also cause a dielectric confinement effect. Because the silicon-oxygen skeleton (Si-O-Si) of octa(aminophenyl)-T8-silsesquioxane has a low polarizability, and its nanoscale dispersion characteristics can form a uniform organic-inorganic hybrid structure, this structure can limit the polarization behavior of the PI molecular chain under the action of an electric field.

[0042] This specific embodiment proposes a breakthrough dual silica modification strategy of "physical doping + chemical crosslinking". By introducing silica with an extremely low thermal expansion coefficient (≈0.5ppm / k) as a filler into the polyamic acid solution, the thermal expansion coefficient of the material can be effectively reduced. Under mechanical stirring and ultrasonic dispersion conditions, silica with smaller particle size can be better dispersed in the matrix, forming more interfacial interactions and enhancing the inhibitory effect on thermal expansion. However, silica microspheres are prone to sedimentation due to gravity or phase separation, resulting in uneven material properties. The introduction of octa(aminophenyl)-T8-silsesquioxane will chemically crosslink with the chain segments. The POSS nodes in the crosslinked network "lock" the SiO2 microspheres (0.2μm~1μm) through chemical bonds, restricting their free movement. Even if the microsphere density is higher than that of the solvent, it is difficult to settle. Moreover, the rigid cage structure of POSS significantly improves the mechanical strength of the crosslinked network and inhibits the displacement of the microspheres under external forces (such as shear and thermal stress). Such a chemically cross-linked network avoids the problem of microsphere reaggregation in traditional physical dispersion and maintains uniformity even after long-term storage.

[0043] The three-dimensional cross-linked network and SiO2 microspheres constructed by octaaminophenyl POSS in this embodiment can achieve low shrinkage, thereby reducing dimensional change. During freeze drying, solvent sublimates from gel, and in conventional aerogels, pore walls collapse inwardly due to capillary forces, causing significant shrinkage. The cage structure of the POSS in this embodiment has extremely high rigidity, and the three-dimensional network formed by its cross-linking provides nanoscale skeleton support when solvent sublimates, resists capillary stress, and suppresses the relaxation shrinkage of the segment due to solvent removal. SiO2 microspheres are uniformly dispersed in the gel network, and their high hardness, as incompressible physical barrier, hinders the collapse of pore walls during freeze drying, due to the chemical crosslinking of SiO2 microspheres formed by POSS, which can avoid stress concentration in polymer weak areas, making shrinkage force uniformly dispersed, and overall deformation capacity is minimal. During thermal imidization, closed-loop reaction occurs in polymer precursors to generate polyimide (PI), with molecular chain shortening and volume shrinkage. The unique design of this specific embodiment significantly inhibits this process. The amino group of POSS reacts with the anhydride group of the polymer chain to form a stable amide bond, which undergoes dehydration and cyclization at high temperature to produce an imide ring, thereby preventing the free shrinkage of the molecular chain during thermal imidization. The thermal decomposition temperature of the Si-O bond of POSS is >400°C, which is much higher than the imidization temperature (usually 250°C to 300°C), ensuring that the network does not degrade at high temperatures. The "interfacial effect" of SiO2 microspheres can inhibit the thermal motion of the chain segments and reduce the driving force for contraction. Moreover, the SiO2 microspheres hardly expand when heated, forcing the surrounding polymer chain segments to remain in place.

[0044] The hydrophobic Si-O-Si core of the POSS in this specific embodiment can increase the contact angle of aerogel surface and water, reduce the permeability of moisture to aerogel, and SiO2 microspheres suppress swelling, and make the material have extremely strong hydrophobicity. After POSS is cross-linked with polymer chains, its hydrophobic core is exposed to material internal pore wall and surface, significantly reduces water molecule permeability. High-density POSS network forms " molecular level barrier ", hinders water molecule diffusion path, reduces moisture absorption rate. SiO2 microspheres play its physical barrier effect, increase the tortuosity of water molecule diffusion and extend the permeation path. Low hygroscopicity and high contact angle water can make dielectric properties and aerogel size more stable.

[0045] Specific embodiment 2: This embodiment differs from specific embodiment 1 in that the polyhedral oligomeric silsesquioxane is octa(aminophenyl)-T8-silsesquioxane. Other components are the same as those of specific embodiment 1.

