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CN-122011367-A - Method for controlling molecular weight distribution of meta-aramid resin through gradient extraction elution and application

CN122011367ACN 122011367 ACN122011367 ACN 122011367ACN-122011367-A

Abstract

The invention discloses a method for controlling molecular weight distribution of meta-aramid resin by gradient extraction elution and application thereof. The method uses N, N-dimethylacetamide aqueous solutions with different mass concentrations to sequentially extract resin powder from high concentration to low concentration, and separates, washes and dries insoluble substances after each extraction stage to obtain a plurality of resin fractions with narrower molecular weight distribution and smaller PDI. The technology not only narrows the overall molecular weight distribution, but also realizes grading according to the molecular size. The high molecular weight fraction is suitable for high-strength fibers and high-performance insulating paper, the medium molecular weight fraction can be used for conventional fibers and insulating paper, and the low molecular weight fraction is suitable for being used as a bonding layer or a functional additive, so that high-value utilization of raw materials is realized. The obtained resin has better processing stability and product performance uniformity, and has important application value in the fields of preparing high-strength high-modulus fibers, high-performance insulating paper, films, composite materials and the like.

Inventors

  • TAN LIN
  • ZHANG SHENG
  • Ren Junwen
  • WANG ZIANG
  • HUANG XIN

Assignees

  • 四川大学

Dates

Publication Date
20260512
Application Date
20260326

Claims (10)

  1. 1. A method for controlling molecular weight distribution of meta-aramid resin by gradient extraction elution, which is characterized by comprising the following steps: S1, mixing m-phenylenediamine, m-phthaloyl chloride and N, N-dimethylacetamide by adopting a low-temperature solution polycondensation process to perform polymerization reaction, so as to obtain a meta-aramid resin solution; S2, adding the meta-aramid resin solution obtained in the step S1 into a non-solvent to precipitate resin, and separating, washing and drying to obtain meta-aramid resin solid powder with wider molecular weight distribution; S3, selecting a good solvent comprising at least one of N, N-dimethylacetamide, dimethylformamide, dimethyl sulfoxide and N-methylpyrrolidone, selecting a poor solvent comprising at least one of water, ethanol and ethylene glycol, and preparing extraction solutions with different mass concentrations from the good solvent and the poor solvent according to different proportions, wherein the extraction solutions sequentially extract the meta-aramid resin solid powder obtained in the step S2 from high to low in concentration, and separate, wash and dry insoluble matters after each stage of extraction to obtain meta-aramid resin fractions with different molecular weight distributions; Wherein the mass concentration gradient range of the extract liquid is 85% -20%, and the concentration difference of two adjacent stages is 10% -25%.
  2. 2. The method for controlling molecular weight distribution of meta-aramid resin through gradient extraction elution according to claim 1, wherein in the step S1, the low-temperature solution polycondensation process is characterized in that m-phenylenediamine is dissolved in dry N, N-dimethylacetamide under the protection of nitrogen, the temperature of the system is reduced to-5 ℃ to 5 ℃, isophthaloyl dichloride is added in batches under stirring, the reaction temperature is controlled to be not more than 10 ℃ for initial prepolymerization, then the temperature is slowly increased to 25 ℃ to 35 ℃ for continuous reaction for 2 to 4 hours, and after the reaction is finished, a neutralizer is added to adjust the pH to 7.0 to 8.0, so that the meta-aramid resin solution is obtained.
  3. 3. The method for controlling molecular weight distribution of meta-aramid resin through gradient extraction elution according to claim 2, wherein the molar ratio of m-phenylenediamine to isophthaloyl dichloride is 1:1.00-1:1.02, and the neutralizer is one or a combination of more of magnesium oxide, magnesium hydroxide, calcium oxide, calcium hydroxide and aluminum oxide.
  4. 4. The method for controlling molecular weight distribution of meta-aramid resin by gradient extraction elution according to claim 3, wherein the apparent viscosity of the meta-aramid resin solution obtained in step S1 ranges from 500 to 2000 poise, and the molecular weight distribution index ranges from 1.8 to 2.5.
  5. 5. The method for controlling molecular weight distribution of meta-aramid resin by gradient extraction elution according to claim 1, wherein in step S2, the non-solvent is deionized water or an alcohol-water mixed solution, the stirring speed during precipitation is 200-400 rpm, the precipitate is washed with deionized water and absolute ethyl alcohol in sequence, and the drying temperature is 70-85 ℃.
  6. 6. The method for controlling molecular weight distribution of meta-aramid resin by gradient extraction elution according to claim 1, wherein in the step S3, the extraction conditions of each stage are that the extraction temperature is 20 ℃ plus or minus 5 ℃, the solid content of the meta-aramid resin solid powder in the extract is 4-10wt%, the stirring speed during the extraction is 600 rpm plus or minus 50 rpm, and the extraction time is 2 hours plus or minus 0.5 hour.
  7. 7. The method for controlling molecular weight distribution of meta-aramid resin by gradient extraction elution according to claim 1, wherein after each stage of extraction is finished, the obtained mixed system is centrifugally separated at a rotation speed of 5000 rpm +/-500 rpm, supernatant and precipitate are collected, the precipitate is washed with deionized water at the same temperature for a plurality of times, centrifugally separated after each washing, and then dried in a vacuum drying oven to obtain residual solids or final fractions of the extraction of the present stage.
  8. 8. The method for controlling molecular weight distribution of meta-aramid resin by gradient extraction elution according to claim 1, wherein in step S3, the multistage sequential extraction includes at least three stages of extraction, in which the first stage extraction is performed by using an extract with a mass concentration of 70% -85%, the second stage extraction is performed by using an extract with a mass concentration of 50% -65%, and the third stage extraction is performed by using an extract with a mass concentration of 20% -40%.
  9. 9. The method for controlling molecular weight distribution of meta-aramid resin by gradient extraction elution according to claim 1, wherein the molecular weight distribution index of the meta-aramid resin fraction is less than 1.8, and the weight average molecular weight ranges from 10000 to 100000 g/mol.
  10. 10. Use of the meta-aramid resin fraction obtained by the method of controlling the molecular weight distribution of a meta-aramid resin by gradient extraction elution as claimed in any one of claims 1 to 9 in the preparation of meta-aramid fibers, films, composites or insulating papers.

