Low-temperature preparation method of high-temperature-resistant semi-aromatic polyamide

Abstract

This invention belongs to the field of nylon polymers and discloses a low-temperature preparation method for high-temperature resistant semi-aromatic polyamide, including the following steps: (1) Weigh diacid, diamine, antioxidant, catalyst and deionized water according to the designed molar number, add the raw materials to a high-temperature and high-pressure polymerization reactor, the predetermined temperature of the polymerization reactor is 190-230℃, the pressure is raised to the first predetermined pressure of 1.2-2.6MPa, and the temperature and pressure are maintained for 0.5-3h. The pressure inside the reactor is gradually reduced to the second predetermined pressure of 0.5-1.0MPa by venting, and the venting time is 0.5-3h. Finally, the prepolymer is sprayed out from the bottom of the polymerization reactor to obtain a loose porous dry powder / small particle prepolymer, and there is no prepolymer residue in the reactor; (2) The prepolymer obtained above is subjected to solid-phase post-polymerization in a solid-phase post-polymerization reactor to obtain a high-temperature resistant semi-aromatic polyamide final polymer with a relative viscosity of 2.0-5.0. The method of this invention is suitable for preparing high-temperature resistant semi-aromatic polyamides with different compositions. The resulting prepolymer has a loose and porous powder / small particle structure, which provides a favorable channel for the discharge of water molecules, a byproduct of the solid-state polymerization reaction. This can significantly improve the efficiency of solid-state polymerization, shorten the polymerization time, and reduce energy consumption.

Description

Technical Field

[0001] This invention belongs to the field of polymer material synthesis technology, specifically relating to a low-temperature preparation method for a high-temperature resistant semi-aromatic polyamide. Background Technology

[0002] High-temperature resistant polyamides refer to polyamide materials that can be used for extended periods in environments above 150°C. Their melting points are generally between 290 and 320°C, and they maintain excellent mechanical properties over a wide temperature range and in high-humidity environments. High-temperature resistant polyamides exhibit good wear resistance, heat resistance, oil resistance, and chemical resistance. The water absorption and shrinkage rates of the raw materials are significantly reduced, demonstrating excellent dimensional stability and superior mechanical strength. Common types of high-temperature resistant polyamides include aliphatic, semi-aromatic, and fully aromatic polyamides. Compared to fully aromatic polyamides, semi-aromatic polyamides have more flexible molecular chains and higher crystallinity. Compared to aliphatic polyamides, the introduction of rigid benzene rings gives semi-aromatic nylon a higher melting point, allowing for conventional melt processing. With excellent overall performance, they are widely used in the plasticization of metal components such as engine parts, fuel systems, exhaust systems, and cooling systems, improving the heat resistance and weight of these components.

[0003] CN 118325071A describes a method for synthesizing bio-based semi-aromatic high-temperature resistant polyamide PA5T / 56 using a "polyamide salt + prepolymerization + post-polymerization thickening" approach. First, PA5T and PA56 salts are synthesized separately at 45℃–55℃ and dried. Then, a mixed salt solution with a mass concentration of 30%–50% is prepared. The solution is concentrated to 60%–80% in a high-pressure reactor at 110–130℃. The reactor is then heated further to 220–230℃ while maintaining a stable pressure of 1.8–2.2 MPa. The reaction proceeds for 2–2.5 hours, followed by venting for 2–4 hours. The reactor is then heated under normal pressure to 240–270℃ for 1–1.5 hours to obtain the prepolymer. The prepolymer is then transferred to a solid-phase thickening reactor or a vacuum solid-phase reactor. In the post-polymerization reactor, the vacuum was reduced to below 80 Pa, and the reaction was carried out at 220–270 °C for 8–16 h to finally obtain bio-based semi-aromatic high-temperature resistant polyamide PA5T / 56; CN115873239B also uses the method of "polyamide salt + prepolymerization + post-polymerization thickening" to synthesize PA10T modified copolymer. The salt formation reaction was carried out at 85–105 °C for 0.5–1.5 h to obtain modified PA10T salt. The obtained modified PA10T salt was heated to 220–280 °C and pressurized to 2.5–3.5 MPa to carry out pre-condensation reaction for 1.5–2.5 h to obtain pre-condensation modified PA10T. The obtained pre-condensation modified PA10T was further heated to 285–325 °C and carried out final condensation reaction at a negative pressure of 5±2 kPa for 1–2 h to obtain copolymerized modified PA10T. This method involves three steps. The PA10T salt requires drying, a cumbersome process that increases system time. The post-solid-phase polymerization temperature is near the melting point, making it prone to side reactions such as oxidation and cross-linking, affecting the product's appearance and quality. CN118667150A, CN112646174B, CN118667149A, and CN110684190B use a "pre-polymerization + post-polymerization thickening" method to synthesize high-temperature resistant polyamides. In the pre-polymerization stage, the material is vented to atmospheric pressure, then cooled, discharged, crushed, and finally thickened in the solid phase. This method is commonly used in laboratory settings and is not suitable for industrial production. Our research group's invention patents CN 112409594B and CN 112321820B employ a "direct solid-state polymerization method" to synthesize short-chain semi-aromatic polyamides and long-chain semi-aromatic polyamides. The method involves the direct solid-state polymerization of the polyamide salt, antioxidant, and catalyst under dynamic mixing conditions. The advantages of this method are that both the polyamide salt and the product are in solid powder form, the reaction temperature is relatively low, and there are few side reactions. However, this method uses semi-aromatic diacids and diamines as starting materials, requiring the prior preparation of the semi-aromatic diacids and diamines before direct solid-state polymerization to obtain the final semi-aromatic polyamide.