[0046] Specific embodiment 3: This embodiment differs from specific embodiment 1 or 2 in that the particle size of the silicon dioxide particles is 0.2 μm to 1 μm. Other aspects are the same as specific embodiment 1 or 2.

[0047] Specific embodiment 4: This embodiment differs from specific embodiments 1 to 3 in that the tertiary amine catalyst is one or a mixture of triethylamine, trialkyl tertiary amine, octadecyldimethyl tertiary amine, and dodecyldimethyl tertiary amine. Other aspects are the same as specific embodiments 1 to 3.

[0048] Specific embodiment 5: This embodiment differs from specific embodiments 1 to 4 in that the aromatic diamine is p-phenylenediamine. Other aspects are the same as specific embodiments 1 to 4.

[0049] Specific embodiment 6: This embodiment differs from specific embodiments 1 to 5 in that the aromatic dianhydride is 3,3′,4,4′-biphenyltetracarboxylic dianhydride. Other aspects are the same as specific embodiments 1 to 5.

[0050] Specific embodiment 7: This embodiment differs from specific embodiments 1 to 6 in that the solvent is water. Other aspects are the same as specific embodiments 1 to 6.

[0051] Specific embodiment eight: This embodiment provides a method for preparing a low CTE polyimide / silicon-doped aerogel substrate, which is carried out according to the following steps:

[0052] 1. Preparation of anhydride-terminated rigid chain-containing polyamic acid salt solution:

[0053] ① Weighing a catalyst tertiary amine, an aromatic diamine, an aromatic dianhydride and a solvent; mixing the solvent and the catalyst tertiary amine to obtain a solvent / catalyst tertiary amine mixture;

[0054] The molar ratio of the aromatic diamine to the aromatic dianhydride is 1:(1.00-1.02); the molar ratio of the aromatic diamine to the catalyst tertiary amine is 1:(0.05-2); the mass ratio of the total mass of the aromatic diamine and the aromatic dianhydride to the solvent is 1:(2-10);

[0055] ② Under nitrogen atmosphere, room temperature and stirring conditions, the solvent / catalyst tertiary amine mixture and aromatic diamine are mixed for 0.5h to 1h to obtain a mixture, the reaction temperature is raised to 40°C to 65°C, and under nitrogen atmosphere, the temperature is 40°C to 65°C and stirring conditions, the aromatic dianhydride is added to the mixture in three portions and stirred for 2h to 5h. Finally, under nitrogen atmosphere, the reaction temperature is lowered from 40°C to 65°C to 25°C to 30°C, and the mixture is allowed to stand for 5h to 10h to obtain an anhydride-terminated rigid chain-containing polyamic acid salt solution;

[0056] 2. Weighing:

[0057] Weigh 100 parts by mass of an anhydride-terminated rigid chain-containing polyamic acid salt solution, 5 to 15 parts by mass of polyhedral oligomeric silsesquioxane, and 5 to 30 parts by mass of silica particles;

[0058] 3. Blending:

[0059] At a temperature of 80° C. to 100° C., under mechanical stirring and ultrasonic dispersion conditions, the weighed silica particles were added to a solution of anhydride-terminated polyamic acid salt containing rigid chains, and stirred for 1 h to 2 h to obtain a reaction system A;

[0060] 4. POSS cross-linking:

[0061] Under nitrogen atmosphere, temperature of 80°C to 100°C and stirring, the weighed polyhedral oligomeric silsesquioxane was added to reaction system A and reacted for 1 hour to 4 hours to obtain reaction system B;

[0062] 5. Freeze drying:

[0063] The reaction system B is placed in a mold, and then frozen in a freeze dryer at a freezing temperature of -50°C to -10°C for 10 hours to 15 hours, and finally freeze-dried at a temperature of -30°C to -10°C for 60 hours to 100 hours to obtain a polyimide precursor aerogel;

[0064] 6. Thermal imidization reaction:

[0065] The polyimide precursor aerogel is subjected to a thermal imidization reaction to obtain a low CTE polyimide / silicon doped aerogel substrate.

