Preparation method of m-xylylenediamine polyamide

Abstract

The invention belongs to the technical field of polyamide, and particularly relates to a preparation method of m-xylylenediamine polyamide. Comprising the following steps: (1) mixing binary acid, m-xylylenediamine and water for salt forming reaction to obtain a salt solution, and then adjusting the pH value of the salt solution to 6.7-7.0 by supplementing the binary acid or the m-xylylenediamine; (2) adding a catalyst and a metal compound into the salt solution for polymerization reaction to obtain polymer particles; the polymerization reaction comprises a pressure increasing stage, a pressure maintaining and temperature increasing stage, a pressure releasing and temperature increasing stage and a normal-pressure and constant-temperature stage, and the temperature of the normal-pressure and constant-temperature stage is 240-250 DEG C; and (3) carrying out solid-phase tackifying treatment on the polymer particles under a vacuum condition to obtain the m-xylylenediamine polyamide. The prepared m-xylylenediamine polyamide is good in chromaticity, low in gel content and uniform in viscosity, can be widely applied to engineering structure materials, plates, films and various packaging materials, and has important application prospects.

Description

Technical Field

[0001] The invention belongs to the technical field of polyamides, and particularly relates to a preparation method of meta-xylylenediamine-based polyamide. Background Art

[0002] Polyamide, also known as nylon, is a thermoplastic resin containing repeating amide groups in its main molecular chain. When used as an engineering plastic, it exhibits high-temperature resistance, high strength, excellent mechanical properties, chemical resistance, and easy processing. Semi-aromatic nylon is produced through the polymerization of aliphatic diamines and dibasic acids containing benzene rings, or vice versa. It combines the advantages of aliphatic nylon and fully aromatic nylon, and is therefore widely used. Poly(m-xylylenediamine adipamide) (MXD6) is a representative semi-aromatic nylon, characterized by good toughness, high strength, chemical resistance, low water absorption, good dimensional stability, and excellent gas barrier properties and weather resistance.

[0003] When MXD6 comes into contact with oxygen or is exposed to high temperatures for extended periods, its active terminal amino groups are easily induced to form chromogenic derivatives, which can cause the resin particles to yellow. While antioxidants such as hindered phenols, aromatic amines, and phosphates, commonly used in polymerization processes, are somewhat effective in inhibiting polyamide yellowing, these antioxidants themselves, particularly aromatic amine heat stabilizers, can cause color contamination. Phosphates and their derivatives are often used as catalysts in MXD6 polymerization. Studies have shown that they inhibit yellowing without posing a risk of color contamination. However, the phosphates and their derivatives added during polymerization are partially used to accelerate the polymerization reaction rate, while the remainder is used to inhibit color change. If unchecked, the portion used to inhibit color change may result in an excessively rapid reaction rate, leading to gel formation.

[0004] In the membrane industry, in addition to yellowing, gelation of MXD6 is also a significant factor affecting membrane performance. Meta-xylylenediamine contains benzyl groups, which are highly reactive at high temperatures and easily lose hydrogen to generate free radicals. This makes MXD6 susceptible to cross-linking reactions at the benzyl methylene sites, leading to gel formation. Furthermore, higher temperatures increase the intensity of MXD6 polymerization, leading to continued polymerization in the reactor during high-temperature discharge, resulting in uneven viscosity and a broadened molecular weight distribution. The higher the viscosity of MXD6 resin, the more susceptible it is to cross-linking during melt polycondensation, which also requires longer reaction times. Producing high-viscosity MXD6 resin through direct polycondensation in a polymerization reactor increases cross-linking and yellowing due to the prolonged high-temperature reaction. Furthermore, this can lead to poor discharge from the reactor, increasing production costs.

[0005] The end group ratio also has a significant impact on the reaction activity, polymer stability and polymer molecular weight. If the diamine content is too high, it is easy to cause gel formation; if the diamine content is too low, it is easy to make it impossible to obtain a product that meets the required viscosity during the solid phase viscosity increase stage. Therefore, in the MXD6 polymerization reaction process, it is also crucial to control the ratio of dibasic acid and diamine.

