A method for preparing poly(p-phenylene terephthalamide) with narrow molecular weight distribution

Abstract

The present invention relates to a preparation method of poly (p-phenylene terephthalamide) with a narrow molecular weight distribution. The preparation method of the present invention comprises the following steps: uniformly mixing p-phenylenediamine, an NMP-CaCl2 mixed solvent and a transition metal salt to obtain a mixed system; before entering a prepolymerization reactor, adding a first portion of terephthaloyl chloride to the mixed system to react to obtain a first prepolymer liquid; in the prepolymerization reactor, adding a second portion of terephthaloyl chloride to the first prepolymer liquid to react to obtain a second prepolymer liquid; in a final polymerization reactor, adding the remaining terephthaloyl chloride to the second prepolymer liquid to react to obtain a polymer; neutralizing, washing and drying the polymer to obtain poly (p-phenylene terephthalamide) with a narrow molecular weight distribution. The present invention prepares poly (p-phenylene terephthalamide) with a narrow molecular weight distribution by adding a transition metal salt and adding a small amount of TPC to react with the PPD solution in the dissolution stage.

Description

Technical Field

[0001] The present invention relates to the technical field of aromatic polyamide polymers, in particular to a method for preparing poly(p-phenylene terephthalamide) with narrow molecular weight distribution. Background Art

[0002] Poly(p-phenylene terephthalamide) (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 a dry-jet wet-spinning process, high-performance PPTA fibers, also known as para-aramid fibers, can be produced. Due to its lightweight, high modulus, high strength, impact resistance, high temperature resistance, and corrosion resistance, para-aramid fibers are widely used in bulletproof and explosion-proofing, aerospace, automotive manufacturing, high-strength ropes, and communications engineering.

[0003] However, since the PPTA polymerization process is a rapidly exothermic and reactive process, and as the degree of reaction increases, the viscosity of the system increases, making the transfer of reaction heat more difficult, and increasing the difficulty of controlling the polymerization reaction, it is still impossible to obtain polymers with exactly the same molecular weight in terms of polymerization degree control, and the molecular weight shows a normal distribution and a wide molecular weight distribution. Because the molecular weight distribution has a significant impact on spinning, high molecular weight PPTA resins require more time to dissolve in concentrated sulfuric acid, which will cause the already dissolved PPTA resin to degrade. The presence of low molecular weight PPTA often easily leads to defects in PPTA fibers, affecting the overall performance of the fibers. Therefore, how to produce PPTA polymers with a narrower molecular weight distribution is crucial to improving the mechanical properties and batch stability of the fibers.

[0004] Patent CN117843948A discloses a method for preparing poly(p-phenylene terephthalamide). This method eliminates the possibility of localized implosion by freeze-granulating the solvent system and then mixing it with PPD and TPC powders for a reaction. This method results in a controllable molecular weight distribution for the resulting PPTA polymer. However, this method requires freezing the solvent system to -80 to -30°C for granulation, significantly increasing production energy costs. Patent CN117258743A discloses a continuous para-aramid polymerization system and method. This method modifies the traditional TPC melt feeding method by dissolving TPC and PPD separately in an NMP system. The polymerization reaction occurs through atomizing nozzles, which combine with improved reaction equipment to promptly remove the heat and small molecule byproducts generated by the reaction from the reaction system, achieving a uniform reaction system. However, the equipment used in this preparation process is relatively complex, and since TPC is fed in solution, it can react with NMP, deactivating its acyl chloride groups and thus affecting the molecular weight of PPTA.

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

[0006] In view of the deficiencies of the prior art, the object of the present invention is to provide a method for preparing poly(p-phenylene terephthalamide) with a narrow molecular weight distribution, which can obtain poly(p-phenylene terephthalamide) with a narrow molecular weight distribution and facilitate subsequent applications.

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

[0008] A method for preparing poly(p-phenylene terephthalamide) with a narrow molecular weight distribution comprises the following steps:

[0009] (1) uniformly mixing p-phenylenediamine, NMP-CaCl2 mixed solvent and transition metal salt to obtain a mixed system;

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

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

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

[0013] (5) The polymer is neutralized, washed and dried to obtain poly(p-phenylene terephthalamide) with a narrow molecular weight distribution.

