Injection molding grade aramid fiber resin and preparation method thereof
The solid-phase polycondensation method is used to prepare injection-molding-grade aramid resin, which solves the problems of difficult processing and high solvent consumption of aramid resin, realizes a low-melting-point amorphous structure, is suitable for a variety of processing methods, expands the scope of application, and reduces costs.
Patent Information
- Application Number
- CN202510854822.4
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- Filing Date
- 2025-06-25
- Publication Date
- 2025-09-16
AI Technical Summary
Aramid resin is difficult to process and has limited processing methods. Traditional preparation methods are complex, consume a lot of solvents, and have poor product morphology, which affects production efficiency and application scope.
By adopting molecular design and process optimization, injection molding grade aramid resin is prepared by solid phase polycondensation method. Functional monomers are introduced to destroy the regularity of molecular chains and form an amorphous structure. Multiple processing methods are adopted to reduce solvent usage and simplify post-processing procedures.
It has low melting point and amorphous properties, is suitable for a variety of processing methods, improves production efficiency and application range, reduces costs, reduces environmental pollution, and is suitable for the molding of complex structural parts.
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Abstract
Description
Technical Field
[0001] The present invention relates to the technical field of polymer materials, and in particular to an injection-grade aramid resin and a preparation method thereof. Background Art
[0002] Fully aromatic polyamides, also known as aramid, are a class of high-performance polymers composed of amide bonds directly linked to aromatic rings. Key varieties include poly(p-phenylene terephthalamide) (PPTA), poly(m-phenylene isophthalamide) (PMPIA), and poly(p-phenylene terephthalamide) (PBA). Due to the high number of aromatic rings in their backbone, the molecular chain is rigid, resulting in high heat resistance, high melting temperature, high strength, and high chemical resistance. Their overall performance significantly surpasses that of aliphatic and semi-aromatic polyamides. However, aramid resins have high melting points and high melt viscosity, making them difficult to process. In contrast, aliphatic and semi-aromatic polyamides, due to their excellent processing fluidity, are particularly well-suited to injection molding and other processing methods, offering a wider range of applications. However, the difficulty of processing aramid resins and the limited number of processing methods limit their application. Currently, fiber products are primarily produced through solution molding, with applications in thermal protective clothing, flame-retardant decorative fabrics, filter cloth, honeycomb components, laminates, high-temperature pipelines, high-temperature electrical insulation paper, and motor components.
[0003] Currently, aramid resin preparation methods include low-temperature solution polycondensation, direct polycondensation, transesterification, and interfacial polycondensation. However, the interfacial polycondensation products have low molecular weight and poor stability, making them unsuitable for injection molding resin production. The diacids used in direct polycondensation are inactive and require activation catalysts, such as triphenyl phosphite and thionyl chloride. This lack of controllability and stability is not as evident in low-temperature solution polycondensation using acyl chlorides. Therefore, the low-temperature solution polycondensation and transesterification methods are the primary methods used.
[0004] The most common method in the existing technology is to use the low-temperature polycondensation process of acyl chloride monomers to prepare aramid resins. However, this process has the following significant drawbacks: 1. Complex post-processing steps: precipitation and crushing, multiple alcohol solvent washing and drying steps are required, resulting in low equipment utilization and long production cycles; 2. High solvent consumption: The washing process requires the use of a large amount of organic solvents, and the subsequent recycling and processing costs are high; 3. Poor product morphology: The bulk density of the resulting resin powder is usually less than 0.3g / cm 3 In the subsequent extrusion granulation process, process problems such as poor feeding, large feeding fluctuations, and uneven stranding are likely to occur, seriously affecting production efficiency. Summary of the Invention
[0005] In order to solve the problems of difficulty in processing existing aramid resins and limitations in processing methods, the present invention provides an injection-molding-grade aramid resin and a preparation method thereof.
