Polyphenylene sulfide having a low chlorine content and a method for producing the same

Abstract

This invention provides a low-chlorine-content polyphenylene sulfide resin and its preparation method. The polyphenylene sulfide resin of this invention has a weight-average molecular weight of less than 55,000, a chlorine content of less than 900 ppm, and a rough surface structure, as well as a chlorine content of 70.00 m² obtained according to the BET test method. 2 The polyphenylene sulfide resin provided by this invention exhibits good flowability, processability, environmental friendliness, and excellent reactivity during processing and use. Furthermore, the preparation method of this invention removes chlorine-containing substances from the reaction system during polymerization by providing reduced pressure at the end of the polymerization reaction, thus obtaining a low-chlorinated polyphenylene sulfide resin with a suitable molecular weight. This method achieves the preparation of low-chlorinated polyphenylene sulfide resin without the use of additional end-capping molecules, making the method simpler and further reducing environmental burden and production costs.

Description

Technical Field

[0001] This invention relates to a low-chlorine-content polyphenylene sulfide, its preparation method, resin composition, and molded body, belonging to the field of engineering plastics preparation and processing, and particularly to the field of polymer material preparation and processing in electronic engineering. Background Technology

[0002] Polyphenylene sulfide (PPS) is an engineering plastic with excellent heat resistance, chemical resistance, flame retardancy, mechanical strength, electrical properties, and dimensional stability. Because PPS can be molded into various molded products, films, sheets, and fibers through common melt processing methods such as extrusion molding, injection molding, and compression molding, it is widely used in electronics and electrical equipment, automotive equipment, and other fields.

[0003] If polymer products such as plastics contain halogens (fluorine, chlorine, bromine, iodine), they will release hydrogen halide gas when burned, which rapidly dilutes the oxygen and extinguishes the fire. However, high concentrations of released hydrogen halide can reduce visibility, making it difficult to identify escape routes; at the same time, hydrogen halide is highly toxic and can affect the human respiratory system. Furthermore, when the hydrogen halide gas released from the combustion of halogen-containing polymers combines with water vapor, it forms a corrosive liquid that can corrode some equipment and buildings. Therefore, polymers used in electronic and electrical equipment have strict requirements regarding halogen content. For example, the European Union typically requires that materials used in electronic and electrical applications contain less than 900 ppm of bromine and less than 900 ppm of chlorine, with a total halogen content of less than 1500 ppm.

[0004] 50%-60% of PPS and its modified materials are used to manufacture electronic and electrical products. Because of its excellent flame retardancy, PPS does not require the addition of brominated flame retardants, and bromine is not involved in commonly used PPS synthesis processes. Therefore, bromine is not present in PPS products.

[0005] Currently, the main method for synthesizing PPS both domestically and internationally is the Phillips process, which involves the condensation polymerization of sulfides and polyhalogenated aromatic compounds at high temperatures in a polar solvent to synthesize PPS resin. The Phillips process typically uses sodium sulfide (or sodium hydrosulfide and sodium hydroxide) and p-dichlorobenzene as the main raw materials to synthesize PPS, and its reaction equation is shown below.

[0006]

[0007] Depending on the ratio of raw materials, the end groups of PPS are mainly chlorine end groups and sodium mercapto end groups. Therefore, chlorine is present in PPS products.

[0008] When synthesizing PPS resin using the Phillips process, a slight excess of p-dichlorobenzene is typically used to ensure reaction stability, and the molecular weight of the PPS resin is controlled by adjusting the degree of p-dichlorobenzene excess. Theoretically, increasing the amount of p-dichlorobenzene will decrease the molecular weight of the PPS resin, leading to an increase in the absolute number of end groups and the proportion of chlorine end groups, thus resulting in a significant increase in the chlorine content of the PPS resin. Conventional PPS resins typically have a chlorine content exceeding 2000 ppm, which fails to meet the halogen content control requirements of the electronics and electrical appliance industry. While reducing the amount of p-dichlorobenzene can appropriately decrease the chlorine content, it will worsen the flowability of the PPS resin, affecting the modification process and its downstream applications.

[0009] According to literature reports, to prepare PPS resin with low chlorine content, the chlorine content can be reduced to the required range by adjusting the raw material ratio, polymerization process, post-treatment purification process, and adding end-group regulators.

[0010] References 1 and 2 both propose adding various additives and adjusting the amount, timing, and polymerization parameters to increase the molecular weight of PPS, thereby reducing the chlorine content in the PPS product. However, this significantly worsens the resin's flowability. When PPS is used in the electronics and electrical instrument industry, glass fiber is usually added to modified PPS materials. Therefore, in addition to reducing halogen content due to environmental regulations, easy molding and processing are also required. A solution is to use PPS with a lower melt viscosity. This is because if the melt viscosity of PPS is too high, it cannot be used for delicate electronic components or large thin sheets. The poor flowability of the material prevents it from effectively covering the entire mold, leading to defects in the injection molded parts. Therefore, the concern remains that chlorine content and processing / molding cannot be balanced.

[0011] Reference 3 proposes a method to reduce chlorine content by heating PPS with a compound containing a thiol group or its alkali metal salt in a solvent capable of dissolving PPS. Reference 4 proposes a method to reduce chlorine content by reacting the finished PPS product with 2-mercaptobenzimidazole and sodium hydroxide in a solvent at high temperature. However, these methods require the separated PPS resin to undergo a prolonged reaction at high temperature and post-treatment, resulting in low efficiency.

