Poly-p-phenylene terephthamide solution and preparation method thereof

Abstract

The invention relates to a poly (p-phenylene terephthalamide) solution and a preparation method thereof. The poly (p-phenylene terephthalamide) solution provided by the invention comprises poly (p-phenylene terephthalamide) and a solvent system, and the solvent system comprises 1, 3-dimethyl-3, 4, 5, 6-tetrahydro-2-pyrimidone and an alkali metal chloride. The poly-p-phenylene terephthamide solution is low in viscosity and high in stability, non-sulfuric acid spinning is achieved, and meanwhile the production cost and the harsh requirement for equipment can be greatly lowered.

Description

Technical Field

[0001] The invention relates to a poly(p-phenylene terephthalamide) solution and a preparation method thereof, belonging to the technical field of polymer synthesis. Background Art

[0002] Poly(p-phenylene terephthalamide) (PPTA) is a liquid crystal polymer formed by the polycondensation of p-phenylenediamine and terephthaloyl chloride (or terephthalic acid). Due to the rigid molecular structure, planar conjugation of the molecular chains, and strong hydrogen bonding between PPTA molecules, materials made from PPTA exhibit excellent properties. For example, PPTA fiber (known as para-aramid or aramid II in my country) is a polymer material with numerous excellent properties, including high strength, high modulus, high temperature resistance, and chemical corrosion resistance. It has important applications in defense, aerospace, and numerous civilian fields.

[0003] However, PPTA also has significant disadvantages: it is infusible and difficult to dissolve, making its polymerization and processing very difficult. For example, the synthesis of PPTA resin using a low-temperature solution polycondensation method is already a well-known technique. This involves low-temperature polycondensation of the monomers terephthaloyl chloride (TPC) and p-phenylenediamine (PPD) in a composite system of the solvent N-methylpyrrolidone (NMP) and the co-solvent calcium chloride (CaCl2), followed by washing and drying to obtain pure PPTA resin. However, due to the limited solubility of the NMP / CaCl2 solvent system for PPTA, the PPTA polymerization process is actually a precipitation polycondensation process. In other words, the monomers (TPC and PPD) and PPTA oligomers used in the polymerization can be dissolved in NMP / CaCl2, but high-molecular-weight PPTA is insoluble in NMP / CaCl2. This leads to many problems: 1) The polymerization of PPTA in the NMP / CaCl2 solvent system is a very complex phase transition process, from a low-viscosity liquid to a gel until it becomes a solid in the later stages of the reaction. After being broken into a crumb-like solid by a reactor (such as a twin-screw extruder); 2) It is very difficult to control the stability of molecular weight. The PPTA molecular chain becomes increasingly unstable as the molecular weight increases, and is significantly affected by many factors such as monomer mixing and reaction temperature; 3) PPTA is insoluble in the polymerization solvent, so after polymerization, it can only be washed and dried and then redissolved in concentrated sulfuric acid for subsequent spinning. However, the concentrated sulfuric acid spinning system not only makes the spinning conditions harsh and the spinning wastewater difficult to treat, but also has poor adjustability of fiber properties. In addition, due to its poor processability, PPTA can currently only be used in the form of fibers.

[0004] Finding a better solvent system has always been a goal in the para-aramid field. Some efforts have been made in the prior art. For example, Non-Patent Document 1 discloses the use of imidazolium chloride ionic liquids as solvents for PPTA polymerization.

[0005] Patent document 1 discloses the use of a solvated ionic liquid composed of N,N-dimethylimidazolidinone (DMI) and an alkali metal chloride as a solvent for PPTA polymerization, wherein tri-n-butylamine is added as an acid absorbent to ensure the growth of the PPTA molecular chain, and the reaction time is also extended to 1 to 5 hours.

[0006] In addition, attempts have been made in the prior art to improve the solubility of PPTA by modifying and adjusting its molecular chain structure. For example, the all-para structure of PPTA was modified to a meta structure, resulting in meta-aramid (poly(m-phenylene isophthalamide, PMIA)). The introduction of the meta structure significantly improves the solubility of meta-aramid compared to para-aramid, allowing it to dissolve in a variety of solvents, such as the common amide solvent N,N-dimethylacetamide (DMAC) and methylated diamide cyclic compounds.

[0007] Patent document 2 discloses the polymerization of meta-aramid (PMIA) using methylated diamide cyclic compounds (DMPU and DMI) as solvents. Even if hydrogen chloride is not neutralized after polymerization, a stable PMIA solution with low viscosity can be obtained. Meta-aramid fibers with excellent performance can be prepared by direct spinning using this low-viscosity solution.

[0008] However, PPTA is a rigid liquid crystalline polymer with strong intermolecular hydrogen bonding, making it prone to spontaneous aggregation, forming unstable aggregates and precipitation. PMIA, on the other hand, is a slightly more rigid non-liquid crystalline polymer and forms stable solutions in common amide solvents, even without the addition of alkali metal chlorides as solubilizing salts. Due to the inherent differences in the molecular chain structures of PPTA and PMIA, most solvents that can dissolve PMIA cannot. Furthermore, due to the loss of PMIA's liquid crystallinity, its material performance is significantly reduced compared to PPTA.