[0006] The technical solutions of the present invention are as follows:
[0007] An injection molding grade aramid resin with the following structural formula:
[0008]
[0009] Wherein, X is one or more of formulas (I) to (IV), and Y is one or more of formulas (I) to (VIII):
[0010]
[0011]
[0012] in,
[0013] Preferably, X comprises a 1,3-phenylene structure of formula (I), wherein formula (I) accounts for 50 mol% to 100 mol%, and the rest is one or more of formulas (II) to (IV).
[0014] Preferably, Y comprises a 1,3-phenylene structure of formula (I), wherein formula (I) accounts for 20 mol% to 80 mol%; the rest are one or more of formulas (II) to (VIII): a 1,4-phenylene structure (II), a 4,4'-biphenyl structure (III, R:—), a 4,4'-diphenylmethane structure (III, R:=CH2), a 3,4' or 4,4'-diphenyl ether structure (III, R:=O), a 3,4' or 4,4'-benzophenone structure (III, R:=CO), a 4,4'-diphenyl sulfone structure (III, R:=SO2), a 4,4'-2,2 -diphenylpropane structure (III, R: = C(CH3)2), 4,4'-2,2-diphenylhexafluoropropane structure (III, R: = C(CF3)2), 3,4' or 4,4'-benzoylanilide structure (III, R: -CONH-), 1,4,3- or 1,4,4-triphenyl diether structure (IV), 1,3,3- or 1,3,4-triphenyl diether structure (V), bis(3,3' or 4,4'-phenoxy)benzophenone structure (VI), 2,5-dimethylenefuran structure (VII), bis(2,2'-dimethylenefuran)methane structure (VIII).
[0015] The present invention also provides a method for preparing the above-mentioned injection-molding grade aramid resin, comprising the following steps:
[0016] Step A:
[0017] Suspend the diacid containing the X structure, the diamine containing the Y structure, the catalyst, and the molecular weight regulator in a solvent, replace the atmosphere with nitrogen three times, stir and heat to 120°C to 150°C, maintain for 1 to 2 hours, then raise the temperature to 200°C, start exhausting when the pressure reaches 1.5 to 2.0 MPa, maintain the pressure constant, exhaust the solvent until the solid content reaches 80 to 95%, stop exhausting, and continue the reaction for 2 to 3 hours; cool to room temperature, and discharge the material;
[0018] Step B:
[0019] The solid obtained in step A is crushed and placed in a vacuum oven. The vacuum is evacuated to -0.098 to -0.1 MPa at 150°C and maintained for 3 hours. The temperature is then raised to 220 to 240°C and maintained for 3 to 4 hours. The crystallization system needs to be further heated to 250 to 320°C for reaction for 1 to 3 hours, and then cooled to obtain aramid resin.
[0020] Preferably, the molar ratio of the diacid to the diamine in step A is (0.95:1) to (1.05:1).
[0021] Preferably, the solvent in step A is one or more of water, methanol, ethanol, isopropanol, ethylene glycol, ethylene glycol monomethyl ether, ethylene glycol monoethyl ether, 1,4-dioxane, acetonitrile, N,N-dimethylformamide (DMF), N,N-dimethylacetamide (DMAC), and N-methylpyrrolidone (NMP). More preferably, it is at least one of water, ethylene glycol monomethyl ether, and ethylene glycol monoethyl ether.
[0022] Preferably, the catalyst in step A is any one of boric acid, zinc hypophosphite, sodium hypophosphite, potassium hypophosphite, magnesium hypophosphite, and calcium hypophosphite, more preferably boric acid or zinc hypophosphite.
[0023] Preferably, the amount of the catalyst is 0.02% to 0.1%.
[0024] Preferably, the molecular weight regulator in step A is any one of benzoic acid, isophthalic acid, aniline, and m-phenylenediamine, more preferably benzoic acid or isophthalic acid.
[0025] Preferably, the molar amount of the molecular weight regulator in step A is 1% to 5% of the total molar amount of the diamine and the dibasic acid.
