Process for the preparation of polyaryletherketone resins

Abstract

This invention relates to the field of high-performance thermoplastic composite materials, and in particular to a method for preparing polyaryletherketone resin. The method includes the following steps: under a non-oxidizing atmosphere, a dihydroxy aromatic monomer containing a bisphenol structure, a dihalogenated aromatic monomer containing a nitrile group, and a dihalogenated aromatic ketone monomer containing a difluorine substituted group are reacted in a polar solvent system with a boiling point above 150°C in the presence of an alkali metal carbonate to form the corresponding phenolate; an aromatic hydrocarbon dehydrating agent is added to the system for azeotropic dehydration to remove water generated during the reaction and promote the formation of the phenolate; a nucleophilic substitution polycondensation reaction is carried out at a higher temperature; during the polycondensation reaction, a capping agent is added to regulate the end-chain structure and molecular weight distribution, wherein the capping agent is 2,4′-difluorobenzophenone; after the reaction is completed, the reaction product is separated and purified to obtain the polyaryletherketone resin.

Description

TECHNICAL FIELD

[0001] The present application relates to the field of high-performance thermoplastic composites, in particular to a preparation method of polyaryletherketone resin. BACKGROUND

[0002] Polyaryletherketone resins are widely used in aerospace, rail transportation and high-end equipment manufacturing due to their excellent heat resistance, chemical corrosion resistance and mechanical properties, and play an important role in continuous fiber reinforced thermoplastic composite systems. With the development of composites towards lightweight and high performance, prepreg as a key intermediate material puts forward higher requirements on the processability, interface adaptability and cost control of the matrix resin. However, the existing polyaryletherketone system still has some deficiencies in resin itself, prepreg preparation, interface performance and synthesis process, etc.

[0003] Firstly, from the performance of the resin itself, the traditional polyaryletherketone resin has high molecular chain rigidity and high crystallinity, and poor solubility, which makes it difficult to form a stable, uniform and suitable viscosity resin solution in conventional organic polar solvents, limiting its application in solution prepreg process. Although some systems can be dissolved, the solution viscosity window is narrow and the storage stability is insufficient, which makes it difficult to meet the requirements of industrial continuous impregnation process.

[0004] Secondly, in the preparation of prepreg, due to the limitation of resin solubility and rheological properties, the existing technology often relies on melt impregnation or high temperature and high pressure equipment, which has a narrow process window, high energy consumption and high equipment investment and operation cost. At the same time, the uniformity of resin impregnation in the fiber bundle is difficult to control, which easily leads to the fluctuation of prepreg quality and further increases the preparation cost.

[0005] Thirdly, in terms of the interface performance of composites, the interfacial bonding strength between polyaryletherketone matrix and reinforcing fibers still has room for improvement. The existing systems often improve the interface through surface treatment or coupling agent, but the research on optimizing the resin molecular structure and end group control is relatively limited, and the interfacial bonding strength and long-term service reliability still have room for improvement.

[0006] In addition, in terms of synthesis process and cost control, the traditional polycondensation process has strict requirements on water control, and improper control of water removal process can affect the molecular weight distribution and product consistency; at the same time, some process flow is relatively complex, and the recycling rate of solvent system is not high, which increases the production cost and environmental burden, and is not conducive to large-scale and sustainable production.

[0007] Therefore, it is necessary to make systematic improvements on the existing polyaryletherketone polycondensation technology, focusing on monomer salt formation and dehydration control, selection and timing of capping agent addition, composition of alkali system, and optimization of solvent system, in order to obtain polyaryletherketone resin with controllable molecular weight distribution, good solubility, improved interfacial compatibility, and facilitate solvent recycling, so as to better meet the comprehensive requirements for the preparation of high-performance prepregs and their composites. Summary of the Invention

[0008] This invention covers the following technical solutions: One aspect of the present invention relates to a method for preparing a polyaryletherketone resin, comprising the following steps: In a non-oxidizing atmosphere, dihydroxy aromatic monomers containing bisphenol structures, dihalo aromatic monomers containing nitrile groups, and dihalo aromatic ketone monomers containing difluorine substitution are placed in a polar solvent system with a boiling point above 150°C in the presence of alkali metal carbonates to form corresponding phenolic salts. An aromatic dehydrating agent is added to the system for azeotropic dehydration to remove the water generated during the reaction and promote the formation of the phenolate. The nucleophilic substitution polycondensation reaction is carried out by heating. When the viscosity of the system increases during the polycondensation reaction, a capping agent is added to regulate the end structure and molecular weight distribution of the molecular chain. The capping agent is 2,4′-difluorobenzophenone. After the reaction is completed, the reaction product is separated and purified to obtain the polyaryletherketone resin.

[0009] Another aspect of the present invention relates to a polyaryletherketone resin, which is obtained by the preparation method described above.

[0010] Another aspect of the present invention relates to a resin solution comprising, as described above, a polyaryletherketone resin and an organic polar solvent, wherein the resin has a mass fraction of 20% to 40%.

[0011] Another aspect of the present invention relates to a prepreg comprising reinforcing fibers and a resin matrix layer formed by impregnation and drying of a resin solution as described above.

[0012] This invention utilizes specific aromatic dehydrating agents for azeotropic dehydration, which improves the salt formation efficiency of dihydroxy monomers and reduces residual moisture in the system. This promotes uniform polycondensation, reduces side reactions, and stabilizes the molecular weight growth process. Simultaneously, by introducing specific end-capping agents during the viscosity-increasing stage of the polycondensation reaction, the structure at the molecular chain ends is controlled, enabling manageable adjustment of molecular weight and molecular weight distribution. This improves the resin's solubility and processing adaptability, thereby enhancing the stability and consistency of the solution processing method. Attached Figure Description

[0013] To more clearly illustrate the specific embodiments of the present invention or the technical solutions in the prior art, the drawings used in the description of the specific embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are some embodiments of the present invention. For those skilled in the art, other drawings can be obtained from these drawings without creative effort.