[0009] References:

[0010] Non-patent literature 1: S. Dewilde, T. Vander Hoogerstraete, W. Dehaen, K. Binnemans. Synthesis of poly-p-phenylene terephthalamide (PPTA) in ionic liquids, ACS Sustainable Chemistry & Engineering, 2018, 6: 1362–1369;

[0011] Patent Document 1: CN101781399A;

[0012] Patent document 2: CN116813902A. Summary of the Invention

[0013] Problems to be solved by the invention

[0014] In non-patent document 1, PPTA is difficult to polymerize into high molecular weight polymer in imidazolium chloride ionic liquids. Even the PPTA obtained by 1-octyl-3-methylimidazolium chloride (3-methyl-1-octylimidazolium chloride), which has the best effect, has a logarithmic viscosity (η inh ) still cannot reach 3, which is far from the requirement of PPTA molecular weight for spinning process (η of PPTA for spinning inh Required to be greater than 5).

[0015] The η of the PPTA prepared in Patent Document 1 is inh The highest value was only 4.27, and the resulting polymerization system was in a solid state and could not be directly used in the spinning process. Furthermore, the long polymerization time resulted in low production efficiency. Furthermore, when the inventors conducted repeated experiments on the DMI / CaCl2 system described in the patent document, they found that the solubility of CaCl2 in DMI was very low, making it impossible to use this system to achieve PPTA polymerization.

[0016] The solvent system in Patent Document 2 has good solubility for PMIA, but the effect of this solvent system when used for the polymerization of PPTA has not been studied.

[0017] Therefore, the object of the present invention is to provide a PPTA solution that can be used even for high molecular weight PPTA (e.g. inh >4) can also exist stably in the form of a solution, and can be directly obtained by polymerization and used for subsequent spinning.

[0018] Solutions for solving problems

[0019] In response to the above problems, the present inventors conducted long and in-depth research and found that a composite solvent system of 1,3-dimethyl-3,4,5,6-tetrahydro-2-pyrimidinone (DMPU) and alkali metal chloride has excellent solubility for PPTA and can obtain high molecular weight PPTA when used for the polymerization of PPTA, thereby completing the present invention.

[0020] Specifically, the present invention solves the problems of the present invention through the following solutions.

[0021] [1] A poly(p-phenylene terephthalamide) solution comprising poly(p-phenylene terephthalamide) and a solvent system comprising 1,3-dimethyl-3,4,5,6-tetrahydro-2-pyrimidinone and an alkali metal chloride.

[0022] [2] The poly(p-phenylene terephthalamide) solution according to claim 1, wherein the content of the poly(p-phenylene terephthalamide) is 1 to 20% by mass; and the content of the solvent system is 80 to 99% by mass.

[0023] [3] The poly(p-phenylene terephthalamide) solution according to claim 1 or 2, wherein the mass ratio of the alkali metal chloride to 1,3-dimethyl-3,4,5,6-tetrahydro-2-pyrimidinone in the solvent system is (0.5-10):100.

[0024] [4] The poly(p-phenylene terephthalamide) solution according to claim 1 or 2, wherein the alkali metal chloride is preferably aluminum chloride, zinc chloride and / or lithium chloride, more preferably lithium chloride.

[0025] [5] A method for preparing a poly(p-phenylene terephthalamide) solution according to any one of [1] to [4], comprising the following steps:

[0026] (a) dissolving the alkali metal chloride in 1,3-dimethyl-3,4,5,6-tetrahydro-2-pyrimidinone, and optionally performing a dehydration treatment to obtain the solvent system;

[0027] (b) subjecting p-phenylenediamine and terephthaloyl chloride to a polymerization reaction in the solvent system.

[0028] [6] The preparation method according to [5], wherein the water content of the solvent system is 200 ppm or less, preferably 150 ppm or less.

[0029] [7] The preparation method according to [5] or [6], wherein in step (a), the alkali metal chloride is mixed with 1,3-dimethyl-3,4,5,6-tetrahydro-2-pyrimidinone in solid form so that the alkali metal chloride is dissolved in 1,3-dimethyl-3,4,5,6-tetrahydro-2-pyrimidinone; or

[0030] An aqueous solution of alkali metal chloride is mixed with 1,3-dimethyl-3,4,5,6-tetrahydro-2-pyrimidinone to obtain a mixed liquid, and then water in the mixed liquid is removed to obtain the solvent system.

[0031] [8] The preparation method according to [5] or [6], wherein step (b) comprises the following sub-steps:

[0032] (b-1) dissolving p-phenylenediamine in the solvent system to obtain a p-phenylenediamine solution, and maintaining the temperature of the p-phenylenediamine solution at -10 to 30° C.;

[0033] (b-2) adding terephthaloyl chloride in the form of solid powder or melt to the p-phenylenediamine solution to carry out polymerization reaction.

[0034] [9] The preparation method according to [5] or [6], wherein the polymerization reaction time is 0.5 to 3 hours; during the polymerization reaction, the temperature of the polymerization system is controlled to be below 70°C; and the polymerization reaction is carried out in a continuous process or a batch process.