[0026] Through innovative molecular design and process optimization, this invention has developed a new aramid resin with low melting point, amorphous state, and a wide processing window. This overcomes the preparation and processing bottlenecks of traditional aramid resins and significantly expands their application range and economic efficiency. Compared with the existing technology, the specific beneficial effects of this invention are as follows:
[0027] 1. Traditional aramid resins rely primarily on low-temperature solution polycondensation, resulting in a single processing method and difficulty in forming complex parts. This invention, by introducing functional monomers, disrupts molecular chain regularity, reduces crystallinity, achieves an amorphous structure, and minimizes dimensional shrinkage during processing. While retaining the high strength and high modulus characteristics of aramid, this invention can be processed using a variety of methods, including solution molding, injection molding, extrusion molding, calendering molding, and compression molding. It is particularly suitable for precision injection molding and can produce complex structural parts such as electronic packaging and high-temperature-resistant gears for aerospace applications.
[0028] 2. Traditional preparation methods, such as low-temperature solution polycondensation, have complex post-processing steps, long production cycles, and high solvent consumption. The present invention adopts solid-phase polycondensation, which uses minimal solvent, reduces VOCs emissions, and is more environmentally friendly. In addition, the present invention does not produce hydrogen chloride by-products, has minimal equipment corrosion, high reaction efficiency, and significantly reduces costs.
[0029] The present invention is expected to replace traditional engineering plastics with lower cost and more convenient processing, which will be conducive to promoting the large-scale application of aramid resin in the fields of automobiles, electronics, military industry, etc. BRIEF DESCRIPTION OF THE DRAWINGS
[0030] Figure 1 This is the infrared spectrum of the aramid resin prepared in Example 1;
[0031] Figure 2 This is the hydrogen nuclear magnetic resonance spectrum of the aramid resin prepared in Example 1;
[0032] Figure 3 is the DSC curve of the aramid resin prepared in Example 1;
[0033] Figure 4 This is the rheological temperature scanning curve of the aramid resin prepared in Example 1;
[0034] Figure 5 This is the infrared spectrum of the aramid resin prepared in Example 2;
[0035] Figure 6 This is the hydrogen nuclear magnetic resonance spectrum of the aramid resin prepared in Example 2. DETAILED DESCRIPTION
[0036] In order to make the technical solution of the present invention clearer, the technical solution in the embodiments of the present invention will be clearly and completely described below in conjunction with the drawings in the specification of the present invention. It should be noted that the following embodiments are only used to better understand the technical solution of the present invention and should not be understood as limiting the present invention.
[0037] Example 1.
[0038] m-Phenylenediamine (21.63 g, 0.2 mmol), 3,4'-diaminodiphenyl ether (40.05 g, 0.2 mol), isophthalic acid (77.7 g, 0.388 mol), benzoic acid (2.93 g, 0.024 mol), boric acid (0.06 g), ethylene glycol monoethyl ether (100 ml) and purified water (200 ml) were added to a pressure reactor, replaced with nitrogen three times, stirred at 140 ° C for 1 h, and then heated to 200 ° C, start exhausting when the pressure is 1.5-2.0 MPa, keep the pressure constant, discharge the solvent until the solid content is 80-95%, stop exhausting, and continue the reaction for 2 hours; cool to room temperature and discharge; the obtained solid is crushed and placed in a vacuum oven, evacuated to -0.098 ~ (-0.1) MPa at 150 ° C and maintained for 3 hours, heated to 220 ° C and maintained for 3 hours, continued to heat to 250 ° C and maintained for 2 hours, cooled to obtain aramid resin.
[0039] The aramid resin prepared in this embodiment was characterized, and its infrared spectrum was as follows: Figure 1 As shown. 3300~3500cm -1 The NH stretching vibration peak at 1650 cm comes from the amino groups of m-phenylenediamine and 3,4'-diaminodiphenyl ether; -1 and 1540cm -1 The characteristic absorption peak of the amide bond (-CO-NH-) at 1600 cm indicates that the diacid and diamine are successfully condensed to form a polyamide structure; -1 and 1500cm -1 The benzene ring skeleton vibrates, proving that the aromatic ring structure is retained; 1240cm -1 The COC ether bond absorption peak at 100 nm indicates that the ether bond was not broken during the reaction. The absence of a free carboxylic acid peak indicates that the diacid has been completely reacted.
