Preparation method of poly (p-phenylene terephthalamide) with narrow molecular weight distribution

Abstract

The invention relates to a preparation method of poly (p-phenylene terephthamide) with narrow molecular weight distribution. The preparation method comprises the following steps: uniformly mixing p-phenylenediamine, an NMP-CaCl2 mixed solvent and transition metal salt to obtain a mixed system; before entering a pre-polymerization reactor, adding a first part of paraphthaloyl chloride into the mixed system, and reacting to obtain a first pre-polymerization solution; in a pre-polymerization reactor, adding a second part of paraphthaloyl chloride into the first pre-polymerization solution, and reacting to obtain a second pre-polymerization solution; in a final polymerization reactor, adding the residual paraphthaloyl chloride into the second pre-polymerization liquid, and reacting to obtain a polymer; and neutralizing, washing and drying the polymer to obtain the poly (p-phenylene terephthamide) with narrow molecular weight distribution. According to the invention, the transition metal salt is added, and a small amount of TPC and PPD solution are added in the dissolving stage for reaction, so that the prepared poly-p-phenylene terephthamide has narrow molecular weight distribution.

Description

Technical Field

[0001] The present invention relates to the technical field of aromatic polyamide polymers, and particularly to a preparation method of poly(p-phenyleneterephthalamide) with a narrow molecular weight distribution. Background Art

[0002] Poly(p-phenyleneterephthalamide) (PPTA) is a polymer formed by the low-temperature polycondensation of p-phenylenediamine (PPD) and terephthaloyl chloride (TPC). It was first developed by DuPont in the United States in the 1960s and 1970s. By dissolving the PPTA polymer in concentrated sulfuric acid and using the dry-jet wet-spinning process, high-performance PPTA fibers, i.e., para-aramid fibers, can be obtained. Due to its excellent properties such as light weight, high modulus, high strength, impact resistance, high temperature resistance, and corrosion resistance, para-aramid fibers are widely used in fields such as bulletproof and explosion-proof, aerospace, automotive manufacturing, high-strength ropes, and communication engineering.

[0003] However, since the PPTA polymerization process is a rapid exothermic and fast-reacting process, and as the reaction progresses, the viscosity of the system increases, making the transfer of reaction heat more difficult, increasing the control difficulty of the polymerization reaction, and resulting in the inability to obtain polymers with exactly the same molecular weight in terms of the control of the degree of polymerization. The molecular weight shows a normal distribution and the molecular weight distribution is relatively wide. Since the molecular weight distribution has a great influence on spinning, high-molecular-weight PPTA resin requires more dissolution time in concentrated sulfuric acid, which will cause the already dissolved PPTA resin to degrade. The presence of low-molecular-weight PPTA usually easily leads to defect points in PPTA fibers, affecting the overall performance of the fibers. Therefore, how to prepare PPTA polymers with a narrower molecular weight distribution is crucial for improving the mechanical properties and batch stability of the fibers.

[0004] Patent CN117843948A discloses a preparation method of poly(p-phenyleneterephthalamide), which solves the possibility of local explosion polymerization in the reaction by freeze granulating the solvent system and mixing it with PPD and TPC powders, and the molecular weight distribution of the prepared PPTA polymer is controllable. However, this method requires freezing the solvent system to -80 to -30 °C for granulation, which greatly increases the energy consumption cost of production. Patent CN117258743A discloses a para-aramid continuous polymerization system and method, which changes the traditional TPC melting feeding method, dissolves TPC and PPD in the NMP system respectively, and atomizes and contacts them through an atomizing nozzle to carry out the polymerization reaction. With the improved reaction equipment, the heat generated by the reaction and small molecule by-products are timely removed from the reaction system to achieve the uniformity of the reaction system. However, the equipment used in this preparation process is relatively complex, and since TPC adopts a solution feeding method, TPC will undergo a side reaction with NMP, causing the inactivation of its acyl chloride group, thereby affecting the molecular weight of PPTA.