Description

Method for controlling molecular weight distribution of meta-aramid resin through gradient extraction elution and application Technical Field The invention relates to the technical field of high-performance polymer material preparation, in particular to a method for precisely controlling and narrowing the molecular weight distribution (Polydispersity Index, PDI) of meta-aramid (poly m-phenylene isophthalamide, PMIA) resin by a multistage gradient solvent extraction technology, and meta-aramid resin fractions with different molecular weight distribution characteristics obtained by the method. Background Meta-aramid is an important high-performance aromatic polyamide, is known for its excellent high temperature resistance, flame retardance, chemical stability and electrical insulation, and is widely used in the fields of protective clothing, electrical insulation, high-temperature filtration, advanced composite materials and the like. The properties, in particular mechanical properties, thermal stability and solution processability, depend to a large extent on the molecular weight of the polymer and its distribution. In the field of electrical insulation, meta-aramid insulation paper is widely applied to power equipment such as transformers, motors and the like due to excellent heat resistance and dielectric properties, and the performance stability of the meta-aramid insulation paper is closely related to the molecular weight distribution of resin. At present, the industrial and laboratory preparation of meta-aramid resin mainly adopts a low-temperature solution polycondensation method. Although a high molecular weight resin can be obtained by controlling the reaction temperature, the monomer ratio, the feeding manner, etc., the polymer obtained by this method generally has a broad molecular weight distribution. A large number of documents and practices show that the PDI value of meta-aramid resin synthesized by a conventional low-temperature polycondensation method is generally about 2.0 or even wider. The broad molecular weight distribution means that extremely long molecular chains and shorter molecular chains are present in the resin at the same time. The non-uniformity can bring a series of problems that 1) molecular chains with different lengths behave differently in the process of subsequent spinning, so that the internal structure of the fiber is uneven, the stability and consistency of the final mechanical properties (such as strength and modulus) are affected, the strength CV value is higher, 2) when a film or a composite material is prepared, the widely distributed resin can cause unstable processing rheological behavior, internal stress concentration points exist in the product, the overall reliability of the product is reduced, and 3) the application of the resin in high-end fields (such as high-strength fiber for aerospace, ultrathin insulating film and insulating paper for transformers) is limited. In order to obtain a material with more excellent performance, the regulation and purification of the molecular weight distribution of meta-aramid resin are particularly important. Traditional polymer fractionation methods such as Gel Permeation Chromatography (GPC) preparation-scale separations, while highly accurate, have low throughput, high cost, and high solvent consumption, and cannot meet the needs of industrial or large-scale laboratory preparations. Other methods, such as precipitation fractionation, are simple to operate, but generally have low fractionation efficiency, difficulty in achieving precise, gradual narrowing of molecular weight distribution, and limited effectiveness on polymers such as meta-aramid that have complex dissolution behavior in common solvent/non-solvent systems. Therefore, the method for separating the meta-aramid resin has the advantages of relatively simple operation, strong controllability, effective narrowing of the molecular weight distribution of the meta-aramid resin, realization of resin separation in different molecular weight intervals, and great significance for improving the overall performance of the meta-aramid material and expanding the application field of the meta-aramid material in high-end application fields including high-performance insulating paper. Disclosure of Invention The invention aims to overcome the defects in the prior art and provide a method which is controllable in operation and can effectively narrow and regulate the molecular weight distribution of meta-aramid resin. The method is based on the gradient extraction elution principle, and utilizes the solubility difference of meta-aramid fiber in water solutions of good solvents (DMAc) with different concentrations to realize the selective dissolution and separation of polymer chains with different molecular weights. In order to achieve the above object, in one aspect, the present invention provides a method for controlling molecular weight distribution of meta-aramid resin by gradi