[0012] Reference 5 proposes adding one or more compounds selected from the group consisting of thiol compounds, metal salts of thiol compounds, phenolic compounds, metal salts of phenolic compounds, and disulfide compounds as end-group regulators to obtain PPS with low halogen content. The principle behind this method is that the -S-substituents from the cracking of thiophenol or diphenyl disulfide replace the terminal chlorine in the PPS, forming -S-C6H5 end groups, thereby reducing the halogen content of the PPS resin. However, in the embodiments of this patent document, the chlorine content of the powdered polyarylene sulfide resin synthesized using additives such as thiophenol, phenol, and disulfide compounds (diphenyl disulfide, abbreviated as DPDS) is still greater than 1200 ppm. Furthermore, thiophenol has an unpleasant odor during the manufacturing process of PPS resin, thus posing environmental problems in both the manufacturing and recycling processes.

[0013] Reference 6 provides a novel method for reducing the chlorine content in polyphenylene sulfide (PPS), wherein the low-chlorine PPS is obtained by end-capping with 4-phenylthio-benzyl mercaptan. The method for preparing PPS in this invention uses sulfur-containing compounds, alkaline substances, and p-dichlorobenzene as raw materials, fatty acids as polycondensation aids, and 4-phenylthio-benzyl mercaptan (PTT) as an end-group regulator, to carry out a polycondensation reaction. The resulting PPS product has a low chlorine content and also exhibits excellent flowability and heat resistance, thus meeting the low-chlorine, high-flowability requirements of the electronics and electrical appliance industries. However, an end-capping agent is used in this process.

[0014] References:

[0015] Reference 1: JP61007332A

[0016] Reference 2: US4038263A

[0017] Reference 3: JP Special Opening No. 62-106929

[0018] Reference 4: US20160208081A1

[0019] Reference 5: JP2010126621A

[0020] Reference 6: CN106633062A Summary of the Invention

[0021] The problem the invention aims to solve

[0022] For polyphenylene sulfide (PPS), taking the sodium sulfide method as an example, the synthesis of PPS using the sodium sulfide method is a step-growth polymerization. The monomers are usually p-dichlorobenzene and sodium sulfide / sodium hydrosulfide. To obtain high molecular weight polymers, the ratio of the two monomers should be approximately 1. However, in actual polymerization, an excess of sulfur source usually leads to the risk of depolymerization. Therefore, during production, p-dichlorobenzene is usually controlled to be in slight excess, resulting in PPS with mostly chlorine-terminated ends. Thus, the chlorine in the PPS polymer mainly comes from the residual p-dichlorobenzene end groups of the polymer chain segments.

[0023] To improve the end groups of polyphenylene sulfide (PPS) aimed at reducing chlorine content, as mentioned in the literature above, the chlorine content of the end groups can be improved by introducing various end-capping agents. However, such methods inevitably affect or limit the control of molecular weight and thermal stability.

[0024] In addition to the end groups mentioned above, factors related to the chlorine content in the polymer also relate to the final molecular weight of the polyphenylene sulfide resin.

[0025] For polyphenylene sulfide resins, if the molecular weight is high, the proportion of end groups will be relatively low. Therefore, for high molecular weight polyphenylene sulfide, the chlorine content is relatively easy to control. However, the application of high molecular weight polyphenylene sulfide is also limited due to its reduced fluidity.

[0026] In contrast, medium and low molecular weight polyphenylene sulfides have good flowability, but due to their increased end group content, it is difficult to achieve low chlorine content in this case.

[0027] Therefore, it can be seen from the existing technology that although some research has been conducted on reducing the chlorine content in the synthesis of polyphenylene sulfide, the reduction of chlorine content cannot be said to be sufficient, and there is still room for further improvement in reducing chlorine content while taking into account processability.

[0028] In view of the above problems, the present invention provides a novel method for synthesizing low-chlorine-content polyphenylene sulfide resin and a low-chlorine-content, highly reactive sulfide resin product. In this method, the chlorine content in the final polyphenylene sulfide resin can be reduced without introducing additional end-capping molecules. Furthermore, by providing reduced pressure at the end of the polymerization reaction, the method removes chlorine-containing substances from the reaction system during polymerization, thereby significantly reducing the chlorine content in the polymer system while obtaining a polymer with a suitable molecular weight. More surprisingly, the final polymer particles obtained through the above process exhibit excellent surface roughness (microporous) characteristics, thus endowing the polymer particles with very good reactivity.

[0029] Solution for solving the problem

[0030] After long-term research, the inventors discovered that the above-mentioned technical problems can be solved by implementing the following technical solution:

[0031] [1]. The present invention first provides a low-chlorine content polyphenylene sulfide resin, wherein the polyphenylene sulfide resin has a weight-average molecular weight of less than 55,000 and a chlorine content of less than 900 ppm.

[0032] Furthermore, the polyphenylene sulfide resin has a rough surface structure and a thickness of 70.00 μm as determined by the BET test method. 2 Specific surface area above / g.

[0033] [2]. According to the polyphenylene sulfide resin described in [1], wherein the weight-average molecular weight of the polyphenylene sulfide is 35,000 to 50,000; and the chlorine content is 500 to 800 ppm.

[0034] [3]. The polyphenylene sulfide resin according to [1] or [2], wherein the polyphenylene sulfide resin is a granular resin and the average particle size of the particles is 800 to 1300 μm.

[0035] [4]. The polyphenylene sulfide resin according to any one of [1] to [3], wherein the polyphenylene sulfide resin further satisfies one or more of the following conditions:

[0036] i. Crystallization temperature is above 240℃;

[0037] ii. The rough structure is a multi-microporous structure, and the pore volume of the micropores is 0.32~0.40 cm³. 3 / g;

[0038] iii. The Na ion content, as determined by ICP, is 15–35 ppm.