[0005] Therefore, it is of great significance to develop a preparation method of poly(p-phenylenediamine terephthalate) with a narrow molecular weight distribution that is low-cost and can avoid side reactions. Summary of the Invention

[0006] In view of the deficiencies of the prior art, the purpose of the present invention is to provide a preparation method of poly(p-phenylenediamine terephthalate) with a narrow molecular weight distribution, which can obtain poly(p-phenylenediamine terephthalate) with a narrow molecular weight distribution and is convenient for subsequent applications.

[0007] To achieve this purpose, the present invention adopts the following technical solutions:

[0008] A preparation method of poly(p-phenylenediamine terephthalate) with a narrow molecular weight distribution, comprising the following steps:

[0009] (1) Mix p-phenylenediamine, NMP-CaCl 2 mixed solvent and transition metal salt evenly to obtain a mixed system;

[0010] (2) Add the first part of terephthaloyl chloride to the obtained mixed system and react to obtain a first prepolymer solution;

[0011] (3) Add the second part of terephthaloyl chloride to the obtained first prepolymer solution and react to obtain a second prepolymer solution;

[0012] (4) Add the remaining terephthaloyl chloride to the second prepolymer solution to obtain a polymer;

[0013] (5) Neutralize, wash and dry the polymer to obtain poly(p-phenylenediamine terephthalate) with a narrow molecular weight distribution.

[0014] In some embodiments of the present invention, in step (1), the transition metal salt is selected from transition metal chloride salts or transition metal acetate salts. Preferably, the transition metal chloride is selected from any one or a combination of copper chloride, zinc chloride, and cobalt chloride; or, the transition metal acetate is selected from any one or a combination of copper acetate, zinc acetate, and cobalt acetate.

[0015] In some embodiments of the present invention, in step (1), the mass fraction of CaCl 2 in the NMP-CaCl 2 mixed solvent is 6%-9%.

[0016] In some embodiments of the present invention, in step (1), the concentration of p-phenylenediamine in the mixed system is 0.3-0.5 mol / L.

[0017] In some embodiments of the present invention, in step (1), the molar ratio of the transition metal salt to p-phenylenediamine is 0.2-2:1.

[0018] In some embodiments of the present invention, in step (2), the first part of terephthaloyl chloride accounts for 10%-15% of the total molar amount of terephthaloyl chloride; and / or, the mixed system is prepared in a dissolution kettle, and the first part of terephthaloyl chloride is added to the dissolution kettle.

[0019] In some embodiments of the present invention, in step (2), the reaction temperature is controlled to be -10 - 0 °C during the preparation of the first prepolymer solution.

[0020] In some embodiments of the present invention, in step (3), in the prepolymerization reactor, the second part of terephthaloyl chloride is added to the first prepolymer solution; and / or, the second part of terephthaloyl chloride accounts for 15%-35% of the total molar amount of terephthaloyl chloride.

[0021] In some embodiments of the present invention, in step (3), the reaction temperature is controlled to be 0 - 5 °C during the preparation of the second prepolymer solution.

[0022] In some embodiments of the present invention, in step (4), in the final polymerization reactor, the remaining terephthaloyl chloride is added to the second prepolymer solution; and / or, the ratio of the total molar amount of terephthaloyl chloride to the molar amount of p-phenylenediamine is 1 - 1.015:1.

[0023] In some embodiments of the present invention, in step (4), the reaction temperature is controlled to be 20 - 30 °C during the preparation of the polymer.

[0024] In some embodiments of the present invention, in step (5), the neutralization includes adding an alkali solution, and the alkali solution is selected from an aqueous sodium hydroxide solution.

[0025] Compared with the prior art, the present invention has the following beneficial effects:

[0026] 1. The preparation method of poly(p-phenylene terephthalamide) with a narrow molecular weight distribution provided by the present invention, in addition to adding CaCl 2 co-solvent, additionally adds a transition metal chloride salt or acetate, and uses the coordination of Cu, Zn, Co and other ions with amino groups to inhibit the reaction between amino groups and acyl chloride groups, thereby reducing the reaction heat, avoiding local explosive polymerization, and thus narrowing the molecular weight.