[0035]

[10] The preparation method according to [5] or [6], wherein the step (b) further comprises the following steps:

[0036] (e) allowing the polymerization system obtained in step (b) to stand for a period of time, or stirring for a period of time under heating conditions;

[0037] The standing or stirring time is 0.5 to 30 days; and the heating temperature is 50 to 150°C.

[0038] Effects of the Invention

[0039] The PPTA solution of the present invention has low viscosity and high stability, and can realize non-sulfuric acid spinning while significantly reducing production costs and stringent requirements on equipment.

[0040] The preparation method of the present invention has the following beneficial effects:

[0041] 1) Improved operational flexibility of the PPTA polymerization process, eliminating the need for strict control of low-temperature conditions and significantly improving industrial polymerization efficiency;

[0042] 2) The polymerization process is stable, without precipitation polycondensation and complex phase change process, which greatly improves the polymerization stability of PPTA. BRIEF DESCRIPTION OF THE DRAWINGS

[0043] Figure 1 (a) is a photograph of the polymerization process of Example 4, and (b) is a photograph of the obtained PPTA solution after standing for 7 days;

[0044] Figure 2 The viscosity of the PPTA solution obtained in Example 4 changes with shear rate after standing for 1 hour, 1 day, 7 days and 14 days. DETAILED DESCRIPTION

[0045] Various exemplary embodiments, features, and aspects of the present invention will be described in detail below. The word "exemplary" is used herein to mean "serving as an example, embodiment, or illustration." Any embodiment described herein as "exemplary" is not necessarily to be construed as superior or preferred over other embodiments.

[0046] In addition, numerous specific details are provided in the following detailed description to better illustrate the present invention. Those skilled in the art will appreciate that the present invention can be practiced without certain specific details. In other instances, methods, means, equipment, and steps well known to those skilled in the art are not described in detail in order to highlight the main points of the present invention.

[0047] <Terms and Definitions>

[0048] Unless otherwise stated, the units used in this specification are international standard units, and the numerical values ​​and numerical ranges appearing in the present invention should be understood to include the inevitable systematic errors in industrial production.

[0049] In this specification, the use of "may" includes both the meaning of performing a certain process and the meaning of not performing a certain process.

[0050] In this specification, references to "some specific / preferred embodiments," "other specific / preferred embodiments," "embodiments," etc., mean that the specific elements (e.g., features, structures, properties, and / or characteristics) described in connection with the embodiments are included in at least one embodiment described herein, and may or may not be present in other embodiments. In addition, it should be understood that the elements may be combined in various embodiments in any suitable manner.

[0051] In this specification, the numerical range expressed using "a numerical value A to a numerical value B" means a range including the endpoints A and B.

[0052] In this specification, when "normal temperature" or "room temperature" is used, the temperature may be 20-30°C.

[0053] <Poly(p-phenylene terephthalamide) Solution>

[0054] An object of the present invention is to provide a poly(p-phenylene terephthalamide) solution comprising poly(p-phenylene terephthalamide) and a solvent system comprising 1,3-dimethyl-3,4,5,6-tetrahydro-2-pyrimidinone and an alkali metal chloride.

[0055] The PPTA solution of the present invention is a stable and uniform solution, usually in a clear and bright yellow state.

[0056] The PPTA solution of the present invention utilizes DMPU as a solvent and an alkali metal chloride as a solubilizing salt. The DMPU and alkali metal chloride form a complex in the solvent, thereby exhibiting excellent solubility for PPTA. By using this DMPU / alkali metal chloride solvent system, the PPTA solution of the present invention remains clear even when the PPTA content is high and / or the PPTA has a high molecular weight.

[0057] In one embodiment, the content of PPTA in the PPTA solution of the present invention is 1 to 20% by mass, preferably 5 to 15% by mass.

[0058] In one embodiment, the inherent viscosity of PPTA is 3 or greater, preferably 4 or greater, and more preferably 5 or greater.

[0059] In one embodiment, the content of the solvent system in the PPTA solution of the present invention is 80 to 99% by mass, preferably 85 to 95% by mass.

[0060] In one embodiment, in the solvent system, the mass ratio of alkali metal chloride to DMPU is (0.5-10):100, preferably (2-5):100.

[0061] In a preferred embodiment, the alkali metal chloride is aluminum chloride, zinc chloride and / or lithium chloride, more preferably lithium chloride.

[0062] In one embodiment, the viscosity of the PPTA solution of the present invention is 1 to 200 Pa·s, preferably 1.5 to 150 Pa·s, and more preferably 2 to 140 Pa·s. In a preferred embodiment, the viscosity of the PPTA solution of the present invention is 1 to 50 Pa·s, preferably 1.2 to 40 Pa·s, more preferably 1.5 to 30 Pa·s, and even more preferably 2 to 25 Pa·s.

[0063] <Preparation method>

[0064] Another object of the present invention is to provide a method for preparing the poly(p-phenylene terephthalamide) solution of the present invention, which comprises the following steps:

[0065] (a) dissolving the alkali metal chloride in 1,3-dimethyl-3,4,5,6-tetrahydro-2-pyrimidinone, and optionally performing a dehydration treatment to obtain the solvent system;

[0066] (b) subjecting p-phenylenediamine and terephthaloyl chloride to a polymerization reaction in the solvent system.

