KR20220084613A - Paraaramid copolymer, method for preparing the same and method for preparing paraaramid fiber using the same - Google Patents

Abstract

The present invention relates to a para-aramid copolymer, a method for producing the same, and a method for producing a para-aramid fiber using the same. In the method for producing the para-aramid copolymer, a cosolvent is used as a polymerization solvent, the order and amount of the monomers are controlled, and the prepolymer is aged at a specific stirring speed to obtain a para-aramid copolymer having high viscosity and excellent solubility. Provided, these para-aramid copolymers can provide aramid fibers with enhanced intrinsic properties expected from aramid fibers.

Description

Para-aramid copolymer, manufacturing method thereof, and method of manufacturing para-aramid fiber using the same

The present invention relates to a para-aramid copolymer, a method for producing the same, and a method for producing a para-aramid fiber using the same.

Aramid fibers composed of an aromatic dicarboxylic acid component and an aromatic diamine component, especially para-aramid fibers such as polyparaphenylene terephthalamide (PPTA) fibers, are widely used in industrial and medical applications due to their excellent strength, elastic modulus and heat resistance. is becoming However, mechanical properties such as strength and modulus of fibers are not yet sufficient depending on the intended use, and efforts are being made to provide fibers with superior physical properties.

The present invention provides a method for preparing a para-aramid copolymer capable of providing aramid fibers with enhanced physical properties than conventional aramid fibers, and a para-aramid copolymer prepared therefrom.

The present invention also provides a method for preparing para-aramid fibers from the para-aramid copolymer.

Hereinafter, a method for producing a para-aramid copolymer according to a specific embodiment of the present invention, a para-aramid copolymer prepared by the method, and a para-aramid fiber formed therefrom will be described.

According to one embodiment of the invention, a) forming a slurry by mixing 2-(4-aminophenyl)-5(6)-aminobenzimidazole with a mixed solvent comprising an organic solvent, a cosolvent, and an inorganic salt ; b) adding and reacting terephthaloyl dichloride in moles less than the moles of 2-(4-aminophenyl)-5(6)-aminobenzimidazole to form an oligomeric solution; c) adding p-phenylene diamine and terephthaloyl dichloride to the oligomer solution, reacting it, and stirring at a speed of 10 to 100 rpm to form an aged prepolymer solution; and d) forming a polymer from the prepolymer, wherein the organic solvent is N-methyl-2-pyrrolidone, N,N-dimethylacetamide, hexamethylphosphoamide, N,N,N'; A method for preparing a para-aramid copolymer comprising at least one selected from the group consisting of N'-tetramethyl urea, N,N-dimethylformamide and dimethyl sulfoxide, and wherein the cosolvent includes acetate or imidazoles provided

The present inventors polymerized 2-(4-aminophenyl)-5(6)-aminobenzimidazole (hereinafter DAPBI), p-phenylene diamine (hereinafter referred to as PPD) and terephthaloyl dichloride (hereinafter referred to as TPC). As a result of research to improve the degree of polymerization of the para-aramid copolymer obtained by was completed.

Hereinafter, a method for preparing the para-aramid copolymer will be described in detail.

In step a), a slurry is formed by mixing DAPBI with a mixed solvent containing an organic solvent, a cosolvent, and an inorganic salt.

HCl, which is a by-product of the reaction of diamine and TPC, including DAPBI and PPD, forms an ionic bond with the para-aramid copolymer, which is a reaction product of diamine and TPC, to reduce the solubility of the product. However, in the preparation method according to the embodiment, the solubility of the para-aramid copolymer can be further improved compared to the conventional combination of an organic solvent and an inorganic salt by using a cosolvent capable of ionically bonding with HCl to form a complex. have.

In particular, by using a co-solvent containing acetate or imidazole as the co-solvent, the amount of inorganic salt used can be reduced, and a para-aramid copolymer having a high degree of polymerization can be prepared at a high concentration.

As the acetate, at least one selected from the group consisting of lithium acetate, sodium acetate, potassium acetate, zinc acetate, calcium acetate, and copper acetate may be used. In addition, two types of acetate may be used as the acetate, a combination of sodium acetate and potassium acetate, a combination of zinc acetate and calcium acetate, or a combination of lithium acetate and copper acetate may be used.