[0040] H NMR spectrum Figure 2 Combining infrared spectroscopy and hydrogen spectrum can prove that the product was successfully synthesized according to the predetermined route.
[0041] The phase change behavior of the material was analyzed and its DSC curve was tested as follows Figure 3 As shown in the figure, it can be seen that the Tg is about 230℃, which can support complex molding processes such as injection molding.
[0042] After testing, the rheological temperature scanning curve of the material is as follows Figure 4 The complex viscosity η* decreases significantly at higher temperatures, indicating that the resin exhibits good fluidity within the 300-350°C temperature range, making it suitable for injection molding and meeting the "low melting point / amorphous" design goals of this application. While traditional crystalline aramid exhibits a sharp drop in viscosity near its melting point, the low-melting point / amorphous resin of this application exhibits a continuous and gradual decrease in viscosity over a wide temperature range, making it suitable for complex molding processes.
[0043] Example 2.
[0044] m-phenylenediamine (10.81 g, 0.1 mmol), 3,4'-diaminodiphenyl ether (80.1 g, 0.4 mol), isophthalic acid (80.57 g, 0.485 mol), benzoic acid (2.93 g, 0.024 mol), zinc hypophosphite (0.08 g), ethylene glycol monomethyl ether (100 ml) and purified water (200 ml) were added to a pressure reactor, replaced with nitrogen three times, stirred at 140° C. for 1 hour, then heated to 200° C. and began to exhaust when the pressure reached 1.5-2.0 MPa. The pressure was maintained constant and the solvent was discharged until the solid content reached 80-95%. The exhaust was stopped and the reaction was continued for 2 hours; the temperature was cooled to room temperature and the material was discharged; the obtained solid was crushed and placed in a vacuum oven. The vacuum was evacuated to -0.098~(-0.1) MPa at 150° C. and maintained for 3 hours. The temperature was increased to 240° C. and maintained for 4 hours, and the temperature was cooled to obtain an aramid resin.
[0045] The aramid resin prepared in this embodiment was characterized, and its infrared spectrum was as follows: Figure 5 The H NMR spectrum is shown as Figure 6 shown.
[0046] Example 3.
[0047] m-Phenylenediamine (43.26 g, 0.4 mmol), isophthalic acid (33.23 g, 0.2 mol), 4,4'-diphenyl ether dicarboxylic acid (56.81 g, 0.22 mol), boric acid (0.06 g), ethylene glycol monoethyl ether (100 ml) and purified water (100 ml) were added to a pressure reactor, replaced with nitrogen three times, stirred at 170°C for 1 hour, then heated to 200°C, and vented until the pressure reached 1.5-2.0 MPa. The pressure was maintained constant, the solvent was discharged until the solid content reached 80-95%, the venting was stopped, and the reaction was continued for 2 hours; the temperature was cooled to room temperature and the material was discharged; the obtained solid was crushed and placed in a vacuum oven, evacuated to -0.098~(-0.1) MPa at 150°C and maintained for 3 hours, heated to 220°C and maintained for 2 hours, further heated to 250°C and maintained for 2 hours, cooled to obtain an aramid resin.
[0048] Example 4.
[0049] m-phenylenediamine (43.26 g, 0.4 mmol), terephthalic acid (16.61 g, 0.1 mol), 1,4-bis(4-carboxyphenoxy)benzene (112.1 g, 0.32 mol), zinc hypophosphite (0.09 g), DMAC (100 ml) and purified water (150 ml) were added to a pressure reactor, replaced with nitrogen three times, stirred at 140° C. for 1 hour, then heated to 210° C., and vented until the pressure reached 1.5-2.0 MPa. The pressure was maintained constant, the solvent was discharged until the solid content reached 80-95%, the venting was stopped, and the reaction was continued for 2 hours; the temperature was cooled to room temperature and the material was discharged; the obtained solid was crushed and placed in a vacuum oven, evacuated to -0.098~(-0.1) MPa at 150° C. and maintained for 3 hours, heated to 210° C. and maintained for 3 hours, then heated to 230° C. and maintained for 2 hours, and cooled to obtain an aramid resin.