[0027] 2. After the Cu, Zn, Co and other ions in the transition metal chloride salt or acetate added by the present invention coordinate with amino groups, the chloride ions in the chloride salt will be released and destroy the intermolecular hydrogen bonds of PPTA, enhancing its solubility; the acetate ions in the acetate will also be released and react with the by-product hydrogen chloride during the polymerization of PPTA, and the generated chloride ions will also destroy the intermolecular hydrogen bonds of PPTA, enhancing the solubility of PPTA.

[0028] 3. In the present invention, by adding a small amount of TPC to react with the PPD solution during the dissolution stage, the oxidation problem of the PPD solution caused by long storage time is reduced, which is beneficial to the growth of molecular chains, reduces the generation of small molecular weight products, and thus narrows the molecular weight. BRIEF DESCRIPTION OF THE DRAWINGS

[0029] Figure 1 It is a process flow chart for the preparation of poly(p-phenylenediamine terephthalate) with a narrow molecular weight distribution according to an embodiment of the present invention. DETAILED DESCRIPTION OF THE INVENTION

[0030] The following will detail the preparation method of poly(p-phenylenediamine terephthalate) with a narrow molecular weight distribution according to the present invention.

[0031] A preparation method of poly(p-phenylenediamine terephthalate) with a narrow molecular weight distribution includes the following steps:

[0032] (1) Mix p-phenylenediamine, NMP-CaCl 2 mixed solvent and transition metal salt evenly to obtain a mixed system;

[0033] (2) Add the first part of terephthaloyl chloride to the obtained mixed system and react to obtain a first prepolymer solution;

[0034] (3) Add the second part of terephthaloyl chloride to the obtained first prepolymer solution and react to obtain a second prepolymer solution;

[0035] (4) Add the remaining terephthaloyl chloride to the second prepolymer solution to obtain a polymer;

[0036] (5) Neutralize, wash and dry the polymer to obtain poly(p-phenylenediamine terephthalate) with a narrow molecular weight distribution.

[0037] In some embodiments of the present invention, in step (1), the transition metal salt is selected from transition metal chloride salts or transition metal acetate salts. Preferably, the transition metal chloride is selected from any one or a combination of copper chloride, zinc chloride, and cobalt chloride; or, the transition metal acetate is selected from any one or a combination of copper acetate, zinc acetate, and cobalt acetate.

[0038] In addition to adding CaCl 2In addition to the cosolvent, transition metal chloride salts or acetates were additionally added. The coordination of Cu, Zn, Co and other ions with amino groups inhibited the reaction between amino groups and acyl chloride groups, thereby reducing the reaction heat, avoiding local explosive polymerization, and narrowing the molecular weight. After the coordination of Cu, Zn, Co and other ions with amino groups, the chloride ions in the chloride salts were released and destroyed the intermolecular hydrogen bonds of PPTA, enhancing its solubility. The acetate ions in the acetates were also released and reacted with the by-product hydrogen chloride during the polymerization of PPTA. The generated chloride ions also destroyed the intermolecular hydrogen bonds of PPTA, enhancing the solubility of PPTA.

[0039] In some embodiments of the present invention, in step (1), in the NMP-CaCl 2 The mass fraction of CaCl in the mixed solvent 2 is 6%-9%, which can be 6%-7%, 7%-8%, or 8%-9%.

[0040] In some embodiments of the present invention, in step (1), the concentration of p-phenylenediamine in the mixed system is 0.3-0.5 mol / L, specifically it can be 0.3-0.35 mol / L, 0.35-0.4 mol / L, 0.4-0.45 mol / L, or 0.45-0.5 mol / L.

