Thermoplastic polyimide resin containing biphenyl structure and preparation method thereof

Abstract

The invention provides thermoplastic polyimide resin containing a biphenyl structure. The thermoplastic polyimide resin has the following structural formula: # imgabs0 #, wherein Ar is a dibasic anhydride monomer residue; n is an integer, and ngt; 0; m is an integer, and m > = 0; transverse lines'-'connected to the benzene ring can be connected to any carbon atom of the benzene ring; the invention also provides a preparation method of the thermoplastic polyimide resin containing the biphenyl structure. The preparation method comprises the following steps: carrying out condensation polymerization on a biphenyl-containing diamine monomer and a binary anhydride monomer to obtain the thermoplastic polyimide resin containing the biphenyl structure; according to the thermoplastic polyimide resin containing the biphenyl structure, the problems that in the prior art, the processability is poor, the melt viscosity is too high, and the high-temperature performance cannot be considered at the same time are solved, and the polyimide resin which is high in processability, high in thermoplasticity and good in heat resistance is provided.

Description

Technical Field

[0001] The present invention relates to the technical field of polyimide resin synthesis, and particularly relates to a thermoplastic polyimide resin containing a biphenyl structure and a preparation method thereof. Background Art

[0002] Polyimide is a class of high-performance special engineering plastics. Due to its excellent heat resistance, chemical resistance, mechanical strength and electrical insulation properties, it is widely used in high-end fields such as aerospace, automotive, and electronics. Traditional polyimide resins are characterized by their highly rigid molecular chain structures, which endow them with extremely high thermal stability and glass transition temperature (Tg). However, this high-rigidity structure results in poor processability of polyimide. Especially during melt processing at high temperatures, the melt viscosity of the resin is relatively high, making it difficult to achieve good forming and processing. The above characteristics of polyimide (especially its high-temperature resistance) are mainly caused by the rigid structure of its molecular chain and imide groups, and their glass transition temperatures are mostly above 250°C, and some can reach 400°C. In addition, due to the poor processability of traditional polyimide materials, secondary processing is often impossible. This is because the stronger the rigid structure, the higher the melt viscosity of polyimide materials, and the more difficult it is to form and process. Therefore, polyimide materials are generally referred to as "pseudo-plastic" materials, which pose great challenges in the production process.

[0003] In the prior art, in order to improve the processability of polyimide, methods such as blending (Chinese patent application with application number CN202010962651.4), copolymerization (Chinese patent applications with application numbers CN202411930921.8, CN202010962688.7), and development of new molecular structure design (Chinese patent applications with application numbers CN202411677947.6, CN202411409399.9) are disclosed in the above patent applications; however, the existing solutions often have some defects. For example, when improving processability by introducing ether bonds or non-coplanar structures, the heat resistance of polyimide is often reduced, or due to the complexity of the structure, the properties of the material are unstable, and it is impossible to balance processability and heat resistance. The Chinese patent application with application number CN202411409399.9 discloses a twisted non-coplanar biphenyl diaryl ether skeleton, which reduces the intermolecular stacking density; and the patent gives the spatial deflection of the skeleton structure when R1 and R2 are benzene ring substituents. However, the two ether bonds in the diamine monomer structure increase the chain segment flexibility, and combined with the deflection of the benzene side group, it exacerbates the distortion of the diamine monomer molecular structure, making the entire molecular chain into a globular structure. The huge steric hindrance will significantly reduce the melt processability of this material and cannot achieve an ideal effect.

[0004] In addition, although some polyimide resins have been improved in terms of enhancing melt processing performance, their heat resistance (especially the glass transition temperature) often fails to meet the requirements of industrial applications. This limits the application of these modified materials in high-temperature environments. VSPEL® SP-1 from DuPont in the United States is a PMDA / ODA polyimide resin. Although it has relatively high heat resistance, it still cannot be melt processed at 400 °C, and fails to fully exploit the application potential of polyimide materials at high temperatures.

[0005] Therefore, there is an urgent need for a new type of polyimide resin that can improve its melt processing performance without sacrificing its heat resistance through innovative molecular structure design to meet the growing industrial demands. Summary of the Invention

[0006] The first technical problem to be solved by the present invention is to provide a thermoplastic polyimide resin containing a biphenyl structure to solve the problems of poor processability, too high melt viscosity and inability to balance high-temperature performance in the prior art.

[0007] To overcome the above defects of the prior art, the present invention provides a thermoplastic polyimide resin containing a biphenyl structure, which has the following structural formula:

[0008] Wherein, Ar is a residue of a dianhydride monomer; n is an integer and n > 0; m is an integer and m ≥ 0; the horizontal lines "-" connecting to the benzene ring all indicate that they can be connected to any carbon atom of the benzene ring.

[0009] The present invention provides a thermoplastic polyimide resin containing a biphenyl structure. The diamine monomer of this resin contains both a biphenyl structure and a benzene ring side group. The biphenyl structure helps to improve the heat resistance of the polymer, but it will also increase the melt viscosity of the polymer and reduce the processing performance. To make up for this deficiency, the present invention connects the biphenyl structure to the benzene ring through an ether bond, making the diamine monomer form an asymmetric structure. This structure increases the free volume between molecular chains by placing the benzene ring side groups on one side of the molecular chain, thereby promoting the flow of molecular chains and significantly improving the processing performance of polyimide; in addition, due to the random arrangement of the positions of the benzene ring side groups, after reacting with the diacid anhydride, the positions of adjacent benzene ring side groups on the molecular chain can be randomly arranged in a tail-to-tail, head-to-tail, tail-to-head manner, and the schematic arrangement of its benzene ring side groups is as follows: , This random arrangement results in a relatively high degree of randomness in the polymer molecular chains, further increasing the free volume and enhancing the thermoplasticity of the resin. Compared with the possible formation of agglomerated structures in the prior art, such as in Patent CN202411409399.9, the resin of the present invention does not form excessive steric hindrance due to steric effects, avoiding the problem of decreased fluidity.

