Preparation process and system of polyhexamethylene sebacamide

Abstract

A preparation process and system of polyhexamethylene sebacate, comprising the following steps: (A) under nitrogen protection, hexamethylene diamine and sebacic acid are subjected to salt formation reaction in deionized water to obtain a salt water solution; (B) the salt water solution is directly heated to a prepolymerization temperature in a closed system, and maintained at the prepolymerization temperature for a first time, after the reaction is completed, the reaction system is under a prepolymerization pressure; (C) the prepolymerization pressure is reduced to a first-stage pressure, maintained at the first-stage pressure for a second time, during which an exhaust valve is kept open to continuously discharge a gas phase component containing water vapor, so that the pressure of the reaction system is maintained at the first-stage pressure; then the exhaust rate is increased until the pressure of the reaction system is reduced to a preset pressure; (D) the reaction system is subjected to tackification treatment under vacuum condition. The present application can produce PA610 products meeting the requirements of high-end molding process of industrial injection molding and extrusion only by using deionized water as a reaction medium without additional addition of an auxiliary agent.

Description

Technical Field

[0001] This invention relates to the field of polymer synthesis technology, specifically to a preparation process and system for polyhexamethylene sebacate. Background Technology

[0002] Polyhexamethylene sebacate (PA610) is a long-chain semi-crystalline high-performance polyamide material with properties such as low water absorption, excellent dimensional stability, oil and corrosion resistance, good low-temperature toughness, and low friction loss. It has important applications in high-end manufacturing fields such as automotive precision parts, electronic and electrical insulation materials, aerospace parts, and precision machinery.

[0003] Currently, the industrial production of PA610 mainly adopts three mainstream processes: melt polymerization, alcohol-water mixed solution polymerization, and salt water phase catalytic polymerization. Melt polymerization is the current mainstream industrial route, with mature technology and ethanol as the reaction medium. Alcohol-water mixed solution polymerization uses pure water to replace part of the organic solvent. Salt water phase catalytic polymerization improves polymerization efficiency, shortens reaction time, reduces energy consumption and the risk of monomer thermal degradation by introducing a catalyst system into the aqueous solution.

[0004] However, the solvent systems of the three mainstream processes all have their own drawbacks. The organic alcohol solvents used in melt polymerization are not environmentally friendly enough, the mixed solvents used in alcohol-water mixed solution polymerization are difficult to recover and have high energy consumption, while the salt water phase catalytic polymerization requires the introduction of metal ion catalysts, and the residual catalysts will affect the performance of PA610.

[0005] Furthermore, existing PA610 preparation processes generally follow a salt formation-concentration-polymerization technical route, where the concentration step is used to concentrate the PA610 salt solution from a low concentration to a high concentration to facilitate subsequent polymerization steps. However, the concentration step is energy-intensive and time-consuming; for example, it typically requires concentration at around 150 °C for nearly one hour to remove a large amount of water from the salt solution. Moreover, existing processes generally rely on various additives, such as antioxidants and heat stabilizers to prevent high-temperature oxidation, and lubricants to improve processing fluidity. While the addition of additives facilitates the reaction, the additives remaining in PA610 and their decomposition products significantly reduce PA610's aging resistance and volume resistivity, leading to a decline in its insulation performance under high-temperature, high-frequency, or high-voltage electric field environments, making it unsuitable for the needs of high-end electronics and precision equipment applications. Summary of the Invention

[0006] One objective of this invention is to provide a preparation process for polyhexamethylene sebacate, which uses only deionized water as the reaction medium. By dynamically maintaining pressure under the first stage pressure of the multi-stage depressurization polymerization process, and venting the gas while heating the system to generate water vapor, the system pressure is kept constant. This eliminates the need for a concentration process, significantly improves reaction efficiency, reduces reaction energy consumption, and requires no additional additives throughout the entire preparation process, further reducing production and recycling costs and breaking through the performance bottleneck of traditional green processes.

[0007] This invention is achieved through the following technical solution:

[0008] A process for preparing polyhexamethylene sebacate includes the following steps:

[0009] (A) Salt formation reaction: Under nitrogen protection, hexamethylenediamine and sebacic acid undergo a salt formation reaction in deionized water to obtain a salt solution;

[0010] (B) Prepolymerization reaction, wherein the salt solution is directly heated to the prepolymerization temperature in a closed system and maintained at the prepolymerization temperature for a first time, and the reaction system is under prepolymerization pressure after the reaction is completed;

[0011] (C) Multi-stage depressurization polymerization reaction, wherein the prepolymer pressure is reduced to the first stage pressure, and the first stage pressure is maintained for a second time. During the second time, the exhaust valve is kept open to continuously discharge the gas phase component containing water vapor, so that the pressure of the reaction system is maintained at the first stage pressure; then the exhaust rate is increased until the pressure of the reaction system drops to the preset pressure.

[0012] (D) Vacuum thickening treatment: The reaction system is thickened under vacuum conditions.