[0041] In some embodiments of the present invention, in step (1), the molar ratio of the transition metal salt to p-phenylenediamine is 0.2-2:1, which can be 0.2-0.4:1, 0.4-0.6:1, 0.6-0.8:1, 0.8-1:1, 1-1.2:1, 1.2-1.4:1, 1.4-1.6:1, 1.6-1.8:1, or 1.8-2:1.

[0042] In some embodiments of the present invention, in step (2), the first part of terephthaloyl chloride accounts for 10%-15% of the total molar amount of terephthaloyl chloride, which can be 10%-11%, 11%-12%, 12%-13%, 13%-14%, or 14%-15%.

[0043] In some embodiments of the present invention, in step (2), the mixed system is prepared in a dissolution kettle, and the first part of terephthaloyl chloride is added to the dissolution kettle. By adding a small amount of TPC to react with the PPD solution during the dissolution stage, the oxidation problem of the PPD solution caused by long storage time is reduced, which is beneficial to the growth of molecular chains, reduces the generation of small molecular weight products, and thus narrows the molecular weight.

[0044] In some embodiments of the present invention, in step (2), during the preparation of the first prepolymer solution, the reaction temperature is controlled to be -10 to 0 °C (including the end point values), which can be -10 to -8 °C, -8 to -6 °C, -6 to -4 °C, -4 to -2 °C, or can also be -2 to 0 °C.

[0045] In some embodiments of the present invention, in step (3), in the prepolymerization reactor, the second part of terephthaloyl chloride is added to the first prepolymer solution.

[0046] In some embodiments of the present invention, in step (3), the second part of terephthaloyl chloride accounts for 15% - 35% of the total molar amount of terephthaloyl chloride, which can be 15% - 20%, 20% - 25%, 25% - 30%, or can also be 30% - 35%.

[0047] In some embodiments of the present invention, in step (3), during the preparation of the second prepolymer solution, the reaction temperature is controlled to be 0 to 5 °C (including the end point values), which can be 0 to 1 °C, 1 to 2 °C, 2 to 3 °C, 3 to 4 °C, or can also be 4 to 5 °C.

[0048] In some embodiments of the present invention, in step (4), in the final polymerization reactor, the remaining terephthaloyl chloride is added to the second prepolymer solution.

[0049] In some embodiments of the present invention, in step (4), the ratio of the total molar amount of terephthaloyl chloride to the molar amount of p-phenylenediamine is 1 - 1.015:1, which can be 1 - 1.005:1, 1.005 - 1.010:1, or can also be 1.010 - 1.015:1.

[0050] In some embodiments of the present invention, in step (4), during the preparation of the polymer, the reaction temperature is controlled to be 20 - 30 °C (including the end point values), which can be 20 to 22 °C, 22 to 24 °C, 24 to 26 °C, 26 to 28 °C, or can also be 28 to 30 °C.

[0051] In some embodiments of the present invention, in step (5), the neutralization includes adding an alkali solution, and the alkali solution is selected from an aqueous sodium hydroxide solution.

[0052] The following further elaborates on the specific implementation manners of the present invention in conjunction with preferred embodiments. When an embodiment gives a numerical range, it should be understood that unless otherwise specified in the present invention, any value between the two endpoints of each numerical range and either of the two endpoints can be selected. Unless otherwise defined, all technical and scientific terms used in the present invention have the same meaning as commonly understood by those skilled in the art of this technology. In addition to the specific methods, equipment, and materials used in the embodiments, any methods, equipment, and materials of the prior art similar or equivalent to those described in the embodiments of the present invention can also be used to implement the present invention according to the knowledge of those skilled in the art of the prior art and the description of the present invention.

[0053] In the following examples and comparative examples, the inherent viscosity was detected by the Ubbelohde viscometer method. After alkylation modification of the PPTA polymer, the molecular weight distribution of the polymer was detected by gel permeation chromatography (GPC), and the polydispersity index (PDI) was calculated.