[0010] Compared with the prior art, the present invention has the following advantages: Improve processing performance: Through the design of asymmetric diamine monomers, the free volume of the molecular chains is increased, promoting the flow of molecular chains, significantly improving the processing performance of polyimide, and overcoming the problem of excessively high melt viscosity brought by the biphenyl structure; Enhance thermoplasticity: The randomly arranged benzene ring side groups increase the randomness of the polymer, improving the thermoplasticity of the resin and endowing it with better processability and fluidity; Enhance heat resistance: The biphenyl structure effectively improves the heat resistance of polyimide without forming agglomerated structures as in some patents, avoiding the problem of decreased fluidity; The thermoplastic polyimide resin containing biphenyl structure of the present invention effectively overcomes the contradiction between heat resistance and processing performance of traditional polyimide by optimizing the structure of diamine monomers, providing a new solution for high-performance thermoplastic polyimide resin. Through the design of the novel diamine monomer structure, the disadvantages of the prior art are overcome, and a thermoplastic polyimide resin with both high heat resistance (glass transition temperature at 300 - 350 °C) and excellent processability (melt processing at 400 °C) is provided.

[0011] In a possible embodiment, the Ar is at least one of the following groups:

[0012] Among them, each horizontal line “-” connecting the outside of each monomer to the benzene ring represents the bonding key between the Ar group and the carbon atom in the repeating unit; each horizontal line “-” connecting the inside of each monomer to the benzene ring represents that it can be connected to any carbon atom on the benzene ring.

[0013] In a possible embodiment, the Ar is at least one of the following groups:

[0014] Among them, each horizontal line “-” connecting the outside of each monomer to the benzene ring represents the bonding key between the Ar group and the carbon atom in the repeating unit; each horizontal line “-” connecting the inside of each monomer to the benzene ring represents that it can be connected to any carbon atom on the benzene ring.

[0015] Compared with the prior art, adopting the above technical solution, the structure of the above group has higher rigidity, which helps to improve the heat resistance and mechanical strength of the polymer. By introducing an Ar group with high rigidity into the polyimide chain, the intermolecular interaction of the resin can be enhanced, and the thermal stability and rigidity of the material can be further improved.

[0016] In a possible implementation manner, the Ar is at least one of the following groups:

[0017] Among them, each horizontal line "-" connected to the benzene ring on the outside of each monomer represents the connection bond between the Ar group and the carbon atom in the repeating unit.

[0018] Compared with the prior art, adopting the above technical solution, the above group structure has certain rigidity and a non-planar structure, which can increase the degree of twisting of the molecular chain, thereby reducing the melt viscosity of the polymer and improving the processing performance. The introduction of the non-planar structure optimizes the intermolecular interaction force, improves the fluidity of the polymer, thereby reducing the energy consumption during the processing process and improving the production efficiency; at the same time, this structure effectively increases the glass transition temperature of the polymer, thereby enhancing the heat resistance of the polymer, especially maintaining higher mechanical strength and chemical stability in a high-temperature environment.

[0019] The second technical problem to be solved by the present invention is to provide a preparation method of a thermoplastic polyimide resin containing a biphenyl structure to solve the problems of poor processing performance and insufficient heat resistance existing in the prior art.

[0020] To overcome the defects of the above prior art, the present invention provides a preparation method of a thermoplastic polyimide resin containing a biphenyl structure, including the following steps: A thermoplastic polyimide resin containing a biphenyl structure is obtained by polycondensing a biphenyl diamine monomer and a dianhydride monomer.

[0021] In a possible implementation manner, the structural formula of the biphenyl diamine monomer is as follows: ; The structural formula of the dianhydride monomer is as follows: ; Among them, Ar is the residue of the dianhydride monomer, and the Ar is at least one of the following groups:

[0022] Among them, the horizontal line "-" connected to the benzene ring represents the connection bond between the Ar group and the carbon atom; Among them, the horizontal line "-" connecting the inner side of the monomer to the benzene ring represents that it can be connected to any carbon atom of the benzene ring. m is an integer and m≥0; Specifically, among them, the horizontal line "-" connecting the inner side of the monomer to the benzene ring represents that it can be connected to any carbon atom of the benzene ring. It can be seen that in the above structure, the biphenyl structure can have multiple connection modes, which can be para-para connection, or para-meta connection or para-ortho connection, etc. The ether bond and the amino group also have three connection modes: para, meta and ortho; C m H 2m+1 is a long carbon chain, m is an integer and m≥0. Compared with the prior art, introducing it in the present invention can further increase the flexibility of the molecular chain, increase the free volume and improve the processing performance.

