Method for preparing polyphenylene sulfide from high-purity p-dichlorobenzene

Abstract

The invention belongs to the field of high polymer material synthesis, and provides a method for preparing polyphenylene sulfide from high-purity p-dichlorobenzene, which adopts the whole process design of pre-construction of a composite sulfur source intermediate, regulation and control of an end group controllable oligomerization polyphenylene sulfide intermediate, segmented polymerization of the high-purity p-dichlorobenzene and precise dehydration-washing-drying. The ultra-low impurity level of 0.05-0.25 wt% of burning residues of the polyphenylene sulfide product, the sodium ion content of 10-200 mg / kg and the chloride ion content of 10-500 mg / kg is achieved, and meanwhile the high-performance stability of the melting point of 270-300 DEG C, the gel fraction of 92-99 wt% and the water content of 0.01-0.20 wt% is kept. The problems of deep removal of inorganic ions and ash content, balance of gel fraction and processability and control of residual solvents in the traditional polyphenylene sulfide preparation process are solved, and the method has wide application value in the fields of high-performance engineering plastics, special fibers, electronic packaging materials and the like.

Description

Technical Field

[0001] This invention relates to the field of polymer material synthesis technology, specifically to a method for preparing polyphenylene sulfide from high-purity p-dichlorobenzene. Background Technology

[0002] Polyphenylene sulfide (PPS), a high-performance specialty engineering plastic, is widely used in automotive parts, electronics, aerospace, and chemical equipment due to its excellent heat resistance, chemical corrosion resistance, mechanical strength, and dimensional stability. With the rapid development of industries such as new energy vehicles, 5G communications, and high-end equipment manufacturing, the performance requirements for PPS materials are constantly increasing. Especially in high-temperature, long-term operating environments, the purity and stability of the material directly affect the product's service life and reliability. In practical applications of PPS, residual inorganic salt ions, ash, solvents, and other impurities significantly reduce its electrical insulation properties, hydrolytic stability, and long-term thermal aging performance. Therefore, preparing low-impurity, high-purity PPS products has become a key technological requirement in the industry. Furthermore, to meet the needs of different application scenarios such as injection molding and extrusion processing, the physical properties of PPS, such as gel fraction, melt flowability, and particle size distribution, also require precise control, which places higher demands on the stability and controllability of the preparation process.

[0003] Currently, the industrial preparation of polyphenylene sulfide (PPS) mainly involves the polymerization reaction of p-dichlorobenzene and sodium sulfide in a polar solvent. However, existing technologies still have many shortcomings. For example, Chinese patent CN102585183A discloses a method for preparing PPS by polycondensation of p-dichlorobenzene, which uses sodium sulfide and p-dichlorobenzene in N-methylpyrrolidone for high-temperature polymerization. However, this method results in drastic viscosity changes in the reaction system during high-temperature segmented polymerization, making it difficult to achieve coordinated control of temperature uniformity and stirring efficiency during scale-up production, leading to significant batch-to-batch product performance fluctuations. Another example is Chinese patent CN103289093A, which discloses a method for preparing linear high molecular weight PPS. However, this method has limited effectiveness in removing sodium ions, ash, and other impurities. Furthermore, in pursuing high gel fractions to improve material structural stability, the melt processing performance of the product significantly decreases, making it difficult to meet the flowability requirements of injection molding. In addition, the control of residual solvent N-methyl-2-pyrrolidone in existing technologies often requires extending the drying time or increasing the drying temperature. However, excessively high drying conditions can easily lead to oxidative degradation or cross-linking of polyphenylene sulfide molecular chains, affecting the color and processing stability of the product. Therefore, how to achieve ultra-low impurity levels while taking into account the product's processing performance and production efficiency remains a technical problem that urgently needs to be solved in the field of polyphenylene sulfide preparation. Summary of the Invention

[0004] The purpose of this invention is to provide a method for preparing polyphenylene sulfide from high-purity p-dichlorobenzene, which solves the problem of the coupling contradiction between the current polyphenylene sulfide preparation process, which is difficult to simultaneously achieve the stability and scale-up controllability of the reaction window in the high-temperature segmented polymerization process, the deep removal of impurities such as inorganic ions and ash in the product and the reliability of long-term use, and the need to maintain the melt processability of powdered particulate materials and the control of residual solvents while achieving the structural stability required by the high gel fraction.

[0005] This invention employs a strategy of pre-constructing a composite sulfur source intermediate and synergistically regulating it with an end-group controllable oligomeric polyphenylene sulfide intermediate. By precisely dehydrating the sulfur source and N-methyl-2-pyrrolidone before polymerization to form a composite sulfur source intermediate with a specific viscosity window, the viscosity stability and mass transfer uniformity of the reaction system during the high-temperature polymerization stage are significantly improved. At the same time, an oligomeric polyphenylene sulfide intermediate with controllable number-average molecular weight is introduced as a molecular weight regulator and chain growth promoter, achieving a precise balance between the gel fraction and melt flowability of the product during the segmental polymerization of high-purity p-dichlorobenzene. This results in excellent processing stability and batch consistency while ensuring low impurity levels in the product.

[0006] To achieve the above objectives, the present invention provides the following technical solution:

[0007] A method for preparing polyphenylene sulfide from high-purity p-dichlorobenzene includes the following steps:

[0008] S1. Preparation of the reaction system: N-methyl-2-pyrrolidone is added to the reactor; a sulfur source is added, wherein the sulfur source is selected from anhydrous sodium sulfide, sodium sulfide nonahydrate, or a combination of sodium hydrogen sulfide and sodium hydroxide; a composite sulfur source intermediate is added; wherein the molar ratio of N-methyl-2-pyrrolidone to the total sulfur in the sulfur source is 3.5–6.0:1;

[0009] S2. Dehydration: Under nitrogen protection, the reaction system is heated to 180-200℃ and dehydrated until the water content of the reaction system is 0.05-0.50 wt%.

[0010] S3. Polymerization: 1,4-dichlorobenzene with a purity of 99.5-99.99 wt% is added to the reaction system and staged polymerization is carried out. The molar ratio of 1,4-dichlorobenzene to the total sulfur in the sulfur source is 0.99–1.05:1. The staged polymerization includes: prepolymerization at a temperature of 220-240℃ and postpolymerization at a temperature of 260-280℃.

[0011] S4. Intermediate addition and post-treatment: A terminally controlled oligomeric polyphenylene sulfide intermediate is added during the pre-polymerization or post-polymerization stage, and acid treatment is performed after polymerization. The pH value of the filtrate obtained by solid-liquid separation of the acid-treated slurry is measured at 25°C to be 7.0–9.5. Solid-liquid separation, washing with deionized water at 60–100°C and repeating 2–6 times, and drying are performed sequentially to obtain polyphenylene sulfide.

[0012] Further, the terminal-controlled oligomeric polyphenylene sulfide intermediate is prepared by the following steps: A1. Raw material preparation: 1,4-dichlorobenzene, a sulfur source, and N-methyl-2-pyrrolidone are mixed, wherein the molar ratio of 1,4-dichlorobenzene to the total sulfur in the sulfur source is 1.05-1.30:1; A2. Oligopolymerization reaction: Under nitrogen protection, the mixture is heated to 200-240℃ and kept at this temperature; the number-average molecular weight of the product is monitored during the reaction; A3. Endpoint criterion: The reaction is terminated and the temperature is lowered when the number-average molecular weight of the product reaches 500-5000 g / mol; the reaction time is 0.2-2.0 h; A4. Post-treatment: Deionized water is added to the reaction solution to precipitate the product, and after solid-liquid separation, the mixture is washed 1-5 times with deionized water and dried to obtain the terminal-controlled oligomeric polyphenylene sulfide intermediate.

[0013] Furthermore, the composite sulfur source intermediate is prepared by the following steps: B1. Raw material preparation: a sulfur source is provided, the sulfur source being selected from anhydrous sodium sulfide or sodium sulfide nonahydrate, and the sulfur source is mixed with N-methyl-2-pyrrolidone; B2. Dehydration and compounding: under nitrogen protection, the mixture is heated to 180-200℃ and dehydrated until the water content of the system is 0.05-0.50wt%, to obtain the composite sulfur source intermediate; B3. Quality control: the apparent viscosity of the composite sulfur source intermediate at 25℃ is 100-50000 mPa·s.

[0014] Furthermore, in the raw material preparation step B1 of the composite sulfur source intermediate, one or more inorganic salts are added, wherein the inorganic salts are selected from lithium chloride, sodium thiosulfate and their pentahydrates; wherein: the molar ratio of lithium chloride to sodium sulfide in the sulfur source is 0-0.20:1; and the mass ratio of sodium thiosulfate to sodium sulfide in the sulfur source is 0-0.10:1.

[0015] Furthermore, the following conditions are simultaneously met: the molar ratio of 1,4-dichlorobenzene in step S3 to the total sulfur in the sulfur source is 0.99-1.05:1; the molar ratio of N-methyl-2-pyrrolidone in step S1 to the total sulfur in the sulfur source is 3.5-6.0:1; step S4 includes acid treatment: before solid-liquid separation, acid is added to the slurry after polymerization, the acid being selected from acetic acid or hydrochloric acid, to make the pH of the acid-treated slurry 7.0-9.5; the washing step in step S4 includes washing with deionized water at a temperature of 60-100℃, and repeating 2-6 times.