[0067] The preparation method of the present invention adopts a DMPU / alkali metal chloride solvent system, so that the polymerization reaction can proceed smoothly and slowly, the polymerization process is mild, the system does not gel, and is always in a solution state.

[0068] Each step of the preparation method of the present invention is described in detail below.

[0069] Step (a)

[0070] In step (a), a solvent system is obtained by dissolving an alkali metal chloride in DMPU and optionally performing a dehydration treatment.

[0071] In one embodiment, the solution obtained by dissolving the alkali metal chloride in DMPU is dehydrated to reduce the water content. The dehydration can be performed by adding molecular sieves and / or calcium hydride to the solution. The dehydration can also be performed by industrially known methods, such as distillation, rectification, and the like.

[0072] In one embodiment, the water content of the solvent system is 200 ppm or less, preferably 150 ppm or less. By setting the water content of the solvent system within the above range, it is advantageous to obtain a high molecular weight polymer.

[0073] In one embodiment, in step (a), the alkali metal chloride is mixed with DMPU in solid form to dissolve the alkali metal chloride in the DMPU. The dissolution can also be carried out under conditions of applying shear force, such as under stirring.

[0074] In one embodiment, in step (a), an aqueous solution of an alkali metal chloride is mixed with DMPU to obtain a mixed solution, thereby dissolving the alkali metal chloride in the DMPU, and then water is removed from the mixed solution to obtain a solvent system. Water can be removed from the mixed solution by distillation, rectification, or the like.

[0075] The content of the alkali metal chloride in the aqueous solution of the alkali metal chloride is 10 to 50% by mass, preferably 20 to 40% by mass.

[0076] In one embodiment, step (a) further comprises the operation of dissolving alkali metal chloride in water to obtain an aqueous solution of alkali metal chloride.

[0077] Step (b)

[0078] In one embodiment, step (b) comprises the following sub-steps:

[0079] (b-1) dissolving p-phenylenediamine in a solvent system to obtain a p-phenylenediamine solution, and maintaining the temperature of the p-phenylenediamine solution at -10 to 30° C.;

[0080] (b-2) mixing terephthaloyl chloride in the form of solid powder or melt with the p-phenylenediamine solution to allow the p-phenylenediamine and terephthaloyl chloride to undergo a polymerization reaction.

[0081] In one embodiment, the polymerization reaction time is 0.1 to 3 hours, preferably 10 to 60 minutes. The "polymerization reaction time" described herein refers to the time during which the polymerization reaction is carried out under polymerization conditions (e.g., in a specific reactor, at a specific temperature, and / or under stirring, an inert gas atmosphere, etc.), and does not include the time during which the polymerization reaction proceeds spontaneously under non-polymerization conditions.

[0082] In one embodiment, during the polymerization reaction, the temperature of the polymerization system is controlled to be below 70°C.

[0083] In one embodiment, the molar ratio of terephthaloyl chloride to p-phenylenediamine is (1-1.02):1, preferably (1-1.01):1.

[0084] In the present invention, the polymerization reaction can be carried out in a continuous process or a batch process.

[0085] In one embodiment, the polymerization reaction is carried out as a batch process. For example, a p-phenylenediamine solution is added to a polymerization reactor, followed by the addition of terephthaloyl chloride (in solid or molten form). The terephthaloyl chloride may be added in a single or multiple additions, preferably in multiple additions (e.g., 2 to 6 additions, and more preferably, 3, 4, 5, etc.) to allow the polymerization reaction to proceed in a gentle and controllable manner.

[0086] In one embodiment, the polymerization reaction is carried out in a continuous process. Specifically, the p-phenylenediamine solution and terephthaloyl chloride (preferably in the form of a melt) are continuously mixed, for example, the p-phenylenediamine solution and terephthaloyl chloride (preferably in the form of a melt) are continuously added to a polymerization reactor, so that the polymerization reaction is carried out continuously.

[0087] In one embodiment, the terephthaloyl chloride melt temperature is 90 to 120°C.

[0088] In a preferred embodiment, the polymerization reaction is carried out in a continuous process, and the polymerization reaction in sub-step (b-2) includes a prepolymerization stage and a final polymerization stage, wherein

[0089] Prepolymerization: continuously feeding p-phenylenediamine solution and terephthaloyl chloride melt into a prepolymerization reactor to carry out prepolymerization reaction to obtain a prepolymerization reaction liquid;

[0090] Final polymerization: The prepolymerization reaction liquid and the terephthaloyl chloride melt are continuously fed into the final polymerization reactor to carry out final polymerization reaction to obtain a final polymerization reaction liquid.

[0091] Preferably, in the prepolymerization stage, the molar feed ratio of terephthaloyl chloride to p-phenylenediamine is (0.30-0.7):1, preferably (0.4-0.6):1, and more preferably (0.45-0.55):1. In the final polymerization stage, the molar feed ratio of terephthaloyl chloride to p-phenylenediamine in the prepolymerization stage is (0.3-0.7):1, preferably (0.4-0.6):1, and more preferably (0.45-0.55):1. During the polymerization of terephthaloyl chloride and p-phenylenediamine, the viscosity of the polymerization system increases rapidly. Keeping the feed ratios in the prepolymerization and final polymerization stages within the above ranges facilitates timely removal of reaction heat.