[0004] CN 114181390 B describes a one-step method for preparing bio-based high-temperature resistant polyamides. Aromatic diacid, bio-based diamine, aliphatic comonomer, composite catalyst, antioxidant, molecular weight regulator, lubricant, and deionized water are sequentially added to a reactor, and stirring is initiated. The reaction is maintained at 50–100°C for 1 hour to allow the diacid and diamine to form a salt and mix evenly. The temperature is then increased to 130–180°C, and the reaction is continued for 0.5–1.5 hours to enhance salt formation and ensure complete dissolution of the raw materials. The temperature is then further increased to 200–230°C to enter the pressure-holding prepolymerization stage, with slight venting and the pressure adjusted to 1.8–2.1 MPa. The reaction is maintained at this temperature for 2–5 hours. h, allowing the raw materials to fully prepolymerize; continue heating to 280℃, and venting to maintain the pressure inside the reactor at 1.8–2.1 MPa; continue heating, raising the temperature to 290℃ within 0.5 hours, while slowly venting to reduce the pressure inside the reactor to atmospheric pressure, then closing the vent valve, and finally polymerizing at 290℃ and atmospheric pressure for 15–60 minutes, continuously venting newly generated water vapor during this period; finally, raise the temperature to 290–310℃, and slowly evacuate, reacting at a negative pressure of -0.06–-0.09 MPa for 5–20 minutes until the stirring speed drops to 20 rpm, then stop stirring, purge with nitrogen to restore a slightly positive pressure, discharge, pelletize, and dry. This method involves a long reaction time and high reaction temperature, making subsequent discharge and pelletizing difficult.

[0005] CN105061755 B uses a "prepolymerization + postpolymerization thickening" method to synthesize high-temperature resistant polyamide. In the prepolymerization stage, the temperature is first raised to above 160°C and the pressure inside the reactor is raised to above 1.2 MPa. Then, the temperature inside the reactor is further increased to above 250°C, and water vapor inside the polymerization reactor is released to gradually reduce the pressure inside the reactor to below 0.8 MPa, resulting in a prepolymer. The prepolymer is then crushed and then melt-thickened using an extruder to synthesize high-temperature resistant polyamide. This method requires the prepolymer to be crushed and uses melt-thickening. The reaction temperature is above the melting point of the final polymer. The high reaction temperature makes the product prone to oxidation and the appearance of black spots.

[0006] Therefore, it is necessary to develop a low-temperature preparation method for producing high-quality, stable, high-temperature resistant semi-aromatic polyamide products. Summary of the Invention

[0007] The purpose of this invention is to provide a low-temperature preparation method for high-temperature resistant semi-aromatic polyamides. This preparation method has the characteristics of low reaction temperature, short polymerization time, high polymerization efficiency, and good product appearance and quality.

[0008] To achieve the above-mentioned objectives, the present invention adopts the following technical solution:

[0009] A low-temperature preparation method for a high-temperature resistant semi-aromatic polyamide includes the following preparation steps:

[0010] (1) Prepolymerization

[0011] Weigh out the diacid, diamine, catalyst, antioxidant, and deionized water according to the specified proportions and add them to a high-temperature and high-pressure polymerization reactor. Under inert gas protection, heat the reactor to a predetermined temperature of 190–230°C and raise the pressure to a first predetermined pressure of 1.2–2.6 MPa, maintaining the temperature and pressure for 0.5–3 hours. Gradually reduce the pressure inside the reactor to a second predetermined pressure of 0.5–1.0 MPa by venting, with a venting time of 0.5–3 hours. Then, under the second predetermined pressure, spray the prepolymer from the bottom of the polymerization reactor to obtain a loose and porous powder / particle polyamide prepolymer with a relative viscosity of 1.1–1.7. The diacid or diamine contains an aromatic ring structure.

[0012] (2) Solid-state post-polymerization

[0013] The prepolymer obtained in step (1) is placed in a solid-phase polymerization reactor. Under inert gas protection, the reactor is heated to 200-250°C and pressure is 0.2-0.8 MPa. The temperature and pressure are maintained for 10-60 min. Then, the gas is vented to atmospheric pressure within 30-60 min. Then, the vacuum is drawn to 5-200 Pa and the temperature and pressure are maintained for 0-6 h. The temperature is then lowered to obtain a powder / small granular high-temperature resistant semi-aromatic polyamide product with a relative viscosity of 2.0-5.0.

[0014] In this invention, the material is kept at a high temperature and pressure in a polymerization reactor for 0.5 to 3 hours. Specifically, after the target polymerization temperature of 190-230°C is reached, the pressure inside the system rises to 1.2 to 2.6 MPa, and the material is kept at this temperature and pressure for 0.5 to 3 hours. Then, the pressure inside the reactor is gradually reduced to a second predetermined pressure of 0.5 to 1.0 MPa by venting the gas, and the venting time is 0.5 to 3 hours. By controlling the polymerization temperature, the holding time, the venting pressure, and the venting time, this invention can promote the effective discharge of the prepolymer and ensure that the viscosity of the sprayed prepolymer is moderate. This is beneficial for both the efficient spraying of the prepolymer and the post-solid phase polymerization. The relative viscosity of the prepolymer in this invention is 1.1 to 1.7. The particle size of the prepolymer sprayed using the process of this invention is between 0.075 and 5.0 mm. It does not need to be crushed and can be directly subjected to post-solid phase polymerization. The particle size of the final polymer is also between 0.075 and 5.0 mm.

[0015] As a further preferred embodiment of the present invention, the diamine is preferably one or a mixture of two or more of the following: pentamethylenediamine, hexanediamine, decanediamine, undecanediamine, dodecadecanediamine, tridecanediamine, tetradecanediamine, m-phenylenediamine, p-phenylenediamine, 4,4'-diamino-dicyclohexylmethane, 3,3'-dimethyl-4,4'-diamino-dicyclohexylmethane, and 1,5-diaminonaphthalene.

[0016] As a further preferred embodiment of the present invention, the dicarboxylic acid is one or a mixture of two or more aliphatic dicarboxylic acids, aromatic dicarboxylic acids, alicyclic dicarboxylic acids, and naphthyl dicarboxylic acids; as a further preferred embodiment of the present invention, the dicarboxylic acid is one or a mixture of two or more succinic acid, glutaric acid, adipic acid, azelaic acid, sebacic acid, dodecanoic acid, tridecanoic acid, terephthalic acid, isophthalic acid, 2,6-naphthalenedicarboxylic acid, and 1,4-cyclohexanedicarboxylic acid.

[0017] As a further preferred embodiment of the present invention, the catalyst is one or a mixture of two or more of phosphorous acid, sodium hypophosphite, triphenyl phosphate, and H10, and the amount of catalyst used is 0.1 to 0.6% of the total weight of the diacid and the diamine.