[0054] Example 1

[0055] The preparation method of the PPTA polymer in this example is as Figure 1 shown, and includes the following steps:

[0056] (1) Prepare an NMP-CaCl₂ 2 mixed solvent with a CaCl₂ content of 9 wt%, and then mix PPD, the NMP-CaCl₂ 2 mixed solvent, and copper chloride uniformly in a dissolution kettle to obtain an NMP mixed system; the concentration of PPD in the NMP mixed system is 0.4 mol / L, and the molar ratio of copper chloride to PPD is 0.2:1. 2

[0057] (2) Add the first part of TPC (accounting for 15% of the total molar amount of TPC) to the NMP mixed system in the dissolution kettle, and react to obtain a first prepolymer solution, while controlling the reaction temperature to be -10 to 0 °C.

[0058] (3) In a prepolymerization reactor, add the second part of TPC (accounting for 15% of the total molar amount of TPC) to the first prepolymer solution, and react to obtain a second prepolymer solution, while controlling the reaction temperature to be 0 to 5 °C.

[0059] (4) In a final polymerization reactor, add the remaining TPC to the second prepolymer solution (the final molar ratio of TPC to PPD reaches 1.015:1) to obtain a polymer, while controlling the reaction temperature to be 20 to 30 °C.

[0060] (5) By neutralizing, washing, and drying the polymer with a sodium hydroxide solution, a PPTA polymer with an inherent viscosity of 5.8 dL / g and a polydispersity index (PDI) of 1.8 is finally obtained.

[0061] Example 2

[0062] The preparation method of the PPTA polymer in this example is as follows Figure 1 shown, including the following steps:

[0063] (1) Prepare NMP-CaCl 2 mixed solvent with a CaCl content of 6 wt%, and then mix PPD, NMP-CaCl 2 mixed solvent and copper chloride evenly in a dissolution kettle to obtain an NMP mixed system. The concentration of PPD in the NMP mixed system is 0.45 mol / L, and the molar ratio of copper chloride to PPD is 2:1. 2

[0064] (2) Add the first part of TPC (accounting for 10% of the total molar amount of TPC) to the NMP mixed system in the dissolution kettle, and react to obtain the first prepolymer solution, while controlling the reaction temperature at -10 to 0 °C.

[0065] (3) In a prepolymerization reactor, add the second part of TPC (accounting for 35% of the total molar amount of TPC) to the first prepolymer solution, and react to obtain the second prepolymer solution, while controlling the reaction temperature at 0 to 5 °C.

[0066] (4) In a final polymerization reactor, add the remaining TPC to the second prepolymer solution (the final molar ratio of TPC to PPD reaches 1.002:1) to obtain a polymer, while controlling the reaction temperature at 20 to 30 °C.

[0067] (5) By neutralizing, washing, and drying the polymer with a sodium hydroxide solution, finally obtain a PPTA polymer with an inherent viscosity of 5.5 dL / g and a polydispersity index (PDI) of 1.6.

[0068] Example 3

[0069] The preparation method of the PPTA polymer in this example is as follows Figure 1 shown, including the following steps:

[0070] (1) Prepare NMP-CaCl 2 mixed solvent with a CaCl content of 8 wt%, and then mix PPD, NMP-CaCl 2 mixed solvent and copper acetate evenly in a dissolution kettle to obtain an NMP mixed system. The concentration of PPD in the NMP mixed system is 0.38 mol / L, and the molar ratio of copper acetate to PPD is 1:1. 2

[0071] ​​(2) Add the first portion of TPC (15% of the total molar amount of TPC) to the NMP mixed system in the dissolution kettle, and react to obtain the first prepolymer solution. During this period, control the reaction temperature at -10 to 0 °C.

[0072] (3) In the prepolymer reactor, add the second portion of TPC (30% of the total molar amount of TPC) to the first prepolymer solution, and react to obtain the second prepolymer solution. During this period, control the reaction temperature at 0 to 5 °C.

[0073] (4) In the final polymerization reactor, add the remaining TPC to the second prepolymer solution (the final molar ratio of TPC to PPD reaches 1:1) to obtain the polymer. During this period, control the reaction temperature at 20 to 30 °C.