[0092] Preferably, the prepolymerization is carried out in a continuous tubular reactor; and the final polymerization is carried out in a twin-screw reactor.

[0093] Preferably, the prepolymerization temperature is 0 to 50° C., and the reaction time is 5 to 30 minutes.

[0094] Preferably, the temperature of the final polymerization reaction is 20-70° C., and the reaction time is 5-60 min.

[0095] In a preferred embodiment, the preparation method of the present invention further comprises the following steps after step (b):

[0096] (e) allowing the polymerization system obtained in step (b) to stand for a period of time, or stirring for a period of time under heating conditions.

[0097] Preferably, the standing time is 0.5 hours to 30 days, preferably 12 hours to 25 days, more preferably 1 to 20 days, for example 2 days, 3 days, 4 days, 5 days, 6 days, 7 days, 8 days, 9 days, 10 days, 11 days, 12 days, 13 days, 14 days, 15 days, 16 days, 17 days, 18 days, 19 days, etc.

[0098] Preferably, the stirring time is 0.5 hours to 30 days, preferably 12 hours to 25 days, more preferably 1 to 20 days, for example 2 days, 3 days, 4 days, 5 days, 6 days, 7 days, 8 days, 9 days, 10 days, 11 days, 12 days, 13 days, 14 days, 15 days, 16 days, 17 days, 18 days, 19 days, etc.

[0099] The heating temperature is 50 to 150°C, preferably 60 to 120°C.

[0100] The inventors have discovered that in the solvent system used in the present invention, the polymerization reaction of p-phenylenediamine and terephthaloyl chloride proceeds relatively slowly. After the polymerization reaction is completed, that is, when polymerization conditions (such as temperature control and shear force application) are no longer applied or the polymerization system leaves the polymerization reactor, the polymerization reaction can still continue. Therefore, by allowing the polymerization system to stand for a period of time after the polymerization is completed, or stirring it for a period of time under heating conditions, the molecular weight of the polymer is increased, thereby obtaining a high molecular weight polymer.

[0101] The inventors also found that the viscosity of the PPTA solution decreased and eventually became constant during the standing or heating stirring process.

[0102] In addition, during the standing or heating stirring process, the bubbles introduced into the system during the polymerization process are removed, so the obtained PPTA solution becomes clearer and more transparent.

[0103] Example

[0104] The embodiments of the present invention will be described in detail below with reference to the examples, but it will be understood by those skilled in the art that the following examples are merely illustrative of the present invention and should not be construed as limiting the scope of the invention. Where specific conditions are not specified in the examples, the methods were performed according to conventional conditions or the conditions recommended by the manufacturer. Where the manufacturers of the reagents or instruments are not specified, they are all conventional products that can be obtained commercially.

[0105] Test Method

[0106] Logarithmic reduced viscosity (η inh ) : Place 0.125g of dry PPTA powder in a 25ml volumetric flask, add approximately 2 / 3 of the volume of concentrated sulfuric acid, and completely dissolve the PPTA at 45-50°C. Then, add concentrated sulfuric acid to the volume, shake thoroughly, and let it stand for a period of time to prepare 25ml of PPTA concentrated sulfuric acid solution. In a constant temperature water bath at 30°C, use an Ubbelohde viscometer (capillary diameter 1.07mm) to measure the outflow times t0 and t1 of the concentrated sulfuric acid and PPTA concentrated sulfuric acid solution, respectively. Calculate the logarithmic reduced viscosity of PPTA according to the following formula:

[0107]

[0108] Where c is the concentration of PPTA concentrated sulfuric acid solution, prepared as above, c = 0.5g / dL. inh The unit should be dL / g. For the convenience of expression, η is omitted in this article. inh The units are given only the numerical values.

[0109] Rotational viscosity: A rotational rheometer (Anton Paar GmbH, Austria, MCR-502) was used. The solution (polymer solution) was placed between parallel plates separated by 1 mm and the test was started. The rotation rate was linearly increased from 0.01 / s to 100 / s, with the rheometer automatically recording the viscosity data throughout the test. The test temperature was 25°C.

[0110] Example 1:

[0111] Add 300kg LiCl to 10m 3 Stir and dissolve in DMPU. After 30 minutes of complete dissolution, pump it into the distillation tower to dehydrate the DMPU / LiCl solution to a water content of 98ppm. Transfer it to a storage tank and cool it to room temperature for later use. The storage tank is protected by nitrogen.