[0039] [5]. The polyphenylene sulfide resin according to any one of [1] to [4], wherein the components in the polyphenylene sulfide resin molecular chain are all derived from the sulfur source and p-dichlorobenzene as reactants.

[0040] [6]. Furthermore, the present invention provides a method for preparing a low-chlorine-content polyphenylene sulfide resin, wherein the method comprises the following steps:

[0041] The steps of the first aggregation; the steps of the second aggregation; and the post-processing steps.

[0042] in,

[0043] The first polymerization step includes a first polymerization of a sulfur source with p-dichlorobenzene.

[0044] The second polymerization step includes reducing pressure based on the first polymerization to perform the second polymerization.

[0045] The post-processing step includes cleaning the polyphenylene sulfide resin obtained in the second polymerization step.

[0046] [7]. According to the method of [6], the step of reducing pressure to carry out the second polymerization is performed when the conversion of dichlorobenzene in the first polymerization is 98.5% to 99.6%.

[0047] [8]. The method according to [6] or [7], wherein the decompression is reduced to the decompression endpoint within 1 to 3 hours.

[0048] [9]. The method according to any one of [6] to [8], wherein the first polymerization step and the second polymerization step are carried out in the presence of fatty acids.

[0049]

[10] . The method according to any one of [6] to [9], wherein, in the first polymerization step, the temperature at which the sodium sulfide is polymerized with p-dichlorobenzene is above 220°C.

[0050]

[11] . The method according to any one of [6] to

[10] , wherein the temperature of the reaction system is kept substantially constant during the decompression in the second polymerization step; the decompression in the second polymerization step results in a pressure reduction of 1 to 3 kgf / cm in the reaction system. 2 .

[0051]

[12] . The method according to any one of [6] to

[11] , wherein the post-processing step includes, under heated conditions, subjecting the polyphenylene sulfide resin obtained in the second polymerization step to one or more acid washing, water washing or combinations thereof.

[0052]

[13] . The method according to any one of [6] to

[12] , wherein the polyphenylene sulfide resin has a weight-average molecular weight of less than 55,000 and a chlorine content of less than 900 ppm.

[0053]

[14] . The method according to any one of [6] to

[13] , wherein the polyphenylene sulfide resin obtained by the method is a granular resin and the average particle size of the granules is 800 to 1300 μm.

[0054]

[15] . According to the method of

[14] , wherein the particles have a rough surface structure and a density of 70.00 m as determined by the BET test method. 2 Specific surface area above / g.

[0055]

[16] . In addition, the present invention also provides a composite material, wherein the composite material comprises a polyphenylene sulfide resin according to any one of [1] to [5] and a filler, the filler comprising fibers.

[0056]

[17] . In addition, the present invention also provides an injection-molded article, wherein it is obtained by injection molding of a composite material according to

[16] .

[0057] The effects of the invention

[0058] By implementing the above technical solution, the present invention can achieve the following technical effects:

[0059] 1. The polyphenylene sulfide resin provided by the present invention has a low chlorine content and a medium to low molecular weight. Specifically, the weight average molecular weight is below 55,000 and the chlorine content is below 900 ppm. This makes the polyphenylene sulfide resin provided by the present invention more environmentally friendly while maintaining good fluidity and processability during processing and use.

[0060] 2. The polyphenylene sulfide resin provided by this invention also has a rough (microporous) surface structure and a high specific surface area. Specifically, its specific surface area is 70.00 m² obtained according to the BET test method. 2 The concentration of the polymer particles is above a certain level (g), thus endowing the polymer particles with very good reactivity.

[0061] 3. The method for preparing polyphenylene sulfide resin provided by this invention can reduce the chlorine content in the final polyphenylene sulfide resin without using additional end-capping molecules, simply by providing reduced pressure at the end of the polymerization reaction. The method is relatively simple and further reduces environmental burden and production costs.

[0062] 4. The polyphenylene sulfide resin provided by the present invention has a higher specific surface area, resulting in a more significant washing effect, higher purity of PPS resin, and lower ash, volatile matter, and sodium ion content. Detailed Implementation

[0063] The present invention will now be described in detail. The descriptions of the technical features described below are based on representative embodiments and specific examples of the present invention, but the present invention is not limited to these embodiments and specific examples. It should be noted that:

[0064] In this specification, the range of values ​​referred to as "value A to value B" refers to the range including the endpoint values ​​A and B.

[0065] Unless otherwise stated, in this instruction manual, "more" in "multiple", "multi-variety", "multiple", etc., means a value of 2 or more.

[0066] In this specification, the terms "substantially" or "truly" mean that the error is less than 1%, or less than 0.8%, or less than 0.6% compared to the relevant perfect or theoretical standard. Furthermore, when "all" or "entire" is used in this specification, it also means "all" or "entire" in the sense of "substantially" or "truly".

[0067] Unless otherwise specified, "%" in this instruction manual refers to the percentage content by mass.

[0068] In this specification, the word "may" has two meanings: to perform a certain process and not to perform a certain process.

[0069] In this specification, "optional" or "optionally" means that the event or situation described below may or may not occur, or may occur in any of the circumstances described, and the description includes both the occurrence and non-occurrence of the event.

[0070] In this specification, references to "some specific / preferred embodiments," "other specific / preferred embodiments," "implementation," etc., refer to specific elements (e.g., features, structures, properties, and / or characteristics) related to that embodiment, which are included in at least one of the embodiments described herein and may or may not be present in other embodiments. Furthermore, it should be understood that these elements may be combined in any suitable manner in various embodiments.