[0066] Specific embodiment 9: This embodiment differs from specific embodiment 8 in that in step 1②, the aromatic dianhydride is added to the mixture in three portions at 1 / 2, 1 / 4, and 1 / 4 of the mass. Other aspects are the same as specific embodiment 8.

[0067] Specific embodiment 10: This embodiment differs from specific embodiment 8 or 9 in that the thermal imidization reaction described in step 6 is specifically carried out according to the following steps: first, maintaining the temperature at 70°C to 100°C for 2 to 4 hours, then maintaining the temperature at 180°C to 230°C for 2 to 4 hours, then maintaining the temperature at 300°C to 320°C for 2 to 6 hours, and finally maintaining the temperature at 400°C to 420°C for 2 to 3 hours. Other steps are the same as specific embodiment 8 or 9.

[0068] The following examples are used to verify the beneficial effects of the present invention:

[0069] Example 1:

[0070] A low CTE polyimide / silicon-doped aerogel substrate is prepared from 100 parts by mass of an anhydride-terminated rigid chain-containing polyamic acid salt solution, 10 parts by mass of polyhedral oligomeric silsesquioxane, and 10 parts by mass of silicon dioxide particles;

[0071] The anhydride-terminated rigid chain-containing polyamic acid salt solution is prepared from a catalyst tertiary amine, an aromatic diamine, an aromatic dianhydride, and a solvent; the molar ratio of the aromatic diamine to the aromatic dianhydride is 1:1.02; the molar ratio of the aromatic diamine to the catalyst tertiary amine is 1:1.5; and the mass ratio of the total mass of the aromatic diamine and the aromatic dianhydride to the solvent is 1:10;

[0072] The structural formula of the repeating unit in the anhydride-terminated rigid chain-containing polyamic acid salt solution is n=50, R is a catalyst tertiary amine.

[0073] The polyhedral oligomeric silsesquioxane is octa(aminophenyl)-T8-silsesquioxane.

[0074] The average particle size of the silicon dioxide particles is 0.2 μm.

[0075] The catalyst tertiary amine is triethylamine.

[0076] The aromatic diamine is p-phenylenediamine (p-PDA).

[0077] The aromatic dianhydride is 3,3',4,4'-biphenyltetracarboxylic dianhydride (S-BPDA).

[0078] The solvent is water.

[0079] A method for preparing a low CTE polyimide / silicon-doped aerogel substrate is carried out according to the following steps:

[0080] 1. Preparation of anhydride-terminated rigid chain-containing polyamic acid salt solution:

[0081] ① Weighing a catalyst tertiary amine, an aromatic diamine, an aromatic dianhydride and a solvent; mixing the solvent and the catalyst tertiary amine to obtain a solvent / catalyst tertiary amine mixture;

[0082] ② Under nitrogen atmosphere, room temperature and stirring speed of 300 rpm, the solvent / catalyst tertiary amine mixture and aromatic diamine were mixed for 1 hour to obtain a mixture, the reaction temperature was raised to 50°C, and under nitrogen atmosphere, temperature of 50°C and stirring speed of 500 rpm, aromatic dianhydride was added to the mixture in three portions and stirred for 4 hours. Finally, under nitrogen atmosphere, the reaction temperature was lowered from 50°C to 25°C and allowed to stand for 10 hours to obtain an anhydride-terminated rigid chain-containing polyamic acid salt solution;

[0083] 2. Weighing:

[0084] Weigh 100 parts by mass of anhydride-terminated rigid chain-containing polyamic acid salt solution, 10 parts by mass of polyhedral oligomeric silsesquioxane, and 10 parts by mass of silica particles;

[0085] 3. Blending:

[0086] Under the conditions of a temperature of 80° C., a stirring speed of 500 rpm, and an ultrasonic power of 50 W, the weighed silica particles were added to the anhydride-terminated rigid chain-containing polyamic acid salt solution and stirred for 2 h to obtain a reaction system A;

[0087] 4. POSS cross-linking:

[0088] Under nitrogen atmosphere, temperature of 90° C. and stirring speed of 400 rpm, the weighed polyhedral oligomeric silsesquioxane was added to reaction system A and reacted for 3 h to obtain reaction system B;

[0089] 5. Freeze drying:

[0090] The reaction system B was placed in a silica gel mold, and then frozen in a freeze dryer at a freezing temperature of -20°C for 15 hours, and finally freeze-dried at a temperature of -20°C for 90 hours to obtain a polyimide precursor aerogel;

[0091] 6. Thermal imidization reaction:

[0092] The polyimide precursor aerogel is subjected to a thermal imidization reaction to obtain a low CTE polyimide / silicon doped aerogel substrate.