The imidazoles refer to derivatives thereof including imidazole, and may be at least one selected from the group consisting of imidazole, C _1-3 alkyl-substituted imidazole, and benzimidazole. More specifically, the imidazoles are selected from the group consisting of imidazole, 1-methylimidazole, 2-methylimidazole, 1,2-dimethylimidazole, 1-ethylimidazole and benzimidazole. There may be more than one type.

The cosolvent may be included in an amount of 0.05 to 5% by weight, 0.5 to 3% by weight, or 1.0 to 2.5% by weight based on the total weight of the mixed solvent to exhibit the above-described effect.

The inorganic salt included in the mixed solvent may include a halogenated alkali metal salt or a halogenated alkaline earth metal salt. For example, the inorganic salt may include at least one selected from the group consisting of CaCl ₂ , LiCl, NaCl, KCl, LiBr, and KBr. The inorganic salt may be included in an amount of 0.01 to 15% by weight, 0.05 to 13% by weight, 0.1 to 11% by weight, or 1 to 10% by weight based on the total weight of the mixed solvent.

In particular, according to the manufacturing method of the one embodiment, it is possible to provide a para-aramid copolymer having a high degree of polymerization even when using a smaller amount of inorganic salt than when preparing the conventional aramid polymer.

The organic solvent included in the mixed solvent is N-methyl-2-pyrrolidone, N,N-dimethylacetamide, hexamethylphosphoamide, N,N,N',N'-tetramethyl urea, N,N - May include at least one selected from the group consisting of dimethylformamide and dimethyl sulfoxide. The organic solvent may be included in the remaining amount excluding the cosolvent and the inorganic salt based on the total weight of the mixed solvent.

In step a), the mixed solvent and DAPBI may be mixed so that the content of DAPBI in the slurry is 0.5 to 10 wt%.

In step b), an oligomer solution may be prepared by adding and reacting TPC in a mole number less than the mole number of DAPBI to the slurry prepared in step a).

The para-aramid copolymer obtained by polymerizing DAPBI, PPD and TPC provides fibers with different properties because solubility in the spinning solvent or alignment of the polymer chains in the fibers formed therefrom varies depending on the arrangement of monomers constituting the polymer chains. In particular, both amine groups of DAPBI show different reactivity, and since the amine group bonded to the benzimidazole group is more reactive than the amine group bonded to the phenyl group, it is difficult to control the arrangement of the monomers in the polymer chain.

Accordingly, in the preparation method according to the embodiment, DAPBI is reacted with TPC in a number of moles less than the number of moles thereof through step b) to prepare an oligomer solution mainly containing a trimer having the following structure. .

Both terminals of the trimer have the same reactivity with an amine group bonded to a phenyl group, and have similar reactivity with PPD. Accordingly, by adding PPD and TPC of the remaining content to the oligomer solution and polymerization, the problem caused by the difference in reactivity between both diamines of DAPBI can be solved, and a para-aramid copolymer with excellent physical properties can be provided.

Specifically, in step b), TPC is added in an amount of 30 to 80 mol%, 40 to 70 mol%, 45 to 60 mol%, or 45 to 55 mol% of the mole number of DAPBI to use the above-mentioned trimer as main. An oligomer solution can be formed.

As an example, when the amount of DAPBI added in step a) is 100 moles, and 50 mole% of TPC of the number of moles of DAPBI is added, 50 moles of TPC may be added.

Since the polymerization reaction of diamine and aromatic diecide halide proceeds at a high speed with exothermic heat, there is a problem in that there is a large difference in the degree of polymerization between the polymers. Specifically, since the polymerization reaction does not proceed simultaneously throughout the reaction system, the polymer in which the polymerization reaction starts first forms a long chain, whereas the polymer in which the polymerization reaction starts later forms a shorter chain compared to the polymer in which the polymerization reaction begins first. Inevitably, if the polymerization rate is fast, the difference becomes even greater. If the difference in the degree of polymerization between the polymers increases, the deviation in physical properties increases, making it difficult to implement desired properties. Therefore, in the manufacturing method according to the exemplary embodiment, a prepolymer having a predetermined length is first formed through a prepolymerization process as in step c), and the difference in polymerization degree is minimized by polymerizing the prepolymer in step d). The finished polymer can be prepared.

In step c), a prepolymer may be prepared by adding PPD and TPC to the oligomer solution formed in step b).

The molar ratio of PPD and DAPBI used in the manufacturing method according to the embodiment is 0.01:99.99 to 99.99:0.01, 1:99 to 99:1, 10:90 to 90:10, or 20:80 to 80:20 days. can Accordingly, in step c), PPD may be added so that the molar ratio of PPD to DAPBI falls within the above-mentioned range in consideration of the content of DAPBI added in step a).