[0014] Figure 1 Test results for different capping agents: A. DSC test; B. TGA test; C. DHR test.

[0015] Figure 2 PEK-CN resins with different end-capping agents applied after molding; the left side is 4-fluorobenzophenone-capped (dark in color and more brittle); the right side is 2,4′-difluorobenzophenone-capped.

[0016] Figure 3 Test results for different water-carrying agents: A. DSC test; B. TGA test; C. DHR test. Detailed Implementation

[0017] Reference will now be made to detailed embodiments of the present invention, one or more of which are described below. Each example is provided for explanation and not for limitation of the invention. In fact, it will be apparent to those skilled in the art that various modifications and variations can be made to the invention without departing from its scope or spirit. For example, features described or illustrated as part of one embodiment may be used in another embodiment to produce further embodiments.

[0018] Unless otherwise stated, all terms used to disclose this invention (including technical and scientific terms) should be understood as having the meaning commonly understood by one of ordinary skill in the art to which this invention pertains. The terminology used herein is for the purpose of describing specific embodiments only and is not intended to limit the scope of protection of this invention. Unless the context clearly defines otherwise, the scientific and technical terms used herein, as well as terms and laboratory procedures in related fields such as polymer chemistry and polymer physics, physical chemistry and solution chemistry, materials science and composite materials engineering, chemical engineering and process engineering, and structure-property relationships and application engineering, are all conventional terms and standard methods well-known and widely used in the art. To facilitate understanding of the technical solutions of this invention, some related terms are further defined and explained below.

[0019] The terms “containing,” “comprising,” and “including” as used in this invention are synonyms and are inclusive or open-ended, not excluding additional, uncited members, elements, or method steps.

[0020] In this invention, the numerical range represented by endpoints includes all numerical values ​​and fractions contained within that range, as well as the endpoints mentioned.

[0021] Furthermore, in describing representative embodiments of the invention, this specification may present the methods and / or processes of the invention as a specific sequence of steps. However, the method or process should not be limited to the specific order of the steps described herein, to the extent that the method or process does not depend on the specific order of the steps presented herein. As will be understood by those skilled in the art, other sequences of steps are also possible. Therefore, the specific order of steps presented in the specification should not be construed as a limitation of the claims. Additionally, the claims relating to the methods and / or processes of the invention should not be limited to the execution of their steps in the order they are written, and those skilled in the art will readily recognize that the sequence can be changed while still remaining within the spirit and scope of the invention.

[0022] This invention relates to concentration values, which include fluctuations within a certain range. For example, fluctuations are allowed within a corresponding precision range. For instance, 2% can fluctuate within ±0.1%. For larger values ​​or values ​​that do not require overly precise control, even greater fluctuations are permitted.

[0023] As used in this invention, unless otherwise stated, the singular forms of the articles “a,” “an,” and “the” include plural referents.

[0024] In this invention, the terms "multiple" or "various" are used unless otherwise specified, referring to a quantity greater than or equal to 2.

[0025] In this invention, the technical features described in an open-ended manner include both closed-ended technical solutions composed of the listed features and open-ended technical solutions that include the listed features.

[0026] In this invention, terms such as "preferred," "better," "more suitable," and "ideal" merely describe implementation methods or embodiments with better effects and should be understood not to limit the scope of protection of this invention. In this invention, terms such as "optionally," "optionally," and "optional" mean that something is optional, that is, selected from either "with" or "without" a parallel solution. If multiple "optional" statements appear in a technical solution, unless otherwise specified and without contradiction or mutual constraint, each "optional" statement is independent.

[0027] In this invention, "polyaryletherketone resin" refers to a thermoplastic polymer material whose main chain is formed by alternating or repeating ether bonds (–O–) and ketone bonds (–CO–) through an alternating or repeating connection of aromatic ring structures. It is prepared by nucleophilic aromatic substitution polycondensation reaction between aromatic dihydroxy monomers and aromatic dihalogenated monomers. The polymer can be a random structure or a partially ordered structure, and its molecular chain ends can contain aromatic ketone structural units introduced by end-capping agents.

[0028] In this invention, "dihydroxy aromatic monomer" refers to an aromatic compound containing two phenolic hydroxyl groups in its molecular structure, which can be selected from bisphenol A, bisphenol S, phenolphthalein or other bisphenol compounds with similar structures; when the dihydroxy aromatic monomer contains phenolphthalein, its dosage can be moderately excessive relative to the theoretical equivalent to regulate the molecular chain growth behavior.

[0029] In this invention, "a dihalogenated aromatic monomer containing a nitrile group" refers to an aromatic compound whose molecular structure simultaneously contains a nitrile group and two halogen substituents capable of nucleophilic substitution reactions, wherein the halogen is preferably a fluorine atom; "a dihalogenated aromatic ketone monomer containing difluorine substitution" refers to an aromatic compound whose molecular structure contains a ketone group and two fluorine substituents on the aromatic ring.

[0030] In this invention, "non-oxidizing atmosphere" refers to atmospheric conditions that can prevent oxidation side reactions from occurring in the reaction system, including but not limited to inert gas atmosphere, low oxygen atmosphere or vacuum conditions.

[0031] In this invention, "aromatic dehydrating agent" refers to an aromatic hydrocarbon solvent that can form an azeotropic system with water and is used to remove water during the reaction process.

[0032] In this invention, "end-capping agent" refers to a monomeric compound used to regulate the end structure and molecular weight distribution of polymer molecular chains during the polycondensation reaction.

[0033] In this invention, the "system viscosity increase stage" refers to the stage in which the rheological resistance of the system increases significantly due to the growth of molecular chains during the polycondensation reaction. It can be characterized by intrinsic viscosity, solution viscosity or other equivalent methods.