[0006] The above problems have restricted the quality improvement and application expansion of MXD6 products. Therefore, a new preparation method is urgently needed to solve the above problems. Summary of the Invention

[0007] In response to the deficiencies in the prior art, the present invention aims to provide a method for preparing meta-xylylenediamine-based polyamide. By adopting a low-temperature polymerization process, the high-temperature reaction process is shortened, and yellowing of the product during the polymerization process can be effectively suppressed. At the same time, the problems of uneven relative viscosity of the discharge material and cross-linked gelation caused by high-temperature operation are solved. By precisely controlling the pH value of the salt formation process and regulating the end group ratio to a specific range, not only can the thermal stability of the polymerization process be improved and the risk of cross-linked gelation and yellowing caused by active end amino groups be reduced, but also the product that meets the target viscosity requirements can be obtained.

[0008] The technical solutions adopted by the present invention are as follows: The preparation method of the meta-xylylenediamine-based polyamide comprises the following steps: (1) mixing a dibasic acid, m-xylenediamine and water to react with each other to form a salt solution, and then adjusting the pH value of the salt solution to 6.7-7.0 by adding dibasic acid or m-xylenediamine; (2) adding a catalyst and a metal compound to the salt solution obtained in step (1) to carry out a polymerization reaction, and obtaining polymer particles after the reaction is completed; the polymerization reaction includes a pressure increase stage, a pressure maintenance and temperature increase stage, a pressure release and temperature increase stage, and a normal pressure and constant temperature stage, wherein the temperature of the normal pressure and constant temperature stage is 240-250°C; (3) Under vacuum conditions, the polymer particles obtained in step (2) are subjected to solid phase viscosity increasing treatment to a relative viscosity of 3.2-3.6, thereby obtaining the m-xylylenediamine-based polyamide.

[0009] The dibasic acid is one or more of an aliphatic dibasic acid or an aromatic dibasic acid; the molar ratio of the dibasic acid to m-xylenediamine is (1-1.05):1.

[0010] The aliphatic dibasic acid includes but is not limited to one or more of glutaric acid, adipic acid, pimelic acid, suberic acid, azelaic acid, sebacic acid, undecanedioic acid, dodecanedioic acid or tetradecanedioic acid; the aromatic dibasic acid includes but is not limited to one or more of terephthalic acid, isophthalic acid or phthalic acid.

[0011] The concentration of the salt solution is 50-60wt.%.

[0012] The temperature of the salt-forming reaction is 50-100°C, preferably 70-90°C.

[0013] The pH value of the salt solution is preferably 6.75-6.95. If the pH value of the salt solution is higher than 7.0, the viscosity of the polymerized product is uneven, and it is easy to yellow and form gel; if the pH value is lower than 6.7, the reaction rate is too slow, making it difficult to produce the target viscosity product.

[0014] The catalyst is one or more of phosphorous acid and its salts, hypophosphorous acid and its salts; for example, one or more of phosphorous acid, potassium phosphite, sodium phosphite, calcium phosphite, magnesium phosphite, manganous phosphate, hypophosphorous acid, potassium hypophosphite, sodium hypophosphite, calcium hypophosphite, magnesium hypophosphite, manganese hypophosphite, or nickel hypophosphite. Hypophosphorous acid or sodium hypophosphite is preferred, and sodium hypophosphite is more preferred.

[0015] The catalyst is added in an amount of 0.007-0.1 wt.% based on the total weight of the dibasic acid and m-xylenediamine. An amount below 0.007 wt.% has no antioxidant or catalytic effect, while an amount above 0.1 wt.% has no additional improvement in color and is likely to result in a high gel content.

[0016] The metal compound is one or more of a metal hydroxide, a metal carbonate, a metal bicarbonate or a metal weak acid salt; preferably a metal hydroxide such as lithium hydroxide, potassium hydroxide, sodium hydroxide, calcium hydroxide, zinc hydroxide, magnesium hydroxide or a metal weak acid salt such as lithium carbonate, potassium carbonate, sodium carbonate, sodium bicarbonate, calcium carbonate, magnesium carbonate, lithium acetate, potassium acetate, sodium acetate, magnesium acetate, calcium acetate, sodium stearate, calcium stearate, etc. The metal compound can be used alone or in combination as a reaction inhibitor, preferably sodium hydroxide, sodium acetate or sodium carbonate, and more preferably sodium carbonate.

[0017] comma The mass ratio of the metal compound to the catalyst is (0.4-1.5):1.