[0093] In step 1②, the aromatic dianhydride is added to the mixture in three portions at 1 / 2, 1 / 4, and 1 / 4 of the mass;

[0094] The thermal imidization reaction described in step six is ​​specifically carried out according to the following steps: first, the temperature is kept constant at 100°C for 4 hours, then the temperature is kept constant at 200°C for 3 hours, then the temperature is kept constant at 300°C for 5 hours, and finally the temperature is kept constant at 400°C for 2 hours.

[0095] Example 2: This example differs from Example 1 in that the amount of the polyhedral oligomeric silsesquioxane is 5 parts. Other aspects are the same as Example 1.

[0096] Example 3: This example differs from Example 1 in that the amount of the polyhedral oligomeric silsesquioxane is 15 parts. Other aspects are the same as Example 1.

[0097] Example 4: This example differs from Example 1 in that the average particle size of the silicon dioxide particles is 0.6 μm. Other aspects are the same as Example 1.

[0098] Example 5: This example differs from Example 1 in that the average particle size of the silicon dioxide particles is 1 μm. Other aspects are the same as Example 1.

[0099] Example 6: This example differs from Example 1 in that the amount of silicon dioxide particles is 20 parts. Other aspects are the same as Example 1.

[0100] Example 7: This example differs from Example 1 in that the amount of silicon dioxide particles is 30 parts. Other aspects are the same as Example 1.

[0101] Comparative Example 1: This comparative example differs from Example 1 in that the weighing of the polyhedral oligomeric silsesquioxane and the silica particles is omitted in step 2, and steps 3 and 4 are omitted. Other steps are the same as Example 1.

[0102] Comparative Example 2: This comparative example differs from Example 1 in that the weighing of the silicon dioxide particles is omitted in step 2 and step 3 is omitted. Other steps are the same as Example 1.

[0103] Comparative Example 3: This comparative example differs from Example 1 in that the use of polyhedral oligomeric silsesquioxane is omitted in step 2 and step 4 is omitted. Other aspects are the same as Example 1.

[0104] Table 1 Raw materials and process conditions for preparing aerogel substrates in Examples 1 to 7 and Comparative Examples 1 to 3

[0105]

[0106]

[0107] The aerogel substrates prepared in Examples 1 to 7 and Comparative Examples 1 to 3 were subjected to performance tests:

[0108] 1. Shrinkage: The X / Y / Z three-axis shrinkage of the aerogel was measured using a vernier caliper. The shrinkage calculation formula is: Shrinkage (%) = [(initial length - final length) / initial length] × 100%, Volume shrinkage (%) = [(initial volume - final volume) / initial volume] × 100%. This shrinkage test includes the X / Y / Z three-axis shrinkage of the freeze-drying process in step five of the preparation process, the volume shrinkage of the thermal imidization process in step six of the preparation process, the X / Y / Z three-axis shrinkage of the aerogel substrate from -196°C to room temperature, the X / Y / Z three-axis shrinkage of the aerogel substrate from room temperature to 200°C, and the X / Y / Z three-axis shrinkage of the aerogel substrate from room temperature to 300°C. Each set of tests was repeated 3 times, and the average value was taken to reduce accidental errors. The test method for the X / Y / Z three-axis shrinkage rate during the freeze-drying process is as follows: the length, width and thickness of the silicone mold are used as the initial length of the sample in the X / Y / Z direction. In the fifth step of the preparation process, the sample is first frozen at a freezing temperature of -20°C for 15 hours, then dried at a freezing temperature of -20°C for 90 hours, and then the length of the sample in the X / Y / Z direction is measured to calculate the shrinkage rate. The test method for the volume shrinkage rate during the thermal imidization process is as follows: the volume shrinkage rate of the thermal imidization process is directly calculated by the initial volume and the final volume. The dried sample is flat and free of deformation. The initial volume is calculated using length × width × height. The final volume is the final volume calculated by the Archimedes drainage method after the imidized sample is naturally cooled to room temperature, thereby calculating the volume shrinkage rate. The test method for the X / Y / Z three-axis shrinkage rate from -196°C to room temperature is as follows: the sample is placed in a room temperature (25°C) environment for equilibration for 24 hours, the initial length in the X / Y / Z direction is measured with a vernier caliper, and the sample is immersed in liquid nitrogen (-196°C) for 1 hour to ensure complete cooling to the target temperature. , take the sample out of liquid nitrogen, place it in room temperature (25℃) and heat it up naturally at a rate of no more than 5℃ / min (to avoid thermal shock), and keep it at room temperature for 2 hours to eliminate the temperature gradient. Measure the length of the sample at room temperature again and calculate the shrinkage rate. The test method for the X / Y / Z three-axis shrinkage rate from room temperature to 200℃ is as follows: place the sample in a room temperature (25℃) environment for 24 hours, measure the initial length in the X / Y / Z direction with a vernier caliper, and then place the sample in an oven at a rate of 5℃ / min. The temperature is raised to 200°C at a rate of 1°C, maintained for 1 hour, and then naturally cooled to room temperature. The length of the sample at room temperature is measured again to calculate the shrinkage rate. The test method for the X / Y / Z three-axis shrinkage rate from room temperature to 300°C is as follows: the sample is placed in a room temperature (25°C) environment for equilibration for 24 hours, and the initial length in the X / Y / Z direction is measured with a vernier caliper. The sample is then placed in an oven and heated to 300°C at a rate of 5°C / min. After maintaining for 1 hour, the sample is naturally cooled to room temperature, and the length of the sample at room temperature is measured again to calculate the shrinkage rate.

[0109] 2. Multi-environment fatigue shrinkage test: A high and low temperature alternating humidity and heat test chamber is used, with a temperature range of -196°C to 300°C and a humidity range of 5% RH to 95% RH, and 100 cycles. The single cycle procedure of the aerogel substrate is to decrease from 25°C to -196°C at a rate of 10°C / min, keep warm for 30 minutes (5% RH), then increase to 300°C at a rate of 5°C / min, keep warm for 30 minutes (95% RH), and finally decrease to 25°C at a rate of 5°C / min, balance for 20 minutes (5% RH). The length changes of the X / Y / Z axes are monitored in real time by a multi-axis laser displacement sensor. After eliminating abnormal values, the single shrinkage rate is calculated according to the shrinkage rate formula. The final fatigue shrinkage rate takes the maximum single value in 100 cycles.

[0110] 3. Contact angle test: Using ASTM D7334 standard, the contact angle of the aerogel substrate was measured using a contact angle meter;

[0111] 4. Water absorption test: Dry the aerogel substrate in a vacuum oven at 80°C to constant weight (mass is recorded as W0), then immerse the sample in 25°C deionized water for 24 hours. Remove and absorb the surface moisture with filter paper. Immediately weigh (mass is recorded as W1). Calculate water absorption: Water absorption (%) = [(W1-W0) / W0] × 100%;

[0112] 5. Mass change test after boiling and drying: Using the IEC 60068-2-20 damp heat test standard, first record the initial mass of the dry aerogel substrate (M0), then put the sample into boiling water and boil it for 2 hours, take out the sample, and dry it in an 80°C oven to constant weight, and record the final mass (M1). Mass change (%) = [(M1-M0) / M0] × 100%;

[0113] 6. Coefficient of thermal expansion (CTE) test: TMA (thermomechanical analyzer) tensile mode test, heating rate of 5 ° C / min, range of 25 ° C ~ 380 ° C;