[0023] Compared with the prior art, the structural formulas of the biphenyl diamine monomer and the dianhydride monomer provide an important basis. The design of these monomers not only enhances the structural diversity of the material, but also can adjust the flexibility and processability of the molecular chain through different connection modes. Since the biphenyl structure has multiple possible connection modes (such as para-para, para-ortho connection or para-meta connection, etc.), the material can form a more complex and elastic molecular network during the polymerization process. The diverse connection modes not only optimize the arrangement and spatial structure of the molecular chain, but also further improve its mechanical properties, thermal stability and chemical resistance. In particular, the connection modes of the ether bond and the amino group (para, meta, ortho, etc.) can effectively adjust the balance between the flexibility and hardness of the material, so as to meet the requirements of different applications. In addition, introducing some monomers with a long carbon chain (C m H 2m+1 ) structure can greatly improve the flexibility of the molecular chain, enhance the plasticity and processability of the material. The presence of the long carbon chain increases the free volume of the material and reduces the crystallinity of the material, which further improves the processing performance and makes the material have better processing adaptability and stability in practical applications.

[0024] In a possible implementation manner, the structural formula of the biphenyl diamine monomer is one of the following structures: .

[0025] In a possible implementation manner, the structural formula of the biphenyl diamine monomer is one of the following structures: .

[0026] In order to further improve the processing performance, a long carbon chain structure can also be connected to the side group of the benzene ring to weaken the regularity of the molecular chain. The structure is as follows:

[0027] Where n is an integer and n > 0.

[0028] In a possible implementation, the preparation method includes the following steps: S1: Add the biphenyl diamine monomer into a polar aprotic solvent under gas protection, stir to completely dissolve it, and then add the dianhydride monomer. After stirring and reacting, a polyamic acid solution is obtained; S2: Use the thermal imidization method or the solution imidization method to prepare the polyamic acid solution obtained in step S1 into a polyimide film or a polyimide film powder resin.

[0029] Compared with the prior art, adopting the above technical solution, the beneficial effects of the present invention are as follows: In the design of the diamine monomer, the biphenyl structure and the benzene ring are connected by an ether bond, and a benzene ring side group is introduced on one side of a benzene ring to obtain an asymmetric diamine monomer. After polymerization with the dianhydride, the positional arrangement of the benzene ring side groups is irregular, increasing the free volume. This polyimide resin has both heat resistance and processability. The glass transition temperature of a series of thermoplastic polyimide resins prepared is 300°C to 350°C, and the lowest melt viscosity is between 4000 Pa•s and 15000 Pa.s.

[0030] In a possible implementation, in step S1, the specific conditions of the gas protection are nitrogen or inert gas protection, and the stirring reaction time is 8 - 24 hours.

[0031] Compared with the prior art, adopting the above technical solution, by further optimizing the reaction conditions, not only the reaction selectivity and yield are improved, but also the energy consumption during the reaction is reduced to a certain extent, enhancing the economy and operability of the entire process. Specific Embodiments

[0032] First of all, those skilled in the art should understand that these embodiments are only used to explain the technical principles of the embodiments of this application and are not intended to limit the protection scope of the embodiments of this application. Those skilled in the art can make adjustments according to needs to adapt to specific application scenarios.

[0033] The present invention provides a thermoplastic polyimide resin containing a biphenyl structure, which has the following structural formula: ; Wherein, Ar is the residue of the dianhydride monomer; n is an integer and n > 0; m is an integer and m ≥ 0; the horizontal lines "-" connecting to the benzene ring all indicate that they can be connected to any carbon atom of the benzene ring.

[0034] As a preferred solution, the Ar is at least one of the following groups:

[0035] Among them, each horizontal line "-" connected to the benzene ring on the outside of each monomer represents the bonding bond between the Ar group and the carbon atom in the repeating unit; each horizontal line "-" connected to the benzene ring on the inside of each monomer represents that it can be connected to any carbon atom on the benzene ring.

[0036] As a preferred embodiment, the Ar is at least one of the following groups:

[0037] Among them, each horizontal line "-" connected to the benzene ring on the outside of each monomer represents the bonding bond between the Ar group and the carbon atom in the repeating unit; each horizontal line "-" connected to the benzene ring on the inside of each monomer represents that it can be connected to any carbon atom on the benzene ring.

[0038] As a preferred embodiment, the Ar is at least one of the following groups:

[0039] Among them, each horizontal line "-" connected to the benzene ring on the outside of each monomer represents the bonding bond between the Ar group and the carbon atom in the repeating unit.

[0040] The present invention also provides a preparation method of the above-mentioned thermoplastic polyimide resin containing a biphenyl structure, comprising the following steps: Obtain a thermoplastic polyimide resin containing a biphenyl structure by polycondensation reaction of a biphenyl diamine monomer and a dianhydride monomer.

[0041] As a preferred embodiment, the structural formula of the biphenyl diamine monomer is as follows: ; The structural formula of the dianhydride monomer is as follows: ; Among them, Ar is the residue of the dianhydride monomer, and the Ar is at least one of the following groups:

[0042] Among them, each horizontal line "-" connected to the benzene ring represents the bonding bond between the Ar group and the carbon atom; Among them, each horizontal line "-" connected to the benzene ring on the inside of the monomer represents that it can be connected to any carbon atom on the benzene ring, m is an integer, and m≥0.

[0043] As a preferred embodiment, the structural formula of the biphenyl diamine monomer is one of the following structures: .