In steps b) and c), TPC may be added in an amount less than the number of moles of diamine including PPD and DAPBI added in the manufacturing method according to the exemplary embodiment. Specifically, the total content of TPC added in steps b) and c) may be 20 to 60 mole % of the number of moles of diamine including DAPBI added in step a) and PPD added in step c). have.

Accordingly, the prepolymer prepared in step c) may include more diamine-derived end groups than aromatic dieside halide-derived end groups. In the preparation method according to the embodiment, since the aromatic diecide halide including TPC is added stepwise, when the end of the prepolymer is a diamine-derived end group rather than an aromatic dieside halide-derived end group, the aromatic to be added in step d) The prepolymers are linked to each other by the diecide halide, so that a final polymer having a uniform molecular weight increase and a small difference in polymerization degree can be obtained.

In step c), after adding PPD and TPC to the oligomer solution, 0 °C to 45 °C, 5 °C to 40 °C, 5 °C to 30 °C, 10 °C to 20 °C or 12 °C to 18 °C for 1 minute The prepolymer solution may be formed by stirring for about 30 minutes or about 5 minutes to 15 minutes. In step c), after adding PPD and TPC to the oligomer solution, the prepolymer solution may be formed by stirring at a speed of 100 to 500 rpm, 150 to 450 rpm, 200 to 400 rpm, or 250 to 350 rpm.

In step c), the prepolymer solution may be subjected to an aging treatment. Through this aging treatment, the prepolymer forms a coordinating bond with the cation, and the strong hydrogen bond between the amide bonds is partially broken, so that the solubility of the prepolymer can be improved, and thus the degree of polymerization of the para-aramid copolymer can be further improved. As a result, the intrinsic viscosity of the final polymer is improved, and the solubility of the para-aramid copolymer in the spinning solvent is also improved, thereby providing para-aramid fibers with excellent mechanical properties as the spinnability is improved.

The aging treatment may be performed by stirring at a speed of 10 to 100 rpm, 20 to 90 rpm, 30 to 70 rpm, or 40 to 60 rpm. When the prepolymer solution is subjected to the aging treatment, the prepolymer may be deteriorated and physical properties may be deteriorated. By adjusting the stirring speed during aerging within the above range, the content of cations in the prepolymer is reduced within the above range without fear of deterioration of the prepolymer. can be adjusted

The aging treatment may be performed for 0.01 to 48 hours to give time for the prepolymer and the cation to be sufficiently coordinated.

In addition, the aging treatment may be performed at a temperature of 20 to 40 ℃ or 25 to 35 ℃. By aging under this temperature range, the prepolymer and the cations can be sufficiently coordinated without fear of deterioration of the prepolymer.

After the aging treatment, the content of cations in the prepolymer may be adjusted to 0.002 to 2% by weight or 0.005 to 1% by weight. The content of cations in the prepolymer means the content of cations coordinated with the prepolymer measured by filtering the prepolymer solution to remove cations that are not coordinated to the prepolymer, and the content of cations in the prepolymer is When it is in the range, the solubility of the prepolymer can be improved, and thus the degree of polymerization of the para-aramid copolymer can be further improved.

In the preparation method according to the embodiment, the content of the inorganic salt may be adjusted so that the content of the inorganic salt used in the preparation method is 40 to 60 parts by weight based on 100 parts by weight of all the monomers used in the preparation method.

Accordingly, in step c), an inorganic salt may be additionally added. The above-mentioned inorganic salt may be used as the inorganic salt, and the inorganic salt may be added such that the total content of the inorganic salt added to 100 parts by weight of all monomers is 40 to 60 parts by weight.

In step d), an aromatic diecide halide such as TPC may be added to the prepolymer solution and reacted to form a final polymer.

Since the molar ratio of the total diamine added to prepare the polymer to the total aromatic dieside halide added to prepare the polymer may be 0.9 to 1.1, the aromatic dieside halide is a wholly aromatic diecide halide and a total diamine It may be added in an appropriate amount so that the molar ratio of is within the above-mentioned range.

In step d), after adding an aromatic diecide halide such as TPC to the prepolymer solution, the prepolymer solution is polymerized at a temperature of 0° C. to 45° C. for 5 minutes to 1 hour or 10 minutes to 40 minutes. Polymers can be prepared. However, the polymerization conditions are not limited thereto, and may be adjusted as known in the art to which the present invention pertains.