[0013] In this technical solution, in step (A), hexamethylenediamine and sebacic acid undergo an acid-base neutralization and salt-forming reaction in deionized water to form a PA610 monomer salt aqueous solution. In some embodiments, hexamethylenediamine and sebacic acid can be reacted in equimolar amounts. In one or more embodiments, the amount of hexamethylenediamine can also be higher, for example, the molar ratio of hexamethylenediamine to sebacic acid is 1~1.1. In one or more embodiments, the chain length of the PA610 product can also be changed by adjusting the amount of hexamethylenediamine and sebacic acid. For example, a moderate excess of hexamethylenediamine can compensate for the ratio deviation caused by high-temperature volatilization, which is beneficial to the full growth of the molecular chain and obtains a high-viscosity PA610 with excellent processing performance. In one or more embodiments, the reaction temperature of the salt-forming reaction is 70~90 °C.

[0014] In this technical solution, after the monomer salt solution is formed, it is not necessary to transfer it to a concentration vessel for concentration as in existing technologies. Instead, the reaction system is directly heated in the same reaction vessel. In step (B), the reaction system is heated to the prepolymerization temperature and held at the prepolymerization temperature for a first time. During the prepolymerization pressure holding process, the reaction system undergoes a prepolymerization reaction to generate a low molecular weight PA610 prepolymer, building the basic molecular chain structure. After the prepolymerization reaction is completed, the reaction system is under prepolymerization pressure.

[0015] In some preferred embodiments, the prepolymerization pressure is 1.6~1.8 MPa, the prepolymerization temperature is 180~200 °C, and the first time is 0.5~1 h. In a more preferred embodiment, the prepolymerization pressure is 1.7~1.8 MPa, and the prepolymerization temperature is 190~200 °C.

[0016] In step (B), the system temperature is gradually increased to the polymerization temperature. A large amount of free water in the brine solution exists in the gas phase space in the form of water vapor at this stage. Since the prepolymerization and pressure holding are carried out in a closed system, this part of the water is not discharged, but is stored in the reactor in the form of high-pressure steam.

[0017] In this technical solution, a multi-stage pressure-relief polymerization reaction is carried out in step (C). Specifically, the heating device is not turned off, and the water in the reaction continues to be converted into steam. After the pressure relief valve is opened, the pressure relief rate is controlled so that the prepolymerization pressure drops to the first-stage pressure and reaches a dynamic pressure equilibrium state. In this state, the rate at which steam is generated by heating in the reaction system is equivalent to the rate at which gas is discharged during pressure relief. That is, the molar flow rate of steam evaporating into the gas phase by heating in the reactor per unit time is equal to the molar flow rate of gas discharged during pressure relief, so that the entire reaction system is under the first-stage pressure and remains under the first-stage pressure for a second time.

[0018] During the second time interval, the pressure is kept constant and the venting is continuous and stable, allowing the water in the reaction system to be removed at a uniform rate. This avoids drastic fluctuations in water concentration caused by rapid depressurization, inhibits the hydrolytic breakage of polyamide molecular chains, ensures continuous molecular chain growth, and prevents widening of the molecular weight distribution and insufficient viscosity of the finished product. Simultaneously, the high-pressure steam accumulated during the prepolymerization and pressure holding stage, as well as the newly generated condensation water from the polycondensation reaction, are systematically removed from the reaction system through continuous venting. Dehydration and chain growth are completed synchronously in the same process. Therefore, there is no need for an additional concentration process to evaporate the water in the system before polymerization. Instead, most of the water in the system is smoothly discharged during polymerization through dynamic pressure holding. This not only simplifies the process of changing reactors and concentration, significantly reducing energy consumption, but also promotes continuous and uniform molecular chain growth.

[0019] In some preferred embodiments, in step (C), the first-stage pressure is 1.45~1.65 MPa, and the second time is 10~30 min. More preferably, the first-stage pressure is 1.55~1.65 MPa.

[0020] Furthermore, the dynamic pressure holding method in step (C) effectively reduces the temperature required by the reaction system, thus reducing the need for antioxidants. Additionally, as the pressure relief valve continues to open and vent, the continuously emerging water vapor forms a continuous positive pressure vapor curtain above the reaction melt, effectively removing air from the reactor and creating a dynamic vapor barrier in the gas phase space to prevent the intrusion of external oxygen. Therefore, experiments have shown that the process described in this application has almost no impact on the performance of PA610 products after the addition of antioxidants. Besides antioxidants, the dynamic pressure holding process continuously removes gaseous components, and bubbles are naturally carried away during venting, thus eliminating the need for defoamers.

[0021] Therefore, by using a dynamic holding pressure step, not only can the concentration process be eliminated, but PA610 products with molecular chain length and intrinsic viscosity that meet the requirements of high-end industrial injection molding and extrusion molding processes can also be obtained without adding any additives. In some preferred embodiments, during the entire polymerization reaction process from steps (A) to (D), the reaction system is in a state without the addition of exogenous additives. Here, exogenous additives refer to chemical substances added for purposes such as adjusting molecular weight, preventing oxidation, improving flowability, or promoting crystallization, excluding trace impurities carried by the reactants themselves, and excluding solvents used as the reaction medium.