[0034] In this invention, "melt flowability" refers to the comprehensive rheological behavior characteristics exhibited by polyaryletherketone resin within the actual processing temperature range. It is not solely evaluated based on the melt viscosity at a single temperature point, but rather by comprehensively considering factors such as the resin's viscosity change trend during heating and shearing, viscosity retention capacity, shear thinning response characteristics, and the stability and tolerance of the processing window. The processing temperature range is typically the actual temperature range used in molding or hot pressing, such as 320℃ to 350℃. Within this range, the resin should be able to achieve sufficient flow and cavity filling under applied pressure, while avoiding defects such as flow runaway or edge overflow caused by excessively rapid viscosity decrease.

[0035] In this invention, "better melt flowability" or similar expressions specifically refer to the resin exhibiting a moderate viscosity level and a relatively gradual viscosity decrease trend within the stated processing temperature range. This means that its rheological response is controllable and stable during temperature increases or shear rate changes, thereby helping to broaden the molding process window, reduce the sensitivity of process parameter fluctuations to product quality, and improve the consistency and molding quality of molded products. This term does not aim for extremely low viscosity, but emphasizes achieving a balance between flowability and flow controllability.

[0036] In this invention, "prepreg" refers to an intermediate material formed by impregnating reinforcing fibers with the resin solution and then drying them, wherein the resin is distributed between the fibers as a matrix and is used for subsequent composite material molding.

[0037] In this invention, "reinforcing fiber" refers to a fibrous reinforcing material used to form a composite system with the polyaryletherketone resin to improve the mechanical properties and structural stability of the composite material. The reinforcing fiber can be a continuous fiber, chopped fiber, fabric, unidirectional tape, or multiaxial fabric structure, and its material includes, but is not limited to, carbon fiber, glass fiber, aramid fiber, basalt fiber, quartz fiber, and other inorganic or organic high-performance fibers. The reinforcing fiber can be surface-treated or untreated and may contain a surface coating or wetting agent system compatible with the polyaryletherketone resin.

[0038] This invention relates to a method for preparing polyaryletherketone resin, which includes the following steps: In a non-oxidizing atmosphere, dihydroxy aromatic monomers containing bisphenol structures, dihalo aromatic monomers containing nitrile groups, and dihalo aromatic ketone monomers containing difluorine substitution are placed in a polar solvent system with a boiling point above 150°C in the presence of alkali metal carbonates to form corresponding phenolic salts. An aromatic dehydrating agent is added to the system for azeotropic dehydration to remove the water generated during the reaction and promote the formation of the phenolate. The nucleophilic substitution polycondensation reaction is carried out by heating. When the viscosity of the system increases during the polycondensation reaction, a capping agent is added to regulate the end structure and molecular weight distribution of the molecular chain. The capping agent is 2,4′-difluorobenzophenone. After the reaction is completed, the reaction product is separated and purified to obtain the polyaryletherketone resin.

[0039] This invention introduces highly polar nitrile (–CN) structural units into the polyaryletherketone (PEEK) molecular chain, significantly increasing the polarity of the resin backbone. This enhances the physicochemical forces between the resin matrix and reinforcements such as carbon fibers, including improved wettability, strengthened intermolecular van der Waals forces, and potential interfacial interactions, thereby improving the interfacial bonding performance and load transfer efficiency of the composite material. Simultaneously, the introduction of nitrile groups modulates the intermolecular forces and chain stacking patterns to some extent, improving the resin's solubility in high-boiling-point polar solvents. Combined with the use of end-capping agents and dehydrating agents, this allows for the formation of stable, homogeneous resin solutions with suitable viscosity, overcoming the limitation of traditional PEEK resins being difficult to dissolve. This provides a technical basis for preparing prepregs using solution impregnation methods.

[0040] Furthermore, this invention innovatively selects structurally asymmetric 2,4′-difluorobenzophenone as the end-capping agent. Its asymmetric molecular structure introduces directional terminal groups after end-capping, influencing the chemical environment and chain segment stacking pattern at the polymer chain ends. This achieves a comprehensive optimization effect of lighter resin color, more suitable melt flow, and excellent solubility, while maintaining the intrinsic heat resistance and mechanical strength of the resin. This end-capping strategy helps improve the precision of molecular weight control and the stability of the processing window, and is one of the key technical factors for obtaining light-colored, high-performance polyaryletherketone resins with good solubility and processing characteristics, meeting the requirements of aerospace and other fields for material appearance and quality.

[0041] In this invention, aromatic dehydrating agents are used to effectively remove water from the system via azeotropic reaction in the early stages of polycondensation, thereby promoting the complete salt formation of dihydroxy aromatic monomers and improving reaction homogeneity. Preferably, the dehydrating agent should possess the characteristics of remaining liquid within the reaction temperature range, forming a stable azeotropic system with water, and having good compatibility with the main reaction solvent. Its boiling point should not be too low to avoid excessive volatilization during dehydration, which would affect the stability of the system; nor should it be too high to avoid increasing the burden on subsequent separation. Preferably, the dehydrating agent is a medium-to-high boiling point aromatic hydrocarbon solvent, typically an alkyl-substituted aromatic hydrocarbon, with a boiling point preferably above approximately 130°C, thereby ensuring effective dehydration while maintaining the thermal stability and operational safety of the reaction system.

[0042] In a preferred embodiment, the aromatic dehydrating agent is a C8-C10 alkyl-substituted aromatic hydrocarbon solvent, including benzene compounds having one or more methyl or ethyl substituents. More preferably, the aromatic dehydrating agent is selected from at least one of mesitylene, diethylbenzene, pseudotrimethylbenzene, and xylene, with mesitylene being a more preferred option. The selection of the above-mentioned dehydrating agent is beneficial for improving dehydration efficiency and reducing the residual moisture content of the system, thereby facilitating the stable progress of the polycondensation reaction and improving the molecular weight control of the final polymer.