In the preparation method of the one embodiment, a para-aramid copolymer may be prepared by using a comonomer other than the above-described DAPBI, PPD and TPC. For example, as the comonomer, in addition to PPD and DAPBI, diamines such as 4,4'-diaminobiphenyl, 2,6-naphthalenediamine, 1,5-naphthalenediamine or 4,4'-diaminobenzanilide or , or [1,1'-biphenyl]-4,4'-dicarbonyl dichloride, 4,4'-oxybis(benzoyl chloride), 2,6-naphthalenedicarboxylic acid dichloride or 1,5-naphthalene Aromatic diecide halides, such as dicarboxylic acid dichloride, etc. can be illustrated. In the case of using a diamine as the comonomer, the comonomer may be added together with the PPD when adding the PPD in step c), and in the case of using an aromatic diecide halide as the comonomer, when adding the TPC in step c) The comonomer can be added together with the TPC or the comonomer can be added in step d).

In the production method of the above embodiment, after step d), any one or more steps of separating the resulting polymer from the polymerization reaction system, washing the polymer, neutralizing the polymer, and pulverizing the polymer are performed in the order described It can be included regardless.

On the other hand, according to another embodiment of the invention, there is provided a para-aramid copolymer prepared according to the preparation method of the embodiment.

The para-aramid copolymer may have an intrinsic viscosity of 7.0 dl/g or more, 8.0 dl/g or more, or 8.5 dl/g or more due to the high degree of polymerization.

In the present specification, the intrinsic viscosity may be a value measured according to Equation 1 below.

[Equation 1]

IV = ln(η _rel )/C

In Equation 1, ln is a natural logarithmic function, C is the concentration of the polymer solution (eg, a solution of 0.5 g of polymer dissolved in 100 mL of 95 to 98 wt% of concentrated sulfuric acid), and the relative viscosity (η _rel ) is 30 ° C. is the ratio of the flow time between the polymer solution and the solvent as measured by a capillary viscometer in

In addition, the content of cations remaining in the para-aramid copolymer may be 0.03 to 0.05 wt%.

On the other hand, according to another embodiment of the invention, there is provided a method for producing para-aramid fibers, comprising the step of spinning a spinning solution containing the para-aramid copolymer.

The spinning solution may be a polymerization solution obtained in the method for preparing the para-aramid copolymer, or a spinning solution obtained by refining the polymer obtained in the method for preparing the para-aramid copolymer and then dissolving it again in a spinning solvent.

As the spinning solvent, sulfuric acid or a solvent obtained by mixing the above-mentioned inorganic salt with the above-mentioned organic solvent may be used.

In the spinning step, the spinning solution is extruded through a spinneret, and the thickness of the para-aramid fiber can be controlled through the pressure and spinning speed during extrusion.

The method for producing the para-aramid fiber may include a step of coagulating the extruded spinning solution after the spinning step to obtain a multifilament, washing and drying the multifilament, and, if necessary, stretching and/or heat treatment may include the step of

The para-aramid fiber prepared by the above-described method is prepared from a high-viscosity para-aramid copolymer with excellent solubility, so that the intrinsic properties of the aramid fiber are further enhanced.

For example, the para-aramid fiber may have a strength of 26 to 32 g/d, a Young's modulus of 800 to 1000 g/d, and an elongation of 3.2 to 3.9%, measured according to ASTM D885.

In addition, the monofilament constituting the para-aramid fiber may have a high strength of 26 to 32 g/d measured according to ASTM D885, and a very low value with a strength standard deviation of 0.1 to 12.

The method for producing a para-aramid copolymer according to an embodiment of the present invention uses a cosolvent as a polymerization solvent, controls the input order and amount of monomers, and ages the prepolymer at a specific stirring speed to have high viscosity and high solubility. It provides an excellent para-aramid copolymer, and this para-aramid copolymer can provide aramid fibers with further enhanced intrinsic properties expected from aramid fibers.

Hereinafter, the action and effect of the invention will be described in more detail through specific examples of the invention. However, this is presented as an example of the invention and the scope of the invention is not limited in any way by this.

Example 1: Preparation of para-aramid copolymer

In a reactor under a nitrogen atmosphere, a mixed solvent in which N,N-dimethylacetamide as an organic solvent, sodium and potassium acetate as a cosolvent, and CaCl ₂ as an inorganic salt in a weight ratio of 97:2:1 was mixed, and DAPBI in the slurry DAPBI was added so that the concentration of was 5% by weight to prepare a slurry.