[0074] (5) By neutralizing, washing, and drying the polymer with sodium hydroxide solution, finally obtain a PPTA polymer with an inherent viscosity of 5.7 dL / g and a polydispersity index (PDI) of 1.9.

[0075] Example 4

[0076] The preparation method of the PPTA polymer in this example is as Figure 1 shown, including the following steps:

[0077] (1) Prepare an NMP-CaCl 2 mixed solvent with a CaCl 2 content of 7 wt%, and then mix PPD, the NMP-CaCl 2 mixed solvent, and zinc chloride evenly in the dissolution kettle to obtain an NMP mixed system. The concentration of PPD in the NMP mixed system is 0.41 mol / L, and the molar ratio of zinc chloride to PPD is 0.4:1.

[0078] (2) Add the first portion of TPC (14% of the total molar amount of TPC) to the NMP mixed system in the dissolution kettle, and react to obtain the first prepolymer solution. During this period, control the reaction temperature at -10 to 0 °C.

[0079] (3) In the prepolymer reactor, add the second portion of TPC (26% of the total molar amount of TPC) to the first prepolymer solution, and react to obtain the second prepolymer solution. During this period, control the reaction temperature at 0 to 5 °C.

[0080] (4) In the final polymerization reactor, add the remaining TPC to the second prepolymer solution (the final molar ratio of TPC to PPD reaches 1.005:1) to obtain the polymer. During this period, control the reaction temperature at 20 to 30 °C.

[0081] (5) By neutralizing, washing, and drying the polymer with sodium hydroxide solution, a PPTA polymer with an inherent viscosity of 5.9 dL / g and a polydispersity index (PDI) of 1.7 is finally obtained.

[0082] Example 5

[0083] The preparation method of the PPTA polymer in this example is as Figure 1 shown and includes the following steps:

[0084] (1) Prepare NMP-CaCl₂ mixed solvent with a CaCl₂ content of 8 wt%, and then mix PPD, NMP-CaCl₂ mixed solvent, and zinc acetate evenly in a dissolution kettle to obtain an NMP mixed system. The concentration of PPD in the NMP mixed system is 0.35 mol / L, and the molar ratio of zinc acetate to PPD is 1.2:1. 2 NMP-CaCl₂ mixed solvent with a CaCl₂ content of 8 wt% 2 and then mix PPD, NMP-CaCl₂ 2 mixed solvent and zinc acetate evenly in a dissolution kettle to obtain an NMP mixed system. The concentration of PPD in the NMP mixed system is 0.35 mol / L, and the molar ratio of zinc acetate to PPD is 1.2:1.

[0085] (2) Add the first part of TPC (accounting for 15% of the total molar amount of TPC) to the NMP mixed system in the dissolution kettle, and react to obtain the first prepolymer solution, while controlling the reaction temperature at -10 to 0 °C.

[0086] (3) In the prepolymer reactor, add the second part of TPC (accounting for 30% of the total molar amount of TPC) to the first prepolymer solution, and react to obtain the second prepolymer solution, while controlling the reaction temperature at 0 to 5 °C.

[0087] (4) In the final polymerization reactor, add the remaining TPC to the second prepolymer solution (the final molar ratio of TPC to PPD reaches 1.006:1) to obtain the polymer, while controlling the reaction temperature at 20 to 30 °C.

[0088] (5) By neutralizing, washing, and drying the polymer with sodium hydroxide solution, a PPTA polymer with an inherent viscosity of 5.6 dL / g and a polydispersity index (PDI) of 1.9 is finally obtained.