[0043] The timing of the addition of the end-capping agent has a significant impact on the molecular weight control and molecular weight distribution optimization of polyaryletherketone resins. Adding the end-capping agent too early may limit molecular chain growth, resulting in a lower final molecular weight; adding it too late may lead to an excessively high molecular weight, affecting processing performance and rheological stability. Therefore, introducing the end-capping agent when the polycondensation reaction has progressed to a certain intrinsic viscosity range is beneficial for achieving effective termination of molecular chain growth, thus balancing molecular weight level and distribution uniformity. In some embodiments, the end-capping agent is added when the polycondensation reaction has progressed to a system intrinsic viscosity of 0.6 dL / g to 1.2 dL / g (e.g., 0.8 dL / g, 1.0 dL / g).

[0044] More preferably, the amount of end-capping agent added is 0.1 mol% to 5 mol% (e.g., 0.5 mol%, 1 mol%, 2 mol%, 3 mol%, 4 mol%) of the molar amount of the dihydroxy aromatic monomer. Within this range, effective control of the molecular chain end structure can be achieved, which is beneficial for obtaining polyaryletherketone resins with a narrow molecular weight distribution, suitable melt flowability, and good solubility.

[0045] A polar solvent system with a boiling point above 150°C is used to dissolve monomers, maintain homogeneous polycondensation, and ensure the reaction system remains in a stable liquid phase at higher temperatures. The solvent should have a high boiling point and good polarity to prevent significant volatilization within the polycondensation temperature range, while simultaneously dissolving the generated phenolates and some of the polymer, thereby promoting uniform chain growth and preventing localized gelation or precipitation. Preferably, the polar solvent with a boiling point above 150°C is selected from at least one of N-methylpyrrolidone, dimethylacetamide, dimethylformamide, diphenyl sulfone, and sulfolane.

[0046] Alkali metal carbonates are used to form corresponding phenolic salts from dihydroxy aromatic monomers and to provide an alkaline environment for subsequent nucleophilic substitution polycondensation reactions. In some embodiments, the alkali metal carbonate is selected from at least one of potassium carbonate, sodium carbonate, or cesium carbonate. In a more preferred embodiment, the alkali metal carbonate is a composite salt containing sodium carbonate and potassium carbonate. More preferably, the mass ratio of sodium carbonate to potassium carbonate is (40-60):1, for example, 45:1, 50:1, or 55:1. Under the above composite salt system conditions, combined with a preferred aromatic dehydrating agent for azeotropic dehydration, the system dehydration efficiency can be improved, the reaction time shortened, and the adverse effects of residual moisture on the polycondensation reaction can be reduced, thereby promoting more regular molecular chain growth. The composite salt system, along with the timing of the addition of the aforementioned end-capping agent and the monomer ratio, synergistically contributes to obtaining polyaryletherketone resins with a more concentrated molecular weight distribution, lighter color, and higher purity, while simultaneously improving the stability and production efficiency of the overall synthesis process.

[0047] Dihydroxy aromatic monomers are the main components for constructing the main chain structure of polyaryletherketones, and their molecular structure affects the chain rigidity, polarity distribution, and solubility of the polymer. In some embodiments, the dihydroxy aromatic monomer containing a bisphenol structure is selected from at least one of bisphenol A, bisphenol S, or phenolphthalein; More preferably, when the dihydroxy aromatic monomer contains phenolphthalein, the amount of phenolphthalein added is 2% to 4% excess relative to the theoretical equivalence, preferably 3% excess. This invention innovatively employs a non-equimolar addition strategy that appropriately exceeds the amount of phenolphthalein monomer. By actively and precisely controlling the excess ratio of phenolphthalein, excessive growth of the polymer molecular chain is gently limited, thereby achieving precise control over the final resin molecular weight and its distribution. This control helps improve the melt flow behavior of the resin, maintaining the material's heat resistance and mechanical properties while providing suitable processing fluidity to meet the process requirements of prepreg preparation and composite material molding. This excess ratio is an optimized equilibrium range obtained through systematic experimental screening, which is beneficial for achieving a synergistic effect between performance maintenance and processing adaptability.

[0048] The nitrile-containing dihaloaromatic monomers used in this invention are employed to introduce nitrile structural units into the polyarylether ketone backbone, thereby enhancing the polarity of the molecular chain and improving interfacial compatibility. Furthermore, the monomer can be a nitrile-substituted difluoroaromatic compound, i.e., introducing a nitrile group onto a benzene ring or biphenyl structure, and introducing two fluorine substituents onto the same or adjacent aromatic rings, thus achieving effective nitrile group insertion while ensuring reactivity.

[0049] In some embodiments, the nitrile-containing dihaloaromatic monomer is a nitrile-substituted difluoro / chlorobenzene compound or a nitrile-substituted difluoro / chlorobenzophenone compound.

[0050] In some embodiments, the nitrile-containing dihaloaromatic monomer is 2,6-dichlorobenzonitrile or 4,4′-difluorobenzophenone nitrile.

[0051] The above structure forms symmetrical or nearly symmetrical active sites on the aromatic ring, which is conducive to effective nucleophilic substitution reaction with phenol salts under alkaline conditions, and stably introduces nitrile groups into the polymer backbone. This improves the solubility and processing performance of the resin and the interfacial compatibility of the composite material while maintaining the resin's heat resistance and mechanical properties.

[0052] According to another aspect of the present invention, there is a polyaryletherketone resin obtained by the preparation method described above.