[0014] In some embodiments of the present invention, in step (1), the transition metal salt is selected from a transition metal chloride salt or a transition metal acetate salt. 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 CaCl2 in the NMP-CaCl2 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 portion 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 portion of terephthaloyl chloride is added to the dissolving 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), a second portion of terephthaloyl chloride is added to the first prepolymer solution in the prepolymerization reactor; and / or the second portion of terephthaloyl chloride accounts for 15% to 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 prepolymerization liquid; 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 comprises 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 comprises the following steps: in addition to adding CaCl2 as a cosolvent, additionally adding a transition metal chloride or acetate, utilizing Cu, Zn, Co ions and amino groups to coordinate, thereby inhibiting the reaction between the amino group and the acyl chloride group, thereby reducing the reaction heat and avoiding local implosion, thereby narrowing the molecular weight.

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

[0028] 3. The present invention reduces the oxidation problem of the PPD solution caused by long-term storage by adding a small amount of TPC to react with the PPD solution during the dissolution stage, which is beneficial to the growth of the molecular chain and reduces the generation of small molecular weight products, thereby narrowing the molecular weight. BRIEF DESCRIPTION OF THE DRAWINGS

[0029] Figure 1 The present invention is a process flow chart for preparing poly(p-phenylene terephthalamide) with narrow molecular weight distribution according to an embodiment of the present invention. DETAILED DESCRIPTION

[0030] The preparation method of the poly(p-phenylene terephthalamide) having a narrow molecular weight distribution of the present invention is described in detail below.

[0031] A method for preparing poly(p-phenylene terephthalamide) with a narrow molecular weight distribution comprises the following steps:

[0032] (1) uniformly mixing p-phenylenediamine, NMP-CaCl2 mixed solvent and transition metal salt to obtain a mixed system;

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

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

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

[0036] (5) The polymer is neutralized, washed and dried to obtain poly(p-phenylene terephthalamide) with a narrow molecular weight distribution.

[0037] In some embodiments of the present invention, in step (1), the transition metal salt is selected from a transition metal chloride salt or a transition metal acetate salt. 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 a CaCl2 cosolvent, the present invention also adds a transition metal chloride salt or acetate salt, utilizes Cu, Zn, Co ions to coordinate with amino groups, inhibits the reaction between amino groups and acyl chloride groups, thereby reducing reaction heat, avoiding local implosion, and narrowing the molecular weight; after the Cu, Zn, Co ions coordinate with the amino groups, chloride ions in the chloride salt are released, destroying the intermolecular hydrogen bonds of PPTA, thereby enhancing its solubility; acetate ions in the acetate salt are also released, reacting with hydrogen chloride, a by-product in the polymerization process of PPTA, and the chloride ions generated by the reaction also destroy the intermolecular hydrogen bonds of PPTA, thereby enhancing the solubility of PPTA.

[0039] In some embodiments of the present invention, in step (1), the mass fraction of CaCl2 in the NMP-CaCl2 mixed solvent 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 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, and 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 portion 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 portion 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, oxidation problems caused by prolonged storage of the PPD solution are reduced, molecular chain growth is promoted, and the formation of low molecular weight products is reduced, thereby narrowing the molecular weight.

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

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

[0046] In some embodiments of the present invention, in step (3), the second portion 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 30%-35%.

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

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

[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, and can be 1-1.005:1, 1.005-1.010:1, or 1.010-1.015:1.

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

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

[0052] Below in conjunction with preferred embodiment, the specific embodiment of the present invention is described in further detail.When embodiment provides numerical range, it should be understood that, unless otherwise specified in the present invention, the two endpoints of each numerical range and any numerical value between the two endpoints can be selected.Unless otherwise defined, all technical and scientific terms used in the present invention have the same meaning as those generally understood by those skilled in the art.Except the specific method, equipment, material used in the embodiment, as those skilled in the art grasp the prior art and record of the present invention, any method, equipment and material of the prior art similar or equivalent to the method, equipment, material in the embodiments of the present invention can also be used to realize the present invention.