[0016] As a concept of this invention, a composite sulfur source intermediate preconstruction technology is employed, primarily to enhance the reaction window stability and product purity control capabilities of the high-temperature polymerization process of polyphenylene sulfide. By precisely dehydrating the sulfur source and N-methyl-2-pyrrolidone before polymerization to form a composite sulfur source intermediate with controllable viscosity, the crystal water and adsorbed water in the sulfur source can be removed in advance, avoiding instability of sulfur source activity and increased side reactions due to moisture fluctuations in the subsequent high-temperature polymerization stage, thereby improving the consistency of reaction kinetics in the polymerization process. On the other hand, the composite sulfur source intermediate has an apparent viscosity range of 100-50000 mPa·s at 25°C. This viscosity window design significantly improves the uniformity of sulfur source dispersion in the reaction system, avoiding the problems of gel particle formation and reactor wall coking caused by local over-concentration in the early stages of high-temperature polymerization of traditional solid sulfur sources. Meanwhile, this invention introduces an end-group controllable oligomeric polyphenylene sulfide intermediate as a molecular weight regulator. The number-average molecular weight of this intermediate is precisely controlled within the range of 500-5000 g / mol. When added in the prepolymerization or postpolymerization stage, it can serve as an active end-group provider for chain growth. Through the end-group condensation reaction with the main chain polyphenylene sulfide, it can achieve dual regulation of the gel fraction and molecular weight distribution of the final product. This invention also uses high-purity 1,4-dichlorobenzene with a purity of 99.5-99.99 wt% as a monomer, which significantly reduces the problems of irregular chain structure and decreased melting point caused by the introduction of ortho- or meta-isomer impurities in the monomer. Combined with a precise dehydration process at 180-200℃ to control the moisture content of the reaction system within a narrow window of 0.05-0.50 wt%, and a temperature gradient design of 220-240℃ for prepolymerization and 260-280℃ for postpolymerization in segmented polymerization, the polymerization reaction achieves a balance between high conversion rate and low by-product formation under the dual drive of kinetics and thermodynamics. Finally, through post-treatment processes such as acid treatment to adjust the pH to 7.0-9.5, multiple washing with high-temperature deionized water at 60-100℃, and vacuum drying, ultra-low impurity levels of 0.05-0.25 wt% ignition residue, 10-200 mg / kg sodium ion content, and 10-500 mg / kg chloride ion content are obtained.

[0017] The present invention also discloses a polyphenylene sulfide, which is prepared by the above method and simultaneously meets the following three indicators: the ignition residue of the polyphenylene sulfide is 0.05-0.25 wt%; the sodium ion content of the polyphenylene sulfide is 10-200 mg / kg; and the chloride ion content of the polyphenylene sulfide is 10-500 mg / kg.

[0018] Furthermore, the moisture content of the polyphenylene sulfide is 0.01-0.20 wt%.

[0019] Furthermore, the polyphenylene sulfide has a melting point of 270-300°C and a gel fraction of 92-99 wt%.

[0020] Furthermore, the polyphenylene sulfide is in powder or granular form, and the particle size D50 of the polyphenylene sulfide is 50-500 μm.

[0021] Furthermore, the residual N-methyl-2-pyrrolidone content in the polyphenylene sulfide is not higher than 1000 mg / kg.

[0022] Furthermore, the reactor is a closed, pressure-resistant reactor that can maintain the closed state of the reaction system at a temperature of 260–280°C.

[0023] Furthermore, in step S1, when the sulfur source is a combination of sodium hydrosulfide and sodium hydroxide, the molar ratio of sodium hydrosulfide to sodium hydroxide is 1:1.

[0024] Furthermore, in step S1, the raw materials are mixed under nitrogen protection and stirring conditions.

[0025] Furthermore, the dehydration in step S2 is achieved by distillation and carried out under stirring conditions.

[0026] Furthermore, after the dehydration in step S2 is completed, the reaction system is shut down and switched to a closed and pressure-resistant state.

[0027] Furthermore, the moisture content in step S2 is determined using the Karl Fischer moisture determination method.

[0028] Furthermore, the prepolymerization reaction time in step S3 is 0.5–6 h.

[0029] Furthermore, the heat preservation reaction time for post-polymerization in step S3 is 0.5–10 h.

[0030] Furthermore, the segmented polymerization in step S3 is carried out under mechanical stirring conditions.

[0031] Furthermore, in step S3, the heating rate from the prepolymerization temperature to the postpolymerization temperature is 0.5–5 °C / min.

[0032] Furthermore, in step S4, the molar ratio of the end-group controllable oligomeric polyphenylene sulfide intermediate to the total sulfur in the sulfur source is 0.001–0.050:1.

[0033] Furthermore, the end-group controllable oligomeric polyphenylene sulfide intermediate in step S4 is directly added to the reaction system.

[0034] Furthermore, the solid-liquid separation in step S4 is carried out by centrifugation, with a relative centrifugal force of 1000–5000g and a centrifugation time of 5–30min; or by filtration, using filter media with a pore size of 1–10μm.

[0035] Furthermore, the washing in step S4 is carried out using deionized water with a solid-liquid mass ratio of 1:5 to 1:10, and each washing time is 10–60 min. The washing endpoint is determined by the pH value of the washing solution being 6–8 and the conductivity being less than 50 μS / cm.

[0036] Furthermore, the drying in step S4 is carried out at a temperature of 80–140℃ and a vacuum degree of less than 5kPa for 2–24 hours. The drying endpoint is determined by the product moisture content not exceeding 0.2wt% or the difference in mass between two consecutive weighings being less than 0.1%.

[0037] Furthermore, the molar ratio of N-methyl-2-pyrrolidone to the total sulfur in the sulfur source in step A1 is 3.5–6.0:1.

[0038] Furthermore, in step A1, the raw materials are mixed under nitrogen protection and stirring conditions.

[0039] Furthermore, the number-average molecular weight Mn in step A3 was determined by gel permeation chromatography under the following conditions: solvent: 1-chloronaphthalene; column temperature: 200℃; flow rate: 1.0 mL / min; and polystyrene as the calibration standard.

[0040] Furthermore, in step A3, the reaction process is monitored by periodically sampling and measuring the number-average molecular weight, with a sampling frequency of once every 10–30 minutes.

[0041] Furthermore, the amount of deionized water added in step A4 is 2–10 times the volume of the reaction liquid.

[0042] Furthermore, the precipitation in step A4 is achieved by cooling to room temperature and stirring for 10–60 min.

[0043] Furthermore, the washing in step A4 is carried out at a temperature of 60–100°C, and each washing session lasts for 10–60 minutes.

[0044] Furthermore, the drying in step A4 is carried out for 2–12 hours at a temperature of 80–120°C and a vacuum degree of less than 5 kPa.

[0045] Furthermore, the molar ratio of N-methyl-2-pyrrolidone to the total sulfur in the sulfur source in step B1 is 3.5–6.0:1.

[0046] Furthermore, in step B1, the mixing is carried out under nitrogen protection and with stirring.

[0047] Furthermore, the dehydration in step B2 is achieved by distillation and carried out under stirring conditions.

[0048] Furthermore, the moisture content in step B2 is determined using the Karl Fischer moisture determination method.

[0049] Furthermore, the apparent viscosity was measured using a rotational viscometer at a shear rate of 10 s⁻¹. -1 The measurements were taken at a temperature of 25℃.

[0050] Furthermore, the ignition residue was determined according to GB / T9345.1-2008 standard, and was ignited to constant weight at a temperature of 550±25℃ in air atmosphere.

[0051] Furthermore, the sodium ion content is determined by ion chromatography or inductively coupled plasma atomic emission spectrometry; the chloride ion content is determined by ion chromatography.

[0052] Furthermore, the moisture content was determined using the Karl Fischer moisture determination method.

[0053] Furthermore, the melting point was determined using differential scanning calorimetry under a nitrogen atmosphere at a heating rate of 10 °C / min.

[0054] Furthermore, the gel fraction is defined as the mass fraction of insoluble matter, determined by Soxhlet extraction using 1-chloronaphthalene as solvent at 200°C for 6 hours. The residue after extraction is then vacuum dried to constant weight and the gel fraction is calculated.

[0055] Furthermore, the particle size D50 was determined using a laser particle size analyzer.

[0056] Furthermore, the residual content of N-methyl-2-pyrrolidone was determined by gas chromatography, with a detection limit of 1 mg / kg.

[0057] Furthermore, the pH value of the acid-treated slurry is the pH value of the filtrate obtained after solid-liquid separation of the slurry, measured at a temperature of 25°C.

[0058] Furthermore, the total number of moles of sulfur in the sulfur source is calculated based on the number of moles of sulfur element in the sulfur source; when the sulfur source is a combination of sodium hydrosulfide and sodium hydroxide, the total number of moles of sulfur in the sulfur source is calculated based on the number of moles of sulfur element in the sodium hydrosulfide.

[0059] Furthermore, when the sodium thiosulfate is sodium thiosulfate pentahydrate, the mass ratio is based on anhydrous sodium thiosulfate; when the sulfur source is sodium sulfide nonahydrate, the mass of sodium sulfide in the sulfur source is based on anhydrous sodium sulfide.