[0044] As a preferred embodiment, the structural formula of the biphenyl diamine monomer is one of the following structures: 。

[0045] As a preferred embodiment, the preparation method includes the following steps: S1: Add the biphenyl diamine monomer into a polar aprotic solvent under gas protection, stir to completely dissolve it, then add the dianhydride monomer, and obtain a polyamic acid solution after stirring and reacting; S2: Use thermal imidization or solution imidization to prepare the polyamic acid solution obtained in step S1 into a polyimide film or polyimide film powder resin.

[0046] As a preferred embodiment, in step S1, the specific conditions of the gas protection are nitrogen or inert gas protection, and the stirring reaction time is 8 - 24 hours. The polar aprotic solvent is one of N,N'-dimethylformamide, N,N'-dimethylacetamide, or N'-methylpyrrolidone; in step S2, the azeotropic water-carrying agent in the solution imidization method is one or two of toluene, xylene, or chlorotoluene.

[0047] The present invention also provides a synthesis method of the diamine containing a biphenyl structure, taking as an example, and its synthesis reaction formula is as follows:

[0048] The specific synthesis steps are as follows: (1) Step one: Preparation of nitrobenzene: Benzene undergoes a nitration reaction with concentrated nitric acid under the catalysis of concentrated sulfuric acid. The nitro group is introduced into the benzene ring to generate nitrobenzene. Reaction mechanism: The hydrogen on the benzene ring is protonated by sulfuric acid to generate an activated intermediate, and the intermediate reacts with nitric acid to introduce the nitro group and generate nitrobenzene. The product needs to be purified to ensure high-purity meta-substituted bromonitrobenzene.

[0049] (2) Step two: Meta-bromination of nitrobenzene: Nitrobenzene, bromine, and iron powder are heated to an appropriate temperature in a polar solvent (such as DMF or DMSO) to generate meta-substituted bromonitrobenzene. Reaction mechanism: The electron-withdrawing effect of the nitro group activates the meta-position of the benzene ring, making it more prone to electrophilic substitution reactions. Bromine generates an active bromine intermediate under the catalysis of iron powder, attacks the meta-position of the benzene ring, substitutes the hydrogen atom, and forms a C-Br bond.

[0050] (3) Step three: Para-phenyl substitution of meta-bromonitrobenzene: Meta-bromonitrobenzene and phenylsodium are heated to an appropriate temperature in a polar solvent (such as DMF) to generate the target product. Reaction mechanism: The nitro group, as a strong electron-withdrawing group, activates the para-position, making it prone to nucleophilic substitution reactions. The phenyl anion, as a nucleophile, attacks the hydrogen atom at the para-position, and a new C-C bond is formed after substitution.

[0051] (4) Step Four: Reaction with biphenol to form an ether bond: The above product, biphenol, and potassium carbonate are heated to an appropriate temperature in a polar solvent (such as DMF). Reaction mechanism: The bromine atom acts as a leaving group, and the phenoxide anion replaces it through a nucleophilic substitution reaction to form an ether bond.

[0052] (5) Step Five: Nitration of the phenolic hydroxyl group: The above product, sodium nitrite, and concentrated hydrochloric acid (HCl) are stirred at low temperature (0 - 5 °C) to generate the diazonium salt of the phenol. The diazonium salt is heated under acidic conditions and undergoes a decomposition reaction to form nitrobenzene.

[0053] (6) Step Six: Reduction reaction of the nitro group: The above nitro product is added with iron powder (Fe) and hydrochloric acid (HCl), and refluxed and heated in ethanol (EtOH). Two nitro groups are simultaneously reduced to amino groups. Reaction mechanism: The nitro group is converted to a nitroso group under acidic conditions and then reduced to an amino group by iron powder.

[0054] Taking as an example, its synthesis reaction formula is as follows:

[0055] The specific synthesis steps are as follows: (1) Step One: Preparation of nitrobenzene: Benzene undergoes a nitration reaction with concentrated nitric acid under the catalysis of concentrated sulfuric acid. A nitro group is introduced into the benzene ring to generate nitrobenzene (C6H5NO2). Reaction mechanism: The hydrogen on the benzene ring is protonated by sulfuric acid to generate an activated intermediate. The intermediate reacts with nitric acid to introduce a nitro group and form nitrobenzene.

[0056] (2) Step Two: Ortho-halogenation of nitrobenzene: Nitrobenzene reacts with HBr under the catalysis of AlBr3 to introduce a bromine atom to the ortho position to generate ortho-bromonitrobenzene. Reaction mechanism: The nitro group acts as a strong electron-withdrawing group, activating the ortho position and making it prone to electrophilic substitution reactions. AlBr3 helps generate Br⁺ for electrophilic attack to replace the hydrogen atom at the ortho position.

[0057] (3) Step Three: Para-phenyl substitution of ortho-bromonitrobenzene Ortho-bromonitrobenzene, phenylsodium (C6H5Na) is heated to an appropriate temperature in a polar solvent (such as DMF). Reaction mechanism: The nitro group acts as a strong electron-withdrawing group, activating the para position and making it prone to nucleophilic substitution reactions. The phenyl anion acts as a nucleophile, attacking the hydrogen atom at the para position, and a new C - C bond is formed after substitution.

[0058] (4) Step Four: Reaction with biphenol to form an ether bond: The above product, biphenol, and potassium carbonate are heated to an appropriate temperature in a polar solvent (such as DMF). Reaction mechanism: The bromine atom acts as a leaving group, and the phenoxide anion replaces it through a nucleophilic substitution reaction to form an ether bond.