[0022] In one or more embodiments, the exogenous adjuvant is at least one of antioxidants, heat stabilizers, light stabilizers, molecular weight regulators, capping agents, catalysts, nucleating agents, lubricants, and flow aids.

[0023] Finally, in step (D), after the multi-stage depressurization polymerization reaction, a water circulation vacuum pump is connected to continuously vacuum the reactor system to deeply remove residual moisture and trace small molecule polycondensation byproducts, remove the reaction equilibrium limitation, promote further growth of molecular chains and increase the degree of polymerization, and discharge the finished product PA610 after cooling.

[0024] In this technical solution, by setting the first stage reaction in the multi-stage pressure relief polymerization reaction to a dynamic pressure holding method, PA610 products that meet the requirements of industrial injection molding and high-end extrusion molding processes can be produced using only deionized water as the reaction medium without the addition of additional additives. At the same time, the concentration process is eliminated in the reaction process, which greatly improves the reaction efficiency, reduces the reaction energy consumption, breaks through the performance bottleneck of traditional green processes, and has broad application value.

[0025] In a preferred embodiment of the present invention, in step (C), after the reaction system is maintained at the first-stage pressure for a second time, the exhaust rate is increased to reduce the first-stage pressure to the second-stage pressure, and the system is maintained at the second-stage pressure for a third time; subsequently, the second-stage pressure is reduced to the third-stage pressure, and the system is maintained at the third-stage pressure for a fourth time; wherein the second-stage pressure is 0.5~1.0 MPa, the third time is 10~30 min, the third-stage pressure is 0.1~0.25 MPa, and the fourth time is 10~30 min.

[0026] In this technical solution, after achieving dynamic pressure holding at the first stage, the opening of the pressure relief valve is further increased to enhance the pressure relief amplitude, smoothly reducing the pressure of the reaction system from the first stage pressure to the second stage pressure. During this process, the temperature rises accordingly. The pressure relief valve is then closed, and the system is maintained at the second stage pressure and temperature for a third time to further remove moisture from the system, gradually promoting the forward polycondensation reaction while ensuring the continuity of molecular chain growth. In one or more embodiments, the second stage pressure is 0.5~1.0 MPa, the second stage temperature is 210~230 °C, and the third time is 10~30 min.

[0027] In this technical solution, after the third pressure holding time, the pressure relief valve is opened again to rapidly reduce the pressure of the reaction system from the second-stage pressure to the third-stage pressure, i.e., the preset pressure. During this process, the temperature drops accordingly. Then, the pressure relief valve is closed, and the system is maintained at the third-stage pressure and temperature for a fourth time to complete the removal of most of the moisture from the system, laying the foundation for subsequent vacuum-deep viscosity enhancement. In one or more embodiments, the third-stage pressure is 0.1~0.25 MPa, the third-stage temperature is 180~200 °C, and the fourth time is 10~30 min.

[0028] In this technical solution, a three-stage precise pressure relief mode is used to gradually remove moisture from the reaction system, precisely control the moisture removal rate, effectively suppress the molecular chain breakage caused by rapid moisture removal, ensure the continuity of molecular chain growth, and avoid the problem of uneven molecular weight distribution of the product.

[0029] In another preferred embodiment of the present invention, in step (A), the salt formation reaction is carried out under the condition of continuously introducing nitrogen gas into the reaction system and venting nitrogen gas.

[0030] In this technical solution, considering the need to omit the concentration step, minimizing the amount of deionized water used in step (A) is more beneficial for shortening the subsequent dynamic pressure holding time and making the reaction conditions milder. Therefore, in order to improve the solubility of hexamethylenediamine and sebacic acid in deionized water, nitrogen gas is continuously introduced into the reaction system from the time of addition until the salt formation reaction is completed. For example, in some preferred embodiments, nitrogen gas can be introduced into deionized water from the bottom of the reactor and then discharged from the top of the reactor to form a stable nitrogen disturbance field inside the reactor. This accelerates the mass transfer and mixing of hexamethylenediamine and sebacic acid, improves the salt formation rate and uniformity, and achieves efficient salt formation under low-temperature conditions without the need for additional additives. This avoids the problems of raw material volatilization and side reactions that are easily caused by high-temperature salt formation, and provides a uniform and stable salt monomer system for subsequent polymerization reactions, thus laying a solid foundation for the controllability of the reaction from the source. At the same time, the continuously introduced nitrogen gas also plays a role in carrying away dissolved oxygen, further reducing the oxygen content in the reaction system and creating more favorable conditions for subsequent additive-free polymerization.