[0050] Example 5.
[0051] m-phenylenediamine (21.63 g, 0.2 mmol), 4,4'-diaminodiphenyl ether (40.05 g, 0.2 mol), isophthalic acid (49.84 g, 0.3 mol), 1,4-bis(4-carboxyphenoxy)benzene (38.54 g, 0.11 mol), zinc hypophosphite (0.06 g), DMAC (100 ml) and purified water (150 ml) were added to a pressure reactor, replaced with nitrogen three times, and stirred at 140°C for 1 h. Then, the temperature is raised to 200°C, and exhaust is started when the pressure reaches 1.5-2.0 MPa. The pressure is kept constant, and the solvent is discharged until the solid content reaches 80-95%. The exhaust is stopped and the reaction is continued for 2 hours. The temperature is lowered to room temperature and the material is discharged. The obtained solid is crushed and placed in a vacuum oven. The temperature is evacuated to -0.098~(-0.1)MPa at 150°C and maintained for 3 hours. The temperature is raised to 210°C and maintained for 3 hours. The temperature is further raised to 230°C and maintained for 2 hours. The temperature is then lowered to obtain aramid resin.
[0052] Example 6.
[0053] m-Phenylenediamine (10.81 g, 0.1 mmol), 4,4'-diaminodiphenylmethane (59.48 g, 0.3 mol), isophthalic acid (65.12 g, 0.392 mol), benzoic acid (1.95 g, 0.016 mol), zinc hypophosphite (0.05 g), ethylene glycol monomethyl ether (100 ml) and purified water (200 ml) were added to the pressure reactor, replaced with nitrogen three times, stirred at 140 ° C for 1 h, and then heated to 40 ° C for 1 h. The temperature was raised to 200° C., and venting was started when the pressure reached 1.5-2.0 MPa, the pressure was kept constant, the solvent was discharged until the solid content reached 80-95%, the venting was stopped, and the reaction was continued for 2 hours; the temperature was lowered to room temperature and the material was discharged; the obtained solid was crushed and placed in a vacuum oven, evacuated to -0.098~(-0.1)MPa at 150° C. and maintained for 3 hours, the temperature was raised to 220° C. and maintained for 3 hours, the temperature was further raised to 250° C. and maintained for 2 hours, and the temperature was lowered to obtain aramid resin.
[0054] Example 7.
[0055] m-Phenylenediamine (21.63 g, 0.2 mmol), 1,3-bis(4'-aminophenoxy)benzene (58.47 g, 0.2 mol), isophthalic acid (65.12 g, 0.392 mol), benzoic acid (1.95 g, 0.016 mol), zinc hypophosphite (0.09 g), ethylene glycol monoethyl ether (100 ml) and purified water (200 ml) were added to a pressure reactor, replaced with nitrogen three times, stirred at 140 ° C for 1 h, and then heated to 200 ℃, start exhausting when the pressure is 1.5-2.0 MPa, keep the pressure constant, discharge the solvent until the solid content is 80-95%, stop exhausting, and continue the reaction for 2 hours; cool to room temperature and discharge; the obtained solid is crushed, placed in a vacuum oven, evacuated to -0.098~(-0.1)MPa at 150℃ and maintained for 3 hours, heated to 210℃ and maintained for 2 hours, continued to heat to 250℃ and maintained for 2 hours, then heated to 290℃ and maintained for 1 hour, cooled to obtain aramid resin.
[0056] Example 8.