[0059] (5) Step Five: Nitration of phenolic hydroxyl group: The above product, sodium nitrite (NaNO2), and concentrated hydrochloric acid (HCl) are stirred at low temperature (0 - 5 °C) to form the diazonium salt of phenol. The diazonium salt is heated under acidic conditions and undergoes a decomposition reaction to form nitrobenzene.

[0060] (6) Step Six: Reduction reaction of nitro group: The above nitro product is added with iron powder (Fe) and hydrochloric acid (HCl), and refluxed and heated in ethanol (EtOH). Two nitro groups are simultaneously reduced to amino groups. Reaction mechanism: The nitro group is converted to a nitroso group under acidic conditions and then reduced to an amino group by iron powder.

[0061] The following will provide examples combined with specific data, specific reaction processes, and specific reaction formulas to further expand the general and scope-related technical solutions of the present invention: Example 1

[0062] In this example, the polyimide resin containing a biphenyl structure has the following structure: , where n is an integer greater than 0.

[0063] The specific preparation method is as follows: S1: Under nitrogen protection, 14.08 g (0.04 mol) of biphenyl diamine and 200 mL of N,N-dimethylacetamide are added to a 500 mL reaction flask, stirred at room temperature. After the biphenyl diamine is completely dissolved, 11.92 g (0.04 mol) of biphenyl tetracarboxylic dianhydride (s-BPDA) is added, and then the solution is diluted to a weight percentage concentration of 10%, and stirred at room temperature for 24 hours to obtain a viscous polyamic acid solution; S2: Then, xylene is added to the polyamic acid solution, heated under reflux to remove water. After the water removal is completed, methanol is gradually added to the solution, and a powder precipitates. After filtration, washing, and drying, a polyimide resin powder is obtained.

[0064] The glass transition temperature of the obtained polyimide resin containing a biphenyl ring measured by DSC is 330 °C. The temperature at which the thermal degradation mass loss of the film prepared by the above method in an air environment is 5% measured by a thermogravimetric analyzer is 550 °C, and the lowest melt viscosity of the corresponding polyimide resin powder is about 7300 Pa·s (380 °C). Example 2

[0065] In this example, the polyimide resin containing a biphenyl structure has the following structure: , where n is an integer greater than 0.

[0066] The specific preparation method is as follows: S1: Under nitrogen protection, add 14.08 g (0.04 mol) of biphenyl diamine and 200 mL of N,N-dimethylacetamide into a 500 mL reaction flask, stir at room temperature. After the biphenyl diamine is completely dissolved, add 11.92 g (0.04 mol) of biphenyl tetracarboxylic dianhydride (s-BPDA), and then dilute the solution to a weight percentage concentration of 10%. Continue to stir at room temperature for 24 hours to obtain a viscous polyamic acid solution; S2: Then add xylene to the polyamic acid solution, heat under reflux to remove water. After the water removal is completed, gradually add methanol to the solution. Powders will precipitate. After filtration, washing, and drying, polyimide resin powders are obtained.

[0067] The glass transition temperature of the obtained biphenyl ring-containing polyimide resin measured by DSC is 322 °C. The temperature at which the thermogravimetric analyzer measures a 5% mass loss of the film prepared by the above method in an air environment is 548 °C. The minimum melt viscosity of the corresponding polyimide resin powder is about 6000 Pa·s (380 °C). Example 3

[0068] In this example, the biphenyl structure-containing polyimide resin has the following structure: , where n is an integer greater than 0.

[0069] S1: The specific preparation method is as follows: Under nitrogen protection, add 14.08 g (0.04 mol) of biphenyl diamine and 200 mL of N,N-dimethylacetamide into a 500 mL reaction flask, stir at room temperature. After the biphenyl diamine is completely dissolved, add 11.92 g (0.04 mol) of isomeric biphenyl tetracarboxylic dianhydride (a-BPDA), and then dilute the solution to a weight percentage concentration of 10%. Continue to stir at room temperature for 24 hours to obtain a viscous polyamic acid solution; S2: Then add xylene to the polyamic acid solution, heat under reflux to remove water. After the water removal is completed, gradually add methanol to the solution. Powders will precipitate. After filtration, washing, and drying, polyimide resin powders are obtained.

[0070] The glass transition temperature of the obtained biphenyl ring-containing polyimide resin measured by DSC is 353 °C. The temperature at which the thermogravimetric analyzer measures a 5% mass loss of the film prepared by the above method in an air environment is 540 °C. The minimum melt viscosity of the corresponding polyimide resin powder is about 5200 Pa·s (380 °C).

[0071] This is mainly because a-BPDA has a non-planar twisted structure. In comparison, the obtained polymer has a higher glass transition temperature and a lower melt viscosity. Example 4

[0072] In this embodiment, the polyimide resin containing a biphenyl structure has the following structure: , where n is an integer greater than 0.

[0073] The specific preparation method is as follows: S1: Under nitrogen protection, 14.08 g (0.04 mol) of biphenyl diamine and 200 ml of N,N-dimethylacetamide are added to a 500 mL reaction flask, stirred at room temperature. After the biphenyl diamine is completely dissolved, 11.92 g (0.04 mol) of isomeric biphenyltetracarboxylic dianhydride (a-BPDA) is added, and then the solution is diluted to a weight percentage concentration of 10%, and stirring is continued at room temperature for 24 hours to obtain a viscous polyamic acid solution; S2: Then, xylene is added to the polyamic acid solution, heated under reflux to remove water. After the water removal is completed, methanol is gradually added to the solution, powder precipitates, and after filtration, washing, and drying, polyimide resin powder is obtained.