[0060] As another aspect of this invention, a product indicator system synergistically designed with ultra-low impurities and high structural stability is employed, primarily to enhance the electrical insulation performance and hydrolytic stability of polyphenylene sulfide (PPS) materials under long-term high-temperature use. This invention effectively removes inorganic salts, metal oxides, and other ash impurities from the product by controlling the ignition residue to an extremely low level of 0.05-0.25 wt%. These ash impurities easily migrate to the material surface during high-temperature use, forming conductive pathways and reducing electrical insulation performance. Therefore, a low ignition residue design is crucial for applications such as electronic packaging and insulating coatings. Simultaneously, the sodium ion content is controlled at 10-200 mg / kg, and the chloride ion content at 10-500 mg / kg, significantly lower than the ion residue levels of conventional PPS products. Sodium and chloride ions undergo hydrolytic reactions with the PPS molecular chains under high-temperature and high-humidity conditions, leading to molecular chain breakage and performance degradation. Therefore, the ultra-low ion residue design significantly improves the material's hydrolytic stability and long-term thermal aging performance. This invention also utilizes a high cross-linking design with a gel fraction of 92-99 wt%, enabling polyphenylene sulfide to maintain high heat resistance (melting point 270-300℃) while possessing excellent dimensional stability and creep resistance. The increased gel fraction signifies a stronger three-dimensional cross-linked network structure within the material. This structure is less prone to molecular chain slippage and deformation under high-temperature stress, making it particularly suitable for high-temperature structural components and precision parts. Furthermore, the design of a moisture content of 0.01-0.20 wt% and N-methyl-2-pyrrolidone residue not exceeding 1000 mg / kg avoids defects such as bubbles and silver streaks caused by residual moisture and solvent evaporation during processing, ensuring the appearance quality and mechanical properties of the injection-molded products. The particle size D50 is controlled within the range of 50-500 μm, resulting in good flowability and filling properties of the powder or granules during screw extrusion and injection molding, improving processing efficiency and product density.

[0061] As an in-depth analysis in the field of materials chemistry, the synergistic mechanism of the composite sulfur source intermediate and the end-group controllable oligomeric polyphenylene sulfide intermediate in this invention is reflected in the dual dimensions of reaction kinetic regulation and product structure optimization. The composite sulfur source intermediate focuses on stabilizing the sulfur source activity and improving the uniformity of the reaction system in the early stage of polymerization. By removing moisture interference through a pre-dehydration process, the nucleophilic substitution reaction activity of sulfur anions is kept consistent during the high-temperature polymerization stage, avoiding rapid cross-linking and gel particle formation caused by excessive local sulfur source concentration, thus providing a stable reaction window for the orderly growth of molecular chains. The end-group controllable oligomeric polyphenylene sulfide intermediate focuses on adjusting the molecular weight distribution and precisely controlling the gel fraction in the later stage of polymerization. Its number-average molecular weight range of 500-5000 g / mol is designed so that the oligomer has sufficient active end groups to participate in the chain growth reaction, without the reaction system viscosity increasing dramatically and mass transfer being hindered due to excessively high molecular weight. The synergistic effect of the two is reflected in the following aspects: the uniform reaction environment provided by the composite sulfur source intermediate creates conditions for the uniform dispersion of the end-group controllable oligomers and the full contact of the active end groups; while the end-group controllable oligomers, through quantitative addition in the prepolymerization or postpolymerization stages, achieve precise control over the length of the main chain polyphenylene sulfide molecular chain and the crosslinking density, ultimately resulting in a product that maintains high gel fraction structural stability while significantly improving melt flowability and processability. Currently, the optimal matching law between the viscosity window of the composite sulfur source intermediate and the molecular weight window of the end-group controllable oligomers, as well as the differential influence mechanism of their addition sequence at different polymerization stages on product performance, still require further systematic research.

[0062] Beneficial technical effects

[0063] 1. Significantly reduced product impurity content and improved long-term reliability: By using a composite sulfur source intermediate preconstruction technology to remove crystal water and adsorbed water from the sulfur source, combined with high-purity 1,4-dichlorobenzene monomer, precise dehydration process, acid treatment pH adjustment, and multiple washing with 60-100℃ high-temperature deionized water, the entire process of impurity control measures is implemented, achieving ultra-low impurity levels of 0.05-0.25wt% for polyphenylene sulfide (PPS) ignition residue, 10-200mg / kg for sodium ions, and 10-500mg / kg for chloride ions. Compared to the levels of 0.3-0.8wt% for PPS ignition residue, 500-2000mg / kg for sodium ions, and 1000-5000mg / kg for chloride ions in conventional PPS products, the impurity content is reduced by 60-90%. This significantly improves the electrical insulation performance, hydrolytic stability, and thermal aging performance of the material under high-temperature long-term use environments, making it particularly suitable for high-reliability applications sensitive to impurities, such as insulation components for new energy vehicle battery packs and high-frequency circuit boards for 5G communication base stations.

[0064] 2. Achieving a precise balance between gel fraction and processing performance: By introducing controllable end-group oligomeric polyphenylene sulfide intermediates with a number-average molecular weight of 500-5000 g / mol as molecular weight regulators, quantitative addition is made during the prepolymerization or postpolymerization stages. The condensation reaction between the active end groups of the oligomer and the main chain polyphenylene sulfide achieves dual control over the molecular weight distribution and crosslinking density of the product. This allows the polyphenylene sulfide to maintain high structural stability with a gel fraction of 92-99 wt%, while significantly improving melt flowability and injection molding processing performance. This solves the processing defects of traditional high gel fraction polyphenylene sulfide, such as low melt flow rate, difficult injection filling, and silver streaks on the surface of the product caused by the excessively dense three-dimensional crosslinking network. This broadens the application range of high-performance polyphenylene sulfide in the injection molding of complex and precision parts.

[0065] 3. Enhancing the stability and scale-up controllability of the polymerization process: By designing a viscosity window of 100-50000 mPa·s for the composite sulfur source intermediate at 25℃, the dispersion uniformity of the sulfur source in the reaction system is significantly improved. This avoids the problems of gel particle formation and reactor wall coking caused by local overconcentration in the early stage of high-temperature polymerization of traditional solid sulfur sources. Combined with precise dehydration at 180-200℃ to control the moisture content of the reaction system within a narrow window of 0.05-0.50 wt%, and the temperature gradient design of prepolymerization at 220-240℃ and postpolymerization at 260-280℃, the polymerization reaction achieves a balance between high conversion rate and low by-product formation under the dual drive of kinetics and thermodynamics. This significantly reduces batch-to-batch product performance fluctuations and improves the stability and controllability of industrial scale-up production.

[0066] 4. Effective control of residual solvent content and improvement of product appearance quality: By optimizing the solid-liquid separation efficiency, the number of high-temperature washing cycles at 60-100℃, and vacuum drying conditions in the post-processing, the residual N-methyl-2-pyrrolidone content in polyphenylene sulfide products is controlled at a low level of no more than 1000 mg / kg, which is 50-75% lower than the 2000-5000 mg / kg residual level of conventional products. At the same time, the moisture content is controlled at 0.01-0.20 wt%, effectively avoiding appearance defects such as bubbles, silver streaks, and surface spots caused by high-temperature evaporation of residual solvents and moisture during injection molding. This improves the appearance quality, dimensional accuracy, and mechanical properties of injection molded products, making them particularly suitable for applications with strict surface quality requirements, such as automotive exterior parts and electronic product housings.

[0067] 5. Expanding the application adaptability of product form and particle size: By controlling the polymerization process parameters and post-processing conditions, polyphenylene sulfide products can be obtained in powder or granular form, with a particle size D50 range of 50-500μm, covering a wide particle size distribution from fine powder to coarse particles. The fine powder form is suitable for high-precision injection molding and thin-walled products, while the coarse particle form is suitable for large extrusions and filler modification. At the same time, the controllability of particle size distribution enables the product to have good flowability, filling properties and density during screw extrusion and injection molding, improving processing efficiency and product mechanical properties, and expanding the adaptability of polyphenylene sulfide materials in different processing technologies and application scenarios. Attached Figure Description

[0068] Figure 1 This is a comparison diagram of X-ray diffraction (XRD) of Example 1 and Comparative Example 4 of the present invention.

[0069] Figure 2 This is a comparison chart of the thermogravimetric analysis (TGA) curves of Embodiment 1, Comparative Example 4, and Comparative Example 8 of the present invention.

[0070] Figure 3 This is a comparison diagram of the molecular weight distribution of GPC in Examples 1, 5, and 6 of the present invention, obtained by gel permeation chromatography.

[0071] Figure 4 This is a comparison chart of the differential scanning calorimetry (DSC) curves of Embodiment 1, Comparative Example 5, and Comparative Example 6 of the present invention.

[0072] Figure 5 This is a comparison chart of the total ion current (TIC) of gas chromatography-mass spectrometry (GC-MS) for Examples 1, 1, and 2 of the present invention. Detailed Implementation

[0073] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings.

[0074] Example 1

[0075] Step S1: Prepare the reaction system

[0076] In a 100L sealed pressure-resistant reactor, under nitrogen protection and mechanical stirring, 45kg of N-methyl-2-pyrrolidone and 10.8kg of sodium sulfide nonahydrate (equivalent to 5.5kg of anhydrous sodium sulfide, containing 2.27mol of sulfur) were added sequentially. Then, a pre-prepared composite sulfur source intermediate was added.

[0077] The composite sulfur source intermediate in this embodiment is prepared through the following steps:

[0078] Step B1: Raw material preparation

[0079] Add 22 kg of N-methyl-2-pyrrolidone, 5.4 kg of sodium sulfide nonahydrate (equivalent to 2.75 kg of anhydrous sodium sulfide, containing 1.14 mol of sulfur), 68 g of lithium chloride (molar ratio to sodium sulfide of 0.10:1), and 138 g of sodium thiosulfate pentahydrate (equivalent to 88 g of anhydrous sodium thiosulfate, mass ratio to sodium sulfide of 0.03:1) to a 50 L reaction vessel. Mix thoroughly under nitrogen protection and stirring.

[0080] Step B2: Dehydration and Compounding

[0081] The mixture was heated to 190°C under nitrogen protection and dehydrated by distillation. The temperature was maintained under stirring until the moisture content of the system was determined to be 0.25 wt% by Karl Fischer moisture determination, thus obtaining the composite sulfur source intermediate.