[0114] 7. After high temperature shock and high and low temperature cycles, the metal patch peel strength test is performed. The preparation method of the metal patch is as follows: first, the sample is treated with plasma (power 100 W, time 2 min) to remove organic matter and activate the surface, and then a layer of metal Cu is deposited on the surface of the aerogel substrate by magnetron sputtering process, a dense transition layer is constructed on the aerogel surface to enhance the interface bonding strength, and copper foil is covered on the Cu layer. The sample is hot pressed at 200°C and 5 MPa for 1 h to obtain the substrate sample after the metal patch. The sample is first kept in a low temperature environment of -55°C for 30 min, and then rapidly heated to 300°C at a rate of 5°C / min to simulate sudden thermal shock (ΔT = 355°C), and maintained at high temperature for 30 min. The above high and low temperature cycles are repeated 100 times to examine the interface stability of the material under long-term thermal shock conditions. The substrate sample after the metal patch is subjected to a 90° peel test to evaluate the bonding strength between the metal patch and the substrate. Finally, the interface delamination is observed using an optical microscope.

[0115] 8. Reflection angle test: Use a laser reflectometer to measure the deviation angle of the reflected light spot when the incident angle is 45°;

[0116] 9. Multi-point relative dielectric performance test: The relative dielectric properties were tested using an Agilent Technologies Inc-E5071C vector network analyzer using the waveguide method at an X-band frequency (8.2 GHz to 12.4 GHz). Five test points (one center and four corners) were selected on each aerogel substrate to test the dielectric consistency of the same material at different locations. The average value (μ) was used to reflect the overall dielectric properties, and the standard deviation (σ) was used to characterize the data dispersion.

[0117] 10. Relative dielectric constant under condensation water cycle test: The aerogel substrate was placed in a condensation-drying cycle environment. The experimental conditions were: 40°C / 95% RH for 4 hours, 25°C / 50% RH for 2 hours, and the above two-stage switching was repeated 50 times to test the stability of the dielectric properties of the material. The frequency was X-band (8.2 GHz to 12.4 GHz).

[0118] 11. Relative dielectric constant after boiling for 2 hours: The aerogel substrate was placed in boiling water and boiled for 2 hours. After taking out the sample, its dielectric constant in the X-band (8.2 GHz to 12.4 GHz) was tested.

[0119] 12. Low-temperature fluidity verification: Use a rotational rheometer in oscillation mode (strain 0.1%, frequency 1 Hz) and cool from 25°C to -40°C at a rate of 2°C / min to test the fluidity of reaction system B prepared in step 4 at low temperature (-40°C).

[0120] Table 2 Performance evaluation of aerogel substrates of Examples 1 to 7 and Comparative Examples 1 to 3

[0121]

[0122]

[0123]

[0124] As can be seen from the results of embodiment one to seven and comparative example one to three tests: embodiment one to seven, by " physical doping and chemical crosslinking " dual strategy, successfully balanced the demand of low shrinkage, low CTE, high hydrophobicity and low dielectric constant. Especially embodiment three, due to more eight (aminophenyl) -T8- silsesquioxane nodes strengthening three-dimensional network rigidity, significantly suppress shrinkage and molecular chain polarization, fatigue shrinkage is only 0.5%, and high crosslinking density suppresses molecular chain slippage, resists the thermal stress in temperature cycle, and uniformly dispersed microspheres reduce the swelling caused by humidity. The relative dielectric constant under X-band of embodiment three is minimum, and the dielectric constant under condensation water circulation test only increases by 0.02, and this is due to the POSS network of high crosslinking density effectively blocking water molecule penetration, SiO2 microspheres are uniformly dispersed and suppress interface defects, and dual modification synergy is significant, and the contact angle of embodiment three is up to 148 °, and the addition of silicon makes the comprehensiveness of modified PI aerogel substrate optimal. In contrast, in Comparative Example 1, since there is only polyimide precursor resin but no cross-linking network, the material has high hygroscopicity, large shrinkage, and fatigue shrinkage as high as 12.5%. This is because the pure PI matrix shrinks and swells violently during temperature and humidity cycles. Although silica particles are added to Comparative Example 3, the silica particles will settle due to gravity, resulting in uneven material properties. Figure 2 As can be seen, the morphologies of the front and back surfaces of the sample without octa(aminophenyl)-T8-silsesquioxane crosslinking are different, and a large amount of silica particles settle on the back of the aerogel sheet, seriously affecting the performance of the final product. Examples 1 to 7 and Comparative Examples 1 to 3 fully demonstrate that the dual modification strategy of doping PI aerogel with octa(aminophenyl)-T8-silsesquioxane and silica microspheres can improve the overall performance of PI aerogel substrates.