[0057] m-phenylenediamine (10.81 g, 0.1 mmol), 1,3-bis(4'-aminophenoxy)benzene (87.7 g, 0.3 mol), isophthalic acid (65.12 g, 0.392 mol), benzoic acid (1.95 g, 0.016 mol), zinc hypophosphite (0.1 g), ethylene glycol monoethyl ether (100 ml) and purified water (200 ml) were added to a pressure reactor, replaced with nitrogen three times, stirred at 140 ° C for 1 h, and then heated to 200 ° C. , start exhausting when the pressure is 1.5-2.0MPa, keep the pressure constant, discharge the solvent until the solid content is 80-95%, stop exhausting, and continue the reaction for 2h; cool to room temperature and discharge; the obtained solid is crushed and placed in a vacuum oven, evacuated to -0.098~(-0.1)MPa at 150℃ and maintained for 3h, heated to 210℃ and maintained for 2h, continued to heat to 250℃ and maintained for 2h, then heated to 290℃ and maintained for 1h, cooled to obtain aramid resin.
[0058] Example 9.
[0059] m-Phenylenediamine (10.81 g, 0.1 mmol), 4,4'-bis(3-aminophenoxy)benzophenone (118.93 g, 0.3 mol), isophthalic acid (33.23 g, 0.2 mol), 4,4'-diphenyl ether dicarboxylic acid (46.48 g, 0.18 mol), benzoic acid (4.89 g, 0.04 mol), boric acid (0.1 g), 1,4-dioxane (100 ml) and purified water (200 ml) were added to a pressure reactor, and the atmosphere was replaced with nitrogen three times at 140°C. The mixture was stirred for 1 hour, then heated to 200°C until the pressure reached 1.5-2.0 MPa, and venting was started. The pressure was kept constant, and the solvent was discharged until the solid content reached 80-95%. The venting was stopped and the reaction was continued for 2 hours. The mixture was cooled to room temperature and discharged. The obtained solid was crushed and placed in a vacuum oven. The temperature was evacuated to -0.098~(-0.1)MPa at 150°C and maintained for 3 hours. The temperature was raised to 230°C and maintained for 2 hours. The temperature was further raised to 260°C and maintained for 2 hours. The temperature was then raised to 300°C and maintained for 0.5 hours. The mixture was cooled to obtain an aramid resin.
[0060] Example 10.
[0061] m-phenylenediamine (21.63 g, 0.2 mmol), 3,4'-diaminobenzophenone (42.45 g, 0.2 mol), isophthalic acid (33.23 g, 0.2 mol), 4,4'-diphenyl ether dicarboxylic acid (56.81 g, 0.22 mol), zinc hypophosphite (0.09 g), ethylene glycol monoethyl ether (100 ml) and purified water (200 ml) were added to a pressure reactor, replaced with nitrogen three times, and stirred at 140°C for 1 h. Then, the temperature is raised to 200°C, and exhaust is started when the pressure reaches 1.5-2.0 MPa. The pressure is kept constant, and the solvent is discharged until the solid content reaches 80-95%. The exhaust is stopped and the reaction is continued for 2 hours; the temperature is lowered to room temperature and the material is discharged; the obtained solid is crushed and placed in a vacuum oven, and evacuated to -0.098~(-0.1)MPa at 150°C and maintained for 3 hours, and then the temperature is raised to 210°C and maintained for 3 hours, and then the temperature is further raised to 260°C and maintained for 2 hours, and then the temperature is lowered to obtain aramid resin.
[0062] Example 11.
[0063] m-Phenylenediamine (21.63 g, 0.2 mmol), 2,5-bis(aminomethyl)furan (25.23 g, 0.2 mol), isophthalic acid (33.23 g, 0.2 mol), 4,4'-diphenyl ether dicarboxylic acid (54.23 g, 0.21 mol), zinc hypophosphite (0.06 g), ethylene glycol monoethyl ether (100 ml) and purified water (200 ml) were added to a pressure reactor, replaced with nitrogen three times, stirred at 140 ° C for 1 h, and then heated to 18 The reaction mixture was kept at 0°C for 1 hour, and the temperature was continuously raised to 200°C until the pressure reached 1.5-2.0 MPa, and the exhaust was started. The pressure was kept constant, and the solvent was discharged until the solid content reached 80-95%. The exhaust was stopped, and the reaction was continued for 2 hours. The reaction mixture was cooled to room temperature and discharged. The obtained solid was crushed and placed in a vacuum oven. The temperature was evacuated to -0.098~(-0.1)MPa at 150°C and the pressure was maintained for 3 hours. The temperature was increased to 220°C and the pressure was maintained for 2 hours. The temperature was further increased to 240°C and the pressure was maintained for 2 hours. The reaction mixture was cooled to obtain an aramid resin.