[0018] The terminal pressure of the pressurization stage in the polymerization reaction is 0.5-2.0 MPa, preferably 1.0-1.5 MPa, and the heating rate is preferably 1-10°C / min, more preferably 2-5°C / min; the pressure of the pressure-maintaining and temperature-raising stage is 0.5-2.0 MPa, the terminal temperature is 220-230°C, and the pressure-maintaining and temperature-raising time is 1-5 h; the pressure relief terminal of the pressure relief and temperature-raising stage is normal pressure, the terminal temperature is 235-245°C, and the pressure relief and temperature-raising time is 1-5 h; the pressure of the normal pressure and constant temperature stage is normal pressure, the temperature is 240-250°C, and the time is 20-100 min, preferably 30-50 min.

[0019] The relative viscosity of the polymer particles is 1.8-2.3.

[0020] The solid phase viscosity increasing treatment is carried out in a vacuum viscosity increasing device, which includes a double cone vacuum dryer, a rake vacuum dryer, a paddle vacuum dryer, a vacuum spiral ribbon dryer, and a single cone spiral ribbon vacuum dryer, preferably a double cone vacuum dryer.

[0021] The solid phase thickening treatment includes three stages: pre-crystallization, continuous thickening and cooling. The pre-crystallization temperature is 90-140°C and the pre-crystallization time is 30-200 minutes; the continuous thickening temperature is 140-240°C and the continuous thickening time is 1-10 hours; the cooling end temperature is below 60°C.

[0022] The terminal amino group content of the meta-xylylenediamine-based polyamide is 5-25 mmol / kg, preferably 10-20 mmol / kg. If the terminal amino group content is less than 5 mmol / kg, the viscosity-increasing time is too long, and the product is prone to gelling or yellowing. If the terminal amino group content is greater than 25 mmol / kg, the active terminal amino group content is high, and the product is prone to gelling.

[0023] Compared with the prior art, the present invention has the following beneficial effects: (1) The present invention adopts a low-temperature polymerization process, which can avoid the yellowing and gelation of the reaction raw materials and polymerization products due to long-term exposure to high-temperature environments, thereby producing a meta-xylylenediamine-based polyamide product with excellent chromaticity and low gel content; (2) The present invention effectively solves the problem of excessively rapid viscosity increase of materials during the discharging process by adopting a low-temperature polymerization process, and successfully produces a meta-xylylenediamine-based polyamide product with stable and uniform viscosity; (3) By adjusting the salt-forming process, the present invention can accurately control the ratio of dibasic acid to diamine, and regulate the content of active terminal amino groups within the range of 5-25 mmol / kg. While achieving the target relative viscosity, it reduces the risk of cross-linking gel and yellowing caused by excessive active terminal amino group content, thereby improving the thermal stability of the polymerization process. (4) The present invention improves the relative viscosity of the polymer product through a solid phase viscosity increasing process, which can shorten the high temperature experience time of the polymer product and reduce the amount of gel generated. DETAILED DESCRIPTION

[0024] The present invention will be further described below with reference to the following examples, but they do not limit the implementation of the present invention.

[0025] Unless otherwise specified, the raw materials used in the examples and comparative examples are conventional commercially available raw materials, and the process methods used in the examples and comparative examples are conventional methods in the art unless otherwise specified.

[0026] Example 1 The preparation method of the meta-xylylenediamine-based polyamide comprises the following steps: (1) Add 12 kg of water to a 50 L stainless steel salting kettle, add 7.1 kg of adipic acid to the salting kettle through the feed port, slowly add 6.6 kg of m-xylenediamine, raise the temperature in the salting kettle to 80 ° C, and start stirring to carry out the salting reaction. After the salt solution is completely clarified, the pH of the salt solution is tested with a pH meter, and the pH value of the salt solution is adjusted to 6.9 by adding adipic acid or m-xylenediamine; (2) After the salt formation is completed, 1000 mg of sodium hypophosphite and 520 mg of sodium carbonate are added to the salt solution, mixed evenly and then pumped into the polymerization reactor, and stirring and heating are started to carry out the polymerization reaction. The polymerization reaction includes a pressure increase stage, a pressure holding and temperature increase stage, a pressure release and temperature increase stage and a normal pressure and constant temperature stage, wherein the terminal pressure of the pressure increase stage is 1.5 MPa; the pressure in the polymerization reactor is maintained at 1.5 MPa and the terminal temperature is 230°C in the pressure holding and temperature increase stage, and the pressure holding and temperature increase time is 3 hours; in the pressure release and temperature increase stage, the exhaust valve opening is adjusted to gradually release the pressure and discharge the water vapor in the polymerization reactor, the pressure release terminal is normal pressure, the terminal temperature is 245°C, and the pressure release and temperature increase time is 2 hours; the pressure in the normal pressure and constant temperature stage is normal pressure, the temperature is 245°C, and the time is 30 minutes. After the reaction is completed, nitrogen is introduced, and the material in the reactor is discharged at 245°C, and pelletized by a pelletizer to obtain polymer particles; (3) Under vacuum conditions of <100 Pa, the polymer particles obtained in step (2) are added to a 100L double-cone vacuum dryer for solid-phase thickening treatment, wherein the solid-phase thickening treatment includes three stages: pre-crystallization, continuous thickening, and cooling, wherein the pre-crystallization temperature is 100°C, and the pre-crystallization time is 60 min; the continuous thickening temperature is 170°C, and the continuous thickening time is 6 h; after the continuous thickening is completed, the material is cooled by blowing nitrogen to below 60°C, thereby obtaining the m-xylylenediamine polyamide.