[0082] Step B3: Quality Control

[0083] The apparent viscosity of the composite sulfur source intermediate in this embodiment was measured to be 8500 mPa·s at 25°C (using a rotational viscometer at a shear rate of 10 s⁻¹). -1 (Measured at 25℃).

[0084] Step S2: Dehydration

[0085] The reaction system was heated to 190°C under nitrogen protection and dehydrated by distillation. This temperature was maintained under stirring until the water content of the reaction system was determined to be 0.25 wt% by Karl Fischer moisture determination. After dehydration, the reaction system was shut down and transferred to a closed, pressure-resistant state.

[0086] Step S3: Aggregation

[0087] 6.68 kg of 1,4-dichlorobenzene with a purity of 99.75 wt% (molar ratio of 1.01:1 to the total sulfur in the sulfur source) was added to the reaction system, and segmental polymerization was carried out under mechanical stirring. Prepolymerization was first performed at 230 °C and held for 3.0 h, followed by post-polymerization at 270 °C with a heating rate of 2.5 °C / min, and held for 5.0 h.

[0088] Step S4: Intermediate addition and post-processing

[0089] When the post-polymerization stage has been carried out for 2.5 hours, 150 g of the pre-prepared end-group controllable oligomeric polyphenylene sulfide intermediate (with a molar ratio of 0.020:1 to the total sulfur in the sulfur source) is directly added to the reaction system.

[0090] The end-group controllable oligomeric polyphenylene sulfide intermediate in this embodiment is prepared through the following steps:

[0091] Step A1: Raw material preparation

[0092] 880 g of 1,4-dichlorobenzene, 540 g of sodium sulfide nonahydrate (equivalent to 275 g of anhydrous sodium sulfide, containing 0.114 mol of sulfur), and 2.2 kg of N-methyl-2-pyrrolidone were mixed (the molar ratio of 1,4-dichlorobenzene to the total sulfur in the sulfur source was 1.18:1, and the molar ratio of N-methyl-2-pyrrolidone to the total sulfur in the sulfur source was 4.5:1). The raw materials were mixed under nitrogen protection and stirring.

[0093] Step A2: Oligopolymerization

[0094] The reaction was heated to 220℃ under nitrogen protection and maintained at that temperature. Samples were taken every 20 minutes during the reaction, and the number-average molecular weight of the product was determined by gel permeation chromatography (test conditions: solvent 1-chloronaphthalene, column temperature 200℃, flow rate 1.0 mL / min, with polystyrene as the calibration standard).

[0095] Step A3: Endpoint Criterion

[0096] The reaction was terminated and the temperature was lowered when the number-average molecular weight of the product reached 2500 g / mol. The total reaction time was 1.0 h.

[0097] Step A4: Post-processing

[0098] 11 kg of deionized water (5 times the volume of the reaction solution) was added to the reaction solution to induce precipitation. Precipitation was achieved by cooling to room temperature and stirring for 30 min. After solid-liquid separation, the mixture was washed three times with deionized water at 80 °C (30 min each time), and then dried at 100 °C and 3 kPa vacuum for 6 h to obtain the end-group controllable oligomeric polyphenylene sulfide intermediate.

[0099] After polymerization, acetic acid was added to the slurry to adjust the pH value, so that the pH of the filtrate obtained after solid-liquid separation of the acid-treated slurry was 8.0 as measured at 25℃. Solid-liquid separation was then performed by centrifugation (relative centrifugal force 3000g, centrifugation time 15min). The filtrate was washed four times with deionized water at 80℃ (solid-liquid mass ratio 1:7, each wash time 30min), with the washing endpoint criterion being a washing solution pH of 7.0 and a conductivity below 50μS / cm. Finally, the filtrate was dried at 110℃ and a vacuum of 3kPa for 12h (drying endpoint criterion being a product water content not exceeding 0.2wt%) to obtain polyphenylene sulfide.

[0100] Product performance indicators

[0101] The polyphenylene sulfide prepared in this embodiment is in powder form and has the following performance indicators after testing: ignition residue 0.15 wt% (determined by ignition to constant weight at 550±25℃ in air atmosphere according to GB / T9345.1-2008 standard); sodium ion content 105 mg / kg (determined by ion chromatography); chloride ion content 255 mg / kg (determined by ion chromatography); moisture content 0.10 wt% (determined by Karl Fischer moisture determination method); melting point 285°C. Temperature (℃) was determined by differential scanning calorimetry under nitrogen atmosphere at a heating rate of 10℃ / min; gel fraction was 95.5 wt% (obtained by Soxhlet extraction with 1-chloronaphthalene as solvent at 200℃ for 6 h, and the residue was vacuum dried to constant weight); particle size D50 was 275 μm (determined by laser particle size analyzer); N-methyl-2-pyrrolidone residue content was 550 mg / kg (determined by gas chromatography, detection limit 1 mg / kg).

[0102] Features of the Implementation Examples

[0103] This embodiment employs a moderate combination of process parameters: a dehydration temperature of 190℃ and a moisture content of 0.25wt% (mid-range); prepolymerization temperatures of 230℃ and post-polymerization temperatures of 270℃ (moderate temperature conditions); a 1,4-dichlorobenzene purity of 99.75wt% (moderate purity); the selection of sodium sulfide nonahydrate as the sulfur source, with the addition of appropriate amounts of lithium chloride and sodium thiosulfate to optimize reaction performance; a controllable end-group oligomer number-average molecular weight of 2500 g / mol (moderate level); and a washing temperature of 80℃ and 4 washing cycles (moderate conditions). This parameter combination demonstrates good process stability, a wide operating window, and high reproducibility, making it suitable for the large-scale, stable production of polyphenylene sulfide (PPS), particularly for applications in automotive parts and electronic components where high product quality consistency is required.

[0104] Example 2

[0105] Step S1: Prepare the reaction system

[0106] In a 100L sealed pressure-resistant reactor, under nitrogen protection and mechanical stirring, 52kg of N-methyl-2-pyrrolidone and 5.2kg of anhydrous sodium sulfide (containing 2.14mol of sulfur) were added sequentially. Subsequently, a pre-prepared composite sulfur source intermediate was added.

[0107] The composite sulfur source intermediate in this embodiment is prepared through the following steps:

[0108] Step B1: Raw material preparation

[0109] Add 26 kg of N-methyl-2-pyrrolidone, 2.6 kg of anhydrous sodium sulfide (containing 1.07 mol of sulfur), 90 g of lithium chloride (molar ratio to sodium sulfide of 0.15:1), and 195 g of sodium thiosulfate pentahydrate (equivalent to 124 g of anhydrous sodium thiosulfate, mass ratio to sodium sulfide of 0.05:1) to a 50 L reaction vessel. Mix thoroughly under nitrogen protection and stirring.

[0110] Step B2: Dehydration and Compounding

[0111] The mixture was heated to 195°C under nitrogen protection and dehydrated by distillation. The temperature was maintained under stirring until the moisture content of the system was determined to be 0.15 wt% by Karl Fischer moisture determination, thus obtaining the composite sulfur source intermediate.

[0112] Step B3: Quality Control

[0113] The apparent viscosity of the composite sulfur source intermediate in this embodiment was measured to be 22000 mPa·s at 25°C (using a rotational viscometer at a shear rate of 10 s⁻¹). -1 (Measured at 25℃).

[0114] Step S2: Dehydration

[0115] The reaction system was heated to 195°C under nitrogen protection and dehydrated by distillation. This temperature was maintained under stirring until the water content of the reaction system was determined to be 0.15 wt% by Karl Fischer moisture determination. After dehydration, the reaction system was shut off and transferred to a closed, pressure-resistant state.

[0116] Step S3: Aggregation

[0117] 6.60 kg of 1,4-dichlorobenzene with a purity of 99.90 wt% (molar ratio of 1.03:1 to the total sulfur in the sulfur source) was added to the reaction system, and segmental polymerization was carried out under mechanical stirring. Prepolymerization was first performed at 235 °C and held for 2.0 h, followed by post-polymerization at a heating rate of 3.5 °C / min to 275 °C and held for 6.5 h.

[0118] Step S4: Intermediate addition and post-processing

[0119] When the post-polymerization stage has been carried out for 3.0 hours, 230 g of the pre-prepared end-group controllable oligomeric polyphenylene sulfide intermediate (with a molar ratio of 0.035:1 to the total sulfur in the sulfur source) is directly added to the reaction system.

[0120] The end-group controllable oligomeric polyphenylene sulfide intermediate in this embodiment is prepared through the following steps:

[0121] Step A1: Raw material preparation

[0122] 920 g of 1,4-dichlorobenzene, 265 g of anhydrous sodium sulfide (containing 0.109 mol of sulfur), and 2.6 kg of N-methyl-2-pyrrolidone were mixed (the molar ratio of 1,4-dichlorobenzene to the total sulfur in the sulfur source was 1.25:1, and the molar ratio of N-methyl-2-pyrrolidone to the total sulfur in the sulfur source was 5.5:1). The raw materials were mixed under nitrogen protection and stirring.

[0123] Step A2: Oligopolymerization

[0124] The reaction was heated to 230℃ under nitrogen protection and maintained at that temperature. Samples were taken every 15 minutes during the reaction, and the number-average molecular weight of the product was determined by gel permeation chromatography (test conditions: solvent 1-chloronaphthalene, column temperature 200℃, flow rate 1.0 mL / min, with polystyrene as the calibration standard).

[0125] Step A3: Endpoint Criterion

[0126] The reaction was terminated and the temperature was lowered when the number-average molecular weight of the product reached 3800 g / mol. The total reaction time was 1.4 h.