[0125] To verify whether the silica particles have settled, the reaction system B prepared in step 4 of Example 1 was allowed to stand for 72 hours, and the reaction system B prepared in step 4 of Comparative Example 3 was allowed to stand for 24 hours, and then the subsequent steps 5 and 6 were carried out. The test results are as follows: Figure 1 and Figure 2 ;

[0126] Figure 1This is a photo of a low-CTE polyimide / silicon-doped aerogel substrate prepared after allowing reaction system B prepared in step 4 of Example 1 to stand for 72 hours. As can be seen from the figure, this is an aerogel substrate prepared after allowing a solution cross-linked with octa(aminophenyl)-T8-silsesquioxane to stand for 72 hours. No silica particles settled on the reverse side of the substrate, indicating that the chemically cross-linked network constructed by octa(aminophenyl)-T8-silsesquioxane prevents silica particles from settling during long-term storage.

[0127] Figure 2 This is a photo of a low-CTE polyimide / silicon-doped aerogel substrate prepared by allowing reaction system B prepared in step 4 of comparative example 3 to stand for 24 hours. The figure shows that this is an aerogel substrate prepared by allowing a solution without octa(aminophenyl)-T8-silsesquioxane crosslinking to stand for 24 hours. The morphologies of the front and back surfaces of the substrate are different, with a large amount of silica particles settled on the back surface of the aerogel plate.

[0128] Figure 3 This is a scanning electron microscope image of the low-CTE polyimide / silicon-doped aerogel substrate prepared in Example 2. As can be seen from the image, the SiO2 particles are evenly dispersed throughout the entire field of view, the edges of the SiO2 particles are well integrated with the substrate, there are no obvious gaps, and no macroscopic defects such as micron-level holes, cracks, and tears are observed at the mesoscopic scale.

[0129] Figure 4 This is a contact angle diagram of the low CTE polyimide / silicon-doped aerogel substrate prepared in Example 3. As can be seen from the figure, the contact angle of the prepared low CTE polyimide / silicon-doped aerogel substrate can reach 148°, indicating that the prepared low CTE polyimide / silicon-doped aerogel substrate has excellent hydrophobicity.

[0130] Figure 5 This is the infrared image of the low CTE polyimide / silicon-doped aerogel substrate prepared in Example 3; as shown in the figure, at 1778 cm -1 (imide C=O asymmetric stretching vibration), 1703 cm -1 (imide C=O symmetric stretching vibration), 1344 cm -1 (CN stretching vibration), 1067cm -1 and 738cm -1 Corresponding characteristic absorption peaks were detected near (imine bond CNC stretching vibration). The appearance of these characteristic peaks clearly indicates that the substrate has been successfully imidized.

Claims

1. A low CTE polyimide / silicon-doped aerogel substrate, characterized in that It is prepared from 100 parts by mass of anhydride-terminated polyamic acid salt solution containing rigid chains, 5 to 15 parts by mass of polyhedral oligomeric silsesquioxane, and 5 to 30 parts by mass of silicon dioxide particles. The anhydride-terminated rigid chain-containing polyamic acid salt solution is prepared from a catalyst tertiary amine, an aromatic diamine, an aromatic dianhydride, and a solvent; the molar ratio of the aromatic diamine to the aromatic dianhydride is 1:(1.00-1.02); the molar ratio of the aromatic diamine to the catalyst tertiary amine is 1:(0.05-2); and the mass ratio of the total mass of the aromatic diamine and the aromatic dianhydride to the solvent is 1:(2-10); The structural formula of the repeating unit in the anhydride-terminated rigid chain-containing polyamic acid salt solution is n=10-90, R is a catalyst tertiary amine.

2. A low CTE polyimide / silicon-doped aerogel substrate according to claim 1, characterized in that The polyhedral oligomeric silsesquioxane is octa(aminophenyl)-T8-silsesquioxane.

3. The low CTE polyimide / silicon-doped aerogel substrate according to claim 1, characterized in that The particle size of the silicon dioxide particles is 0.2 μm to 1 μm.