[0027] Example 2 The difference from Example 1 is that in step (1), the pH value of the salt solution is adjusted to 6.7, and the rest is the same as Example 1.

[0028] Example 3 The difference from Example 1 is that in step (1), the pH value of the salt solution is adjusted to 7.0, and the rest is the same as Example 1.

[0029] Example 4 The difference from Example 1 is that in step (2), the temperature of the constant temperature stage at normal pressure during the polymerization reaction is 240°C, nitrogen is introduced after the reaction is completed, and the materials in the kettle are discharged at 240°C. Other aspects are the same as in Example 1.

[0030] Example 5 The difference from Example 1 is that in step (2), the temperature of the constant temperature stage at normal pressure during the polymerization reaction is 250°C, nitrogen is introduced after the reaction is completed, and the material in the kettle is discharged at 250°C. Other aspects are the same as in Example 1.

[0031] Comparative Example 1 The difference from Example 1 is that in step (1), the pH value of the salt solution is adjusted to 6.3, and the rest is the same as Example 1.

[0032] Comparative Example 2 The difference from Example 1 is that in step (1), the pH value of the salt solution is adjusted to 6.6, and the rest is the same as Example 1.

[0033] Comparative Example 3 The difference from Example 1 is that in step (1), the pH value of the salt solution is adjusted to 7.2, and the rest is the same as Example 1.

[0034] Comparative Example 4 The difference from Example 1 is that in step (1), the pH value of the salt solution is adjusted to 7.5, and the rest is the same as Example 1.

[0035] Comparative Example 5 The difference from Example 1 is that in step (2), the temperature of the constant temperature stage at normal pressure during the polymerization reaction is 255°C, nitrogen is introduced after the reaction is completed, and the materials in the kettle are discharged at 255°C. Other aspects are the same as in Example 1.

[0036] Comparative Example 6 The difference from Example 1 is that in step (2), the temperature of the constant temperature stage at normal pressure during the polymerization reaction is 265°C, nitrogen is introduced after the reaction is completed, and the material in the kettle is discharged at 265°C. Other aspects are the same as in Example 1.

[0037] Comparative Example 7 The difference from Example 1 is that in step (2), sodium hypophosphite and sodium carbonate are not added, and the rest is the same as Example 1.

[0038] Comparative Example 8 The difference from Example 1 is that in step (2), 70 mg of sodium hypophosphite and 40 mg of sodium carbonate are added to the saline solution, and the rest is the same as in Example 1.

[0039] Comparative Example 9 The difference from Example 1 is that in step (2), 21000 mg of sodium hypophosphite and 11400 mg of sodium carbonate are added to the saline solution, and the rest is the same as in Example 1.

[0040] Comparative Example 10 The difference from Example 1 is that in step (2), 1000 mg of sodium hypophosphite and 0 mg of sodium carbonate are added to the saline solution, and the rest is the same as in Example 1.

[0041] Comparative Example 11 The difference from Example 1 is that in step (2), 1000 mg of sodium hypophosphite and 270 mg of sodium carbonate are added to the saline solution, and the rest is the same as in Example 1.

[0042] Comparative Example 12 The difference from Example 1 is that in step (2), 1000 mg of sodium hypophosphite and 100 mg of sodium carbonate are added to the saline solution, and the rest is the same as Example 1.