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

[0054] Example 1

[0055] The preparation method of the PPTA polymer of this embodiment is as follows Figure 1 As shown, the following steps are included:

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

[0057] (2) Adding the first portion of TPC (accounting for 15% of the total molar amount of TPC) to the NMP mixed system in the dissolving kettle, reacting to obtain a first prepolymer solution, during which the reaction temperature is controlled at -10 to 0°C.

[0058] (3) In the prepolymerization reactor, a second portion of TPC (accounting for 15% of the total molar amount of TPC) was added to the first prepolymer solution to obtain a second prepolymer solution. During the reaction, the reaction temperature was controlled at 0-5°C.

[0059] (4) In the final polymerization reactor, the remaining TPC was added to the second prepolymer solution (the final molar ratio of TPC to PPD reached 1.015:1) to obtain a polymer, during which the reaction temperature was controlled at 20-30°C.

[0060] (5) The polymer was neutralized with sodium hydroxide solution, washed, and dried to obtain a PPTA polymer having an inherent viscosity of 5.8 dL / g and a polydispersity index (PDI) of 1.8.

[0061] Example 2

[0062] The preparation method of the PPTA polymer of this embodiment is as follows Figure 1 As shown, the following steps are included:

[0063] (1) A NMP-CaCl2 mixed solvent containing 6 wt% CaCl2 was prepared, and PPD, the NMP-CaCl2 mixed solvent, and copper chloride were uniformly mixed in a dissolution kettle to obtain an NMP mixed system. The concentration of PPD in the NMP mixed system was 0.45 mol / L, and the molar ratio of copper chloride to PPD was 2:1.

[0064] (2) Adding the first portion of TPC (accounting for 10% of the total molar amount of TPC) to the NMP mixed system in the dissolving kettle, reacting to obtain the first prepolymer solution, during which the reaction temperature is controlled at -10 to 0°C.

[0065] (3) In the prepolymerization reactor, a second portion of TPC (accounting for 35% of the total molar amount of TPC) was added to the first prepolymer solution to obtain a second prepolymer solution. During the reaction, the reaction temperature was controlled at 0-5°C.

[0066] (4) In the final polymerization reactor, the remaining TPC was added to the second prepolymer solution (the final molar ratio of TPC to PPD reached 1.002:1) to obtain a polymer, during which the reaction temperature was controlled at 20-30°C.

[0067] (5) The polymer was neutralized with sodium hydroxide solution, washed, and dried to obtain a PPTA polymer having 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 of this embodiment is as follows Figure 1 As shown, the following steps are included:

[0070] (1) A NMP-CaCl2 mixed solvent containing 8 wt% CaCl2 was prepared, and PPD, the NMP-CaCl2 mixed solvent, and copper acetate were uniformly mixed in a dissolution kettle to obtain an NMP mixed system. The concentration of PPD in the NMP mixed system was 0.38 mol / L, and the molar ratio of copper acetate to PPD was 1:1.

[0071] (2) Adding the first portion of TPC (accounting for 15% of the total molar amount of TPC) to the NMP mixed system in the dissolving kettle, reacting to obtain a first prepolymer solution, during which the reaction temperature is controlled at -10 to 0°C.

[0072] (3) In the prepolymerization reactor, a second portion of TPC (accounting for 30% of the total molar amount of TPC) was added to the first prepolymer solution to obtain a second prepolymer solution. During the reaction, the reaction temperature was controlled at 0-5°C.

[0073] (4) In the final polymerization reactor, the remaining TPC is added to the second prepolymer solution (the final molar ratio of TPC to PPD reaches 1:1) to obtain a polymer, during which the reaction temperature is controlled at 20-30°C.