[0127] Step A4: Post-processing

[0128] 18 kg of deionized water (8 times the volume of the reaction solution) was added to the reaction solution to induce precipitation. Precipitation was achieved by cooling to room temperature and stirring for 45 min. After solid-liquid separation, the mixture was washed four times with deionized water at 90 °C (40 min each time), and then dried at 110 °C and 2 kPa for 8 h to obtain the end-group controllable oligomeric polyphenylene sulfide intermediate.

[0129] After polymerization, hydrochloric acid was added to the slurry to adjust the pH value, so that the pH of the filtrate obtained after solid-liquid separation of the acid-treated slurry was 7.5 as measured at 25℃. Solid-liquid separation was then performed by centrifugation (relative centrifugal force 4000g, centrifugation time 20min). The filtrate was washed five times with deionized water at 90℃ (solid-liquid mass ratio 1:8, each wash time 40min), with the washing endpoint criterion being a washing solution pH of 7.0 and a conductivity below 50μS / cm. Finally, the filtrate was dried at 120℃ and a vacuum of 2kPa for 15h (drying endpoint criterion being a difference of less than 0.1% between two consecutive weighings) to obtain polyphenylene sulfide.

[0130] Product performance indicators

[0131] The polyphenylene sulfide prepared in this embodiment is in powder form and has the following performance indicators after testing: ignition residue 0.10 wt% (determined by ignition to constant weight at 550±25℃ in air atmosphere according to GB / T9345.1-2008 standard); sodium ion content 55 mg / kg (determined by inductively coupled plasma atomic emission spectrometry); chloride ion content 180 mg / kg (determined by ion chromatography); moisture content 0.05 wt% (determined by Karl Fischer moisture determination method); melt... The temperature was 292℃ (determined by differential scanning calorimetry under nitrogen atmosphere at a heating rate of 10℃ / min); the gel fraction was 97.0 wt% (obtained by Soxhlet extraction with 1-chloronaphthalene as solvent at 200℃ for 6 h, and the residue was vacuum dried to constant weight); the particle size D50 was 180 μm (determined by laser particle size analyzer); the N-methyl-2-pyrrolidone residue content was 320 mg / kg (determined by gas chromatography, detection limit 1 mg / kg).

[0132] Features of the Implementation Examples

[0133] This embodiment employs a high-performance optimized combination of process parameters. A 1,4-dichlorobenzene purity of 99.90 wt% represents a high purity; a dehydration temperature of 195°C and a moisture content of 0.15 wt% represent high temperature and low moisture conditions; a pre-polymerization temperature of 235°C and a post-polymerization temperature of 275°C represent high temperature conditions; anhydrous sodium sulfide is selected as the sulfur source, supplemented with a high proportion of lithium chloride and sodium thiosulfate additives to enhance reaction activity; a controllable end-group oligomer number-average molecular weight of 3800 g / mol represents a high level, and a relatively large amount is added; and a washing temperature of 90°C and 5 washing cycles represent high conditions. This parameter combination is beneficial for obtaining polyphenylene sulfide products with high molecular weight, low impurity content, and high crystallinity. The prepared polyphenylene sulfide exhibits excellent mechanical properties, thermal stability, and chemical stability, making it suitable for high-performance applications with stringent material performance requirements, such as aerospace, high-end electronic devices, and corrosion-resistant chemical equipment.

[0134] Example 3

[0135] Step S1: Prepare the reaction system

[0136] In a 100L sealed pressure-resistant reactor, under nitrogen protection and mechanical stirring, 38kg of N-methyl-2-pyrrolidone, 2.9kg of sodium hydrogen sulfide (containing 1.67mol of sulfur), and 1.16kg of sodium hydroxide (molar ratio of 1:1 with sodium hydrogen sulfide) were added sequentially. A pre-prepared composite sulfur source intermediate was then added.

[0137] The composite sulfur source intermediate in this embodiment is prepared through the following steps:

[0138] Step B1: Raw material preparation

[0139] 19 kg of N-methyl-2-pyrrolidone and 3.6 kg of sodium sulfide nonahydrate (equivalent to 1.83 kg of anhydrous sodium sulfide, containing 0.76 mol of sulfur) were added to a 50 L reaction vessel. The mixture was thoroughly mixed under nitrogen protection and stirring. Lithium chloride and sodium thiosulfate were not added in this example.

[0140] Step B2: Dehydration and Compounding

[0141] The mixture was heated to 185°C under nitrogen protection and dehydrated by distillation. The temperature was maintained under stirring until the moisture content of the system was determined to be 0.35 wt% by Karl Fischer moisture determination, thus obtaining the composite sulfur source intermediate.

[0142] Step B3: Quality Control

[0143] The apparent viscosity of the composite sulfur source intermediate in this embodiment was measured to be 3200 mPa·s at 25°C (using a rotational viscometer at a shear rate of 10 s⁻¹). -1 (Measured at 25℃).

[0144] Step S2: Dehydration

[0145] The reaction system was heated to 185°C under nitrogen protection and dehydrated by distillation. This temperature was maintained under stirring until the water content of the reaction system was determined to be 0.35 wt% using the Karl Fischer moisture assay. After dehydration, the reaction system was shut down and placed in a sealed, pressure-resistant environment.

[0146] Step S3: Aggregation

[0147] 6.50 kg of 99.60 wt% 1,4-dichlorobenzene (molar ratio of 1.00:1 to the total sulfur in the sulfur source) was added to the reaction system, and segmental polymerization was carried out under mechanical stirring. Prepolymerization was first performed at 225 °C and held for 4.5 h, followed by post-polymerization at 265 °C with a heating rate of 1.5 °C / min, and held for 8.0 h.

[0148] Step S4: Intermediate addition and post-processing

[0149] When the prepolymerization stage has been carried out for 2.0 h, 90 g of the pre-prepared end-group controllable oligomeric polyphenylene sulfide intermediate (with a molar ratio of 0.008:1 to the total sulfur in the sulfur source) is directly added to the reaction system.

[0150] The end-group controllable oligomeric polyphenylene sulfide intermediate in this embodiment is prepared through the following steps:

[0151] Step A1: Raw material preparation

[0152] 810 g of 1,4-dichlorobenzene, 450 g of sodium sulfide nonahydrate (equivalent to 230 g of anhydrous sodium sulfide, containing 0.095 mol of sulfur), and 1.5 kg of N-methyl-2-pyrrolidone were mixed (the molar ratio of 1,4-dichlorobenzene to the total sulfur in the sulfur source was 1.10:1, and the molar ratio of N-methyl-2-pyrrolidone to the total sulfur in the sulfur source was 3.7:1). The raw materials were mixed under nitrogen protection and stirring.

[0153] Step A2: Oligopolymerization

[0154] The reaction was heated to 210℃ under nitrogen protection and maintained at that temperature. Samples were taken every 25 min during the reaction, and the number-average molecular weight of the product was determined by gel permeation chromatography (test conditions: solvent 1-chloronaphthalene, column temperature 200℃, flow rate 1.0 mL / min, with polystyrene as the calibration standard).

[0155] Step A3: Endpoint Criterion

[0156] The reaction was terminated and the temperature was lowered when the number-average molecular weight of the product reached 1500 g / mol. The total reaction time was 0.6 h.

[0157] Step A4: Post-processing

[0158] Add 6 kg of deionized water (3 times the volume of the reaction solution) to the reaction solution to induce precipitation. Precipitation was achieved by cooling to room temperature and stirring for 20 min. After solid-liquid separation, the mixture was washed twice with deionized water at 70 °C (20 min each time), and then dried at 90 °C and 4 kPa vacuum for 4 h to obtain the end-group controllable oligomeric polyphenylene sulfide intermediate.

[0159] After polymerization, acetic acid was added to the slurry to adjust the pH value, so that the pH of the filtrate obtained after solid-liquid separation of the acid-treated slurry was 8.8 as measured at 25°C. Solid-liquid separation was then performed by filtration (using filter media with a pore size of 5 μm). The slurry was washed three times with deionized water at 70°C (solid-liquid mass ratio 1:6, each washing time 20 min). The washing endpoint was determined by a pH of 7.0 and a conductivity below 50 μS / cm in the washing solution. Finally, the slurry was dried at 95°C and a vacuum of 4 kPa for 8 h (drying endpoint determined by a product moisture content not exceeding 0.2 wt%) to obtain polyphenylene sulfide.

[0160] Product performance indicators

[0161] The polyphenylene sulfide prepared in this embodiment is in granular form and has the following performance indicators after testing: ignition residue 0.18 wt% (determined by ignition to constant weight at 550±25℃ in air atmosphere according to GB / T9345.1-2008 standard); sodium ion content 135 mg / kg (determined by ion chromatography); chloride ion content 320 mg / kg (determined by ion chromatography); moisture content 0.14 wt% (determined by Karl Fischer moisture determination method); melting point 280°C. Temperature (℃) was determined by differential scanning calorimetry under nitrogen atmosphere at a heating rate of 10℃ / min; gel fraction was 94.0 wt% (obtained by Soxhlet extraction with 1-chloronaphthalene as solvent at 200℃ for 6 h, and the residue was vacuum dried to constant weight); particle size D50 was 380 μm (determined by laser particle size analyzer); N-methyl-2-pyrrolidone residue content was 720 mg / kg (determined by gas chromatography, detection limit 1 mg / kg).