[0071] In this specification, the terms “comprising” and / or “including” are used to indicate the presence of features, steps, operations, devices, components and / or combinations thereof.

[0072] In this instruction manual, "normal temperature" or "room temperature" refers to an indoor ambient temperature of "23±2℃".

[0073] This invention primarily provides a low-chlorine-content polyphenylene sulfide resin, particularly a polyphenylene sulfide resin with a medium to low molecular weight. The polyphenylene sulfide resin is prepared using a segmented synthesis method, where reduced pressure in the post-reaction stage lowers the chlorine content of the final product. Therefore, even without the use of additional end-capping agents, a polyphenylene sulfide resin product with reduced chlorine content and excellent surface properties can be obtained.

[0074] <First Aspect>

[0075] A first aspect of the present invention provides a polyphenylene sulfide resin with low chlorine content and medium or low molecular weight.

[0076] Specifically, the polyphenylene sulfide resin of the present invention has a weight-average molecular weight of less than 55,000 and a chlorine content of less than 900 ppm. In some specific embodiments, the weight-average molecular weight of the polyphenylene sulfide is 35,000 to 50,000, such as 38,000, 40,000, 42,000, 44,000, 46,000, 48,000, etc. When the weight-average molecular weight of the PPS resin is less than 55,000, good flowability and processability can be maintained. The chlorine content is preferably 100 to 800 ppm, such as 150 ppm, 200 ppm, 300 ppm, 400 ppm, 500 ppm, 600 ppm, 700 ppm, etc.

[0077] In this invention, the polyphenylene sulfide resin has a rough (microporous) surface structure, and the 70.00 μm obtained according to the BET test method... 2 Specific surface area above / g, for example, 72.00m² 2 / g or more, 73.00m 2 / g or more, 74.00m 2 / g or more, 75.00m 2 / g or higher, for example, 76~85m 2 / g etc. The surface roughness (microporous) structure of the PPS resin of the present invention increases the specific surface area of ​​the PPS resin, thereby endowing the PPS resin with excellent reactivity. In addition, in the washing process of PPS preparation described below, due to the surface roughness (microporous) structure of the PPS resin, the washing effect is more significant, resulting in higher purity and lower impurity content of the PPS resin. Compared with the glass fiber and glass mineral modified system, there is less injection molding fume, making it more suitable for the processing of electronic devices.

[0078] In some specific embodiments, the polyphenylene sulfide resin is a particulate resin, and in some specific embodiments, the average particle size of the particulate resin is 800~1300μm, such as 900μm, 1000μm, 1100μm, 1200μm, etc.

[0079] The pore volume of the polyphenylene sulfide resin microporous structure is not particularly limited, as long as the specific surface area mentioned above is achieved. Preferably, the pore volume of the polyphenylene sulfide resin microporous structure is 0.32~0.40 cm³. 3 / g, for example 0.33cm 3 / g, 0.34cm 3 / g, 0.35cm 3 / g, 0.36cm 3 / g, 0.37cm 3 / g, 0.38cm 3 / g, 0.39cm 3 / g etc.

[0080] In other specific embodiments, the polyphenylene sulfide resin also has a high crystallization temperature, specifically, it can be above 240°C (based on DSC testing), such as above 242°C, above 245°C, above 248°C, above 250°C, above 255°C, etc., preferably 240~260°C. The higher crystallization temperature gives the polyphenylene sulfide resin of the present invention higher mechanical and performance properties.

[0081] Furthermore, the polyphenylene sulfide resin has a low impurity content, which includes ash, volatile matter, and metal ions, such as Na ions commonly used in the preparation of polyphenylene sulfide resin. The Na ion content measured by ICP is 15~35 ppm, such as 18ppm, 20ppm, 22ppm, 25ppm, 28ppm, 30ppm, 32ppm, etc.

[0082] Furthermore, in some preferred embodiments of the present invention, the components in the polyphenylene sulfide resin molecular chain are all derived from the sulfur source and p-dichlorobenzene, which are reactants. In other words, the polyphenylene sulfide resin of the present invention forms its molecular chain structure solely through the above two components during the synthesis process, without the need for other end-capping molecules, thus achieving the goal of reducing chlorine content. Regarding the sulfur source, there is no particular limitation in principle; commonly used sulfur elements, alkali metal sulfides, and alkali metal hydrosulfides can be used. Alkali metal sulfides, such as sodium sulfide, are preferred in the present invention.

[0083] The polyphenylene sulfide resin provided by this invention has the characteristics of low chlorine content, high specific surface area, good fluidity, high crystallization temperature, and low impurity content, which endows the polyphenylene sulfide resin with excellent reactivity and processability. In some specific embodiments, the polyphenylene sulfide resin of this invention is particularly suitable for semiconductor electronic and electrical applications such as insulated gate bipolar transistors (IGBTs) and as a natural coloring agent.

[0084] <Second aspect>

[0085] A second aspect of the present invention provides a method for preparing a polyphenylene sulfide resin with low chlorine content, particularly a method for preparing a polyphenylene sulfide resin as described in the first aspect above.

[0086] Specifically, the preparation method may include the following steps:

[0087] The steps of the first aggregation; the steps of the second aggregation; and the steps of post-processing.

[0088] The first polymerization step includes a first polymerization of a sulfur source and p-dichlorobenzene; the second polymerization step includes a second polymerization performed under reduced pressure based on the first polymerization.

[0089] The post-processing step includes cleaning the polyphenylene sulfide resin obtained in the second polymerization step.