[0018] As a further preferred embodiment of the present invention, the antioxidant is one or a mixture of two or more of sodium hypophosphite, antioxidant 1010, antioxidant S9228, antioxidant SH120, antioxidant B215, magnesium hypophosphite, calcium hypophosphite and zinc hypophosphite, and the amount of antioxidant used is 0.1 to 0.5% of the total weight of the diacid and diamine.

[0019] As a further preferred embodiment of the present invention, in step (1), when the prepolymer is ejected, it needs to be protected by an inert gas, which is one of nitrogen, carbon dioxide and argon.

[0020] In this invention, the solid-state post-polymerization is divided into a positive pressure stage and a negative pressure stage. The purpose of the positive pressure stage is to ensure constant composition and further increase molecular weight, while the purpose of the negative pressure stage is to further prepare high-viscosity, high-temperature resistant semi-aromatic polyamide. The method of this invention is applicable not only to the preparation of homopolymer high-temperature resistant semi-aromatic polyamide, but also to the preparation of copolymer high-temperature resistant semi-aromatic polyamide.

[0021] This invention prepares a prepolymer of a certain molecular weight at low temperature, achieves stable output of powdered or granular prepolymer, and then performs solid-phase post-polymerization. The reaction temperature of the entire system is 190-250℃, which is more than 80℃ lower than the melting point of the product. The low reaction temperature results in fewer by-products, less oxidation, and good product quality.

[0022] The overall reaction temperature of this process is between 190 and 250℃. The low reaction temperature results in a short polymerization time, high polymerization efficiency, and good product appearance and quality. The prepolymer is directly discharged under a pressure of 0.5–1.0 MPa, appearing as a dry, porous powder / granule, requiring no crushing and allowing for direct solid-state post-polymerization. Simultaneously, the porous structure of the prepolymer provides a favorable channel for the discharge of water molecules, a byproduct of the solid-state polymerization reaction, promoting the forward reaction and significantly improving the efficiency of solid-state polymerization, shortening the polymerization time, and increasing overall polymerization efficiency. The final polymer is a white polyamide product with stable composition, suitable particle size, and a relative viscosity of 2.0–5.0.

[0023] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0024] The method of the present invention (1) is applicable to the preparation of homopolymer or copolymer high-temperature resistant semi-aromatic polyamide; (2) the prepolymerization reaction temperature is low, it is not easy to oxidize and the prepolymer is easy to be discharged from the reactor with basically no residue; (3) the discharged prepolymer is a powder / small particle porous structure, which provides a favorable channel for the discharge of water molecules, a by-product of solid-phase polymerization reaction, which can greatly improve the efficiency of solid-phase polymerization, shorten the polymerization time and reduce energy consumption; (4) the discharged prepolymer does not need to be cooled, dried and crushed, and can be directly subjected to solid-phase polymerization reaction; (5) the prepolymerization and solid-phase polymerization reaction temperatures of the method of the present invention are both more than 80°C lower than the melting point of the product, which effectively avoids the occurrence of side reactions, and the product has good performance and high whiteness. Attached Figure Description

[0025] Figure 1 The TG diagrams are for the final polymers of Examples 1, 4, 5, 7, and 14.

[0026] Figure 2 The following are the DSC diagrams of the final polymers from Examples 1, 4, 5, 7, and 14.

[0027] Figure 3 The image shows the FT-IR spectrum of the final polymer of the copolyamide PA6T / 66 obtained in Example 6.

[0028] Figure 4 The image shows the 1H-NMR spectrum of the final polymer of the copolyamide PA6T / 66 obtained in Example 6.

[0029] Figure 5 This is a diagram of the prepolymer of the copolyamide PA6T / 66 obtained in Example 6.

[0030] Figure 6 The image shows the SEM image of the prepolymer of copolyamide PA6T / 66 obtained in Example 6.

[0031] Figure 7 The image shows the prepolymer of the copolyamide PA6T / 10T obtained in Comparative Example 4. Detailed Implementation

[0032] The present invention will be further described below with reference to specific embodiments.

[0033] In the embodiments of the present invention, the preparation method of high-temperature resistant polyamide includes the following steps: (1) prepolymerization

[0034] Weigh the raw materials—diacid, diamine, catalyst, antioxidant, and deionized water—according to the designed molar amounts, and add them to a high-temperature, high-pressure polymerization reactor. Seal the reactor and replace the air inside with inert gas three times. Heat the polymerization reactor to a predetermined temperature of 190–230°C, and raise the pressure to a first predetermined pressure of 1.2–2.6 MPa, maintaining the temperature and pressure for 0.5–3 hours. Gradually reduce the pressure inside the reactor to a second predetermined pressure of 0.5–1.0 MPa by venting, venting for 0.5–3 hours. Finally, under the second predetermined pressure, spray the prepolymer from the bottom of the polymerization reactor to obtain a loose, porous powder / particle polyamide prepolymer with a relative viscosity of 1.1–1.7. The diacid or diamine contains an aromatic ring structure.

[0035] (2) Solid-state post-polymerization

[0036] The prepolymer obtained in (1) above was placed in a solid-phase polymerization reactor for solid-phase post-polymerization. The reactor was sealed, and the air inside was replaced three times with inert gas. The reactor was heated to 200–250°C and pressure was 0.2–0.8 MPa, and the temperature and pressure were maintained for 10–60 min. Then, the pressure was reduced to atmospheric pressure for 30–60 min. The pressure was then evacuated to 5–200 Pa and maintained for 0–6 h. The reactor was cooled to obtain a powder / small granular high-temperature resistant semi-aromatic polyamide product with a relative viscosity of 2.0–5.0.

[0037] Specific embodiments of the preparation method of the high-temperature resistant semi-aromatic polyamide of the present invention are as follows:

[0038] Example 1:

[0039] This embodiment describes a method for preparing high-temperature resistant semi-aromatic polyamide PA10T, including the following steps:

[0040] (1) Preparation of PA10T prepolymer

[0041] The following ingredients were weighed: 688g of decanediamine, 664g of terephthalic acid, 338g of water, 0.4% of the total weight of sodium hypophosphite (dicarboxylic acid and diamine), and 0.3% of the total weight of antioxidant 1010 (dicarboxylic acid and diamine). These were added to a high-temperature, high-pressure polymerization reactor. The reactor was purged three times with nitrogen, heated to 200°C, and pressurized to 2.0 MPa. The reactor was held at this temperature and pressure for 1.5 hours, then vented to 0.9 MPa for 2.0 hours. The prepolymer was ejected from the bottom of the reactor, resulting in a loose, porous powder / particle prepolymer with a relative viscosity of 1.1.