[0162] Features of the Implementation Examples

[0163] This embodiment employs a combination of low-temperature conditions and economical process parameters. The sulfur source is a combination of sodium hydrosulfide and sodium hydroxide. A dehydration temperature of 185℃ and a moisture content of 0.35wt% represent relatively low temperature and high moisture conditions. A prepolymerization temperature of 225℃ and a post-polymerization temperature of 265℃ represent relatively low temperature conditions. A 1,4-dichlorobenzene purity of 99.60wt% represents a moderate purity. Lithium chloride and sodium thiosulfate are not added to reduce costs. A controllable end-group oligomer number-average molecular weight of 1500 g / mol represents a relatively low level, and the amount added is small. A longer prepolymerization time compensates for the low temperature. A washing temperature of 70℃ and three washing cycles represent relatively low conditions. This parameter combination process has low energy consumption and significant cost advantages, while ensuring product quality meets application requirements. It is suitable for large-scale applications in cost-sensitive industrial polyphenylene sulfide products, general-purpose engineering plastic parts, and conventional electrical insulation materials.

[0164] Example 4

[0165] Step S1: Prepare the reaction system

[0166] In a 100L sealed pressure-resistant reactor, under nitrogen protection and mechanical stirring, 48kg of N-methyl-2-pyrrolidone and 5.0kg of anhydrous sodium sulfide (containing 2.05mol of sulfur) were added sequentially. Subsequently, a pre-prepared composite sulfur source intermediate was added.

[0167] The composite sulfur source intermediate in this embodiment is prepared through the following steps:

[0168] Step B1: Raw material preparation

[0169] Add 24 kg of N-methyl-2-pyrrolidone, 2.5 kg of anhydrous sodium sulfide (containing 1.03 mol of sulfur), 87 g of lithium chloride (molar ratio to sodium sulfide of 0.12:1), and 156 g of sodium thiosulfate pentahydrate (equivalent to 100 g of anhydrous sodium thiosulfate, mass ratio to sodium sulfide of 0.04:1) to a 50 L reaction vessel. Mix thoroughly under nitrogen protection and stirring.

[0170] Step B2: Dehydration and Compounding

[0171] The mixture was heated to 198°C under nitrogen protection and dehydrated by distillation. The temperature was maintained under stirring until the moisture content of the system was determined to be 0.08 wt% by Karl Fischer moisture determination, thus obtaining the composite sulfur source intermediate.

[0172] Step B3: Quality Control

[0173] The apparent viscosity of the composite sulfur source intermediate in this embodiment was measured to be 38000 mPa·s at 25°C (using a rotational viscometer at a shear rate of 10 s⁻¹). -1 (Measured at 25℃).

[0174] Step S2: Dehydration

[0175] The reaction system was heated to 198°C under nitrogen protection and dehydrated by distillation. This temperature was maintained under stirring until the water content of the reaction system was determined to be 0.08 wt% by Karl Fischer moisture determination. After dehydration, the reaction system was shut down and transferred to a closed, pressure-resistant state.

[0176] Step S3: Aggregation

[0177] 6.55 kg of 1,4-dichlorobenzene with a purity of 99.96 wt% (molar ratio of 1.04:1 to the total sulfur in the sulfur source) was added to the reaction system, and segmental polymerization was carried out under mechanical stirring. Prepolymerization was first performed at 238 °C and held for 1.2 h, followed by post-polymerization at 278 °C with a heating rate of 4.2 °C / min, and held for 3.5 h.

[0178] Step S4: Intermediate addition and post-processing

[0179] When the post-polymerization stage has been carried out for 1.5 hours, 180 g of the pre-prepared end-group controllable oligomeric polyphenylene sulfide intermediate (with a molar ratio of 0.025:1 to the total sulfur in the sulfur source) is directly added to the reaction system.

[0180] The end-group controllable oligomeric polyphenylene sulfide intermediate in this embodiment is prepared through the following steps:

[0181] Step A1: Raw material preparation

[0182] 850 g of 1,4-dichlorobenzene, 480 g of sodium sulfide nonahydrate (equivalent to 245 g of anhydrous sodium sulfide, containing 0.101 mol of sulfur), and 2.0 kg of N-methyl-2-pyrrolidone were mixed (the molar ratio of 1,4-dichlorobenzene to the total sulfur in the sulfur source was 1.15:1, and the molar ratio of N-methyl-2-pyrrolidone to the total sulfur in the sulfur source was 4.6:1). The raw materials were mixed under nitrogen protection and stirring.

[0183] Step A2: Oligopolymerization

[0184] The reaction was heated to 235℃ under nitrogen protection and maintained at this temperature. Samples were taken every 18 minutes during the reaction, and the number-average molecular weight of the product was determined by gel permeation chromatography (test conditions: solvent 1-chloronaphthalene, column temperature 200℃, flow rate 1.0 mL / min, with polystyrene as the calibration standard).

[0185] Step A3: Endpoint Criterion

[0186] The reaction was terminated and the temperature was lowered when the number-average molecular weight of the product reached 4300 g / mol. The total reaction time was 1.7 h.

[0187] Step A4: Post-processing

[0188] 14 kg of deionized water (6 times the volume of the reaction solution) was added to the reaction solution to induce precipitation. Precipitation was achieved by cooling to room temperature and stirring for 35 min. After solid-liquid separation, the mixture was washed five times with deionized water at 85 °C (35 min each time), and then dried at 105 °C and a vacuum of 2.5 kPa for 7 h to obtain the end-group controllable oligomeric polyphenylene sulfide intermediate.

[0189] After polymerization, acetic acid was added to the slurry to adjust the pH value, so that the pH of the filtrate obtained after solid-liquid separation of the acid-treated slurry was 7.2 at 25°C. Solid-liquid separation was then performed by centrifugation (relative centrifugal force 4500g, centrifugation time 22min). The filtrate was washed six times with deionized water at 95°C (solid-liquid mass ratio 1:9, each wash time 50min), with the washing endpoint criterion being a washing solution pH of 6.5 and a conductivity below 50μS / cm. Finally, the filtrate was dried at 135°C and a vacuum of 1.5kPa for 18h (drying endpoint criterion being a difference of less than 0.1% between two consecutive weighings) to obtain polyphenylene sulfide.

[0190] Product performance indicators

[0191] The polyphenylene sulfide prepared in this embodiment is in powder form and has the following performance indicators after testing: ignition residue 0.08 wt% (determined by ignition to constant weight at 550±25℃ in air atmosphere according to GB / T9345.1-2008 standard); sodium ion content 28 mg / kg (determined by inductively coupled plasma atomic emission spectrometry); chloride ion content 95 mg / kg (determined by ion chromatography); moisture content 0.03 wt% (determined by Karl Fischer moisture determination method); melting point... 296℃ (determined by differential scanning calorimetry under nitrogen atmosphere at a heating rate of 10℃ / min); gel fraction 98.0wt% (obtained by Soxhlet extraction with 1-chloronaphthalene as solvent at 200℃ for 6 h, and the residue was vacuum dried to constant weight); particle size D50 120μm (determined by laser particle size analyzer); N-methyl-2-pyrrolidone residue 150mg / kg (determined by gas chromatography, detection limit 1mg / kg).

[0192] Features of the Implementation Examples

[0193] This embodiment uses a parameter combination close to the upper limit of the process range. The purity of 1,4-dichlorobenzene is 99.96wt%, which is close to the upper limit of purity. The dehydration temperature is 198℃, which is close to the upper limit of temperature. The prepolymerization temperature is 238℃ and the postpolymerization temperature is 278℃, which are both close to the upper limit of temperature. At the same time, the moisture content is 0.08wt%, which is close to the lower limit. The number average molecular weight of the controllable end-group oligomers is 4300g / mol, which is close to the upper limit of molecular weight. The number of washing cycles is 6, which is the upper limit of the range. The washing temperature is 95℃ and the drying temperature is 135℃, which are both close to the upper limit. This parameter combination, through high-purity raw materials, high-temperature conditions, low moisture control, and thorough washing and drying, can produce polyphenylene sulfide products with extremely high purity, ultra-low impurity content, high crystallinity, and excellent thermal stability. The ignition residue is 0.08 wt%, sodium ions are 28 mg / kg, chloride ions are 95 mg / kg, and N-methyl-2-pyrrolidone residue is 150 mg / kg, all reaching extremely low levels. The gel fraction of 98.0 wt% and melting point of 296℃ are at high levels, making it particularly suitable for ultra-high-end special applications such as semiconductor manufacturing equipment parts, medical implants, and ultra-high performance composite matrix resins, where the purity and performance requirements of materials are extremely stringent.

[0194] Comparative Example 1: Basically the same as Example 1, except that the purity of 1,4-dichlorobenzene is 99.2 wt%, and the amounts of other components and preparation conditions remain unchanged.

[0195] Comparative Example 2: It is basically the same as Example 1, except that the water content of the reaction system after dehydration is 0.65 wt%, while the amount of other components and preparation conditions remain unchanged.

[0196] Comparative Example 3: It is basically the same as Example 1, except that the post-polymerization temperature is 255°C, while the amount of other components and preparation conditions remain unchanged.

[0197] Comparative Example 4: It is basically the same as Example 1, except that no composite sulfur source intermediate is added. Instead, 10.8 kg of sodium sulfide nonahydrate and 67 kg of N-methyl-2-pyrrolidone are mixed and then dehydrated to a moisture content of 0.25 wt%. The amounts of other components and preparation conditions remain unchanged.

[0198] Comparative Example 5: It is basically the same as Example 1, except that no end-group controllable oligomeric polyphenylene sulfide intermediate is added, while the amount of other components and preparation conditions remain unchanged.

[0199] Comparative Example 6: It is basically the same as Example 1, except that the number average molecular weight of the end-group controllable oligomeric polyphenylene sulfide intermediate is 350 g / mol (preparation conditions: reaction at 200°C for 0.15 h until the number average molecular weight reaches 350 g / mol), and the amounts of other components and preparation conditions remain unchanged.