[0090] In the second polymerization step, the pressure in the system is reduced to a lower pressure than in the first polymerization step, thereby removing at least a portion of the small molecule chlorine-containing substances from the reaction system.

[0091] (Steps of the first aggregation)

[0092] The first polymerization step of the present invention mainly includes a polymerization reaction between a sulfur source and dichlorobenzene, especially sodium sulfide and dichlorobenzene, to obtain a polyphenylene sulfide polymer of a certain molecular weight.

[0093] In the first polymerization step, using sulfur in 1 mol of sulfur source as a reference, the amount of p-dichlorobenzene used is 0.99~1.05 mol, for example 1.00 mol, 1.02 mol, etc.

[0094] In some specific embodiments, the first polymerization is carried out in a solvent, which can be selected from commonly used polar solvents in the art, preferably high-boiling-point polar solvents such as DMF, DMAc, or NMP, with NMP being the most preferred. Further, based on 1 mol of sulfur, the amount of solvent used is 3.5 to 4.5 mol. In other specific embodiments, when the sulfur source is used in the form of an aqueous solution, the first polymerization step may further include a dehydration step to control the water content to 1.0 to 1.2 mol / mol sulfur.

[0095] In the first polymerization step, the polymerization of the sulfur source with p-dichlorobenzene is carried out under heating conditions. The heating temperature can be above 220°C, preferably 220~270°C, such as 230°C, 240°C, 250°C, or 260°C. In some specific embodiments, the heating process of the first polymerization step can adopt a segmented heat preservation method to promote the polymerization reaction. In some preferred embodiments, the first heat preservation reaction includes heating to 220~240°C within 1~1.5h and holding the temperature for 1~3h; the second heat preservation reaction includes heating to 250~270°C at a rate of 0.5~1°C / min and holding the temperature for 0.5~1h.

[0096] In some more specific embodiments, water can be added to the system as needed after the first heat preservation reaction. Adding an appropriate amount of water to separate the phases of the system can increase the conversion rate of p-dichlorobenzene while simultaneously increasing the molecular weight of the PPS resin. Specifically, the amount of water added is not particularly limited in principle. Considering both increasing molecular weight and balancing cost and efficiency, the ratio of added water to sulfur in the system can be 1.5~3 mol water / mol sulfur, preferably 1.8~2.8 mol water / mol sulfur.

[0097] Furthermore, in some preferred embodiments of the present invention, the sodium sulfide used as the sulfur source in the first polymerization step can be obtained by a dehydration reaction between an alkaline substance and NaHS. Specifically, the dehydration reaction includes mixing NaHS, an alkaline substance, and a solvent (NMP), wherein the alkaline substance can be sodium hydroxide, potassium hydroxide, or a mixture thereof used in aqueous solution. The specific reaction formula for the dehydration reaction is shown below:

[0098]

[0099] Among them, formula (1) is the main reaction of the dehydration reaction, formula (2) is the possible side reaction of the dehydration reaction, formula (3) is the reaction of partial hydrolysis of the solvent in alkaline substances, and the product SMAB generated after solvent hydrolysis can further improve the solubility of NaHS, as shown in formula (4), so as to obtain sodium sulfide more efficiently.

[0100] From the perspective of further promoting the formation of sodium sulfide, in the dehydration reaction, based on 1 mol NaHS, the amount of alkaline substance can be 1.00~1.04 mol, such as 1.01 mol, 1.02 mol, 1.03 mol, etc.; the amount of NMP can be 2.4~3.0 mol, such as 2.5 mol, 2.6 mol, 2.7 mol, 2.8 mol, 2.9 mol, etc.

[0101] In some specific embodiments, a fatty acid salt may be added to the dehydration reaction. Preferably, the fatty acid salt is a sodium or potassium salt of a C5-C6 fatty acid, including one or more sodium or potassium salts of hexanoic acid, valeric acid, isovaleric acid, 2-ethylbutyric acid, etc. On the one hand, the fatty acid salt can further increase the solubility of the sulfur source; on the other hand, the fatty acid salt can act as a catalyst in subsequent polymerization reactions, promoting the increase of PPS molecular weight and reducing polymerization side reactions.

[0102] In some specific implementations, a stirring step may be included in the dehydration reaction to ensure the uniformity of the reaction. The stirring method is not particularly limited and can be selected as needed. In some preferred implementations, the stirring speed can be 100-200 rpm, such as 110 rpm, 130 rpm, 150 rpm, 170 rpm, 190 rpm, etc.

[0103] (The second aggregation step)

[0104] In this embodiment, a pressure reduction is applied to the first polymerization process to induce a second polymerization. The term "pressure reduction" refers to a decrease in pressure under the conditions of the first polymerization.

[0105] In some preferred embodiments of the present invention, the decompression step includes reducing the pressure in the reaction system by 1-3 kgf / cm² while keeping the temperature of the reaction system substantially constant. 2 For example, a pressure reduction of 1.2 kgf / cm 2 1.4 kgf / cm 2 1.6 kgf / cm 2 1.8 kgf / cm 2 2.0 kgf / cm 2 2.2 kgf / cm 2 2.4 kgf / cm 2 2.6 kgf / cm 2 2.8 kgf / cm 2 wait.

[0106] When the pressure in the reaction system decreases by 1~3 kgf / cm 2 When the pressure drop is too small, the chlorine content in the system may not decrease significantly; when the pressure drop is too large, the molecular weight of the finished polymer is low, and because a large amount of water is discharged during the cooling process, if not properly controlled, it can easily cause changes in particle morphology, which may result in the partial loss of the microporous structure.