Then, the temperature of the reactor is cooled to 10° C., and TPC corresponding to about 50 mol% of the number of moles of DAPBI is added to the reactor, and then reacted. TPC and the amine group bound to the benzimidazole of DAPBI are reacted and bound to the trimer An oligomer solution containing as the main was obtained.

The temperature of the reactor was raised to room temperature again, and PPD was added to the oligomer solution so that the molar ratio of DAPBI:PPD was 20:80, and the mixture was stirred until all of the PPD was dissolved. Thereafter, TPC was added so that the amount of TPC containing the previously added TPC corresponds to about 30 mol% of the number of moles of DAPBI and PPD added previously, and stirred at about 15° C. at a speed of about 300 rpm. After about 5 minutes, a gelled prepolymer solution was obtained, and the prepolymer solution was stirred at about 30° C. at a speed of about 50 rpm for 12 hours to perform aging treatment. After confirming that the content of cations in the prepolymer is about 0.453 wt%, TPC is additionally added so that the molar ratio of the total amount of TPC to the diamine added to the prepolymer solution becomes 1.0, and then about 300 at about 15 ° C. A polymer was prepared from the prepolymer by stirring at a speed of rpm for about 30 minutes. The intrinsic viscosity of the prepared polymer was 8.6 dl/g.

<Method for measuring cation content>

A portion of the prepolymer solution was collected and filtered to remove cations that were not coordinated to the prepolymer, and after drying the prepolymer at 50 °C for 10 hours, using an inductively coupled plasma atomic emission spectrometer (Inductively Coupled Plasma Spectrophotometer) The content of cations in the prepolymer was measured.

Comparative Example 1: Preparation of para-aramid copolymer

In a reactor under a nitrogen atmosphere, a mixed solvent mixed with N,N-dimethylacetamide as an organic solvent and CaCl ₂ as an inorganic salt in a weight ratio of 97:3 was added, and DAPBI was added so that the concentration of DAPBI in the slurry was 5% by weight. A slurry was prepared.

Then, the temperature of the reactor is cooled to 10° C., and TPC corresponding to about 50 mol% of the number of moles of DAPBI is added to the reactor, and then reacted. TPC and the amine group bound to the benzimidazole of DAPBI are reacted and bound to the trimer An oligomer solution containing as the main was obtained.

The temperature of the reactor was raised to room temperature again, and PPD was added to the oligomer solution so that the molar ratio of DAPBI:PPD was 20:80, and the mixture was stirred until all of the PPD was dissolved. Thereafter, TPC was added so that the amount of TPC containing the previously added TPC was equal to the number of moles of DAPBI and PPD previously added, and the mixture was stirred at about 15° C. at a speed of about 300 rpm. After about 5 minutes, a gelled prepolymer solution was obtained, and the prepolymer solution was further stirred at about 15° C. at a speed of about 300 rpm for about 30 minutes to prepare a polymer from the prepolymer. A portion of the prepolymer solution was taken to check the cation concentration. As a result, the content of cations in the prepolymer was about 0.0017 wt%, and the intrinsic viscosity of the prepared polymer was 8.15 dl/g.

Test Example: Evaluation of physical properties of fibers formed from para-aramid copolymer

Para-aramid fibers were prepared in the following manner from the para-aramid copolymers prepared in Examples and Comparative Examples.

<Production of fibers>

After dissolving the para-aramid copolymer prepared in Examples and Comparative Examples in 97 wt% sulfuric acid at 20 wt% based on the total weight to prepare a spinning dope, the prepared spinning dope was spun using a spinneret, followed by an air gap A filament was prepared by coagulation in a coagulation bath through Then, the filament was washed with water and dried, and then wound to prepare a para-aramid fiber.

<Evaluation of physical properties>

The multifilament properties and the monofilament properties of each para-aramid fiber prepared in Examples and Comparative Examples were measured by the methods described below, and the results are shown in Table 1.

(1) Multifilament strength, modulus, and elongation

According to ASTM D885 standard test method (sample length 250 mm, elongation speed 25 mm/min) using INSTRON's testing machine (Instron Engineering Corp, Canton, Mass) for each para-aramid fiber prepared through Examples and Comparative Examples Strength, Young modulus and elongation were measured.