[0112] In volume 5m 3 In the dissolving vessel, 3000 kg of dehydrated DMPU / LiCl solution was first metered in, followed by 64.80 kg of p-phenylenediamine (PPD) while stirring. The dissolving temperature was approximately 20°C, and the dissolving time was approximately 30 minutes. The dissolved p-phenylenediamine solution was cooled to 10°C and then continuously and stably delivered to a tubular prepolymerization reactor via a metering pump and flowmeter. Terephthaloyl chloride (TPC) melt (95°C) was also metered continuously and stably delivered to the tubular prepolymerization reactor via a metering pump and flowmeter for mixing and reaction with the p-phenylenediamine solution. The flow rate was adjusted to ensure that the molar flow rate of TPC was 50% of that of PPD. Specifically, the p-phenylenediamine solution was delivered at 1021.60 kg / h, and the terephthaloyl chloride melt was delivered at 20.44 kg / h. The residence time of the polymerization system in the tubular reactor was approximately 20 minutes, the prepolymerization temperature was controlled to not exceed 30°C, and the stirring speed was 300 rpm.

[0113] After prepolymerization, the prepolymer liquid was directly pumped into the final twin-screw reactor. Simultaneously, the TPC melt was metered by a flow meter and continuously and stably pumped into the twin-screw reactor for mixing. The TPC addition rate was 20.44 kg / h (the final molar ratio of TPC to PPD was 1.006:1). The final polymerization temperature was controlled to not exceed 50°C, and the reaction time was 20 minutes.

[0114] After the reaction is completed, a bright yellow PPTA solution is obtained. Figure 1 As shown, the rotational viscosity is 11 Pa·s. After the resulting PPTA solution was left in a tank for 7 days, the rotational viscosity was 3.5 Pa·s. After the resulting PPTA solution was stored at room temperature for one month, it remained a clear, bright yellow solution, with no change in state.

[0115] In addition, the original PPTA solution was taken from the outlet of the twin-screw reactor, washed with water and separated to obtain the PPTA polymer, and the inherent viscosity (η inh ) is 3.50. Then, polymer samples were taken at room temperature and left to stand for different time intervals (1h, 12h, 1 day, 5 days, 10 days, 15 days, 30 days) to measure the logarithmic viscosity. It was found that the η of the 1h and 12h samples was inh 3.97 and 4.11 respectively, and the η of the samples after inh The value is basically stable at around 4.1 (η inh This indicates that the PPTA solution can continue to react during the static period after polymerization, but it is in a stable state after a period of reaction.

[0116] Example 2:

[0117] 1000 kg of LiCl aqueous solution with a mass concentration of 35% is added to 10 m 3 The mixture is mixed evenly with DMPU, then pumped into a distillation tower to dehydrate the DMPU / LiCl solution to 180ppm, and then transported to a storage tank to cool to 10°C. The storage tank is protected by nitrogen.

[0118] The DMPU / LiCl solution in the storage tank is continuously metered into a continuous dissolver to dissolve p-phenylenediamine. P-phenylenediamine (PPD) is first heated to 140°C to form a melt, then continuously metered into the continuous dissolver for dissolution. The molar concentration of dissolved PPD is 0.3 mol / l. The dissolution temperature is controlled at approximately 10°C.

[0119] The continuously dissolved p-phenylenediamine solution is cooled online to -10°C and then continuously and stably delivered to a tubular reactor via a metering pump and flowmeter. Terephthaloyl chloride (TPC) melt (95°C) is also continuously and stably delivered to the tubular reactor via a metering pump and flowmeter for mixing and reaction with the p-phenylenediamine solution. The tubular reactor is divided into three stages, each with a TPC melt feed port. PPD is added to the three stages at 50%, 40%, and 10.8% of the molar feed volume, respectively. This means that after all TPC has been added, the molar ratio of TPC to PPD is 1.008:1. The polymerization system resides in the tubular reactor for approximately 30 minutes, with a maximum polymerization temperature not exceeding 60°C.

[0120] After the reaction is completed, a clear bright yellow PPTA solution is obtained. Figure 1 As shown, the rotational viscosity was 24.7 Pa·s. After the resulting PPTA solution was allowed to stand in a storage tank for 7 days, the rotational viscosity was 5.3 Pa·s. After the resulting PPTA solution was stored at room temperature for one month, it remained a clear, bright yellow solution, with no change in state.

[0121] The obtained PPTA solution was washed with water to separate the PPTA polymer, and the inherent viscosity after drying was measured to be 3.18.

[0122] Example 3:

[0123] Add about half volume of dry Molecular sieves were sealed and stored in a desiccator for at least 3 days before use in polymerization. The water content of DMPU after drying over the molecular sieves for 3 days was approximately 150 ppm. 100 ml of dried DMPU was placed in a 500 ml three-necked flask and, under nitrogen, 2 g of LiCl was added with stirring. The lithium chloride was dehydrated by calcination at high temperature before use. After stirring for 30 minutes, the mixture was completely dissolved. Then, 2.160 g of p-phenylenediamine (PPD) was added directly to the mixture and dissolved at room temperature of approximately 25°C. After approximately 30 minutes, the mixture was completely dissolved. Then, 4.684 g of terephthaloyl chloride (TPC) powder was weighed and added to the mixture in two separate additions of approximately 50% each, with a 10-minute interval between additions. The molar ratio of TPC to PPD was 1.1:1. After all the TPC was added, the stirring rate was increased and the reaction was allowed to complete after 30 minutes.