[0042] (2) Preparation of PA10T

[0043] The PA10T prepolymer obtained in (1) above was put into a solid-phase post-polymerization reactor for solid-phase post-polymerization. The temperature and pressure were maintained at 230°C and 0.4 MPa for 10 min. Then the pressure was reduced to normal and the pressure was reduced for 40 min. Then a vacuum was drawn with a vacuum degree of 10 Pa and the temperature and pressure were maintained for 5 h to obtain a high-temperature resistant semi-aromatic polyamide product with a relative viscosity of 3.5.

[0044] Example 2:

[0045] This embodiment describes a method for preparing high-temperature resistant semi-aromatic polyamide PA12T, including the following steps:

[0046] (1) Preparation of PA12T prepolymer

[0047] Weigh out 800g of dodecyl diamine, 664g of terephthalic acid, and 366g of water. Add sodium hypophosphite at 0.4% of the total weight of the diacid and diamine, and antioxidant 1010 at 0.3% of the total weight of the diacid and diamine. Place these ingredients into a high-temperature, high-pressure polymerization reactor. Replace the gas with nitrogen three times, heat to 210℃, maintain the pressure at 2.2MPa for 1.0h, then vent to 0.9MPa for 2.0h. The prepolymer is then sprayed from the bottom of the reactor, resulting in a loose, porous powder / particle prepolymer with a phase viscosity of 1.2.

[0048] (2) Preparation of PA12T

[0049] The PA12T prepolymer obtained in (1) above was put into a solid-phase post-polymerization reactor for solid-phase post-polymerization. The temperature and pressure were maintained at 230°C and 0.6 MPa for 50 min. Then the pressure was reduced to normal and the pressure was reduced for 50 min. Then a vacuum was drawn with a vacuum degree of 10 Pa and the temperature and pressure were maintained for 5 h to obtain a high-temperature resistant semi-aromatic polyamide product with a relative viscosity of 3.8.

[0050] Example 3:

[0051] This embodiment describes a method for preparing high-temperature resistant semi-aromatic polyamide PA10N, including the following steps:

[0052] (1) Preparation of PA10N prepolymer

[0053] The following materials were weighed: 516g of decanediamine, 648g of 2,6-dinaphtholic acid, and 291g of water. The mass of sodium hypophosphite was 0.1% of the total weight of the diacid and diamine. The mass of antioxidant 1010 was also 0.1% of the total weight of the diacid and diamine. These materials were then added to a high-temperature and high-pressure polymerization reactor. The reactor was purged with nitrogen three times, heated to 230°C, and the pressure was 2.6 MPa. The reactor was held at this temperature and pressure for 3 hours. The pressure was then vented to 1.0 MPa for 3 hours. The prepolymer was then sprayed from the bottom of the polymerization reactor, resulting in a loose and porous powder / particle prepolymer with a relative viscosity of 1.7.

[0054] (2) Preparation of PA10N

[0055] The PA10N prepolymer obtained in (1) above was put into a solid-phase post-polymerization reactor for solid-phase post-polymerization. The temperature and pressure were maintained at 250°C and 0.8 MPa for 60 min. Then the pressure was reduced to normal and the pressure was reduced for 60 min. Then the vacuum was drawn with a vacuum degree of 5 Pa and the temperature and pressure were maintained for 6 h to obtain a high-temperature resistant semi-aromatic polyamide product with a relative viscosity of 3.6.

[0056] Example 4:

[0057] This embodiment describes a method for preparing high-temperature resistant semi-aromatic polyamide PA6T / 6, including the following steps:

[0058] (1) Preparation of PA6T / 6 prepolymer

[0059] The following ingredients were weighed: hexamethylenediamine (278.4 g), terephthalic acid (398.4 g), caprolactam (180.8 g), and water (214.4 g). Sodium hypophosphite was added at 0.4% of the total weight of the diacid and diamine, and antioxidant 1010 was added at 0.3% of the total weight of the diacid and diamine. These were then added to a high-temperature, high-pressure polymerization reactor. The reactor was purged with nitrogen three times, heated to 210°C, and pressurized at 2.2 MPa for 0.5 h. The pressure was then reduced to 0.5 MPa and the venting time was 2.5 h. The prepolymer was ejected from the bottom of the reactor, resulting in a loose, porous powder / particle prepolymer with a relative viscosity of 1.1.

[0060] (2) Preparation of PA6T / 6

[0061] The PA6T / 6 prepolymer obtained in (1) above was put into a solid-phase post-polymerization reactor for solid-phase post-polymerization. The temperature and pressure were maintained at 220℃ and 0.2MPa for 10 minutes. Then the pressure was reduced to normal and the venting time was 1.5h. Then a vacuum was drawn with a vacuum degree of 100Pa and the temperature and pressure were maintained for 0h to obtain a high-temperature resistant semi-aromatic polyamide product with a relative viscosity of 2.0.

[0062] Example 5:

[0063] This embodiment describes a method for preparing high-temperature resistant semi-aromatic polyamide PA5T / 56, including the following steps:

[0064] (1) Preparation of PA5T / 56 prepolymer

[0065] The following ingredients were weighed: 510g of pentanediamine, 415g of terephthalic acid, 340g of adipic acid (molar ratio of terephthalic acid to adipic acid 5 / 5), 316.25g of water, 0.4% of the total weight of sodium hypophosphite (dicarboxylic acid and diamine), and 0.3% of the total weight of antioxidant 1010 (dicarboxylic acid and diamine). These were added to a high-temperature, high-pressure polymerization reactor. The reactor was purged three times with nitrogen, heated to 190°C, and pressurized to 1.2 MPa. The reactor was held at this temperature and pressure for 0.5 hours, then vented to 0.8 MPa for 1 hour. The prepolymer was ejected from the bottom of the reactor, resulting in a loose, porous powder / particle prepolymer with a relative viscosity of 1.3.