4. The low CTE polyimide / silicon-doped aerogel substrate according to claim 1, characterized in that The catalyst tertiary amine is one of triethylamine, trialkyl tertiary amine, octadecyl dimethyl tertiary amine and dodecyl dimethyl tertiary amine, or a mixture of several of them.

5. The low CTE polyimide / silicon-doped aerogel substrate according to claim 1, characterized in that The aromatic diamine is p-phenylenediamine.

6. The low CTE polyimide / silicon-doped aerogel substrate according to claim 1, characterized in that The aromatic dianhydride is 3,3',4,4'-biphenyltetracarboxylic dianhydride.

7. The low CTE polyimide / silicon-doped aerogel substrate according to claim 1, characterized in that The solvent is water.

8. The method for preparing a low CTE polyimide / silicon-doped aerogel substrate according to claim 1, wherein It is carried out in the following steps:

1. Preparation of anhydride-terminated rigid chain-containing polyamic acid salt solution: ① Weighing a catalyst tertiary amine, an aromatic diamine, an aromatic dianhydride and a solvent; mixing the solvent and the catalyst tertiary amine to obtain a solvent / catalyst tertiary amine mixture; The molar ratio of the aromatic diamine to the aromatic dianhydride is 1:(1.00-1.02); the molar ratio of the aromatic diamine to the catalyst tertiary amine is 1:(0.05-2); the mass ratio of the total mass of the aromatic diamine and the aromatic dianhydride to the solvent is 1:(2-10); ② Under nitrogen atmosphere, room temperature and stirring conditions, the solvent / catalyst tertiary amine mixture and aromatic diamine are mixed for 0.5h to 1h to obtain a mixture, the reaction temperature is raised to 40°C to 65°C, and under nitrogen atmosphere, the temperature is 40°C to 65°C and stirring conditions, the aromatic dianhydride is added to the mixture in three portions and stirred for 2h to 5h. Finally, under nitrogen atmosphere, the reaction temperature is lowered from 40°C to 65°C to 25°C to 30°C, and the mixture is allowed to stand for 5h to 10h to obtain an anhydride-terminated rigid chain-containing polyamic acid salt solution; 2. Weighing: Weigh 100 parts by mass of an anhydride-terminated rigid chain-containing polyamic acid salt solution, 5 to 15 parts by mass of polyhedral oligomeric silsesquioxane, and 5 to 30 parts by mass of silica particles; 3. Blending: At a temperature of 80° C. to 100° C., under mechanical stirring and ultrasonic dispersion conditions, the weighed silica particles were added to a solution of anhydride-terminated polyamic acid salt containing rigid chains, and stirred for 1 h to 2 h to obtain a reaction system A; 4. POSS cross-linking: Under nitrogen atmosphere, temperature of 80°C to 100°C and stirring, the weighed polyhedral oligomeric silsesquioxane was added to reaction system A and reacted for 1 hour to 4 hours to obtain reaction system B; 5. Freeze drying: The reaction system B is placed in a mold, and then frozen in a freeze dryer at a freezing temperature of -50°C to -10°C for 10 hours to 15 hours, and finally freeze-dried at a temperature of -30°C to -10°C for 60 hours to 100 hours to obtain a polyimide precursor aerogel; 6. Thermal imidization reaction: The polyimide precursor aerogel is subjected to a thermal imidization reaction to obtain a low CTE polyimide / silicon doped aerogel substrate.

9. The method for preparing a low CTE polyimide / silicon-doped aerogel substrate according to claim 8, characterized in that In step 1②, the aromatic dianhydride is added to the mixture in three portions at 1 / 2, 1 / 4 and 1 / 4 of the mass.

10. The low CTE polyimide / silicon-doped aerogel substrate according to claim 8, characterized in that The thermal imidization reaction described in step six is ​​specifically carried out according to the following steps: first, at a temperature of 70°C to 100°C, the constant temperature is 2h to 4h, then at a temperature of 180°C to 230°C, the constant temperature is 2h to 4h, then at a temperature of 300°C to 320°C, the constant temperature is 2h to 6h, and finally at a temperature of 400°C to 420°C, the constant temperature is 2h to 3h.

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