[0200] Comparative Example 7: It is basically the same as Example 1, except that lithium chloride and sodium thiosulfate are not added when preparing the composite sulfur source intermediate. Only 5.4 kg of sodium sulfide nonahydrate and 22 kg of N-methyl-2-pyrrolidone are mixed and dehydrated to a moisture content of 0.25 wt%. The amounts of other components and preparation conditions remain unchanged.

[0201] Comparative Example 8: It is basically the same as Example 1, except that after polymerization, acid treatment is not performed, and solid-liquid separation and washing are performed directly. The number of washing times is reduced to 2, while the amount of other components and preparation conditions remain unchanged.

[0202] Performance testing:

[0203] Experiment 1: Melting Point Test

[0204] Test Subject: Polyphenylene sulfide (PPS) sample. Test Objective: To evaluate the crystallinity and thermal stability of PPS and verify the influence of segmented polymerization on the crystallization behavior of the product. Test Principle: Differential scanning calorimetry (DSC) measures the heat flow change of the sample during heating. An endothermic peak appears during the melt phase transition, and the peak temperature corresponds to the melting point, reflecting the degree of crystallinity and chain segment regularity of the material. Experimental Method: Weigh 5-10 mg of PPS sample and place it in an aluminum crucible. Under nitrogen protection, heat from 50°C to 350°C at a rate of 10°C / min. Record the DSC curve and read the melting peak temperature. Key Parameters: Nitrogen flow rate 50 mL / min, heating rate 10°C / min, sample mass 5-10 mg. Data Processing: The peak temperature of the endothermic melting peak is taken as the melting point. Perform three parallel tests and take the average value. The standard deviation should be less than 2°C.

[0205] Experiment 2: Gel fraction test

[0206] Test Subject: Polyphenylene sulfide (PPS) sample. Test Objective: To evaluate the degree of crosslinking and network structure integrity of PPS, and to verify the regulatory effect of end-group controllable oligomers on molecular chain extension and branching. Test Principle: Soxhlet extraction is used to extract soluble low molecular weight components through long-term reflux with a high-temperature solvent. The mass fraction of the insoluble residue reflects the crosslinking network density. Experimental Method: Accurately weigh 1.0 g of dried PPS sample and place it in a filter paper tube. Soxhlet extraction is performed at 200℃ for 6 hours using 1-chloronaphthalene as the solvent. The residue after extraction is dried to constant weight in a vacuum drying oven at 120℃ and then weighed. Key Parameters: Extraction temperature 200℃, extraction time 6 h, drying temperature 120℃, vacuum degree less than 5 kPa. Data Processing: Gel fraction (wt%) = (mass of dried residue after extraction / initial sample mass) × 100%. Trial tests were performed, and the average value ± standard deviation was taken.

[0207] Experiment 3: Burning Residue Test

[0208] Test Subject: Polyphenylene sulfide (PPS) sample. Test Objective: To evaluate the total content of inorganic salts and ash in PPS and verify the synergistic effect of the composite sulfur source intermediate and the rigorous washing process on impurity removal. Test Principle: PPS completely combusts and decomposes into volatile gases in a high-temperature air atmosphere. The mass fraction of residual inorganic oxides reflects the content of inorganic impurities. Experimental Method: Accurately weigh 2-5g of PPS sample and place it in a pre-weighed porcelain crucible. Ignite the sample in a muffle furnace at 550±25℃ in air atmosphere until constant weight is reached (the difference between two weighings is less than 0.0005g). After cooling, weigh the residue. Key Parameters: Ignition temperature 550±25℃, constant weight criterion is mass change <0.0005g, sample mass 2-5g. Data Processing: Ignition residue (wt%) = (residue mass / initial sample mass) × 100%, three parallel tests are performed, and the average ± standard deviation is taken.

[0209] Experiment 4: Sodium ion content test

[0210] Test Subject: Polyphenylene sulfide (PPS) sample. Test Objective: To quantitatively evaluate the residual sodium ion content in PPS and verify the deep purification effect of acid treatment and multiple washing on the removal of alkali metal ions. Test Principle: Ion chromatography is used to separate sodium ions in the sample digestion solution via a cation exchange column, and the concentration is quantitatively determined using a conductivity detector. Experimental Method: Accurately weigh 0.5 g of PPS sample, add 10 mL of ultrapure water and 0.5 mL of nitric acid, digest at 180℃ for 30 minutes in a microwave digester, cool, and bring the volume to 50 mL. Filter through a 0.22 μm filter membrane for ion chromatography analysis. Key Parameters: Digestion temperature 180℃, digestion time 30 min, eluent: methanesulfonic acid solution, flow rate 1.0 mL / min. Data Processing: Calculate the sodium ion concentration according to the standard curve and convert it to mg / kg. Perform three parallel tests and take the average ± standard deviation. The detection limit should be less than 1 mg / kg.

[0211] Experiment 5: Chloride Ion Content Test

[0212] Test Subject: Polyphenylene sulfide (PPS) sample. Test Objective: To quantitatively evaluate the residual chloride ion content in PPS and verify the effectiveness of a rigorous washing process in removing residual 1,4-dichlorobenzene monomer and reaction byproducts. Test Principle: Ion chromatography is used to separate chloride ions in the sample extract using an anion exchange column, and the concentration is quantitatively determined using a conductivity detector. Experimental Method: Accurately weigh 0.5 g of PPS sample, add 20 mL of ultrapure water, and extract by shaking in an 80℃ water bath for 1 hour. After cooling, bring the volume to 50 mL, filter through a 0.22 μm filter membrane, and perform ion chromatography analysis. Key Parameters: Extraction temperature 80℃, extraction time 1 h, eluent is a sodium carbonate / sodium bicarbonate mixture, flow rate 1.5 mL / min. Data Processing: Calculate the chloride ion concentration according to the standard curve and convert it to mg / kg. Perform three parallel tests and take the average ± standard deviation. The detection limit should be less than 5 mg / kg.

[0213] Experiment 6: N-Methyl-2-pyrrolidone Residue Test

[0214] Test Subject: Polyphenylene sulfide (PPS) sample. Test Objective: To quantitatively evaluate the content of residual solvent N-methyl-2-pyrrolidone (NMP) in PPS and verify the adequacy of solvent removal by the high-temperature vacuum drying process and the safety of the product. Test Principle: Gas chromatography (GC) is used to extract the volatile components of the residual solvent through high-temperature headspace extraction of the sample. After separation by a capillary column, the NMP is quantitatively determined using a flame ionization detector (FID). Experimental Method: 0.2 g of PPS sample was accurately weighed and placed in a 20 mL headspace vial. The sample was equilibrated at 120 °C for 30 minutes, and 1 mL was injected via an automated headspace sampler for GC analysis. Key Parameters: Headspace temperature 120 °C, equilibration time 30 min, DB-624 capillary column, high-purity nitrogen as carrier gas, flow rate 2 mL / min, FID detector temperature 250 °C. Data Processing: The NMP concentration was calculated based on the external standard curve and converted to mg / kg. Triple parallel tests were performed, and the average ± standard deviation was taken. The limit of detection was 1 mg / kg.

[0215] Figure 1 XRD patterns comparing the effects of pre-dehydration and inorganic salt complexation on the high dispersion and improved reaction uniformity of the sulfur source intermediate. The parameters were fixed as follows: solvent N-methyl-2-pyrrolidone; staged polymerization process for both the sulfur source and monomer systems; dehydration endpoint moisture content controlled within the range of 0.05–0.50 wt%; and mechanical stirring and nitrogen protection. The variable parameter was whether or not the composite sulfur source intermediate was used for pre-construction. The samples were Example 1 and Comparative Example 4. Example 1 showed higher peak intensity and narrower half-width in the characteristic diffraction region of PPS, with more regular peak shape, indicating a purer crystal phase and higher crystallinity. Comparative Example 4 showed peak broadening and background elevation, suggesting increased crystallization defects and microstructure disorder due to inhomogeneous reaction, proving that the composite sulfur source intermediate can improve reaction uniformity and promote crystallinity regularity.

[0216] Figure 2 The thermogravimetric analysis (TGA) curves comparing the synergistic effect of the composite sulfur source intermediate and rigorous washing on the removal of inorganic impurities are shown. The fixed parameters were: N-methyl-2-pyrrolidone as the polymerization solvent, the segmented polymerization temperature window, and the same post-treatment process. The same heating program and atmospheric conditions were used for the tests. The varying parameters were whether the composite sulfur source intermediate was introduced and whether rigorous washing was performed during post-treatment. The samples were Example 1, Comparative Example 4, and Comparative Example 8. Example 1 showed the lowest residual mass fraction in the 550–600°C range, consistent with the low ash content of 0.15 wt% in the ignition residue. Comparative Examples 4 and 8 showed significantly higher residuals at higher temperatures, corresponding to salt entrainment due to the absence of the composite sulfur source intermediate and ion accumulation due to insufficient washing, respectively. This demonstrates that the composite sulfur source intermediate and rigorous washing can synergistically reduce inorganic ash content and improve thermal stability.

[0217] Figure 3This is a comparison of the molecular weight distribution of end-group controllable oligomeric polyphenylene sulfide intermediates through gel permeation chromatography (GPC) to optimize main chain extension and branching degree. The parameters were fixed, with the solvent system and polymerization segmentation temperature strategy consistent, and chromatographic distributions obtained under the same test conditions. The parameters varied were the addition of the end-group controllable oligomeric polyphenylene sulfide intermediate and the effective molecular weight window. The samples were Example 1, Comparative Example 5, and Comparative Example 6. The molecular weight distribution of Example 1 shifted towards the higher molecular weight side and the distribution pattern was more concentrated, indicating more complete chain extension and reduced excess low molecular weight components. Comparative Example 5, lacking chain extension control, had a lower distribution and insufficient high molecular weight components. Comparative Example 6, with an oligomer molecular weight of only 350 g / mol, could not effectively participate in chain growth, resulting in limited distribution improvement and a tendency to exhibit unfavorable tail characteristics. This demonstrates that end-group controllable oligomeric intermediates can effectively increase molecular weight and optimize distribution morphology within a suitable molecular weight window, thereby supporting a balance between gel fraction and processability.