[0107] Regarding the conditions for initiating the decompression step, considering the freedom of molecular weight control and production efficiency, in some preferred embodiments, the decompression is performed to proceed to the second polymerization step when the conversion rate of p-dichlorobenzene in the first polymerization is 98.5%–99.6%, for example, 98.8%, 99.0%, 99.2%, 99.4%, etc. Decompression when the conversion rate of p-dichlorobenzene is too low will result in a large amount of p-dichlorobenzene being discharged, potentially making it difficult to obtain a product with the desired molecular weight. Conversely, decompression when the conversion rate of p-dichlorobenzene is too high will result in most of the polymer chains being end-capped with chlorine due to excess monomer, thus preventing a reduction in the chlorine content of the final product. Decompression when the conversion rate of p-dichlorobenzene is 98.5%–99.6% can significantly reduce the chlorine content in the polymer system while obtaining a polymer with a suitable molecular weight.

[0108] Additionally, in some other preferred embodiments, although not mandatory, the step of performing the reduced pressure to carry out the second polymerization can also be performed when the weight-average molecular weight of the polyphenylene sulfide in the first polymerization is 30,000 to 38,000, for example, 31,000, 33,000, 35,000, 37,000, etc. Performing reduced pressure when the weight-average molecular weight of the polyphenylene sulfide in the first polymerization is 30,000 to 38,000 can further obtain polymers with suitable molecular weights and achieve lower chlorine content.

[0109] There are no particular restrictions on the depressurization time in principle, and it can be determined according to the equipment and reaction conditions. In some specific implementation schemes, the depressurization time can be 1 to 3 hours, preferably 1.5 to 2.5 hours, such as 1.2 hours, 1.5 hours, 1.8 hours, 2.2 hours, 2.4 hours, etc. In some extreme cases, if the depressurization rate is too fast, the control requirements will be higher; if the depressurization rate is too slow, the chlorine reduction effect will be reduced.

[0110] This invention removes chlorine-containing substances from the reaction system during polymerization by reducing pressure, thereby significantly reducing the chlorine content in the polymer system while obtaining a polymer with a suitable molecular weight. The reduced chlorine content in the polymer system leads to an increase in sodium mercaptoterminal groups and a decrease in chlorine terminators in PPS upon reaction termination, ultimately achieving the goal of reducing the chlorine content in PPS. Furthermore, during the depressurization process, low-boiling-point substances in the molten PPS in the concentrated reaction phase continuously form microbubbles due to the decrease in external gas pressure. When the pressure inside the bubble exceeds the strength of the bubble wall formed by the molten PPS, the molten PPS cannot withstand the wall film stretching caused by the pressure difference between the inside and outside gases, and the bubble wall ruptures, allowing gas to escape and forming open channels. This morphology is retained during subsequent cooling and crystallization, forming high specific surface area multi-microporous PPS particles.

[0111] (Post-processing steps)

[0112] In addition to the polymerization steps described above, optional post-processing steps can be used to process the polymerized product after the polymerization reaction is completed.

[0113] In some specific implementations, the system temperature can be lowered to 90-110°C, such as 95°C, 100°C, or 105°C, before performing the post-processing steps.

[0114] The post-processing steps may include one or more washing, distillation, and other steps.

[0115] In some specific embodiments, the cleaning can be carried out under heated conditions, subjecting the polyphenylene sulfide resin obtained in the second polymerization step to one or more acid washes, water washes, or combinations thereof. In the acid-washed PPS, the sodium mercaptoterminal groups are converted to mercaptoterminal groups, increasing the crystallization temperature of the PPS.

[0116] The distillation step can be performed before and / or after the above cleaning process. It mainly removes residual solvents (NMP) and fatty acid salts from the resin.

[0117] The polyphenylene sulfide resin prepared by the method of the present invention is a granular resin with an average particle size of 800–1300 μm. The polyphenylene sulfide resin has a weight-average molecular weight of less than 55,000 and a chlorine content of less than 900 ppm. Furthermore, the particles have a rough surface (microporous) structure and a particle size of 70.00 μm as determined by the BET test method. 2 Specific surface area above / g.

[0118] (Typical preparation method)

[0119] In some specific embodiments of the present invention, the preparation method of the low-chlorine content polyphenylene sulfide of the present invention may include the following steps:

[0120] (1) Add sulfur source, alkaline substance, part of organic solvent and fatty acid salt to the reaction vessel, and heat up to carry out dehydration reaction;

[0121] (2) After step (1) is completed, add p-dichlorobenzene and the remaining organic solvent to the reactor, heat to 210~250℃, and carry out the heat preservation reaction;

[0122] (3) After step (2) is completed, deionized water is added to the reactor and the temperature is raised to 250-270°C for heat preservation reaction.

[0123] (4) Monitor the conversion rate of dichlorobenzene in the system of step (3). When the conversion rate reaches 98.5% to 99.6%, reduce the pressure while keeping the temperature constant, so that the internal pressure drops by 1 to 3 kgf / cm. 2 The polyphenylene sulfide reaction slurry was obtained.

[0124] (5) The polyphenylene sulfide reaction slurry from step (4) is post-treated to obtain polyphenylene sulfide resin.