[0074] The glass transition temperature of the obtained polyimide resin containing a biphenyl ring measured by DSC is 342 °C. The temperature at which the mass loss of the film prepared by the above method is 5% under air environment by thermogravimetric analyzer is 543 °C, and the minimum melt viscosity of the corresponding polyimide resin powder is about 4200 Pa·s (380 °C). Example 5

[0075] In this embodiment, the polyimide resin containing a biphenyl structure has the following structure: , where n is an integer greater than 0.

[0076] The specific preparation method is as follows: S1: Under nitrogen protection, 16.32 g (0.04 mol) of biphenyl diamine and 200 ml of N,N-dimethylacetamide are added to a 500 mL reaction flask, stirred at room temperature. After the biphenyl diamine is completely dissolved, 11.92 g (0.04 mol) of isomeric biphenyltetracarboxylic dianhydride (a-BPDA) is added, and then the solution is diluted to a weight percentage concentration of 10%, and stirring is continued at room temperature for 24 hours to obtain a viscous polyamic acid solution; S2: Then, xylene is added to the polyamic acid solution, heated under reflux to remove water. After the water removal is completed, methanol is gradually added to the solution, powder precipitates, and after filtration, washing, and drying, polyimide resin powder is obtained.

[0077] The glass transition temperature of the obtained polyimide resin containing biphenyl rings measured by DSC was 318 °C. The temperature at which the thermodegradation mass loss of the film prepared by the above method was 5% in an air environment measured by a thermogravimetric analyzer was 524 °C. The minimum melt viscosity of the corresponding polyimide resin powder was approximately 5430 Pa·s (380 °C). Example 6

[0078] In this example, the polyimide resin containing a biphenyl structure has the following structure: , where n is an integer greater than 0.

[0079] The specific preparation method is as follows: S1: Under nitrogen protection, 14.08 g (0.04 mol) of benzidine diamine and 200 ml of N,N-dimethylacetamide were added to a 500 mL reaction flask, stirred at room temperature. After the benzidine diamine was completely dissolved, 8.724 g (0.04 mol) of pyromellitic dianhydride (PMDA) was added, and then the solution was diluted to a weight percentage concentration of 10%, and stirring was continued at room temperature for 24 hours to obtain a viscous polyamic acid solution; S2: Then, xylene was added to the polyamic acid solution, and the mixture was heated under reflux to remove water. After the water removal was completed, methanol was gradually added to the solution, and a powder precipitated. After filtration, washing, and drying, a polyimide resin powder was obtained.

[0080] The glass transition temperature of the obtained polyimide resin containing biphenyl rings measured by DSC was 350 °C. The temperature at which the thermodegradation mass loss of the film prepared by the above method was 5% in an air environment measured by a thermogravimetric analyzer was 554 °C. The minimum melt viscosity of the corresponding polyimide resin powder was approximately 9000 Pa·s (380 °C). Example 7

[0081] In this example, the polyimide resin containing a biphenyl structure has the following structure: , where n is an integer greater than 0.

[0082] The specific preparation method is as follows: S1: Under nitrogen protection, 14.08 g (0.04 mol) of benzidine diamine and 200 ml of N,N-dimethylacetamide were added to a 500 mL reaction flask, stirred at room temperature. After the benzidine diamine was completely dissolved, 8.724 g (0.04 mol) of pyromellitic dianhydride (PMDA) was added, and then the solution was diluted to a weight percentage concentration of 10%, and stirring was continued at room temperature for 24 hours to obtain a viscous polyamic acid solution; S2: Then, xylene is added to the polyamic acid solution, and the mixture is heated under reflux to remove water. After the water removal is completed, methanol is gradually added to the solution, and a powder precipitates. After filtration, washing, and drying, polyimide resin powder is obtained.

[0083] The glass transition temperature of the obtained polyimide resin containing biphenyl rings measured by DSC is 343 °C. The temperature at which the thermogravimetric analyzer measures a 5% mass loss of the film prepared by the above method in an air environment is 550 °C. The minimum melt viscosity of the corresponding polyimide resin powder is approximately 8400 Pa·s (380 °C). Example 8

[0084] In this example, the polyimide resin containing a biphenyl structure has the following structure: , where n is an integer greater than 0.

[0085] The specific preparation method is as follows: S1: Under nitrogen protection, 14.08 g (0.04 mol) of benzidine and 200 mL of N,N-dimethylacetamide are added to a 500 mL reaction flask and stirred at room temperature. After the benzidine is completely dissolved, 8.724 g (0.04 mol) of pyromellitic dianhydride (PMDA) is added, and then the solution is diluted to a weight percentage concentration of 10%. Stirring is continued at room temperature for 24 hours to obtain a viscous polyamic acid solution. S2: Then, xylene is added to the polyamic acid solution, and the mixture is heated under reflux to remove water. After the water removal is completed, methanol is gradually added to the solution, and a powder precipitates. After filtration, washing, and drying, polyimide resin powder is obtained.

[0086] The glass transition temperature of the obtained polyimide resin containing biphenyl rings measured by DSC is 338 °C. The temperature at which the thermogravimetric analyzer measures a 5% mass loss of the film prepared by the above method in an air environment is 550 °C. The minimum melt viscosity of the corresponding polyimide resin powder is approximately 7800 Pa·s (380 °C). Example 9

[0087] In this example, the polyimide resin containing a biphenyl structure has the following structure: , where n is an integer greater than 0.