[0124] After the reaction is completed, a clear bright yellow PPTA solution is obtained. Figure 1 As shown, the rotational viscosity was 16.5 Pa·s. After the resulting PPTA solution was allowed to stand in a tank for 7 days, the rotational viscosity was 2.1 Pa·s. After the resulting PPTA solution was stored at room temperature for one month, it remained a clear, bright yellow solution, with no change in state.

[0125] The obtained PPTA solution was washed with water to separate the PPTA polymer, and the inherent viscosity after drying was measured to be 2.59.

[0126] Example 4:

[0127] Add about half volume of dry Molecular sieves, sealed and stored in a desiccator. After 3 days, calcium hydride was added to achieve deep dehydration via chemical reaction. The amount of calcium hydride added was adjusted to the point where no noticeable gas production in the DMPU was observed. After adding calcium hydride, the mixture was sealed and stored in a desiccator. After 1 day, the DMPU contained approximately 50 ppm of water. 100 ml of dehydrated DMPU was placed in a 500 ml three-necked flask and, under nitrogen, 8 g of LiCl was added with stirring. The lithium chloride was calcined at high temperature for dehydration before use. Stirring was applied to 80°C to completely dissolve the LiCl. The solution was then cooled to 10°C and 4.320 g of p-phenylenediamine (PPD) was added and dissolved. Dissolution took approximately 30 minutes. The solution was then cooled to 0°C and 8.580 g of terephthaloyl chloride (TPC) powder was weighed and added in two separate additions of approximately 50% each, with a 20-minute interval between additions. The molar ratio of TPC to PPD was 1.007:1. After all the TPC was added, the stirring rate was increased and the reaction was completed after 60 minutes.

[0128] After the reaction is completed, a clear bright yellow PPTA solution is obtained. Figure 1 As shown, the rotational viscosity is 133.8 Pa·s. After the resulting PPTA solution was left in a tank for 7 days, the rotational viscosity was 15.3 Pa·s. After the resulting PPTA solution was stored at room temperature for one month, it remained a clear, bright yellow solution, with no change in state.

[0129] The obtained PPTA solution was washed with water to separate the PPTA polymer, and the inherent viscosity after drying was measured to be 5.63.

[0130] Comparative Example 1:

[0131] In Comparative Example 1, the DMPU / LiCl system was replaced with the NMP / CaCl2 composite solvent system, which is currently the most commonly used solvent for PPTA polymerization in the industry. The PPTA polymerization solution was prepared using the same material treatment and polymerization process as in Example 4, as follows:

[0132] Add about half volume of dry NMP to 500ml of NMP reagent. Molecular sieves, sealed and stored in a desiccator. After 3 days, calcium hydride was added to achieve deep dehydration via chemical reaction. The amount of calcium hydride added was sufficient to eliminate noticeable gas production in the NMP. After adding calcium hydride, the mixture was sealed and stored in a desiccator. After 1 day, the water content in the NMP was approximately 50 ppm. 100 ml of dehydrated NMP was placed in a 500 ml three-necked flask and 8 g of CaCl2 was added under nitrogen and stirred. The calcium chloride was calcined at high temperature for dehydration before use. Stirring was applied to 80°C to completely dissolve the CaCl2. The solution was then cooled to 10°C and 4.320 g of p-phenylenediamine (PPD) was added and dissolved. Dissolution took approximately 30 minutes. The solution was then cooled to 0°C and 8.580 g of terephthaloyl chloride (TPC) powder was weighed and added in two separate additions of approximately 50% each, with a 20-minute interval between additions. The molar ratio of TPC to PPD was 1.007:1.

[0133] Unlike the DMPU / LiCl system used in Example 4, the viscosity of PPTA in the NMP / CaCl2 system in Comparative Example 1 increased very rapidly. In particular, after the second addition of TPC, the polymerization system transformed into a very viscous gel within 3-5 minutes, exhibiting severe pole-climbing. Continued reaction resulted in the gel breaking into a crumb-like solid. The high-viscosity gel and the crumbs were precipitated and washed with water to yield PPTA polymers. After drying, the inherent viscosities were measured to be 2.53 and 5.87, respectively.

[0134] In Comparative Example 1, when the polymerization system was in the form of a high-viscosity gel and crumbs, the molecular weight of the polymer was similar to that of Examples 3 and 4, respectively, but the state of the polymerization system was significantly different. This shows that the NMP / CaCl2 system cannot produce a stable PPTA polymer solution.