[0066] (2) Preparation of PA5T / 56

[0067] The PA5T / 56 prepolymer obtained in (1) above was put into a solid-phase post-polymerization reactor for solid-phase post-polymerization. The temperature and pressure were maintained at 220℃ and 0.2MPa for 10 minutes. Then the pressure was reduced to normal and the venting time was 1.5h. Then a vacuum was drawn with a vacuum degree of 30Pa and the temperature and pressure were maintained for 4h to obtain a high-temperature resistant semi-aromatic polyamide product with a relative viscosity of 3.5.

[0068] Example 6:

[0069] This embodiment describes a method for preparing high-temperature resistant semi-aromatic polyamide PA6T / 66, including the following steps:

[0070] (1) Preparation of PA6T / 66 prepolymer

[0071] The following ingredients were weighed: 580g hexamethylenediamine, 415g terephthalic acid, 340g adipic acid (molar ratio of terephthalic acid to adipic acid 5 / 5), 333.75g water, 0.1% sodium hypophosphite (based on the total weight of the dicarboxylic acid and diamine), and 0.1% antioxidant 1010 (based on the total weight of the dicarboxylic acid and diamine). These were added to a high-temperature, high-pressure polymerization reactor. The reactor was purged three times with nitrogen, heated to 210℃, and held at 2.2MPa for 1 hour. The pressure was then reduced to 0.9MPa and the venting time was 1.5 hours. The prepolymer was ejected from the bottom of the reactor, resulting in a loose, porous powder / particle prepolymer with a relative viscosity of 1.1.

[0072] (2) Preparation of PA6T / 66

[0073] The PA6T / 66 prepolymer obtained in (1) above was put into a solid-phase post-polymerization reactor for solid-phase post-polymerization. The temperature and pressure were maintained at 220°C and 0.7 MPa for 40 min. Then the pressure was reduced to normal and the pressure was reduced for 40 min. Then the vacuum was drawn with a vacuum degree of 10 Pa and the temperature and pressure were maintained for 3 h to obtain a high-temperature resistant polyamide product with a relative viscosity of 3.3.

[0074] Example 7:

[0075] The difference between this embodiment and Embodiment 6 is that the amounts of each raw material are different. In this embodiment, the raw materials are: hexamethylenediamine (580 g), terephthalic acid (498 g), adipic acid (292 g, with a molar ratio of terephthalic acid to adipic acid of 6:4), and water (342.5 g).

[0076] Example 8:

[0077] The difference between this embodiment and Embodiment 6 is that the amounts of each raw material are different. In this embodiment, the raw materials are: hexamethylenediamine (580 g), terephthalic acid (581 g), adipic acid (219 g, with a molar ratio of terephthalic acid to adipic acid of 7:3), and water (345 g).

[0078] Example 9:

[0079] This embodiment describes a method for preparing high-temperature resistant semi-aromatic polyamide PA6T / 10T, including the following steps:

[0080] (1) Preparation of PA6T / 10T prepolymer

[0081] The following materials were weighed: 139.2 g of hexamethylenediamine, 481.6 g of decanediamine, 664 g of terephthalic acid (molar ratio of hexamethylenediamine to decanediamine 3 / 7), 321.2 g of water, 0.2% of sodium hypophosphite (based on the total weight of the diacid and diamine), and 0.2% of antioxidant 1010 (based on the total weight of the diacid and diamine). These were added to a high-temperature, high-pressure polymerization reactor. The reactor was purged three times with nitrogen, heated to 220°C, and held at 2.4 MPa for 1 hour. The pressure was then reduced to 1.0 MPa, and the venting time was 1.5 hours. The prepolymer was ejected from the bottom of the reactor, yielding a loose, porous powder / particle prepolymer with a relative viscosity of 1.5.

[0082] (2) Preparation of PA6T / 10T

[0083] The PA6T / 10T prepolymer obtained in (1) above was put into a solid-phase post-polymerization reactor for solid-phase post-polymerization at 230°C and 0.8 MPa for 60 min. Then the pressure was reduced to normal and the pressure was reduced for 60 min. Then the vacuum was drawn with a vacuum degree of 5 Pa and the pressure was maintained for 2 h to obtain a high-temperature resistant polyamide product with a relative viscosity of 3.3.

[0084] Example 10:

[0085] The difference between this embodiment and embodiment 9 is that the polymerization time after solid-state polymerization is different; the polymerization time is 4 hours.

[0086] Example 11:

[0087] The difference between this embodiment and embodiment 9 is that the polymerization time after solid-state polymerization is different; the polymerization time is 6 hours.

[0088] Example 12:

[0089] The difference between this embodiment and Embodiment 9 is that the polymerization temperature after solid-state polymerization is different; during the vacuum stage, the polymerization temperature is 240°C.

[0090] Example 13:

[0091] The difference between this embodiment and Embodiment 9 is that the polymerization temperature after solid-state polymerization is different; during the vacuum stage, the polymerization temperature is 250°C.

[0092] Example 14:

[0093] This embodiment describes a method for preparing high-temperature resistant semi-aromatic polyamide PA6T / 6I / 6, including the following steps:

[0094] (1) Preparation of PA6T / 6I / 6 prepolymer

[0095] The following ingredients were weighed: 580g of hexamethylenediamine, 332g of isophthalic acid, 332g of terephthalic acid, 226g of caprolactam (molar ratio of isophthalic acid / terephthalic acid / caprolactam 1 / 1 / 1), 367.5g of water, 0.2% of the total weight of sodium hypophosphite (dicarboxylic acid and diamine), and 0.2% of the total weight of antioxidant 1010 (dicarboxylic acid and diamine). These were added to a high-temperature, high-pressure polymerization reactor. The reactor was purged three times with nitrogen, heated to 220℃, and held at 2.4MPa for 1 hour. The pressure was then reduced to 1.0MPa and the venting time was 1.5 hours. The prepolymer was ejected from the bottom of the reactor, resulting in a loose, porous powder / particle prepolymer with a relative viscosity of 1.2.

[0096] (2) Preparation of PA6T / 6I / 6

[0097] The PA6T / 6I / 6 prepolymer obtained in (1) above was put into a solid-phase post-polymerization reactor for solid-phase post-polymerization at 230°C and 0.8 MPa for 50 min. Then the pressure was reduced to normal and the pressure was reduced for 30 min. Then the vacuum was drawn with a vacuum degree of 5 Pa and the pressure was maintained for 2 h to obtain a high-temperature resistant polyamide product with a relative viscosity of 4.1.