[0031] By agitating with nitrogen, the salt formation reaction time can be significantly shortened, further reducing the overall production process time. In some preferred embodiments, adjusting the nitrogen flow rate can alter the agitation effect, thereby reducing the salt formation reaction time to 15–45 minutes.

[0032] The present invention also provides a preparation system for polyhexamethylene sebacate, which is used to carry out any of the aforementioned preparation processes for polyhexamethylene sebacate, the preparation system comprising:

[0033] The reactor is configured to sequentially carry out salt formation reaction, prepolymerization reaction, multi-stage depressurization polymerization reaction, and vacuum thickening treatment within the same reactor.

[0034] A heating device is used to heat the reaction system inside the reactor.

[0035] A pressure control system is used to control the pressure inside the reactor.

[0036] A vacuum system is used to evacuate the reactor.

[0037] In this technical solution, there is no need to set up an additional concentration tank or polymerization tank. Instead, the salt formation reaction, prepolymerization reaction, multi-stage depressurization polymerization reaction, and vacuum thickening treatment can be completed in a single reaction tank, which effectively reduces production costs.

[0038] In some preferred embodiments, a nitrogen control system is also included, which is used to provide stable nitrogen to the reactor to form a nitrogen disturbance field.

[0039] Compared with the prior art, the present invention has the following advantages and beneficial effects:

[0040] 1. This invention sets the first stage reaction in the multi-stage pressure relief polymerization reaction to a dynamic pressure holding method, which enables the production of PA610 products that meet the requirements of industrial injection molding and high-end extrusion molding processes using only deionized water as the reaction medium without the addition of additional additives.

[0041] 2. The reaction process of this invention eliminates the concentration process, which greatly improves reaction efficiency, reduces reaction energy consumption, breaks through the performance bottleneck of traditional green processes, and has wide application value.

[0042] 3. By adjusting the pressure and holding time of each stage in the multi-stage depressurization polymerization reaction, the present invention can gradually remove water from the reaction system, precisely control the water removal rate, effectively suppress the molecular chain breakage caused by rapid water removal, ensure the continuity of molecular chain growth, and avoid the problem of uneven molecular weight distribution of the product.

[0043] 4. This invention accelerates the mass transfer and mixing of hexamethylenediamine and sebacic acid by forming a stable nitrogen disturbance field in the reactor, thereby improving the salt formation rate and uniformity. It can achieve efficient salt formation under low-temperature conditions without additional additives, avoiding the problems of raw material volatilization and side reactions that are easily caused by high-temperature salt formation. It also provides a uniform and stable salt monomer system for subsequent polymerization reactions, laying a solid foundation for the controllability of the reaction from the source. At the same time, the continuously introduced nitrogen also plays a role in carrying away dissolved oxygen, further reducing the oxygen content in the reaction system and creating more favorable conditions for subsequent additive-free polymerization.

[0044] 5. This invention eliminates the need for additional concentration and polymerization reactors. Instead, it enables the completion of salt formation, prepolymerization, multi-stage depressurization polymerization, and vacuum thickening treatment within a single reactor, effectively reducing production costs. Attached Figure Description

[0045] The accompanying drawings, which are included to provide a further understanding of embodiments of the invention and form part of this application, do not constitute a limitation thereof. In the drawings:

[0046] Figure 1 A photograph of product PA610-1 in a specific embodiment of the present invention is shown;

[0047] Figure 2 This is a flowchart of the preparation process in a specific embodiment of the present invention. Detailed Implementation

[0048] To make the objectives, technical solutions, and advantages of the present invention clearer, the present invention will be further described in detail below with reference to the embodiments and accompanying drawings. The illustrative embodiments and descriptions of the present invention are only used to explain the present invention and are not intended to limit the present invention.

[0049] All raw materials used in this invention are not particularly limited in their source; they can be purchased commercially or prepared using conventional methods well-known to those skilled in the art. The purity of all raw materials used in this invention is not particularly limited; however, analytical grade or the purity requirements conventional in the synthesis of PA610 are preferred. All raw materials used in this invention have common designations and abbreviations in the art, and each designation and abbreviation is clearly defined within its relevant application. Those skilled in the art can obtain them commercially available or prepared using conventional methods based on the designation, abbreviation, and corresponding application.

[0050] The present invention does not impose any particular restrictions on the expression of the substituents, and all expressions are well known to those skilled in the art. Based on common sense, those skilled in the art can correctly understand their meaning according to their expression.

[0051] In this invention, the viscosity of the PA610 product was determined according to the GB / T 12006.1-2009 standard; the number-average molecular weight (Mn) and weight-average molecular weight (Mw) of the product were determined by gel permeation chromatography (GPC).

[0052] Example 1:

[0053] (a) Feeding and gas replacement

[0054] 87.16 g hexamethylenediamine, 151.68 g sebacic acid, and 239 ml deionized water were added into a high-pressure polymerization reactor at one time. Nitrogen gas was continuously introduced into the bottom of the reactor, and the vent was kept open at the top of the reactor. The nitrogen gas moved from the bottom of the reactor through the reaction system to the top of the reactor, forming a stable nitrogen gas disturbance field in the reaction system.