[0089] Example 6

[0090] The preparation method of the PPTA polymer in this example is as Figure 1 shown and includes the following steps:

[0091] (1) Prepare NMP-CaCl₂ mixed solvent with a CaCl₂ content of 7 wt%, and then mix PPD, NMP-CaCl₂ mixed solvent, and cobalt chloride evenly in a dissolution kettle to obtain an NMP mixed system. The concentration of PPD in the NMP mixed system is 0.38 mol / L, and the molar ratio of cobalt chloride to PPD is 0.6:1. 2 NMP-CaCl₂ mixed solvent with a CaCl₂ content of 7 wt% 2 and then mix PPD, NMP-CaCl₂ 2 mixed solvent and cobalt chloride evenly in a dissolution kettle to obtain an NMP mixed system. The concentration of PPD in the NMP mixed system is 0.38 mol / L, and the molar ratio of cobalt chloride to PPD is 0.6:1.

[0092] (2) Add the first part of TPC (12% of the total molar amount of TPC) to the NMP mixed system in the dissolution kettle, and react to obtain the first prepolymer solution. During this period, control the reaction temperature at -10 to 0 °C.

[0093] (3) In the prepolymer reactor, add the second part of TPC (23% of the total molar amount of TPC) to the first prepolymer solution, and react to obtain the second prepolymer solution. During this period, control the reaction temperature at 0 to 5 °C.

[0094] (4) In the final polymerization reactor, add the remaining TPC to the second prepolymer solution (the molar ratio of the final TPC to PPD reaches 1.002:1) to obtain the polymer. During this period, control the reaction temperature at 20 to 30 °C.

[0095] (5) By neutralizing, washing and drying the polymer with sodium hydroxide solution, finally obtain a PPTA polymer with an inherent viscosity of 5.7 dL / g and a polydispersity index (PDI) of 1.7.

[0096] Example 7

[0097] The preparation method of the PPTA polymer in this example is as Figure 1 shown, including the following steps:

[0098] (1) Prepare an NMP-CaCl 2 mixed solvent with a CaCl 2 content of 9 wt%, and then mix PPD, the NMP-CaCl 2 mixed solvent and cobalt acetate evenly in the dissolution kettle to obtain the NMP mixed system. The concentration of PPD in the NMP mixed system is 0.4 mol / L, and the molar ratio of cobalt acetate to PPD is 0.8:1.

[0099] (2) Add the first part of TPC (12% of the total molar amount of TPC) to the NMP mixed system in the dissolution kettle, and react to obtain the first prepolymer solution. During this period, control the reaction temperature at -10 to 0 °C.

[0100] (3) In the prepolymer reactor, add the second part of TPC (33% of the total molar amount of TPC) to the first prepolymer solution, and react to obtain the second prepolymer solution. During this period, control the reaction temperature at 0 to 5 °C.

[0101] (4) In the final polymerization reactor, add the remaining TPC to the second prepolymer solution (the molar ratio of the final TPC to PPD reaches 1.005:1) to obtain the polymer. During this period, control the reaction temperature at 20 to 30 °C.

[0102] (5) By neutralizing, washing, and drying the polymer with sodium hydroxide solution, a PPTA polymer with an inherent viscosity of 5.6 dL / g and a polydispersity index (PDI) of 1.9 was finally obtained.

[0103] Comparative Example 1

[0104] The difference between this comparative example and Example 1 is that copper chloride is not added, and the process of preparing the first prepolymer solution in the dissolution kettle is not included, that is, both the first part of TPC and the second part of TPC are added in the prepolymerization reactor, and finally a PPTA polymer with an inherent viscosity of 5.1 dL / g and a polydispersity index (PDI) of 2.5 is obtained.

[0105] Comparative Example 2

[0106] The difference between this comparative example and Example 1 is that copper chloride is not added, and finally a PPTA polymer with an inherent viscosity of 5.4 dL / g and a polydispersity index (PDI) of 2.2 is obtained.

[0107] Comparative Example 3

[0108] The difference between this comparative example and Example 1 is that the process of preparing the first prepolymer solution in the dissolution kettle is not included, that is, both the first part of TPC and the second part of TPC are added in the prepolymerization reactor, and finally a PPTA polymer with an inherent viscosity of 5.3 dL / g and a polydispersity index (PDI) of 2.1 is obtained.