[0098] Example 15:

[0099] This embodiment describes a method for preparing high-temperature resistant semi-aromatic polyamide PA6T / 6I / 66, including the following steps:

[0100] (1) Preparation of PA6T / 6I / 66 prepolymer

[0101] The following ingredients were weighed: 580g of hexamethylenediamine, 332g of isophthalic acid, 332g of terephthalic acid, 292g of adipic acid (molar ratio of isophthalic acid / terephthalic acid / adipic acid 1 / 1 / 1), 384g of water, 0.2% of the total weight of sodium hypophosphite (dicarboxylic acid and diamine), and 0.2% of the total weight of antioxidant 1010 (dicarboxylic acid and diamine). These were added to a high-temperature, high-pressure polymerization reactor. The reactor was purged three times with nitrogen, heated to 220℃, and held at 2.4MPa for 1 hour. The pressure was then reduced to 0.8MPa and the venting time was 1.5 hours. The prepolymer was ejected from the bottom of the reactor, resulting in a loose, porous powder / particle prepolymer with a relative viscosity of 1.3.

[0102] (2) Preparation of PA6T / 6I / 66

[0103] The PA6T / 6I / 66 prepolymer obtained in (1) above was put into a solid-phase post-polymerization reactor for solid-phase post-polymerization at 230°C and 0.8 MPa for 50 min. Then the pressure was reduced to normal and the pressure was reduced for 30 min. Then the vacuum was drawn with a vacuum degree of 5 Pa and the pressure was maintained for 2 h to obtain a high-temperature resistant polyamide product with a relative viscosity of 4.0.

[0104] Example 16:

[0105] This embodiment describes a method for preparing high-temperature resistant semi-aromatic polyamide PA6T / 6C / 66, including the following steps:

[0106] (1) Preparation of PA6T / 6C / 66 prepolymer

[0107] The following ingredients were weighed: 580g of hexamethylenediamine, 344g of 1,4-cyclohexanedicarboxylic acid, 332g of terephthalic acid, 292g of adipic acid (molar ratio of isophthalic acid / terephthalic acid / adipic acid 1 / 1 / 1), 387g of water, 0.2% of the total weight of sodium hypophosphite and diamine, and 0.2% of the total weight of antioxidant 1010 and diamine. These were added to a high-temperature, high-pressure polymerization reactor. The reactor was purged three times with nitrogen, heated to 220℃, and held at 2.4MPa for 1 hour. The pressure was then reduced to 0.8MPa and the venting time was 1.5 hours. The prepolymer was ejected from the bottom of the reactor, resulting in a loose, porous powder / particle prepolymer with a relative viscosity of 1.4.

[0108] (2) Preparation of PA6T / 6C / 66

[0109] The PA6T / 6C / 66 prepolymer obtained in (1) above was put into a solid-phase post-polymerization reactor for solid-phase post-polymerization at 230°C and 0.8 MPa for 50 min. Then, the pressure was reduced to normal and the pressure was reduced for 30 min. Then, a vacuum was drawn with a vacuum degree of 5 Pa and the pressure was maintained for 2 h to obtain a high-temperature resistant polyamide product with a relative viscosity of 3.8.

[0110] Comparative Example 1:

[0111] The preparation method of the high-temperature resistant polyamide PA6T / 66 in Comparative Example 1 differs from that in Example 6 only in that the prepolymerization temperature is 190°C, while the other process parameters are the same as in Example 6.

[0112] Comparative Example 2:

[0113] The preparation method of the high-temperature resistant polyamide PA6T / 66 in Comparative Example 2 differs from that in Example 6 only in that, during solid-phase post-polymerization, the obtained PA6T / 66 prepolymer is placed into a solid-phase post-polymerization reactor for solid-phase post-polymerization at 190°C and 0.7 MPa for 40 min, then the pressure is reduced to atmospheric pressure for 40 min, and then a vacuum is drawn with a vacuum degree of 10 Pa for 5 h.

[0114] Comparative Example 3:

[0115] The preparation method of the high-temperature resistant polyamide PA6T / 66 in Comparative Example 3 differs from that in Example 6 only in that, during the solid-phase post-polymerization, there is no positive pressure stage; it directly enters the vacuum stage with a vacuum degree of 10 Pa and a heat and pressure holding time of 3 hours.

[0116] Comparative Example 4:

[0117] The preparation method of the high-temperature resistant polyamide PA6T / 10T in this comparative example differs from that in Example 9 only in that the polymerization temperature is 300°C during solid-phase post-polymerization.

[0118] Comparative Example 5:

[0119] The high-temperature resistant polyamide PA6T / 10T in this comparative example differs from that in Example 9 in that the prepolymer is taken out from the top of the reactor. The prepolymer is a solid block with a non-porous structure. After drying and crushing, the prepolymer is then subjected to solid-phase post-polymerization.

[0120] Comparative Example 6

[0121] The preparation method of the high-temperature resistant polyamide PA6T / 6C / 66 in this comparative example differs from that in Example 16 only in that the prepolymer is vented to 1.5 MPa and ejected from the bottom of the reactor.

[0122] Comparative Example 7

[0123] The preparation method of the high-temperature resistant polyamide PA6T / 6C / 66 in this comparative example differs from that in Example 16 only in that the prepolymer is vented to 0.3 MPa and sprayed out from the bottom of the reactor.

[0124] Effect Experiment

[0125] The final polymer products prepared in Examples 1-16 and Comparative Examples 1-7 were tested for melting point, viscosity, and thermal decomposition temperature.

[0126] The test results are shown in Table 1.

[0127] Examples 1-16 and Comparative Examples 1-7

[0128]

[0129]

[0130]

[0131] Table 1 shows the performance parameters of homopolymer high-temperature resistant semi-aromatic polyamides in Examples 1-3: the relative viscosity of the polyamide prepolymer is 1.1-1.5, and the relative viscosity of the final polymer is 3.5-3.8. Examples 4-5 show the performance parameters of copolymer high-temperature resistant semi-aromatic polyamides. The obtained high-temperature resistant polyamides have good properties, with a melting point between 295-308℃, a relative viscosity between 2.0-3.5, an initial thermal decomposition temperature between 388-389℃, and a maximum thermal decomposition temperature between 462-469℃. Examples 14-15 show the performance parameters of multicomponent copolymer high-temperature resistant polyamides. The obtained high-temperature resistant polyamides have good properties, with a melting point between 291-312℃ and a relative viscosity between 4.0-4.1. Therefore, the method of this invention has a wide range of applications, suitable for the preparation of homopolymer or copolymer high-temperature resistant semi-aromatic polyamides, and also suitable for multicomponent copolymer high-temperature resistant polyamides. The obtained products have good performance, and the process is stable and feasible.