[0088] The specific preparation method is as follows: S1: Under nitrogen protection, add 16.32 g (0.04 mol) of biphenyl diamine and 200 mL of N,N-dimethylacetamide into a 500 mL reaction flask, stir at room temperature. After the biphenyl diamine is completely dissolved, add 12.4 g (0.04 mol) of 4,4'-oxydiphthalic anhydride (ODPA), then dilute the solution to a weight percentage concentration of 10%, and continue to stir at room temperature for 24 hours to obtain a viscous polyamic acid solution; S2: Then add xylene to the polyamic acid solution, heat under reflux to remove water. After the water removal is completed, gradually add methanol to the solution. Powders will precipitate out. After filtration, washing, and drying, polyimide resin powders are obtained.

[0089] DSC measurement shows that the glass transition temperature of the obtained biphenyl ring-containing polyimide resin is 300 °C. The temperature at which the thermogravimetric analyzer measures a 5% mass loss of the film prepared by the above method in an air environment is 545 °C, and the minimum melt viscosity of the corresponding polyimide resin powder is about 5200 Pa·s (380 °C).

[0090] In this example, the biphenyl structure-containing polyimide resin has the following structure: , where n is an integer greater than 0.

[0091] The specific preparation method is as follows: S1: Under nitrogen protection, add 16.32 g (0.04 mol) of biphenyl diamine and 200 mL of N,N-dimethylacetamide into a 500 mL reaction flask, stir at room temperature. After the biphenyl diamine is completely dissolved, add 12.4 g (0.04 mol) of 4,4'-oxydiphthalic anhydride (a-ODPA), then dilute the solution to a weight percentage concentration of 10%, and continue to stir at room temperature for 24 hours to obtain a viscous polyamic acid solution; S2: Then add xylene to the polyamic acid solution, heat under reflux to remove water. After the water removal is completed, gradually add methanol to the solution. Powders will precipitate out. After filtration, washing, and drying, polyimide resin powders are obtained.

[0092] DSC measurement shows that the glass transition temperature of the obtained biphenyl ring-containing polyimide resin is 318 °C. The temperature at which the thermogravimetric analyzer measures a 5% mass loss of the film prepared by the above method in an air environment is 542 °C, and the minimum melt viscosity of the corresponding polyimide resin powder is about 4400 Pa·s (380 °C).

[0093] Comparative Example 1: In this comparative example, the polyimide resin is VSPEL® SP-1 of DuPont Company in the United States with a PMDA / ODA structure, and the specific structure is as follows: , The specific preparation method is as follows: S1: Under nitrogen protection, 8 g (0.04 mol) of 4,4'-diaminodiphenyl ether and 200 mL of N,N-dimethylacetamide are added to a 500 mL reaction flask, stirred at room temperature. After the diamine containing biphenyl is completely dissolved, 8.724 g (0.04 mol) of pyromellitic dianhydride (PMDA) is added, and then the solution is diluted to a weight percentage concentration of 10%. Stir at room temperature for another 24 hours to obtain a viscous polyamic acid solution; S2: Then, xylene is added to the polyamic acid solution, and the mixture is heated under reflux to remove water. After the water removal is completed, a powder precipitates directly. After filtration, washing, and drying, a polyimide resin powder is obtained.

[0094] The glass transition temperature of the obtained polyimide resin containing biphenyl rings measured by DSC is 360 °C. The temperature at which the mass loss of the film prepared by the above method is 5% in an air environment measured by a thermogravimetric analyzer is 561 °C. At 380 °C, the polyimide resin powder cannot be plasticized and processed.

[0095] Through the verification of the above examples and the further comparison between the examples and the comparative examples, it is proved that the present invention provides a polyimide resin containing a biphenyl structure and its preparation method. The prepared polyimide resin containing a biphenyl structure has significant excellent properties. Specifically, by introducing the biphenyl structure, the thermal stability and mechanical properties of the polyimide resin are enhanced, enabling it to have a higher glass transition temperature (Tg) and better thermal degradation properties. In addition, the melt viscosity of the prepared resin is moderate, facilitating processing.

[0096] Compared with the polyimide resin with the PMDA / ODA structure used in Comparative Example 1, the polyimide resin with a biphenyl structure adopted in the present invention has significant differences in structure, which directly leads to different properties. Specifically, the polyimide resin in the examples forms an asymmetric diamine monomer by introducing a biphenyl structure and adopting the design of ether bond connection and benzene ring side groups in the diamine monomer. This structural design increases the free volume in the polymer chain and makes the resin have higher flexibility and better processing performance at high temperatures; in contrast, the polyimide resin with the PMDA / ODA structure in Comparative Example 1 is polymerized from symmetric diamine (4,4'-diaminodiphenyl ether) and dianhydride (pyromellitic dianhydride) monomers. Due to the high symmetry of this structure, the molecular arrangement of the polyimide resin is relatively regular and lacks sufficient free volume. This makes the flexibility and processability of the resin poor at high temperatures. Especially at high temperature conditions, its melt viscosity is too high, resulting in difficult processing. In addition, although the polyimide resin in Comparative Example 1 has a high glass transition temperature (360 °C) and good thermal stability, its processability in practical applications is limited, and the polyimide resin powder cannot be plasticized at 380 °C and cannot be further processed, restricting the scope of its practical applications; while the structure of the present invention by introducing biphenyl ring side groups and ether bond connection not only increases the free volume but also improves the flexibility of the resin, making it more adaptable to various molding processes during processing. In addition, the resin of the present invention still maintains a high glass transition temperature (300 °C - 350 °C), but due to its lower melt viscosity (between 4000 Pa·s and 15000 Pa·s), it has better operability during processing and can maintain good performance in high temperature environments.