[0125] In some more specific embodiments of the present invention, the method for preparing the low-chlorine content polyphenylene sulfide of the present invention may include the following steps:

[0126] (1) Add sulfur source, alkaline substance, N-methylpyrrolidone (NMP) and fatty acid salt to the reaction vessel, heat to 180~210℃ to carry out dehydration reaction to obtain intermediate product, until the water content in the system is 1.0~1.2 mol / mol sulfur, and then cool down to 160~180℃;

[0127] (2) After step (1) is completed, add p-dichlorobenzene and another N-methylpyrrolidone to the reactor, raise the temperature to 210-250℃ within 1-2 h, and keep it at the temperature for 1-4 h;

[0128] (3) After step (2) is completed, add 1.5-3.0 mol / mol sulfur deionized water to the reactor, then raise the temperature to 250-270°C at a rate of 0.5-1°C / min, hold for 0.5-1 h, and achieve a gas pressure of 16-17.5 kgf / cm². 2 .

[0129] (4) Monitor the conversion rate of dichlorobenzene in the system of step (3). When the conversion rate reaches 98.5% to 99.6%, control the pressure reducing valve to release gas slowly. After the gas absorbs the monomer through NMP, it enters the tail gas system. While keeping the temperature constant, reduce the pressure to 13 to 15.5 kgf / cm³ within 1 to 3 hours. 2 (Reduced by 1-3 kgf / cm) 2 The reaction was carried out to obtain a polyphenylene sulfide reaction slurry; after the reaction was completed, the system temperature was lowered to 90~110℃.

[0130] (5) The polyphenylene sulfide reaction slurry from step (4) is post-treated to obtain polyphenylene sulfide resin.

[0131] The post-processing steps of step (5) include: centrifuging and filtering the PPS reaction slurry after step (4), rinsing with NMP and rinsing with hydrochloric acid solution, collecting the filtrates, and recovering C5-C6 fatty acids and NMP; washing the filter cake with deionized water multiple times and drying it to obtain polyphenylene sulfide resin.

[0132] In a further preferred embodiment of the present invention, the method for preparing the low-chlorine content polyphenylene sulfide of the present invention may include the following steps:

[0133] (1) Add NMP, 45-55wt% NaOH aqueous solution, 40-55wt% sodium hydrosulfide aqueous solution and 35-45wt% C5-C6 fatty acid salt aqueous solution to the reaction vessel. Under stirring and nitrogen protection, heat the mixture to 180-200℃ at a rate of 0.7-1.5℃ / min for dehydration until the water content in the system is 1.0-1.2 mol / mol sulfur, and then cool it down to 160-180℃.

[0134] (2) After step (1) is completed, add p-dichlorobenzene (PDCB) and NMP to the reactor, raise the temperature to 220-240℃ within 1.0-1.5h, and keep it at that temperature for 1-3h;

[0135] (3) After step (2) is completed, add 1.5–3.0 mol / mol sulfur deionized water to the reactor, then raise the temperature to 250–270°C at a rate of 0.5–1°C / min, hold for 0.5–1 h, and achieve a gas pressure of 16–17.5 kgf / cm². 2 .

[0136] (4) Monitor the conversion rate of dichlorobenzene in the system of step (3). When the conversion rate reaches 98.7% to 99.5%, control the pressure reducing valve to slowly release the gas. After the gas absorbs the monomer through NMP, it enters the tail gas system. While keeping the temperature constant, reduce the pressure to 14 to 15.5 kgf / cm³ within 1.5 to 2.5 hours. 2 (Reduced by 1-3 kgf / cm) 2 PPS reaction solution was obtained; after the reaction was completed, the system temperature was lowered to 90~110℃.

[0137] (5) After step (4), the PPS reaction solution is filtered through a 150-200 mesh sieve, rinsed with NMP at 130-150℃ with an equal mass of the filter cake, and dried. Then rinsed with hydrochloric acid solution with an equal mass of the filter cake and dried. The filtrates are combined and collected.

[0138] (6) Wash the filter cake obtained in step (5) with deionized water at 70-100℃ three times or more until the conductivity of the filtrate is below 100μs / cm. Dry the filter cake to obtain polyphenylene sulfide resin.

[0139] (7) Stir and mix the filtrate obtained in step (6), and first separate the C5-C6 fatty acids by azeotropic distillation in a distillation apparatus equipped with a water separator, then remove the water by distillation, and finally recover the solvent NMP by vacuum distillation. The distillation residue can be treated by incineration.

[0140] The C5-C6 fatty acid salt aqueous solution in step (1) is preferably an organic sodium salt formed by hexanoic acid, valeric acid, isovaleric acid, 2-ethylbutyric acid and liquid alkali, or a mixture thereof in any proportion.

[0141] The raw materials used in step (1) are based on 1.0 mol NaHS, with a total amount of 0.05 to 0.5 mol of C5 to C6 fatty acid salts, 2.4 to 3.0 mol of NMP, and 1.00 to 1.04 mol of NaOH.

[0142] The raw materials used in step (2) are based on 1.0 mol NaHS. After adding PDCB and NMP, the amount of PDCB is 0.99 to 1.05 mol, and the total amount of NMP in the system is 3.5 to 4.5 mol.

[0143] The raw materials used in step (3) are based on 1.0 mol NaHS, and the preferred amount of deionized water added is 1.5 to 2.5 mol, with a total water content of 2.5 to 4.2 mol.

[0144] The hydrochloric acid concentration in step (5) is 0.1 to 0.3 wt%.

[0145] The preparation method of the present invention allows for the reduction of chlorine content in PPS resin by providing reduced pressure at the end of the polymerization reaction without using any other capping agents. Furthermore, and more unexpectedly, the final polymer particles obtained through the above process exhibit excellent surface roughness characteristics, thereby endowing the polymer particles with very good reactivity.