[0132] Examples 6-8 in Table 1 illustrate the effect of adjusting the molar ratio of PA6T to PA66 in PA6T / 66 on the properties of the obtained semi-aromatic polyamide. The results show that adjusting the raw material molar ratio has a significant impact on the melting point (Tm), initial thermal decomposition temperature (Td 5%), and fastest thermal decomposition temperature (Td max) of PA6T / 66. Comparing Examples 6-8, when the polymerization process conditions are the same, as the molar ratio of terephthalic acid increases, the melting point of PA6T / 66 gradually increases, while the initial thermal decomposition temperature does not change much, but all of them can meet the processing requirements of high-temperature resistant semi-aromatic polyamide.

[0133] To illustrate the effects of process conditions such as prepolymerization temperature and post-solid-state polymerization temperature on the properties of semi-aromatic polymers, Comparative Examples 1-3 illustrate the effects of adjusting different prepolymerization temperatures, post-solid-state polymerization temperatures, and polymerization stages of the post-solid-state polymerization system on the properties of semi-aromatic polyamides. The results show that lowering the prepolymerization temperature is detrimental to increasing the relative viscosity of the prepolymer and also affects the increase in the final relative viscosity of the post-solid-state polymerization. Lowering the post-solid-state polymerization temperature results in a lower reaction rate, which is detrimental to increasing the relative molecular weight. Furthermore, eliminating the positive pressure polymerization system for post-solid-state polymerization is also detrimental to improving the relative viscosity of the final polymer.

[0134] Examples 9-12 illustrate the effect of adjusting the polymerization time of PA6T / 10T post-solid-state polymerization on the final polymer product. The results show that with increasing polymerization time, the relative viscosity of PA6T / 10T gradually increases, while the melting point and thermal decomposition temperature remain almost unchanged. By adjusting the post-solid-state polymerization temperature (see Examples 9, 12, and 13), it was found that with increasing post-solid-state polymerization temperature, the relative viscosity of PA6T / 10T gradually increases, while the melting point and thermal decomposition temperature remain almost unchanged. However, excessively high temperatures (Comparative Example 4) are not conducive to increasing the relative viscosity; excessively high temperatures will cause PA6T / 10T to oxidize, increasing the yellowing index. This indicates that increasing the post-solid-state polymerization temperature and extending the polymerization time are effective in increasing the relative viscosity of PA6T / 10T. However, excessively high post-solid-state polymerization temperatures will be accompanied by oxidation, which is detrimental to molecular weight growth, and the product will turn yellow, resulting in a decrease in quality. Figure 7 The results of Comparative Example 4, when solid-phase post-polymerization was carried out at a polymerization temperature of 300°C, showed that the final polymer, in its final state, retained the original granular powder structure but exhibited a significant yellowing phenomenon with a yellowness value of 30.

[0135] To investigate the effect of prepolymer discharge method on final polymer product, Example 16 and Comparative Examples 6-7 illustrate the effect of spray pressure on final polymer product. The results show that when the spray pressure is too high, there is more moisture in the system, and agglomeration occurs during spraying. The prepolymer has a relatively low viscosity, which is not conducive to increasing the molecular weight of the final polymer after solid-state polymerization. When the spray pressure is 1.5 MPa, the particle size is too large, which is not conducive to increasing the molecular weight of the final polymer after solid-state polymerization. When the spray pressure is too low, the prepolymer cannot be sprayed and needs to be dried and crushed before solid-state polymerization, which increases the experimental time.

[0136] Performance testing

[0137] To further illustrate the effects of this invention, taking the high-temperature resistant PA10T, PA6T / 6, PA5T / 56, PA6T / 66, and PA6T / 6I / 6 obtained in Examples 1, 4, 5, 7, and 14 as examples, the obtained final polymer products were subjected to TG and DSC tests, and the results are as follows: Figure 1 and Figure 2 As shown. Taking the high-temperature resistant PA6T / 66 obtained in Example 6 as an example, the final polymer was subjected to FT-IR and final polymer analysis. 1 H-NMR and SEM tests of the prepolymer yielded the following results: Figure 3 , Figure 4 and Figure 5 As shown. Among them, TG, DSC, FT-IR, 1 The testing standards used for H-NMR and SEM are:

[0138] TG test standard: Take about 2-3 mg of semi-aromatic high-temperature resistant nylon into an alumina crucible, place the crucible in the tray of the thermogravimetric analyzer, and then heat it from 25℃ to 600℃ at a heating rate of 10℃ / min in a N2 atmosphere, and obtain the data of weight change with temperature.

[0139] DSC test standard: Take about 2-3 mg of semi-aromatic high-temperature resistant nylon in a crucible to prepare the sample. Place the sample crucible into the DSC furnace and heat it from 25℃ to 300-350℃ at a heating rate of 10℃ / min under nitrogen atmosphere. Save the experimental data.

[0140] FT-IR testing standard: Take a small amount of dried semi-aromatic high-temperature resistant nylon sample in an agate mortar, add a certain amount of dried potassium bromide (KBr), grind it into powder under an infrared lamp, prepare a sample pellet with a thickness of less than 0.5 mm, and then test it in a German Bruker TENSOR II infrared spectrometer at a wavenumber of 4000–400 cm⁻¹. -1 4cm resolution -1 .

[0141] 1H-NMR testing standard: Take 3 mg of dried nylon salt sample into an NMR tube and test it using deuterated trifluoroacetic acid (C2DF3O2) as solvent.

[0142] SEM testing standard: Measurements were performed using a Hitachi SU3500 high-tech scanning electron microscope from Japan. The samples were first surface-plated with gold, and then their morphology was observed at different magnifications. For example... Figure 1 and Figure 2 As shown, Figure 1 PA5T / 56(60 / 40) is shown, with an initial thermal decomposition temperature of 389℃ and a fastest thermal decomposition temperature of 469℃. Figure 2 The melting points of different types of high-temperature resistant polyamides are shown, indicating that high-temperature resistant semi-aromatic polyamides have been successfully prepared using the method of the present invention.