[0053] By introducing nitrile units into its molecular chain structure and regulating it with a specific end-capping agent, the resin exhibits both a high molecular weight and good solubility and processing properties. Preferably, the weight-average molecular weight of the resin is 2 × 10⁻⁶. 4 ~6×10 4 The molecular weight distribution index is 1.5 to 2.5. Within this range, it is beneficial to balance mechanical properties and processing fluidity, and avoid performance fluctuations caused by insufficient melt fluidity or excessively wide distribution due to excessively high molecular weight.

[0054] Preferably, when the resin contains 30% N-methylpyrrolidone by mass, it can form a homogeneous and transparent solution at 25°C, and the dissolution time does not exceed 60 minutes. More preferably, in the 30% mass fraction solution state, the apparent viscosity measured by a rotational rheometer at 25°C is 1–10 Pa·s. These solubility and viscosity windows are beneficial for meeting the requirements for resin wettability and rheological stability during the preparation of solution-based prepregs.

[0055] Furthermore, preferably, the resin solution does not produce obvious gel or precipitates after being stored in a sealed environment at 25°C for 7 days, indicating that it has good solution stability and storage stability, which is beneficial to improving the continuity and process consistency of the prepreg production process.

[0056] According to another aspect of the invention, there is a resin solution comprising the polyaryletherketone resin as described above and an organic polar solvent, wherein the resin has a mass fraction of 20% to 40%.

[0057] The organic polar solvent should possess strong dissolving power and good thermal stability, capable of dissolving the polyaryletherketone resin at room temperature or under moderate heating conditions, and maintaining stable rheological properties during the solution-based prepreg preparation process. Preferably, the organic polar solvent is a high-boiling-point polar solvent, typically with a boiling point above 150°C, capable of controlled volatilization during prepreg drying without triggering resin degradation or precipitation.

[0058] Preferably, the organic polar solvent is selected from at least one of N-methylpyrrolidone, dimethylacetamide, dimethylformamide, dimethyl sulfoxide, sulfolane, and diphenyl sulfone, or a combination of two or more thereof. The above solvents have good compatibility with the polyaryletherketone resin, which is beneficial for forming a uniform and transparent resin solution and provides a suitable solution viscosity window at a mass fraction of 20%–40%, thereby meeting the requirements of the reinforcing fiber impregnation and subsequent prepreg preparation processes. Within this concentration range, the resin solution has suitable rheological properties and wetting ability, enabling sufficient impregnation of the reinforcing fibers at room temperature or under moderate heating conditions, which is beneficial for improving the uniformity of resin distribution within the fiber bundle and reducing dry spots and porosity defects.

[0059] Meanwhile, the resin solution has good storage stability and batch consistency, making it suitable for continuous and large-scale prepreg production processes, which helps to reduce manufacturing costs and improve production efficiency.

[0060] The present invention also relates to a prepreg comprising reinforcing fibers and a resin matrix layer formed by impregnation and drying of a resin solution as described above.

[0061] Due to the introduction of nitrile groups into the resin molecular structure and specific end-capping regulation, the resulting prepreg maintains high heat resistance and mechanical properties while exhibiting good interfacial bonding performance and processing fluidity. This facilitates full wetting and densification during subsequent hot pressing or automated lay-up molding processes. The prepreg is suitable for preparing high-strength, high-modulus, and high-temperature-resistant composite structural components, particularly suitable for aerospace applications where weight, strength, and long-term service stability are critical.

[0062] The embodiments of the present invention will be described in detail below with reference to examples. It should be understood that these examples are only used to illustrate the technical content of the present invention and are not intended to limit the scope of protection of the present invention. Unless otherwise specified, the specific experimental conditions in the following examples should be referred to the guidelines given in this specification, or implemented according to generally accepted experimental manuals or conventional experimental conditions, or other experimental methods known in the art, or according to the conditions recommended by the relevant reagent or instrument manufacturers. In specific embodiments, unless otherwise specified, minor deviations within the weighing accuracy range are allowed for the measurement parameters involving raw material components; reasonable deviations due to instrument detection accuracy or operational accuracy are also allowed for parameters such as temperature and time.

[0063] Example 1: Synthesis of PEK-CN resin with different end-capping agents (1) Raw materials and proportions: The total monomer input was 0.15 mol.

[0064] Phenolphthalein: 49.18 g (molar amount, calculated as 3% excess) 2,6′-Dichlorobenzonitrile (DCBN): 18.06 g 4,4'-Difluorobenzophenone (DFK): 9.82 g Compound salt: 15.90 g of anhydrous sodium carbonate (Na2CO3), 0.32 g of potassium carbonate (K2CO3) (mass ratio ~50:1) Water-removing agent: Xylene, 80 mL Solvent: Sulfolane Capping agents: 4-fluorobenzophenone, 0.6 g; 2,4′-difluorobenzophenone, 0.65 g (approximately 0.003 mol) (2) Synthesis steps: Assembly: Assemble a mechanical stirrer, water separator, condenser and nitrogen inlet tube on a 500 mL three-necked flask.

[0065] Feeding and Dehydration: Add phenolphthalein, DCBN, DFK, compound salt, sulfolane, and xylene sequentially. Purge with high-purity nitrogen for protection, start stirring, and slowly heat to 180°C. Perform the azeotropic dehydration reaction at this temperature for approximately 2 hours, until no water droplets are separated from the separator.

[0066] Polymerization: The temperature of the reaction system was raised to 220℃ and the reaction was continued to be stirred for 1.5 hours. The viscosity of the system increased significantly.

[0067] End cap: ① Quickly add the weighed 2,4′-difluorobenzophenone end-capping agent through a feeding funnel, and continue the reaction at 220℃ for 1.5 hours.

[0068] ② Quickly add the weighed 4-fluorobenzophenone end-capping agent through a feeding funnel, and continue the reaction at 220°C for 1.5 hours.