[0043] The relative viscosity of the product at the beginning and at the end of the material discharge process in step (2) of Examples 1-5 and Comparative Examples 1-12 was tested. The relative viscosity, terminal amino group content, gel content, and yellowness value of the m-xylylenediamine-based polyamide prepared in step (3) of Examples 1-5 and Comparative Examples 1-12 were tested. The test results are shown in Tables 1-5.

[0044] The test method is as follows: Relative viscosity: Tested in accordance with GB / T 12006.1-2009.

[0045] Yellowness value: Tested using a colorimeter.

[0046] Gel content: Weigh 0.5g of m-xylylenediamine polyamide into a 100mL Erlenmeyer flask and add 50mL of concentrated sulfuric acid (98wt%). Place the flask in a 60°C oil bath and dissolve with constant stirring for 2 hours (to ensure complete dispersion and dissolution). After dissolution is complete, remove the flask and allow the solution to cool to room temperature. Then, filter the solution under reduced pressure into a clean beaker using a G2 sand-core funnel that has been pre-dried to constant weight and accurately measured (recorded as m1). After filtration, slowly rinse the sand core funnel with anhydrous ethanol three times (to ensure that the residual solution is completely transferred), then place the G2 sand core funnel in a 110°C hot air oven and dry it to constant weight. After taking it out, place it in a desiccator and cool it to room temperature. Accurately weigh its mass (recorded as m2), and calculate the gel content using the following formula: Gel content (100wt.%) = (m1-m2) / m0 mass of meta-xylylenediamine polyamide × 100%, where m0 is the mass of meta-xylylenediamine polyamide (g).

[0047] Terminal amino group content: Weigh 0.5 g of m-xylylenediamine polyamide into a 100 mL Erlenmeyer flask and add 50 mL of m-cresol. The flask is then placed in a 140°C oil bath and heated until the sample is completely dissolved. Once dissolved, remove the flask and cool to room temperature. Transfer the entire solution to the measuring cup of a potentiometric titrator. Rinse the flask three times with ethanol, combining the rinses after each rinse and transferring them to the measuring cup to ensure no residue remains. Finally, determine the terminal amino group content (mmol / kg) by potentiometric titration.

[0048] Table 1 Performance test results of the embodiment

[0049] As can be seen from Examples 1-3 in Table 1, adjusting the pH value of the salt solution within the range of 6.7-7.0 can meet the performance target of the developed product. As can be seen from Examples 1, 4, and 5, the target product can be obtained by adjusting the temperature of the constant temperature stage at normal pressure during the polymerization reaction within the range of 240-250°C.

[0050] Table 2 Performance test results of Example 1 and Comparative Examples 1-4

[0051] As can be seen from Table 2, the pH value of the salt solution in Comparative Examples 1-2 is too low, the reaction activity is poor, and the target viscosity product cannot be obtained; the pH value of the salt solution in Comparative Examples 3-4 is too high, resulting in fluctuations in the viscosity of the discharge during the polymerization process. At the same time, the viscosity-increasing process is highly active, the product is prone to excessive viscosity increase, and is prone to gel formation and yellowing.

[0052] Table 3 Performance test results of Example 1 and Comparative Examples 5-6

[0053] Table 3 shows that, compared to higher polymerization temperatures, controlling the temperature during both the atmospheric and constant-pressure polymerization and discharge stages at 245°C resulted in better relative viscosity stability during the discharge process. Furthermore, after subsequent viscosity-enhancing treatment, the gel content and yellowness of the product remained relatively low. This is because lower polymerization temperatures significantly enhance the thermal stability of the polymer, effectively suppressing high-temperature-induced cross-linking and gelation reactions and color formation caused by oxidation of end-amino groups during polymerization and discharge, thereby ensuring uniform viscosity and color performance. When the temperature during both the atmospheric and constant-pressure polymerization and discharge stages exceeded 250°C, the gel content and color of the product tended to increase.