[0074] (5) The polymer was neutralized with sodium hydroxide solution, washed, and dried to obtain a PPTA polymer having 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 of this embodiment is as follows Figure 1 As shown, the following steps are included:

[0077] (1) A NMP-CaCl2 mixed solvent containing 7 wt% CaCl2 was prepared, and PPD, the NMP-CaCl2 mixed solvent, and zinc chloride were uniformly mixed in a dissolution kettle to obtain an NMP mixed system. The concentration of PPD in the NMP mixed system was 0.41 mol / L, and the molar ratio of zinc chloride to PPD was 0.4:1.

[0078] (2) Adding the first portion of TPC (accounting for 14% of the total molar amount of TPC) to the NMP mixed system in the dissolving kettle, reacting to obtain the first prepolymer solution, during which the reaction temperature is controlled at -10 to 0°C.

[0079] (3) In the prepolymerization reactor, a second portion of TPC (accounting for 26% of the total molar amount of TPC) was added to the first prepolymer solution to obtain a second prepolymer solution. During the reaction, the reaction temperature was controlled at 0-5°C.

[0080] (4) In the final polymerization reactor, the remaining TPC was added to the second prepolymer solution (the final molar ratio of TPC to PPD reached 1.005:1) to obtain a polymer, during which the reaction temperature was controlled at 20-30°C.

[0081] (5) The polymer was neutralized with sodium hydroxide solution, washed, and dried to obtain a PPTA polymer having an inherent viscosity of 5.9 dL / g and a polydispersity index (PDI) of 1.7.

[0082] Example 5

[0083] The preparation method of the PPTA polymer of this embodiment is as follows Figure 1 As shown, the following steps are included:

[0084] (1) A NMP-CaCl2 mixed solvent containing 8 wt% CaCl2 was prepared, and PPD, the NMP-CaCl2 mixed solvent, and zinc acetate were uniformly mixed in a dissolution kettle to obtain an NMP mixed system. The concentration of PPD in the NMP mixed system was 0.35 mol / L, and the molar ratio of zinc acetate to PPD was 1.2:1.

[0085] (2) Adding the first portion of TPC (accounting for 15% of the total molar amount of TPC) to the NMP mixed system in the dissolving kettle, reacting to obtain a first prepolymer solution, during which the reaction temperature is controlled at -10 to 0°C.

[0086] (3) In the prepolymerization reactor, a second portion of TPC (accounting for 30% of the total molar amount of TPC) was added to the first prepolymer solution to obtain a second prepolymer solution. During the reaction, the reaction temperature was controlled at 0-5°C.

[0087] (4) In the final polymerization reactor, the remaining TPC was added to the second prepolymer solution (the final molar ratio of TPC to PPD reached 1.006:1) to obtain a polymer, during which the reaction temperature was controlled at 20-30°C.

[0088] (5) The polymer was neutralized with sodium hydroxide solution, washed, and dried to obtain a PPTA polymer having an inherent viscosity of 5.6 dL / g and a polydispersity index (PDI) of 1.9.

[0089] Example 6

[0090] The preparation method of the PPTA polymer of this embodiment is as follows Figure 1 As shown, the following steps are included:

[0091] (1) A NMP-CaCl2 mixed solvent containing 7 wt% CaCl2 was prepared, and PPD, the NMP-CaCl2 mixed solvent, and cobalt chloride were uniformly mixed in a dissolution kettle to obtain an NMP mixed system. The concentration of PPD in the NMP mixed system was 0.38 mol / L, and the molar ratio of cobalt chloride to PPD was 0.6:1.

[0092] (2) Adding the first portion of TPC (accounting for 12% of the total molar amount of TPC) to the NMP mixed system in the dissolving kettle, reacting to obtain a first prepolymer solution, during which the reaction temperature is controlled at -10 to 0°C.

[0093] (3) In the prepolymerization reactor, a second portion of TPC (accounting for 23% of the total molar amount of TPC) was added to the first prepolymer solution to obtain a second prepolymer solution. During the reaction, the reaction temperature was controlled at 0-5°C.

[0094] (4) In the final polymerization reactor, the remaining TPC was added to the second prepolymer solution (the final molar ratio of TPC to PPD reached 1.002:1) to obtain a polymer, during which the reaction temperature was controlled at 20-30°C.