[0055] (b) Salt formation reaction

[0056] The reactor is heated to 80 °C and kept at a constant temperature for 20 min to allow hexamethylenediamine and sebacic acid to complete the acid-base neutralization and salt formation reaction, forming a homogeneous and stable PA610 monomer salt solution. After the process is completed, the vent is closed, the container is filled with nitrogen, and a closed protection system is constructed.

[0057] (c) Prepolymerization reaction

[0058] The reactor was heated to 200 °C and prepolymerized at a constant temperature for 1 h. The monomer salt underwent a preliminary condensation reaction to generate a low molecular weight PA610 prepolymer, which built the basic molecular chain structure. After the reaction, the prepolymerization pressure of the system was 1.8 MPa.

[0059] (d) Multistage depressurization polymerization reaction

[0060] First stage: Without shutting off the heating device, slowly open the pressure relief valve and control the pressure relief rate. The pressure of the reaction system slowly decreases from the prepolymerization pressure to the first stage pressure of 1.65 MPa, and the temperature decreases accordingly to the first stage temperature of 190 °C. Maintain the first stage pressure and temperature for 20 min. During this stage, the rate of gas generation from heating in the reaction system reaches a dynamic equilibrium with the rate of gas release from pressure relief, so the pressure remains constant during this period.

[0061] Second stage: Continue to increase the opening of the pressure relief valve to increase the pressure relief range, and steadily reduce the pressure of the reaction system from the first stage pressure to the second stage pressure of 1.0 MPa. The temperature will then rise to the second stage temperature of 230 °C. After that, close the pressure relief valve and maintain the second stage pressure and temperature for 10 min.

[0062] Third stage: Open the pressure relief valve to rapidly reduce the pressure of the reaction system from the second stage pressure to the third stage pressure of 0.1 MPa, and the temperature will drop to the third stage temperature of 200 °C. Close the pressure relief valve and maintain the third stage pressure and temperature for 10 minutes.

[0063] (e) Post-treatment after vacuum thickening

[0064] The reactor is connected to a water-circulating vacuum pump, and the reactor system is continuously evacuated for 30 minutes to deeply remove residual moisture and trace small molecule polycondensation byproducts, thereby removing the reaction equilibrium limitation, promoting further growth of molecular chains and increasing the degree of polymerization. Finally, after cooling, the product PA610-1 is discharged.

[0065] Testing of product PA610-1 revealed that its number-average molecular weight (Mn) is 18989, weight-average molecular weight (Mw) is 36942, and intrinsic viscosity is 1.31 dL / g. It exhibits excellent molecular chain length, uniform molecular weight distribution, and high viscosity characteristics that meet the requirements of high-end industrial injection molding and extrusion processes. A photo of PA610-1 is shown below. Figure 1 As shown, it is transparent, with a uniform and clear color, and free from defects such as yellowing, blackening, spots, and impurities.

[0066] In one or more embodiments, the salt formation reaction is carried out at a temperature of 70–90 °C for 15–45 min.

[0067] In some embodiments, the prepolymerization temperature is 180–200 °C, and the prepolymerization time is 0.5–1 h. After the prepolymerization reaction is completed, the prepolymerization pressure of the system is 1.6–1.8 MPa.

[0068] In one or more embodiments, the first-stage pressure is 1.45~1.65 MPa, the first-stage temperature is 170~190 °C, and the dynamic pressure holding time is 10~30 min.

[0069] In one or more embodiments, the second-stage pressure is 0.5~1.0 MPa, the second-stage temperature is 210~230 °C, and the second-stage pressure and temperature are maintained for 10~30 min.

[0070] In one or more embodiments, the third-stage pressure is 0.1~0.25 MPa, the third-stage temperature is 180~200 °C, and the third-stage pressure and temperature are maintained for 10~30 min.

[0071] In one or more embodiments, the vacuuming time for the post-vacuum thickening treatment is 10 to 30 minutes.

[0072] Example 2:

[0073] This embodiment is based on Embodiment 1, but the amount of raw materials used is increased fivefold.

[0074] (a) Feeding and gas replacement

[0075] 430.80 g hexamethylenediamine, 758.40 g sebacic acid, and 1195 ml deionized water were added into a high-pressure polymerization reactor at one time. Nitrogen gas was continuously introduced into the bottom of the reactor, and the vent was kept open at the top of the reactor. The nitrogen gas moved from the bottom of the reactor through the reaction system to the top of the reactor, forming a stable nitrogen gas disturbance field in the reaction system.

[0076] (b) Salt formation reaction

[0077] The reactor is heated to 80 °C and kept at a constant temperature for 45 min to allow hexamethylenediamine and sebacic acid to complete the acid-base neutralization and salt formation reaction, forming a homogeneous and stable PA610 monomer salt solution. After the process is completed, the vent is closed, the container is filled with nitrogen, and a closed protection system is constructed.