[0143] Figure 3 It shows 3308cm -1 It is the stretching vibration peak of NH, 2930 cm⁻¹ -1 and 2859cm -1 These are the antisymmetric stretching vibration peak and the symmetric stretching vibration peak of CH2, respectively, at 1638 cm⁻¹. -1 It is the stretching vibration peak of C=O (amide I band), 1535 cm⁻¹ -1 It is the in-plane bending vibration peak of NH (amide II band), 3083 cm⁻¹ -1 The peak is an overtone of the combination of NH and CN vibration peaks, at 865 cm⁻¹. -1 It is the in-plane bending vibration peak of CH on the benzene ring. Figure 4The chemical shifts of each H group are shown: δ = 2.60 ppm represents the hydrogen on the α-carbon near the N-terminal amino group; δ = 2.78 ppm represents the hydrogen on the α-carbon near the N-terminal amide bond; δ = 3.54 ppm represents the hydrogen on the α-carbon near the carbonyl group of adipic acid; δ = 3.53 ppm represents the hydrogen on the α-carbon near the carbonyl group of adipic acid; δ = 3.63 ppm represents the hydrogen on the α-carbon near the carbonyl group of terephthalic acid; δ = 8.28 ppm represents the hydrogen on the α-carbon near the N-terminal carboxyl group of terephthalic acid; and δ = 7.86 ppm represents the hydrogen on the α-carbon near the N-terminal amide bond of terephthalic acid. Figure 5 The morphology of the prepolymer is shown, and it can be clearly seen that the prepolymer has a powder / small particle structure. Figure 6 It shows Figure 5 SEM images of the prepolymer at different magnifications clearly show the porous structure in the prepolymer powder / particles, which is beneficial for the escape of water molecules during solid-phase post-polymerization and promotes the forward reaction.

[0144] The above embodiments are only used to illustrate the detailed method of the present invention, but the present invention is not limited to the above detailed method, that is, it does not mean that the present invention must rely on the above detailed method to be implemented. Those skilled in the art should understand that any improvement to the method of the present invention, equivalent substitution of raw materials for the product, addition of auxiliary components, selection of specific methods, etc., all fall within the protection scope and disclosure scope of the present invention.

Claims

1. A low-temperature preparation method for a high-temperature resistant semi-aromatic polyamide, characterized in that, Includes the following steps: (1) Prepolymerization Weigh out the diacid, diamine, catalyst, antioxidant, and deionized water according to the specified proportions and add them to a high-temperature and high-pressure polymerization reactor. Under inert gas protection, heat the reactor to a predetermined temperature of 190–230°C (excluding 190°C) and raise the pressure to a first predetermined pressure of 1.2–2.6 MPa, maintaining the temperature and pressure for 0.5–3 hours. Gradually reduce the pressure inside the reactor to a second predetermined pressure of 0.5–1.0 MPa by venting, with a venting time of 0.5–3 hours. Then, under the second predetermined pressure, spray the prepolymer from the bottom of the polymerization reactor to obtain a loose and porous powder / particle polyamide prepolymer with a relative viscosity of 1.0–1.

7. The diacid or diamine contains an aromatic ring structure. (2) Solid-state post-polymerization The prepolymer obtained in step (1) is placed in a solid-phase polymerization reactor. Under inert gas protection, the reactor is heated to 200-250°C and pressure is 0.2-0.8 MPa. The temperature and pressure are maintained for 10-60 min. Then, the gas is vented to atmospheric pressure within 30-60 min. Then, the vacuum is drawn to 5-200 Pa and the temperature and pressure are maintained for 0-6 h. The temperature is then lowered to obtain a powder / small granular high-temperature resistant semi-aromatic polyamide product with a relative viscosity of 2.0-5.

0.

2. The low-temperature preparation method of a high-temperature resistant semi-aromatic polyamide according to claim 1, characterized in that, In step (1), the diamine is one or a mixture of two or more of the following: pentanediamine, hexanediamine, decanediamine, undecanediamine, dodecanediamine, tridecanediamine, tetradecanediamine, m-phenylenediamine, p-phenylenediamine, 4,4'-diamino-dicyclohexylmethane, 3,3'-dimethyl-4,4'-diamino-dicyclohexylmethane, and 1,5-diaminonaphthalene; and the diacid is one or a mixture of two or more of the following: aliphatic diacid, aromatic diacid, and alicyclic diacid.

3. The low-temperature preparation method of a high-temperature resistant semi-aromatic polyamide according to claim 2, characterized in that, The dicarboxylic acid is one or a mixture of two or more of the following: succinic acid, glutaric acid, adipic acid, azelaic acid, sebacic acid, dodecanoic acid, tridecanoic acid, terephthalic acid, isophthalic acid, 2,6-naphthalenedicarboxylic acid, and 1,4-cyclohexanedicarboxylic acid.

4. The low-temperature preparation method of a high-temperature resistant semi-aromatic polyamide according to claim 1, characterized in that, In step (1), the catalyst is one or a mixture of two or more of phosphorous acid, sodium hypophosphite, triphenyl phosphate, and H10, and the amount of catalyst used is 0.1 to 0.6% of the total weight of the dicarboxylic acid and diamine.

5. The low-temperature preparation method of a high-temperature resistant semi-aromatic polyamide according to claim 1, characterized in that, In step (1), the antioxidant is one or a mixture of two or more of sodium hypophosphite, antioxidant 1010, antioxidant S9228, antioxidant SH120, antioxidant B215, magnesium hypophosphite, calcium hypophosphite or zinc hypophosphite, and the amount of antioxidant used is 0.1 to 0.5% of the total weight of the dicarboxylic acid and diamine.

6. The low-temperature preparation method of a high-temperature resistant semi-aromatic polyamide according to claim 1, characterized in that, In step (1), when the prepolymer is ejected, it needs to be protected by an inert gas, which is one of nitrogen, carbon dioxide and argon.

7. The low-temperature preparation method of a high-temperature resistant semi-aromatic polyamide according to claim 1, characterized in that, In step (1), the prepolymer particles sprayed out have a particle size of 0.075 to 5.0 mm, and in step (2), the final polymer particles have a particle size of 0.075 to 5.0 mm.

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