[0069] Termination and Post-treatment: After the reaction was completed, heating was stopped. While still hot, the viscous polymer melt was slowly poured into a deionized water / ethanol (3:1 v / v) mixture under high-speed stirring to obtain a white fibrous precipitate. The precipitate was crushed, washed several times with boiling water, then washed with ethanol, and finally dried in a vacuum oven at 150°C for 12 hours to obtain a light ivory-white powder.

[0070] (3) Performance test results are as follows Figures 1-2 , and as shown in the table below.

[0071] Table 1: Thermal Properties of PEK-CN Resins with Different End-Capping Agents

[0072] Table 2: Molecular weight test of PEK-CN resin with different end-capping agents

[0073] Table 3: Mechanical property test of PEK-CN resin with different end-capping agents (taking the resin film with a thickness of 100 μm after molding as the test object)

[0074] As can be seen from the above results, when 2,4'-difluorobenzophenone is used as the end-capping agent, the glass transition temperature and thermal decomposition temperature of the material are both increased. It is particularly noteworthy that the melt rheological behavior ( Figure 1 in C and the data in Table 1): Although the high-temperature end-point viscosities of the two end-capping agents are similar at 380 °C, significant differences are shown in the key molding processing temperature range of 320 - 350 °C. The resin capped with 2,4'-difluorobenzophenone shows a more gentle viscosity decrease in the whole temperature range, showing a more stable temperature-dependent rheological response, which is beneficial to broaden the molding process window and reduce the risk of bleeding; it maintains an appropriate viscosity of 5300 Pa·s at 340 °C, ensuring that the resin can flow fully and fill the cavity evenly at the initial stage of molding. While the viscosity of the resin capped with 4-fluorobenzophenone has dropped to 4000 Pa·s at 340 °C, and the viscosity decrease rate from 320 °C to 340 °C is significantly faster, showing excessive shear thinning behavior.

[0075] It should be emphasized that for the molding process, the temperature dependence of the resin viscosity is more critical than the absolute viscosity value. Too fast viscosity decrease will lead to: the resin flows too violently inside the cavity and is difficult to control; under high pressure, the resin is easy to bleed from the corners of the mold, causing material loss and product defects; the processing window becomes narrower and is more sensitive to the fluctuations of process parameters.

[0076] Therefore, although the resin capped with 2,4'-difluorobenzophenone has a higher "apparent" viscosity value, it shows better rheological stability and process tolerance in actual processing, which is exactly the technical connotation of "better melt fluidity" emphasized in this invention in the molding process. Combining its advantage of being more easily dissolved in DMAc solvent to form a stable colloidal solution (specific viscosity 0.53 dL / g), this resin has comprehensive processing advantages in the preparation of prepregs by solution method and subsequent molding.

[0077] As can be seen from the above results, when 2,4’-difluorobenzophenone is used as an asymmetric end-capping agent, the introduced terminal structure further promotes the regulatory effect of nitrile group dipole interaction. Compared with the 4-fluorobenzophenone end-capping system, the glass transition temperature, initial decomposition temperature and 5% thermal decomposition temperature of the material are all increased. It shows a certain degree of optimization while maintaining the original heat resistance performance.

[0078] Regarding rheological behavior, the two systems exhibit similar viscosities at the high-temperature endpoint. However, within the molding temperature range of 320–350°C, the viscosity of the resin of this invention decreases more gradually, demonstrating a more stable temperature-dependent rheological response. This is beneficial for broadening the molding process window and reducing the impact of processing fluctuations on product quality. Simultaneously, the lower specific viscosity measured in DMAc solvent facilitates the formation of a homogeneous and stable resin solution, thus benefiting the solution-based preparation of CF / PEK-CN prepreg.

[0079] In summary, the results show that by using 2,4′-difluorobenzophenone to regulate the end-chain structure and molecular weight distribution, the resin exhibits good processing adaptability in both solution processing and melt processing while maintaining the material's heat resistance and mechanical properties. Therefore, this end-capping system was selected as the subject of further research in subsequent experiments.

[0080] Example 2: Synthesis of PEK-CN resin with different dehydrating agents PEK-CN resin was synthesized under the same conditions, with the experimental conditions modified based on Example 1.

[0081] The water-removing agents selected were xylene / diethylbenzene / metrimethylbenzene / paraben, and the experimental results are as follows: Figure 3 As shown in Tables 5-7.

[0082] Table 4: Synthesis of PEK-CN resin with different water-removing agents

[0083] A copolymerization reaction was conducted using phenolphthalein in excess (3%) and a molar ratio of 2,6′-dichlorobenzonitrile to 4,4′-difluorobenzophenone of 7 / 3, with 2,4′-difluorobenzophenone as the end-capping agent. Xylene, diethylbenzene, mesitylene, and pseudotrimethylbenzene were used as dehydrating agents in the experiments, and the reactions were carried out at different reflux temperatures. The reflux temperature for xylene was controlled at 180℃, while the reflux temperatures for diethylbenzene, mesitylene, and pseudotrimethylbenzene were controlled at 190℃. All polymerization reactions were carried out at 220℃.