[0109] The above embodiments merely illustrate the principles and effects of the present invention and are not intended to limit the present invention. Any person familiar with this technology can modify or change the above embodiments without departing from the spirit and scope of the present invention. Therefore, all equivalent modifications or changes made by those with ordinary knowledge in the technical field without departing from the spirit and technical idea disclosed by the present invention should still be covered by the claims of the present invention.

Claims

1. A method for preparing poly(p-phenylene terephthalamide) with a narrow molecular weight distribution, characterized in that: The steps include: (1) uniformly mixing p-phenylenediamine, NMP-CaCl2 mixed solvent and transition metal salt to obtain a mixed system; (2) adding a first portion of terephthaloyl chloride to the obtained mixed system to react and obtain a first prepolymer solution; (3) adding a second portion of terephthaloyl chloride to the obtained first prepolymer liquid to react to obtain a second prepolymer liquid; (4) adding the remaining terephthaloyl chloride to the second prepolymer solution to react and obtain a polymer; (5) The polymer is neutralized, washed and dried to obtain poly(p-phenylene terephthalamide) with a narrow molecular weight distribution.

2. The method for preparing poly(p-phenylene terephthalamide) with narrow molecular weight distribution according to claim 1, characterized in that: The transition metal salt is selected from transition metal chloride salts or transition metal acetate salts.

3. The method for preparing poly(p-phenylene terephthalamide) with narrow molecular weight distribution according to claim 2, characterized in that: The transition metal chloride is selected from any one of copper chloride, zinc chloride, and cobalt chloride, or a combination of several thereof; or, the transition metal acetate is selected from any one of copper acetate, zinc acetate, and cobalt acetate, or a combination of several thereof.

4. The method for preparing poly(p-phenylene terephthalamide) with narrow molecular weight distribution according to claim 1, characterized in that: In step (1), one or more of the following features are included: 1) The mass fraction of CaCl2 in the NMP-CaCl2 mixed solvent is 6%-9%; 2) the concentration of p-phenylenediamine in the mixed system is 0.3-0.5 mol / L; 3) The molar ratio of the transition metal salt to p-phenylenediamine is 0.2-2:

1.

5. The method for preparing poly(p-phenylene terephthalamide) with narrow molecular weight distribution according to claim 1, characterized in that: In step (2), the first part of terephthaloyl chloride accounts for 10%-15% of the total molar amount of terephthaloyl chloride; and / or, the mixed system is prepared in a dissolving kettle, and the first part of terephthaloyl chloride is added to the dissolving kettle.

6. The method for preparing poly(p-phenylene terephthalamide) with narrow molecular weight distribution according to claim 1, characterized in that: In step (2), the reaction temperature is controlled to be -10-0°C during the preparation of the first prepolymer solution.

7. The method for preparing poly(p-phenylene terephthalamide) with narrow molecular weight distribution according to claim 1, characterized in that: In step (3), in the prepolymerization reactor, a second portion of terephthaloyl chloride is added to the first prepolymerization liquid; and / or the second portion of terephthaloyl chloride accounts for 15% to 35% of the total molar amount of terephthaloyl chloride.

8. The method for preparing poly(p-phenylene terephthalamide) with narrow molecular weight distribution according to claim 1, characterized in that: In step (3), the reaction temperature is controlled at 0-5°C during the preparation of the second prepolymer solution.

9. The method for preparing poly(p-phenylene terephthalamide) with narrow molecular weight distribution according to claim 1, characterized in that: In step (4), in the final polymerization reactor, the remaining terephthaloyl chloride is added to the second prepolymer solution; and / or, the ratio of the total molar amount of terephthaloyl chloride to the molar amount of p-phenylenediamine is 1-1.015:1; and / or, the reaction temperature is controlled to be 20-30° C. during the preparation of the polymer.

10. The method for preparing poly(p-phenylene terephthalamide) with narrow molecular weight distribution according to claim 1, characterized in that: In step (5), the neutralization comprises adding an alkali solution, and the alkali solution is selected from an aqueous sodium hydroxide solution.

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