(2) strength and deviation of monofilament

Each of 20 monofilaments were collected from the para-aramid fibers prepared in Examples and Comparative Examples, and the strength of each monofilament was measured using an INSTRON testing machine (Instron Engineering Corp, Canton, Mass) using ASTM D885 standard test method (sample length 250). mm, stretching speed 25 mm/min). The average strength of 20 monofilaments was obtained and defined as the strength of the monofilaments, and the strength standard deviation was obtained and shown in Table 1.

Example 1 Comparative Example 1 multifilament Strength (g/d) 28.2 24.3 Young's modulus (g/d) 846 793 Elongation (%) 3.29 3.08 monofilament Strength (g/d) 29.65 28.15 Standard Deviation 11.2 13.6

Referring to Table 1, the para-aramid copolymer prepared according to the manufacturing method of the embodiment provides para-aramid fibers with improved physical properties required for aramid fibers even when compared to fibers prepared from copolymers produced from the same monomer. it is confirmed that

Claims (16)

a) forming a slurry by mixing 2-(4-aminophenyl)-5(6)-aminobenzimidazole with a mixed solvent containing an organic solvent, a cosolvent, and an inorganic salt;
b) adding and reacting terephthaloyl dichloride in moles less than the moles of 2-(4-aminophenyl)-5(6)-aminobenzimidazole to form an oligomeric solution;
c) adding p-phenylene diamine and terephthaloyl dichloride to the oligomer solution, reacting it, and stirring at a speed of 10 to 100 rpm to form an aged prepolymer solution; and
d) forming a polymer from the prepolymer;
The organic solvent is N-methyl-2-pyrrolidone, N,N-dimethylacetamide, hexamethylphosphoamide, N,N,N',N'-tetramethyl urea, N,N-dimethylformamide and A method for producing a para-aramid copolymer comprising at least one selected from the group consisting of dimethyl sulfoxide, and wherein the cosolvent includes acetate or imidazoles.
The method according to claim 1, wherein the cosolvent comprises at least one acetate selected from the group consisting of lithium acetate, sodium acetate, potassium acetate, zinc acetate, calcium acetate, and copper acetate.
The method of claim 1, wherein the cosolvent comprises at least one imidazole selected from the group consisting of imidazole, C _1-3 alkyl-substituted imidazole, and benzimidazole.
The method of claim 1, wherein the cosolvent is included in an amount of 0.05 to 5% by weight based on the total weight of the mixed solvent.
The method of claim 1, wherein the inorganic salt comprises at least one selected from the group consisting of CaCl ₂ , LiCl, NaCl, KCl, LiBr and KBr.
The para-aramid according to claim 1, wherein, in step b), the terephthaloyl dichloride is added in an amount of 30 to 80 mole % of the mole number of 2-(4-aminophenyl)-5(6)-aminobenzimidazole. A method for preparing a copolymer.
The preparation of the para-aramid copolymer according to claim 1, wherein the molar ratio of p-phenylene diamine and 2-(4-aminophenyl)-5(6)-aminobenzimidazole is 0.01:99.99 to 99.99:0.01. Way.
According to claim 1, wherein the total content of terephthaloyl dichloride added in step b) and terephthaloyl dichloride added in step c) is 2-(4-aminophenyl) added in step a) -5(6)-Aminobenzimidazole and 20 to 60 mol% of the number of moles of the diamine including p-phenylene diamine added in step c), A method for producing a para-aramid copolymer.
The method of claim 1, wherein the aging treatment is performed for 0.01 to 48 hours.
According to claim 1, wherein the aging treatment is carried out at a temperature of 20 to 40 ℃, the method for producing a para-aramid copolymer.
The method of claim 1, wherein the prepolymer solution has a content of cations in the prepolymer controlled to be 0.002 to 2 wt%.
The method of claim 1, wherein an aromatic diecide halide is added to the prepolymer solution in step d).
The method according to claim 1, wherein the molar ratio of the total diamine added to prepare the polymer to the total aromatic diecide halide added to prepare the polymer is 0.9 to 1.1.
A para-aramid copolymer prepared according to the method for preparing the para-aramid copolymer of claim 1.
15. The para-aramid copolymer according to claim 14, wherein the para-aramid copolymer has an intrinsic viscosity of 7.0 dl/g or more.
A method for producing para-aramid fibers, comprising the step of spinning a spinning solution containing the para-aramid copolymer of claim 14.