[0078] (c) Prepolymerization reaction

[0079] The reactor was heated to 200 °C and prepolymerized at a constant temperature for 1 h. The monomer salt underwent a preliminary polycondensation reaction to generate a low molecular weight PA610 prepolymer, which built the basic molecular chain structure. After the reaction was completed, the prepolymerization pressure of the system was 1.7 MPa.

[0080] (d) Multistage depressurization polymerization reaction

[0081] First stage: Without shutting off the heating device, slowly open the pressure relief valve and control the pressure relief rate. The pressure of the reaction system slowly decreases from the prepolymerization pressure to the first stage pressure of 1.5 MPa, and the temperature decreases accordingly to the first stage temperature of 190 °C. Maintain the first stage pressure and temperature for 30 min. During this stage, the rate of gas generation from heating in the reaction system reaches a dynamic equilibrium with the rate of gas release from pressure relief, so the pressure remains constant during this period.

[0082] Second stage: Continue to increase the opening of the pressure relief valve to increase the pressure relief range, and steadily reduce the pressure of the reaction system from the first stage pressure to the second stage pressure of 1.0 MPa. The temperature will then rise to the second stage temperature of 220 °C. After that, close the pressure relief valve and maintain the second stage pressure and temperature for 20 min.

[0083] Third stage: Open the pressure relief valve to rapidly reduce the pressure of the reaction system from the second stage pressure to the third stage pressure of 0.1 MPa, and the temperature will drop to the third stage temperature of 200 °C. Close the pressure relief valve and maintain the third stage pressure and temperature for 10 minutes.

[0084] (e) Post-treatment after vacuum thickening

[0085] The reactor is connected to a water-circulating vacuum pump, and the reactor system is continuously evacuated for 30 minutes to deeply remove residual moisture and trace small molecule polycondensation byproducts, thereby removing the reaction equilibrium limitation, promoting further growth of molecular chains and increasing the degree of polymerization. Finally, after cooling, the product PA610-2 is discharged.

[0086] Testing of product PA610-2 revealed a number-average molecular weight (Mn) of 17637, a weight-average molecular weight (Mw) of 37246, and an intrinsic viscosity of 1.29 dL / g. This demonstrates that even with increased raw material quantity, the process can still produce PA610 products with excellent molecular chain length and high viscosity.

[0087] Comparative Example 1:

[0088] The preparation process of this comparative example is similar to that of Example 1, except that in step (a), after hexamethylenediamine, sebacic acid, and deionized water are added to the high-pressure polymerization reactor all at once, nitrogen gas is introduced to replace the oxygen in the reactor, and the reactor vent is closed after the replacement is completed. During the salt formation reaction in step (b), the reactor is in a closed state with no nitrogen disturbance. The final product PA610-3 is obtained.

[0089] In this comparative example, after eliminating nitrogen disturbance in the salt formation reaction, the salt formation reaction time was only 20 minutes, resulting in some hexamethylenediamine and sebacic acid not reacting. Therefore, the performance test results of the final product PA610-3 showed that the number average molecular weight Mn=12442 and the weight average molecular weight Mw=20412, indicating a low degree of polymerization and insufficient mechanical properties. At the same time, the intrinsic viscosity of the product was 0.51dL / g, indicating a low melt viscosity.

[0090] In some embodiments, by extending the salt formation reaction time, for example, to 40-60 min, the molecular chain length and intrinsic viscosity of PA610-3 can be effectively increased.

[0091] Comparative Example 2:

[0092] The preparation process of this comparative example is similar to that of Example 1, except that in step (d), a single-stage pressure-relief polymerization reaction is used instead of a multi-stage pressure-relief polymerization reaction. Specifically, after the prepolymerization reaction is completed, the heating device is not turned off, and the pressure relief valve is gradually opened, so that the pressure of the reaction system is reduced from 1.8 MPa to 0.25 MPa within 30 minutes. After most of the water in the system is removed, the subsequent vacuum thickening post-treatment step (e) is carried out, and finally the product PA610-4 is obtained.

[0093] PA610-4 has a number-average molecular weight (Mn) of 9846 and a weight-average molecular weight (Mw) of 13652, indicating a moderate molecular weight distribution, classifying it as a medium-molecular-weight PA610 product. However, its intrinsic viscosity is 0.61 dL / g, resulting in insufficient melt strength to meet the requirements of extrusion molding processes. This may be because, after removing the first-stage dynamic holding pressure process, the absence of a concentration step allows moisture in the raw materials and generated during the prepolymerization reaction to inhibit the polymerization reaction, ultimately leading to shorter molecular chains.