[0097] All in all, it is precisely because the PMDA / ODA structure in Comparative Example 1 lacks the asymmetric design of the biphenyl structure and benzene ring side groups introduced in the present invention that leads to its poor processing performance at high temperatures and the problem of inability to be plasticized in practical applications. The present invention successfully solves this problem by increasing the free volume and optimizing the molecular structure, making the polyimide resin not only have excellent heat resistance at high temperatures but also have good processability, with a broader application prospect.

[0098] In the description of the present application, the descriptions with reference to the terms "one embodiment", "some embodiments", "in this embodiment", "specific examples", or "some examples", etc. mean that the specific features, structures, materials, or characteristics described in connection with the embodiment or example are included in at least one embodiment or example of the present application. In this specification, the schematic expressions of the above terms do not necessarily refer to the same embodiment or example. Moreover, the specific features, structures, materials, or characteristics described can be combined in a suitable manner in any one or more embodiments or examples. In addition, without contradiction, those skilled in the art can combine and combine the different embodiments or examples described in this specification and the features of different embodiments or examples.

[0099] As described above, it is only the specific implementation manner of the present application, but the protection scope of the present application is not limited thereto. Any changes or substitutions that can be easily thought of by those skilled in the art within the technical scope disclosed by the present application should be covered by the protection scope of the present application. Therefore, the protection scope of the present application should be subject to the protection scope of the claims.

Claims

1. A thermoplastic polyimide resin containing a biphenyl structure, characterized in that, It has the following structural formula: Wherein, Ar is a residue of a dianhydride monomer; n is an integer and n > 0; m is an integer and m ≥ 0; the horizontal lines "-" connecting to the benzene ring each represent that they can be connected to any one carbon atom of the benzene ring.

2. The thermoplastic polyimide resin containing a biphenyl structure according to claim 1, characterized in that The Ar is at least one of the following groups: Among them, each horizontal line "-" connecting the outside of each monomer to the benzene ring represents the bonding connection between the Ar group and the carbon atom in the repeating unit; each horizontal line "-" connecting the inside of each monomer to the benzene ring represents that it can be connected to any carbon atom on the benzene ring.

3. The thermoplastic polyimide resin containing a biphenyl structure according to claim 2, wherein The Ar is at least one of the following groups: Among them, each horizontal line "-" connecting the outside of each monomer to the benzene ring represents the bonding bond between the Ar group and the carbon atom in the repeating unit; each horizontal line "-" connecting the inside of each monomer to the benzene ring represents that it can be connected to any carbon atom on the benzene ring.

4. The thermoplastic polyimide resin containing a biphenyl structure according to claim 3, characterized in that, The Ar is at least one of the following groups: Among them, each horizontal line "-" connecting the outside of each monomer to the benzene ring represents the bonding link between the Ar group and the carbon atom in the repeating unit.

5. A method for preparing the thermoplastic polyimide resin containing a biphenyl structure according to any one of claims 1-4, characterized in that, It includes the following steps: A thermoplastic polyimide resin containing a biphenyl structure is obtained by polycondensation of a biphenyl diamine monomer and a dianhydride monomer.

6. The preparation method of the thermoplastic polyimide resin containing a biphenyl structure according to claim 5, characterized in that, The structural formula of the biphenyl diamine monomer is as follows: The structural formula of the dicarboxylic anhydride monomer is as follows: Wherein, Ar is a residue of a dianhydride monomer, and the Ar is at least one of the following groups: Among them, the horizontal line "-" connected to the benzene ring represents the bonding of the Ar group to the carbon atom; Among them, the horizontal line "-" connected to the benzene ring inside the monomer represents that it can be connected to any carbon atom of the benzene ring, m is an integer, and m≥0.

7. The preparation method of the thermoplastic polyimide resin containing a biphenyl structure according to claim 6, wherein, The structural formula of the biphenyl diamine monomer is one of the following structures: 。 8. The preparation method of the thermoplastic polyimide resin containing a biphenyl structure according to claim 7, characterized in that, The structural formula of the biphenyl diamine monomer is one of the following structures: 。 9. The preparation method of the thermoplastic polyimide resin containing a biphenyl structure according to claim 5, characterized in that, The preparation method includes the following steps: S1: Add the biphenyl diamine monomer to a polar aprotic solvent protected by gas, stir to completely dissolve it, and then add the dianhydride monomer, and stir and react to obtain a polyamic acid solution; S2: Prepare the polyamic acid solution obtained in step S1 into a polyimide film or a polyimide film powder resin by a thermal imidization method or a solution imidization method.

10. The preparation method of the thermoplastic polyimide resin containing a biphenyl structure according to claim 9, wherein, In step S1, the specific condition of the gas protection is nitrogen or inert gas protection, and the stirring reaction time is 8-24 hours. The polar aprotic solvent is one of N,N'-dimethylformamide, N,N'-dimethylacetamide or N'-methylpyrrolidone; in step S2, the azeotropic water-carrying agent in the solution imidization method is one or two of toluene, xylene or chlorotoluene.

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