[0084] Xylene has significantly lower flash and boiling points than other dehydrating agents, posing a considerable experimental hazard under high-temperature reflux conditions. Furthermore, from an environmental protection perspective, xylene is classified as a Class A hazardous chemical, posing significant risks to human health and the environment. Experimental results showed a theoretical water yield of 2.7 ml (calculated based on the principle that one molecule of water is removed for each ether bond formed during the polycondensation reaction. Using a total monomer feed of 0.15 mol as a baseline, with equimolar reactions of dihydroxy and dihalogenated monomers, and complete participation of the phenolic hydroxyl group in the polycondensation, the theoretical water production is 0.15 mol, which translates to 2.7 mL in volume (water density 1 g / mL). Actual water yield is affected by factors such as salt formation efficiency and dehydration degree, and can be used as a reference indicator for reaction progress). However, the actual xylene recovery was only 2.2 ml, falling short of the theoretical value. This indicates that high-temperature reflux with added water can more effectively promote phenolphthalein salt formation, thus better facilitating the polymerization reaction. Further comparison of the recovered and added amounts of dehydrating agents revealed that only mesitylene met the normal recovery loss standard, while the remaining dehydrating agents, especially diethylbenzene and pseudotrimethylbenzene, remained in the reaction system in significant quantities. These residues are prone to aggregation during the boiling and washing process, leading to difficulties in subsequent washing. Although alcohol soaking can alleviate this problem, it significantly increases the complexity and workload of the operation, making it unsuitable for large-scale synthesis.

[0085] Table 5: Comparison of thermal properties of PEK-CN resin synthesized under different dehydrating agents

[0086] Table 6: Molecular weight test of PEK-CN resin with different water-removing agents

[0087] When different dehydrating agents were used to synthesize PEK-CN resin, the effect on the molecular weight of the resin was relatively small, but the effect on the PDI (polydispersity index) was more significant. Among them, when mesitylene was used as the dehydrating agent, the PDI value reached the optimal level of 1.30, indicating that the molecular weight distribution of the resin was most uniform at this point. Furthermore, the specific viscosity test results were consistent with the molecular weight test results, showing no significant difference.

[0088] Table 7: Mechanical Properties of PEK-CN Resins with Different Water-Removing Agents

[0089] Different dehydrating agents significantly affect the mechanical properties of PEK-CN resin. PEK-CN resin synthesized using mesitylene as a dehydrating agent exhibits better impact resistance, tensile strength, and tensile modulus than other PEK-CN resins. Compared to the residual amount of diethylbenzene, xylene has a lower flash point and boiling point, while mesitylene has the worst mechanical and thermal properties. Mesitylene is a more suitable dehydrating agent than xylene, not only achieving the theoretical water yield with a more complete reaction, but also producing PEK-CN resin with more stable thermal properties and superior mechanical properties under the same conditions. Therefore, mesitylene was chosen as the dehydrating agent.

[0090] Example 3: Verification of the synergistic effect of end-capping agent and dehydrating agent To demonstrate the synergistic effect between the technical features of this invention, a 2×2 cross-control experiment was designed under the same monomer system, the same polymerization conditions, and the same post-processing.

[0091] Fixed conditions: • Total monomer feed: 0.15 mol • Phenolphthalein dosage: 3% excess (49.18 g) • 2,6′-Dichlorobenzonitrile: 18.06 g • 4,4′-Difluorobenzophenone: 9.82 g • Compound salt: Na2CO3 / K2CO3 = 50:1 (15.90 g / 0.32 g) • Solvent: Sulfolane • Polymerization temperature: 220℃ • Capping agent dosage: approximately 0.003 mol • Post-processing conditions: Completely consistent Table 8: Variable Settings

[0092] Table 9: Test Results

[0093] Simply changing the end-capping agent to 2,4′-DFBP (comparative example X2) resulted in an approximately 55% increase in impact strength; By simply replacing the water-absorbing agent with mesitylene (Comparative Example X1), the impact strength increased by approximately 22%. When both are used simultaneously (Example 3), the impact strength is increased by 137%, and the PDI is reduced from 1.75 to 1.25.

[0094] The results indicate that 2,4′-DFBP provides a more regular and controllable end structure for the molecular chain, while mesitylene provides a more stable and thorough dehydration environment for the reaction system. When the two work together, they amplify the controllability of the molecular weight distribution, thereby achieving a leap in mechanical properties.

[0095] Example 4: Preparation of CF / PEK-CN prepreg Raw materials and equipment: Resin: PEK-CN resin powder prepared in Example 1 (terminated with 2,4′-difluorobenzophenone, η=0.53 dL / g).

[0096] Solvent: N,N-dimethylacetamide (DMAc), analytical grade.

[0097] Fiber: T700 unidirectional carbon fiber cloth, areal density 220 g / m 2 .

[0098] Equipment: Mixer, continuous impregnation tester (equipped with metering rollers), programmable temperature hot air circulating oven, universal material testing machine.

[0099] Preparation process: Preparation of adhesive solution: Mix PEK-CN resin and DMAc at a weight ratio of 35:65 and stir at 50°C for 6 hours to obtain a uniform transparent adhesive solution with a solid content of 35% and a viscosity of about 2800 mPa·s (25°C).

[0100] Impregnation: The dried carbon fiber cloth is passed through the impregnation tank at a speed of 1.0 m / min, and the adhesive temperature is maintained at 50℃. The amount of adhesive applied per unit area of ​​the wet prepreg is controlled by adjusting the gap between the metering rollers.

[0101] Gradient drying (process of this invention, group A): The wet prepreg is fed into a programmable temperature-controlled oven and the drying program is executed as follows: ① 80℃ / 30 min → ② 150℃ / 30 min → ③ 200℃ / 10 min.

[0102] Preparation of control samples (conventional one-step drying, Group B): Using the same adhesive and fiber, under the same impregnation parameters, the conventional one-step drying method was adopted: baking at a constant temperature of 150℃ for 70 min.

[0103] Table 10: Comparison of Results for Different Drying Methods

[0104] This embodiment directly demonstrates that the three-stage gradient drying process of the present invention can effectively control the solvent residue rate to an extremely low level (0.1%), which is far superior to the conventional one-step drying method (3%). This directly results in a better prepreg appearance and significantly higher interlaminar shear strength of the composite material (an increase of approximately 22.5%), highlighting the key role of the process of the present invention in solving solvent residue and optimizing the interface.

[0105] Example 5: Effect of different adhesive solid content on prepreg properties This embodiment aims to verify the scientific validity of the optimal solid content range (20%-40%) proposed in this invention.