[0054] Table 4 Performance test results of Example 1 and Comparative Examples 7-9

[0055] As shown in Table 4, sodium hypophosphite has both antioxidant and catalytic effects during the polymerization process. When the sodium hypophosphite addition level is too low, both its antioxidant and catalytic effects are poor. When the sodium hypophosphite addition level is too high, while it significantly improves the polymer color, it can lead to large fluctuations in relative viscosity during discharging, and significantly increase the gel content of the product after subsequent thickening treatment. Sodium carbonate neutralizes the acid activity of sodium hypophosphite, inhibiting reaction activity and gelation. This effect gradually weakens with increasing sodium hypophosphite content. When the sodium hypophosphite content is below 0.01%, the reaction activity is too low, which is not conducive to product thickening. When the sodium hypophosphite content is above 0.1%, the inhibitory effect of sodium carbonate becomes poor, making the product polymerization and thickening process difficult to control, and the viscosity fluctuates greatly.

[0056] Table 5 Performance test results of Example 1 and Comparative Examples 10-12

[0057] It can be seen from Table 5 that an appropriate amount of sodium carbonate can control the abnormal growth of gel in the polymer during polymerization and thickening, but an excessive proportion will also hinder the solid phase thickening rate.

Claims

1. A method for preparing meta-xylylenediamine polyamide, characterized in that: The following steps are involved: (1) mixing a dibasic acid, m-xylenediamine and water to react with each other to form a salt solution, and then adjusting the pH value of the salt solution to 6.7-7.0 by adding dibasic acid or m-xylenediamine; (2) adding a catalyst and a metal compound to the salt solution obtained in step (1) to carry out a polymerization reaction, and obtaining polymer particles after the reaction is completed; the polymerization reaction includes a pressure increase stage, a pressure maintenance and temperature increase stage, a pressure release and temperature increase stage, and a normal pressure and constant temperature stage, wherein the temperature of the normal pressure and constant temperature stage is 240-250°C; (3) Under vacuum conditions, the polymer particles obtained in step (2) are subjected to solid phase viscosity increasing treatment to a relative viscosity of 3.2-3.6, thereby obtaining the m-xylylenediamine-based polyamide; The added amount of the catalyst is 0.007-0.1wt.% of the total weight of the dibasic acid and m-xylenediamine, and the mass ratio of the metal compound to the catalyst is (0.4-1.5):

1.

2. The method for preparing meta-xylylenediamine polyamide according to claim 1, wherein The dibasic acid is one or more of an aliphatic dibasic acid or an aromatic dibasic acid; the molar ratio of the dibasic acid to m-xylenediamine is (1-1.05):

1.

3. The method for preparing meta-xylylenediamine polyamide according to claim 1, wherein: The concentration of the salt solution is 50-60wt.%.

4. The method for preparing meta-xylylenediamine-based polyamide according to claim 1, wherein: The temperature of the salt-forming reaction is 50-100°C.

5. The method for preparing meta-xylylenediamine-based polyamide according to claim 1, wherein: The catalyst is one or more of phosphorous acid and its salt compounds, hypophosphorous acid and its salt compounds.

6. The method for preparing meta-xylylenediamine-based polyamide according to claim 1, wherein: The metal compound is one or more of metal hydroxide, metal carbonate, metal bicarbonate or metal weak acid salt.

7. The method for preparing meta-xylylenediamine-based polyamide according to claim 1, wherein: The terminal pressure of the pressure-raising stage in the polymerization reaction is 0.5-2.0 MPa; the pressure of the pressure-maintaining and temperature-raising stage is 0.5-2.0 MPa, the terminal temperature is 220-230°C, and the pressure-maintaining and temperature-raising time is 1-5 hours; the pressure-relieving and temperature-raising stage has a pressure-relieving terminal at normal pressure, a terminal temperature at 235-245°C, and a pressure-relieving and temperature-raising time of 1-5 hours; and the pressure of the normal pressure and constant temperature stage is normal pressure, and the time is 20-100 minutes.

8. The method for preparing meta-xylylenediamine-based polyamide according to claim 1, wherein: The relative viscosity of the polymer particles is 1.8-2.

3.

9. The method for preparing meta-xylylenediamine-based polyamide according to claim 1, wherein: The solid phase thickening treatment includes three stages: pre-crystallization, continuous thickening and cooling. The pre-crystallization temperature is 90-140°C and the pre-crystallization time is 30-200 minutes; the continuous thickening temperature is 140-240°C and the continuous thickening time is 1-10 hours; the cooling end temperature is below 60°C.

10. The method for preparing meta-xylylenediamine-based polyamide according to claim 1, wherein: The terminal amino group content of the meta-xylylenediamine polyamide is 5-25 mmol / kg.

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