[0095] (5) The polymer was neutralized with sodium hydroxide solution, washed, and dried to obtain a PPTA polymer having 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 of this embodiment is as follows Figure 1 As shown, the following steps are included:

[0098] (1) A NMP-CaCl2 mixed solvent containing 9 wt% CaCl2 was prepared, and PPD, the NMP-CaCl2 mixed solvent, and cobalt acetate were uniformly mixed in a dissolution kettle to obtain an NMP mixed system. The concentration of PPD in the NMP mixed system was 0.4 mol / L, and the molar ratio of cobalt acetate to PPD was 0.8:1.

[0099] (2) Adding the first portion of TPC (accounting for 12% of the total molar amount of TPC) to the NMP mixed system in the dissolving kettle, reacting to obtain a first prepolymer solution, during which the reaction temperature is controlled at -10 to 0°C.

[0100] (3) In the prepolymerization reactor, a second portion of TPC (accounting for 33% of the total molar amount of TPC) was added to the first prepolymer solution to obtain a second prepolymer solution. During the reaction, the reaction temperature was controlled at 0-5°C.

[0101] (4) In the final polymerization reactor, the remaining TPC was added to the second prepolymer solution (the final molar ratio of TPC to PPD reached 1.005:1) to obtain a polymer, during which the reaction temperature was controlled at 20-30°C.

[0102] (5) The polymer was neutralized with sodium hydroxide solution, washed, and dried to obtain a PPTA polymer having an inherent viscosity of 5.6 dL / g and a polydispersity index (PDI) of 1.9.

[0103] Comparative Example 1

[0104] This comparative example differs from Example 1 in that copper chloride is not added, and the process of preparing the first prepolymer solution in the dissolution kettle is not included. That is, the first part of TPC and the second part of TPC are both 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] This comparative example differs from Example 1 in that copper chloride is not added, and a PPTA polymer having an inherent viscosity of 5.4 dL / g and a polydispersity index (PDI) of 2.2 is finally obtained.

[0107] Comparative Example 3

[0108] This comparative example differs from Example 1 in that the process of preparing the first prepolymer solution in the dissolution kettle is not included, that is, the first part of TPC and the second part of TPC are both 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 are merely illustrative of the principles and effects of the present invention and are not intended to limit the present invention. Anyone skilled in the art may modify or alter the above embodiments without departing from the spirit and scope of the present invention. Therefore, all equivalent modifications or alterations made by one of ordinary skill in the art without departing from the spirit and technical principles disclosed herein are intended to 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 solution to react and obtain a second prepolymer solution; (4) adding the remaining terephthaloyl chloride to the second prepolymer solution to react and obtain a polymer; (5) neutralizing, washing, and drying the polymer to obtain poly(p-phenylene terephthalamide) with a narrow molecular weight distribution; The transition metal salt is selected from a transition metal chloride or a transition metal acetate; 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; In step (2), the first portion of terephthaloyl chloride accounts for 10% to 15% of the total molar amount of terephthaloyl chloride; the mixed system is prepared in a dissolving kettle, and the first portion of terephthaloyl chloride is added to the dissolving kettle; In step (3), the second portion of terephthaloyl chloride accounts for 15% to 35% of the total molar amount of terephthaloyl chloride.

2. The method for preparing poly(p-phenylene terephthalamide) with a narrow molecular weight distribution according to claim 1, wherein: 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.

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

4. The method for preparing poly(p-phenylene terephthalamide) with narrow molecular weight distribution according to claim 1, wherein: In step (3), in the prepolymerization reactor, the second portion of terephthaloyl chloride is added to the first prepolymerization liquid.

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

6. The method for preparing poly(p-phenylene terephthalamide) with narrow molecular weight distribution according to claim 1, wherein: 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 at 20-30° C. during the preparation of the polymer.

7. The method for preparing poly(p-phenylene terephthalamide) with narrow molecular weight distribution according to claim 1, wherein: 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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