[0106] Preparation process: Using the same resin and fiber as in Example 1, and the gradient drying process of this invention (80 / 150 / 200°C, 30 / 30 / 10 min), four samples were prepared by varying only the solid content of the adhesive solution. Sample C: Solid content 25%, viscosity ~800 mPa·s Sample D: Solid content 30%, viscosity ~1500 mPa·s Sample E: Solid content 35%, viscosity ~2800 mPa·s Sample F: Solid content 40%, viscosity ~5200 mPa·s The impregnation speed was uniformly set at 1.0 m / min.

[0107] When the solid content is 30%–35%, the viscosity of the adhesive solution is within the ideal window of 1000–4000 mPa·s. At this point, the adhesive solution has both good fluidity and liquid retention, enabling deep and uniform wetting of the fibers, thereby obtaining a prepreg with optimal resin distribution, best processing performance, and highest final mechanical properties.

[0108] The remaining solids content all led to varying degrees of performance degradation.

[0109] Table 11: Comparison of results for different solid contents

[0110] Example 6: Performance Comparison of CF / PEEK and CF / PEK-CN Composites PEK-CN resin was dissolved in DMAc solvent to form a 35% resin content adhesive solution, which was then poured onto T700 unidirectional carbon fiber cloth and spread evenly. Gradient drying was then performed at 80℃-150℃-210℃ (refer to Example 4) to obtain CF / PEK-CN prepreg. The test results of the composite material prepared by compression molding are shown in Table 10. Table 12: Performance Comparison of PEK-CN Composites and PEEK Composites

[0111] Overall, the T700 / PEK-CN composite material exhibits superior mechanical properties compared to the T700 / PEEK composite material.

[0112] The comparative example was the conventional synthesis of PEK-CN resin, with no excess phenolphthalein, using a single salt Na2CO3 catalyst, without end-capping, and with xylene as the water-carrying agent.

[0113] The viscosity increases rapidly during the reaction, with a rapid climbing reaction occurring within 2-3 hours, making subsequent settling impossible. After crushing and washing, the intrinsic viscosity at 340℃, measured by DHR, is 30000 Pa·s, making processing difficult. The specific viscosity measured in the DMAc solution is 0.97 (too viscous). Therefore, it is completely unsuitable for solution-based prepreg preparation. The embodiments described above are merely illustrative of several implementations of the present invention, and while the descriptions are relatively specific and detailed, they should not be construed as limiting the scope of the invention patent. It should be noted that those skilled in the art can make various modifications and improvements without departing from the concept of the present invention, and these all fall within the protection scope of the present invention. Therefore, the protection scope of this invention patent should be determined by the appended claims, and the specification and drawings can be used to interpret the content of the claims.

Claims

1. A method for preparing a polyaryletherketone resin, characterized in that, Includes the following steps: In a non-oxidizing atmosphere, dihydroxy aromatic monomers containing bisphenol structures, dihalo aromatic monomers containing nitrile groups, and dihalo aromatic ketone monomers containing difluorine substitution are placed in a polar solvent system with a boiling point above 150°C in the presence of alkali metal carbonates to form corresponding phenolic salts. An aromatic dehydrating agent is added to the system for azeotropic dehydration to remove the water generated during the reaction and promote the formation of the phenolate. The nucleophilic substitution polycondensation reaction is carried out by heating. When the viscosity of the system increases during the polycondensation reaction, a capping agent is added to regulate the end structure and molecular weight distribution of the molecular chain. The capping agent is 2,4′-difluorobenzophenone. After the reaction is completed, the reaction product is separated and purified to obtain the polyaryletherketone resin.

2. The preparation method according to claim 1, characterized in that, The aromatic dehydrating agent is selected from at least one of mesitylene, diethylbenzene, pseudotrimethylbenzene, and xylene, preferably mesitylene.

3. The preparation method according to claim 1, characterized in that, The end-capping agent is added when the polycondensation reaction proceeds to a system intrinsic viscosity of 0.6 dL / g to 1.2 dL / g, and preferably the amount of end-capping agent added is 0.1 mol% to 5 mol of the molar amount of the dihydroxy aromatic monomer.

4. The preparation method according to claim 1, characterized in that, The polar solvent with a boiling point of 150°C or higher is selected from at least one of N-methylpyrrolidone, dimethylacetamide, dimethylformamide, diphenyl sulfone, and sulfolane.

5. The preparation method according to any one of claims 1 to 4, characterized in that, The alkali metal carbonate is selected from at least one of potassium carbonate, sodium carbonate, or cesium carbonate; preferably, it is a composite salt containing sodium carbonate and potassium carbonate; more preferably, the mass ratio of sodium carbonate to potassium carbonate is (40~60):

1.

6. The preparation method according to any one of claims 1 to 4, characterized in that, The dihydroxy aromatic monomer containing the bisphenol structure is selected from at least one of bisphenol A, bisphenol S or phenolphthalein; Preferably, when the dihydroxy aromatic monomer contains phenolphthalein, the amount of phenolphthalein added is 2% to 4% excess relative to the theoretical equivalent, preferably 3% excess.

7. The preparation method according to any one of claims 1 to 4, characterized in that, The nitrile-containing dihaloaromatic monomer is 2,6-dichlorobenzonitrile or 4,4′-difluorobenzophenone nitrile.

8. A polyaryletherketone resin, characterized in that, Obtained by the preparation method according to any one of claims 1 to 7.

9. A resin solution, characterized in that, The resin comprises the polyaryletherketone resin of claim 8 and an organic polar solvent, wherein the resin has a mass fraction of 20% to 40%.

10. A prepreg, characterized in that, It includes reinforcing fibers and a resin matrix layer formed by impregnation and drying of the resin solution of claim 9.

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