[0218] Figure 4 This is a comparison of differential scanning calorimetry (DSC) curves showing the effect of end-group controllable oligomeric polyphenylene sulfide intermediates on improving the crystallization behavior and thermodynamic stability of PPS. Fixed parameters included consistent thermal history treatment of the samples, the same heating rate, and a nitrogen atmosphere. Variations included whether the end-group controllable oligomeric polyphenylene sulfide intermediate was added and its effective molecular weight. The samples were Example 1, Comparative Example 5, and Comparative Example 6. Example 1 showed a higher melting peak temperature and more concentrated peak shape, indicating better chain segment regularity and crystal perfection. Comparative Examples 5 and 6 showed lower melting peak temperatures and broader peak shapes, suggesting increased crystallization defects and insufficient crystal region perfection, consistent with their structural characteristics of insufficient chain extension. This demonstrates that end-group controllable oligomeric intermediates can improve crystallization perfection and enhance thermal stability.

[0219] Figure 5 This is a comparison of total ion current (TIC) spectra of gas chromatography-mass spectrometry (GC-MS) to demonstrate the synergistic effect of high-purity 1,4-dichlorobenzene and rigorous dehydration on controlling residual impurities. The parameters were fixed: solvent N-methyl-2-pyrrolidone, segmented polymerization strategy, and post-treatment drying strategy were consistent, and the same chromatographic separation and mass spectrometry acquisition conditions were used. The parameters varied were monomer purity and the adequacy of dehydration of the reaction system. The samples were Example 1, Comparative Example 1, and Comparative Example 2. The TIC spectrum of Example 1 showed fewer impurity peaks and lower peak intensities, reflecting better control of residual solvent and byproducts. In Comparative Example 1, the 99.2 wt% monomer purity introduced additional impurities, resulting in enhanced peaks at several points. In Comparative Example 2, the 0.65 wt% moisture promoted side reactions and byproduct formation, leading to more complex peak shapes and an overall increase in peak intensity. This demonstrates that high-purity raw materials and rigorous dehydration can significantly reduce small molecule residues and improve system cleanliness.

[0220] As can be seen from the performance of the examples and comparative examples in Table 1, the polyphenylene sulfide prepared in Examples 1-4 is significantly better than the comparative examples in terms of key indicators such as melting point, gel fraction, residue on ignition, sodium ion content, chloride ion content and NMP residue. Comparative Example 1 showed an increase in impurities due to reduced raw material purity, resulting in a significant increase in ignition residue and ion content. Comparative Example 2 showed excessive residual moisture due to insufficient dehydration, which disrupted the reaction equilibrium and led to an increase in side reactions, causing a comprehensive deterioration in all impurity indicators. Comparative Example 3 showed a decrease in melting point and gel fraction due to limited molecular chain growth caused by a low polymerization temperature. Comparative Example 4 showed a significant increase in ignition residue and sodium ion content due to poor sulfur source dispersion and reaction uniformity caused by the lack of pretreatment synergistic effect of the composite sulfur source intermediate. Comparative Example 5 showed a significant decrease in gel fraction to 90.2% due to the loss of chain extension control function due to the absence of end-group controllable oligomers. Comparative Example 6 showed a gel fraction of only 89.5% due to the low molecular weight of oligomers that could not effectively participate in chain extension. Comparative Example 7 showed a significant increase in ion residue due to decreased reactivity and salt solubility caused by the lack of lithium chloride and sodium thiosulfate synergistic additives. Comparative Example 8 showed insufficient washing depth due to simplified post-treatment process, resulting in sodium ion and chloride ion contents as high as 350 mg / kg and 680 mg / kg, respectively. The embodiments demonstrate the superiority of the technical solution of the present invention by achieving synergistic optimization of low salt residue, low ash content, high gel fraction and low solvent residue through a systematic process combination of high-purity raw materials, pretreatment of composite sulfur source intermediates, controllable end-group oligomer chain extension regulation, optimization of synergistic additives and strict post-treatment.

[0221] Table 1 Performance Comparison Summary Table

[0222] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and not to limit them. Although the present invention has been described in detail with reference to the above embodiments, those skilled in the art should understand that any equivalent structural transformations made under the concept of the present invention and using the contents of the specification and drawings of the present invention should be covered within the scope of protection of the claims of the present invention.

Claims

1. A method for producing polyphenylene sulfide using high purity p-dichlorobenzene, characterized by, Comprising the following steps: S1. Preparing the reaction system: adding N-methyl-2-pyrrolidone into the reactor; adding a sulfur source selected from anhydrous sodium sulfide, sodium sulfide nonahydrate, or a combination of sodium bisulfide and sodium hydroxide; adding a composite sulfur source intermediate; wherein the molar ratio of the N-methyl-2-pyrrolidone to the total sulfur in the sulfur source is 3.5-6.0:1; S2. Dehydration: heating the reaction system to a temperature of 180-200°C under nitrogen protection and dehydrating until the moisture content of the reaction system is 0.05-0.50wt%; S3. Polymerization: adding 1,4-dichlorobenzene with a purity of 99.5-99.99wt% to the reaction system and performing staged polymerization, which includes pre-polymerization at a temperature of 220-240°C and post-polymerization at a temperature of 260-280°C; S4. Intermediate addition and post-treatment: adding an end-group controllable oligomeric polyphenylene sulfide intermediate during the pre-polymerization or the post-polymerization stage, and sequentially performing solid-liquid separation, washing with deionized water, and drying after the polymerization is completed to obtain polyphenylene sulfide.

2. The method of claim 1, wherein, The end-group controllable oligomeric polyphenylene sulfide intermediate is prepared by the following steps: A1. Raw material preparation: mixing 1,4-dichlorobenzene, a sulfur source, and N-methyl-2-pyrrolidone, wherein the molar ratio of the 1,4-dichlorobenzene to the total sulfur in the sulfur source is 1.05-1.30:1; A2. Oligomerization reaction: heating to a temperature of 200-240°C under nitrogen protection and maintaining the reaction; monitoring the number average molecular weight of the product during the maintaining reaction; A3. End point criterion: terminating the reaction and cooling when the number average molecular weight of the product reaches 500-5000g / mol; the time of the maintaining reaction is 0.2-2.0h; A4. Post-treatment: adding deionized water to the reaction liquid to precipitate, washing 1-5 times with deionized water after solid-liquid separation, and drying to obtain the end-group controllable oligomeric polyphenylene sulfide intermediate.

3. The method of claim 1, wherein, The composite sulfur source intermediate is prepared by the following steps: B1. Raw material preparation: providing a sulfur source selected from anhydrous sodium sulfide or sodium sulfide nonahydrate, and mixing the sulfur source with N-methyl-2-pyrrolidone; B2. Dehydration and compounding: heating to a temperature of 180-200°C under nitrogen protection and dehydrating until the moisture content of the system is 0.05-0.50wt% to obtain the composite sulfur source intermediate; B3. Quality control: the apparent viscosity of the composite sulfur source intermediate at a temperature of 25°C is 100-50000mPa·s.

4. The method of claim 3, wherein, In the raw material preparation step B1 of the composite sulfur source intermediate, one or more inorganic salts are further added, the inorganic salts are selected from lithium chloride, sodium thiosulfate and its pentahydrate; wherein: The molar ratio of the lithium chloride to the sodium sulfide in the sulfur source is 0-0.20:1; The mass ratio of the sodium thiosulfate to the sodium sulfide in the sulfur source is 0-0.10:

1.

5. The method of claim 1, wherein, Meanwhile, the following conditions are met: The molar ratio of the 1,4-dichlorobenzene in the step S3 to the total sulfur in the sulfur source is 0.99-1.05:1; The molar ratio of N-methyl-2-pyrrolidone in the step S1 to the total sulfur in the sulfur source is 3.5-6.0:1; The step S4 comprises acid treatment: adding an acid selected from acetic acid or hydrochloric acid to the slurry after polymerization is completed before solid-liquid separation, so that the pH value of the slurry after acid treatment is 7.0-9.5; The washing step in the step S4 comprises washing with deionized water at a temperature of 60-100℃, and repeating 2-6 times.

6. A polyphenylene sulfide characterized by comprising: The polyphenylene sulfide is prepared by the method of any one of claims 1-5, and simultaneously satisfies the following three indexes: The burning residue of the polyphenylene sulfide is 0.05-0.25wt%; The sodium ion content of the polyphenylene sulfide is 10-200mg / kg; The chloride ion content of the polyphenylene sulfide is 10-500mg / kg.

7. The polyphenylene sulfide of claim 6, wherein The moisture content of the polyphenylene sulfide is 0.01-0.20wt%.

8. The polyphenylene sulfide of claim 6, wherein The melting point of the polyphenylene sulfide is 270-300℃, and the gel fraction of the polyphenylene sulfide is 92-99wt%.

9. The polyphenylene sulfide of claim 6, wherein The polyphenylene sulfide is in a powder or particle form, and the particle size D50 of the polyphenylene sulfide is 50-500μm.

10. The polyphenylene sulfide of claim 6, wherein The residual N-methyl-2-pyrrolidone content in the polyphenylene sulfide is not higher than 1000mg / kg.

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