[0064] Effect example.
[0065] The aramid resins prepared in Examples 1 to 11 were subjected to performance tests, including a tensile strength test, an elongation at break test, a flexural strength test, a melting point test, and a viscosity test.
[0066] The test results are as follows:
[0067]
[0068]
[0069] Obviously, the above embodiments are merely examples for clarity of explanation and are not intended to limit the implementation methods. Those skilled in the art will readily appreciate that other variations or modifications based on the above descriptions are possible. It is not necessary and impossible to enumerate all implementation methods here. Obvious variations or modifications arising therefrom remain within the scope of protection of the present invention.
Claims
1. An injection molding grade aramid resin, characterized in that: The structural formula is shown below: Wherein, X is one or more of formulas (I) to (IV), and Y is one or more of formulas (I) to (VIII): in, 2. The injection molding grade aramid resin according to claim 1, characterized in that: X comprises formula (I), wherein formula (I) accounts for 50 mol% to 100 mol%, and the rest is one or more of formulas (II) to (IV).
3. The injection molding grade aramid resin according to claim 2, characterized in that: Y includes formula (I), wherein formula (I) accounts for 20 mol% to 80 mol%; the rest is one or more of formulas (II) to (VIII).
4. A method for preparing an injection molding grade aramid resin according to any one of claims 1 to 3, characterized in that: The steps include: Step A: Suspend the diacid containing the X structure, the diamine containing the Y structure, the catalyst, and the molecular weight regulator in a solvent, replace the atmosphere with nitrogen three times, stir and heat to 120°C to 150°C, maintain for 1 to 2 hours, then raise the temperature to 200°C, start exhausting when the pressure reaches 1.5 to 2.0 MPa, maintain the pressure constant, exhaust the solvent until the solid content reaches 80 to 95%, stop exhausting, and continue the reaction for 2 to 3 hours; cool to room temperature, and discharge the material; Step B: The solid obtained in step A is crushed and placed in a vacuum oven. The vacuum is evacuated to -0.098 to -0.1 MPa at 150°C and maintained for 3 hours. The temperature is then raised to 220 to 240°C and maintained for 3 to 4 hours. The crystallization system needs to be further heated to 250 to 320°C for reaction for 1 to 3 hours, and then cooled to obtain aramid resin.
5. The method for preparing injection molding grade aramid resin according to claim 4, characterized in that: The molar ratio of the diacid to the diamine in step A is (0.95:1) to (1.05:1).
6. The method for preparing injection molding grade aramid resin according to claim 4, characterized in that: The solvent in step A is one or more of water, methanol, ethanol, isopropanol, ethylene glycol, ethylene glycol monomethyl ether, ethylene glycol monoethyl ether, 1,4-dioxane, acetonitrile, N,N-dimethylformamide, N,N-dimethylacetamide, and N-methylpyrrolidone.
7. The method for preparing injection molding grade aramid resin according to claim 4, characterized in that: The catalyst in step A is any one of boric acid, zinc hypophosphite, sodium hypophosphite, potassium hypophosphite, magnesium hypophosphite, and calcium hypophosphite.
8. The method for preparing injection molding grade aramid resin according to claim 4, characterized in that: The dosage of the catalyst is 0.02% to 0.1%.
9. The method for preparing injection molding grade aramid resin according to claim 4, characterized in that: The molecular weight regulator in step A is any one of benzoic acid, isophthalic acid, aniline and m-phenylenediamine.
10. The method for preparing injection molding grade aramid resin according to claim 4, characterized in that: The molar amount of the molecular weight regulator in step A is 1% to 5% of the total molar amount of the diamine and the dibasic acid.