[0094] Comparative Example 3:

[0095] The preparation process of this comparative example is similar to that of Example 1, except that in step (c), the prepolymerization temperature is reduced from 200 °C to 150 °C, and the initial prepolymerization pressure of the system after prepolymerization is 1.25 MPa; simultaneously, in step (d), some pressures and temperatures of the multi-stage depressurization polymerization reaction are adjusted, specifically:

[0096] First stage: Without turning off the heating device, slowly open the pressure relief valve and control the pressure relief rate. The pressure of the reaction system slowly decreases from the prepolymerization pressure to the first stage pressure of 1.05 MPa and the temperature decreases to the first stage temperature of 140 °C. During this stage, by adjusting the pressure relief valve, the rate of gas generation by heating in the reaction system and the rate of gas exhaust by pressure relief are dynamically balanced. Therefore, the pressure remains constant for 20 min during this period.

[0097] Second stage: Continue to increase the opening of the pressure relief valve to increase the pressure relief range, and steadily reduce the pressure of the reaction system from the first stage pressure to the second stage pressure of 0.5 MPa, and raise the temperature to the second stage temperature of 170 °C. Then close the pressure relief valve and maintain the second stage pressure and temperature for 10 min.

[0098] Third stage: Open the pressure relief valve to rapidly reduce the pressure of the reaction system from the second stage pressure to the third stage pressure of 0.1 MPa and the temperature to the third stage temperature of 150 °C. Close the pressure relief valve and maintain the third stage pressure and temperature for 10 minutes.

[0099] Finally, PA610-5 was obtained through vacuum thickening and subsequent cooling. Due to the reduction in the temperature and pressure of the prepolymerization reaction, as well as some of the pressure and temperature of the multi-stage depressurization polymerization reaction, the performance of PA610-5 was significantly inferior to PA610-1 in Example 1. Test results showed that PA610-5 had a number-average molecular weight Mn=13505, a weight-average molecular weight Mw=21027, and a acceptable molecular chain length, but its intrinsic viscosity was only 0.62 dL / g.

[0100] Comparative Example 4:

[0101] The preparation process of this comparative example is similar to that of Example 1, except that in step (a), 87.16 g of hexamethylenediamine, 151.68 g of sebacic acid, 239 ml of deionized water, and 120 μL of hypophosphoric acid were added to the high-pressure polymerization reactor in one step. Hypophosphoric acid was used as a catalyst. Other reaction conditions were the same as in Example 1, and the final product PA610-6 was obtained.

[0102] Performance analysis of PA610-6 revealed that its number-average molecular weight Mn=19357, weight-average molecular weight Mw=37226, excellent molecular chain length, and uniform molecular weight distribution. In addition, its intrinsic viscosity is 1.29 dL / g, and its high viscosity characteristics meet the requirements of high-end industrial injection molding and extrusion molding processes.

[0103] Therefore, the performance of PA610-6 prepared with the addition of hypophosphoric acid is comparable to that of PA610-1 prepared without the addition of hypophosphoric acid, indicating that the addition of the catalyst has no significant impact on the product performance. This may be because the aqueous high-pressure salt-forming-multi-stage depressurization polymerization process in this system has high reactivity. During the salt-forming stage, the monomers are in full contact, and the high-temperature and high-pressure conditions during the prepolymerization and polycondensation stages are sufficient to drive the amidation chain growth reaction to proceed fully. Although a small amount of hypophosphoric acid can act as a polycondensation catalyst, the catalytic gain is limited under these reaction conditions and cannot further increase the molecular weight and intrinsic viscosity of the polymer product. Therefore, there is no significant difference in resin performance before and after the addition of hypophosphoric acid.

[0104] Comparative Example 5:

[0105] The preparation process of this comparative example is similar to that of Example 1, except that in step (a), 89.77 g of hexamethylenediamine, 151.68 g of sebacic acid, and 242 ml of deionized water were added to the high-pressure polymerization reactor all at once. The molar ratio of hexamethylenediamine to sebacic acid was changed (hexamethylenediamine: sebacic acid = 1.03:1), while other reaction conditions remained the same as in Example 1, and the final product PA610-7 was obtained.

[0106] Performance analysis of PA610-7 revealed that its number-average molecular weight Mn=22357, weight-average molecular weight Mw=39351, excellent molecular chain length, and uniform molecular weight distribution. Furthermore, its intrinsic viscosity is 1.36 dL / g, and its high viscosity characteristics meet the requirements of high-end industrial injection molding and extrusion molding processes.

[0107] This indicates that by adjusting the monomer molar ratio of hexamethylenediamine to sebacic acid, the molecular weight and intrinsic viscosity of the polymer product can be effectively increased. A moderate excess of hexamethylenediamine can offset the ratio shift caused by its high-temperature volatilization, promoting sufficient molecular chain growth and thus obtaining a high-viscosity polyamide 610 product with excellent processing properties.

[0108] Comparative Example 6:

[0109] The preparation process of this comparative example is similar to that of Example 1, except that in step (a), 87.16 g of hexamethylenediamine, 151.68 g of sebacic acid, 239 ml of deionized water, and 120 μL of antioxidant 1010 were added to the high-pressure polymerization reactor all at once. Other reaction conditions were the same as in Example 1, and the final product PA610-8 was obtained.