[0135] Comparative Example 2:

[0136] In Comparative Example 2, DMPU was replaced with 1,3-dimethyl-2-imidazolidinone, which has a similar structure to DMPU, and a DMI / LiCl system was used. DMI has better solubility in PPTA than NMP. Aside from the different solvents, all other conditions were the same as in Example 4. The details are as follows:

[0137] Add about half volume of dry Molecular sieves, sealed and stored in a desiccator. After 3 days, calcium hydride was added to achieve deep dehydration via chemical reaction. The amount of calcium hydride added was adjusted to the point where no noticeable gas production in the DMI was observed. After adding calcium hydride, the mixture was sealed and stored in a desiccator. After 1 day, the DMI contained approximately 70 ppm of water. 100 ml of dehydrated DMI was placed in a 500 ml three-necked flask and, under nitrogen, 8 g of LiCl was added with stirring. The lithium chloride was calcined at high temperature for dehydration before use. Stirring was applied to 80°C to completely dissolve the LiCl. The solution was then cooled to 10°C and 4.320 g of p-phenylenediamine (PPD) was added and dissolved. Dissolution took approximately 30 minutes. The solution was then cooled to 0°C and 8.580 g of terephthaloyl chloride (TPC) powder was weighed and added in two separate additions of approximately 50% each, with a 20-minute interval between additions. The molar ratio of TPC to PPD was 1.007:1. After all the TPC was added, the stirring rate was increased and the reaction was completed after 60 minutes.

[0138] Unlike the DMPU / LiCl system used in Example 4, the viscosity of PPTA in the DMI / LiCl system in Comparative Example 2 increased rapidly. In particular, after the second addition of TPC, the polymerization system transformed into a very viscous gel within 10-20 minutes, exhibiting severe rod climbing. With continued reaction, the gel broke down into a creamy semisolid. After 12 hours of aging, the polymerization system showed significant precipitation, with the solvent precipitating in the upper layer and the lower layer becoming a cohesive solid.

[0139] The very viscous gel obtained during the polymerization and the lower polymer layer after standing for 12 hours were taken separately, and PPTA polymer was obtained by precipitation and washing with water. After drying, the inherent logarithmic viscosities were tested to be 2.06 and 3.79, respectively.

[0140] In Comparative Example 2, the polymerization process, the state of the final polymerization system, and the molecular weight of the obtained polymer are significantly different from those in Example 4. In particular, Comparative Example 2 does not produce a high molecular weight PPTA polymer, nor does it produce a stable PPTA polymer solution.

[0141] Industrial applicability

[0142] The PPTA solution and preparation method thereof can be widely used in industry for producing para-aramid and related materials, for example, for non-sulfuric acid spinning.

Claims

1. A poly(p-phenylene terephthalamide) solution, characterized in that: The invention comprises poly(p-phenylene terephthalamide) and a solvent system. The solvent system comprises 1,3-dimethyl-3,4,5,6-tetrahydro-2-pyrimidinone and an alkali metal chloride.

2. The poly(p-phenylene terephthalamide) solution according to claim 1, characterized in that The content of the poly(p-phenylene terephthalamide) is 1 to 20% by mass; and the content of the solvent system is 80 to 99% by mass.

3. The poly(p-phenylene terephthalamide) solution according to claim 1 or 2, characterized in that: In the solvent system, the mass ratio of alkali metal chloride to 1,3-dimethyl-3,4,5,6-tetrahydro-2-pyrimidinone is (0.5-10):

100.

4. The poly(p-phenylene terephthalamide) solution according to claim 1 or 2, characterized in that: The alkali metal chloride is preferably aluminum chloride, zinc chloride and / or lithium chloride, more preferably lithium chloride.

5. A method for preparing a poly(p-phenylene terephthalamide) solution according to any one of claims 1 to 4, characterized in that: The following steps are involved: (a) dissolving the alkali metal chloride in 1,3-dimethyl-3,4,5,6-tetrahydro-2-pyrimidinone, and optionally performing a dehydration treatment to obtain the solvent system; (b) subjecting p-phenylenediamine and terephthaloyl chloride to a polymerization reaction in the solvent system.

6. The preparation method according to claim 5, characterized in that The water content of the solvent system is 200 ppm or less, preferably 150 ppm or less.

7. The preparation method according to claim 5 or 6, characterized in that: In step (a), an alkali metal chloride is mixed with 1,3-dimethyl-3,4,5,6-tetrahydro-2-pyrimidinone in solid form so that the alkali metal chloride is dissolved in 1,3-dimethyl-3,4,5,6-tetrahydro-2-pyrimidinone; or An aqueous solution of alkali metal chloride is mixed with 1,3-dimethyl-3,4,5,6-tetrahydro-2-pyrimidinone to obtain a mixed liquid, and then water in the mixed liquid is removed to obtain the solvent system.

8. The preparation method according to claim 5 or 6, characterized in that: Step (b) comprises the following sub-steps: (b-1) dissolving p-phenylenediamine in the solvent system to obtain a p-phenylenediamine solution, and maintaining the temperature of the p-phenylenediamine solution at -10 to 30° C.; (b-2) adding terephthaloyl chloride in the form of solid powder or melt to the p-phenylenediamine solution to carry out polymerization reaction.

9. The preparation method according to claim 5 or 6, characterized in that: The polymerization reaction time is 0.5 to 3 hours; during the polymerization reaction, the temperature of the polymerization system is controlled to be below 70° C.; the polymerization reaction is carried out in a continuous process or a batch process.

10. The preparation method according to claim 5 or 6, characterized in that: Optionally, the following steps are further included after step (b): (e) allowing the polymerization system obtained in step (b) to stand for a period of time, or stirring for a period of time under heating conditions; The standing or stirring time is 0.5 to 30 days; and the heating temperature is 50 to 150°C.

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