[0110] Performance analysis of PA610-8 revealed that its number-average molecular weight Mn=17212, weight-average molecular weight Mw=36114, excellent molecular chain length, and uniform molecular weight distribution. Furthermore, its intrinsic viscosity is 1.21 dL / g, and its high viscosity meets the requirements of high-end industrial injection molding and extrusion molding processes, while maintaining its color.

[0111] Therefore, it is evident that PA610-8 prepared with the addition of antioxidants has comparable performance to PA610-1 prepared without antioxidants, indicating that the addition of antioxidants has no significant impact on product performance. This may be because the dynamic pressure maintenance and steam removal method used in the first stage of the multi-stage depressurization polymerization reaction effectively removes oxygen. Furthermore, after the salt formation reaction, the reactor directly undergoes the prepolymerization reaction without concentration, so the solute remains unchanged and no oxygen is introduced. Therefore, excellent product performance can be obtained without the addition of antioxidants.

[0112] The terms "first," "second," etc., used in this document (e.g., first time, second time; first-stage pressure, second-stage pressure, etc.) are merely for clarity of description and are not intended to restrict any order or emphasize importance. Furthermore, the term "connection" used herein, unless otherwise specified, can refer to a direct connection or an indirect connection via other groups.

[0113] The specific embodiments described above further illustrate the purpose, technical solution, and beneficial effects of the present invention. It should be understood that the above description is only a specific embodiment of the present invention and is not intended to limit the scope of protection of the present invention. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the scope of protection of the present invention.

Claims

1. A preparation process for polyhexamethylene sebacate, characterized in that, Includes the following steps: (A) Salt formation reaction: Under nitrogen protection, hexamethylenediamine and sebacic acid undergo a salt formation reaction in deionized water to obtain a salt solution; (B) Prepolymerization reaction, wherein the salt solution is directly heated to the prepolymerization temperature in a closed system and maintained at the prepolymerization temperature for a first time, and the reaction system is under prepolymerization pressure after the reaction is completed; (C) Multi-stage depressurization polymerization reaction, wherein the prepolymer pressure is reduced to the first stage pressure, and the first stage pressure is maintained for a second time. During the second time, the exhaust valve is kept open to continuously discharge the gas phase component containing water vapor, so that the pressure of the reaction system is maintained at the first stage pressure; then the exhaust rate is increased until the pressure of the reaction system drops to the preset pressure. (D) Vacuum thickening treatment: The reaction system is thickened under vacuum conditions.

2. The preparation process of polyhexamethylene sebacate according to claim 1, characterized in that, In step (B), the prepolymerization pressure is 1.6~1.8 MPa, the prepolymerization temperature is 180~200 °C, and the first time is 0.5~1 h.

3. The preparation process of polyhexamethylene sebacate according to claim 2, characterized in that, In step (C), the first stage pressure is 1.45~1.65 MPa, and the second time is 10~30 min.

4. The preparation process of polyhexamethylene sebacate according to claim 2, characterized in that, In step (C), after the reaction system is maintained at the first-stage pressure for a second time, the exhaust rate is increased to reduce the first-stage pressure to the second-stage pressure, and it is maintained at the second-stage pressure for a third time; subsequently, the second-stage pressure is reduced to the third-stage pressure, and it is maintained at the third-stage pressure for a fourth time. The second stage pressure is 0.5~1.0 MPa, and the third time is 10~30 min; the third stage pressure is 0.1~0.25 MPa, and the fourth time is 10~30 min.

5. The preparation process of polyhexamethylene sebacate according to claim 1, characterized in that, In step (A), the salt formation reaction is carried out under conditions of continuous introduction and discharge of nitrogen gas into the reaction system.

6. The preparation process of polyhexamethylene sebacate according to claim 5, characterized in that, In step (A), the salt formation reaction takes 15 to 45 minutes.

7. The preparation process of polyhexamethylene sebacate according to claim 1, characterized in that, No separate concentration step is set between the salt formation reaction and the prepolymerization reaction.

8. The preparation process of polyhexamethylene sebacate according to claim 1, characterized in that, In steps (A) to (D), the reaction system is in a state where no exogenous additives are added.

9. The preparation process of polyhexamethylene sebacate according to claim 8, characterized in that, The exogenous additive is at least one of the following: antioxidant, heat stabilizer, light stabilizer, molecular weight regulator, capping agent, catalyst, nucleating agent, lubricant, and flow aid.

10. A system for preparing polyhexamethylene sebacate, characterized in that, A preparation system for carrying out a preparation process of polyhexamethylene sebacate as described in any one of claims 1 to 9, the preparation system comprising: The reactor is configured to sequentially carry out salt formation reaction, prepolymerization reaction, multi-stage depressurization polymerization reaction, and vacuum thickening treatment within the same reactor. A heating device is used to heat the reaction system inside the reactor. A pressure control system is used to control the pressure inside the reactor. A vacuum system is used to evacuate the reactor.

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