[0146] <Third aspect>

[0147] A third aspect of the present invention provides a composite material comprising the polyphenylene sulfide resin according to the first aspect of the present invention and a filler, wherein the filler is not particularly limited and may be fibers, etc.

[0148] <Fourth Aspect>

[0149] A fourth aspect of the present invention provides an injection-molded article obtained by injection molding of the composite material described in the third aspect.

[0150] Example

[0151] The embodiments of the present invention will be described in detail below with reference to examples. However, those skilled in the art will understand that the following examples are for illustrative purposes only and should not be considered as limiting the scope of the invention. Unless otherwise specified in the examples, conventional conditions or conditions recommended by the manufacturer are followed. Reagents or instruments whose manufacturers are not specified are all commercially available conventional products.

[0152] The methods for determining physical properties and characteristics in this invention are as follows:

[0153] (1) Method for determining halogen content

[0154] The halogen content in PPS was determined according to EN 14582:2007, and the chlorine content was determined by oxygen bomb combustion ICP.

[0155] (2) Method for determining melt viscosity (Mv)

[0156] The melt viscosity of PPS was determined using an LCR7001 capillary rheometer manufactured by Dynisco. The set temperature was 310°C. The polymer sample was introduced into the apparatus and held for 5 minutes, followed by a shear rate of 1216 sec. -1 The melt viscosity was measured.

[0157] (3) Methods for determining melting point (Tm) and crystallization temperature (Tc)

[0158] The melting point and crystallization temperature of PPS resin were determined by differential scanning calorimeter (DSC). 4.5-5.5 mg of PPS resin was heated to 340°C at a heating rate of 20°C / min, held at that temperature for 5 min, and then cooled to 40°C at a cooling rate of 10°C / min for measurement.

[0159] (4) Methods for determining ash content

[0160] Accurately weigh 1.50 g of PPS and place it in a crucible, recording the precise mass as G0. Calcine in a muffle furnace at 750℃ for 2 hours, then turn off the furnace for 0.5 hours. Remove and cool in a desiccator for 30 minutes. Add 5 mL of nitric acid, slowly dripping it along the inner wall of the crucible using a pipette, ensuring no sample residue remains and that the nitric acid completely covers the sample. Place the crucible in an electric heating furnace for carbonization for 45 minutes, heating until no smoke is emitted. Calcine the carbonized crucible in a muffle furnace at 750℃ for 3 hours, cool for 0.5 hours, remove, confirm complete calcination, and place in a sealed desiccator for 1.5 hours. Weigh the sample and record the weight as G1.

[0161] [Ash content] = G1 / G0 × 100%.

[0162] (5) Methods for determining volatile matter

[0163] Accurately weigh 3g of sample and place it in an aluminum foil dish. Record the precise weight as G2. Dry the sample in a 300℃ oven for 1 hour. After drying, place it in a desiccator to cool for 30 minutes and weigh it again. Record the weight as G3.

[0164] [Volatile content] = (G2 - G3) / G2 × 100%.

[0165] (6) Methods for determining specific surface area

[0166] The specific surface area of ​​PPS resin was determined according to GB / T 21650.2, which specifies the determination of pore size distribution and porosity of solid materials by mercury intrusion porosimetry and gas adsorption method. The gas used for adsorption was nitrogen.

[0167] (7) Methods for determining the content of metal ions

[0168] The metal ion content in the PPS was determined using inductively coupled plasma optical emission spectrometry (ICP-OES) according to the test method in GB / T23942-2009. The plasma power was 1300W, the cooling gas flow rate was 12 L / min, the auxiliary gas flow rate was 0.8 L / min, the nebulizing gas flow rate was 0.8 L / min, and the supplementary gas flow rate was 0 L / min.

[0169] Example 1:

[0170] Dehydration: In a 100L reactor, add 24.80 kg (250.0 mol) of NMP, 11.00 kg (100.0 mol) of 51.0 wt% sodium hydrosulfide aqueous solution, 7.74 kg (102.5 mol) of 53.0 wt% liquid alkali, and 2.00 kg (6.45 mol) of 40.0 wt% sodium valerate aqueous solution. After purging the reactor with nitrogen, heat the reactor at a stirring speed of 130 rpm and a rate of 1.0℃ / min. When the temperature reaches 198℃ and the water content in the reaction system is close to 1.1 mol / mol of sulfur, the dehydration process ends. At this point, 10.31 kg of solution (containing 98.0 wt% water and 2 wt% NMP) has been removed from the reactor. The calculated hydrogen sulfide loss is 1.5 mol, the sulfur source in the reactor is 98.5 mol, and the water / sulfur molar ratio is 1.08.

[0171] Polymerization: After the mixture in the reactor has cooled to 170°C, add 14.92 kg (101.0 mol) of PDCB and 15.02 kg of NMP. The molar ratio of PDCB to total sulfur is 1.025, and the molar ratio of NMP to total sulfur is 4.0. Raise the temperature to 225°C over approximately 1.5 hours and hold for 2 hours. Then, add water containing 1.5 mol / mol sulfur using a high-pressure pump and continue raising the temperature (0.5°C / min) to 260°C and hold. At this point, the pressure should stabilize at 16.5 kgf / cm³. 2 When the conversion rate of dichlorobenzene in the system reached 99.0%, the pressure reducing valve was adjusted to slowly release the pressure, gradually reducing it to 14.5 kgf / cm³ over 2 hours. 2 The temperature was kept constant during the reaction. After the reaction was completed, the temperature was rapidly reduced to 100°C. The resin was filtered through a 150-mesh sieve, rinsed with an equal mass of 140°C NMP solution, and dried. Then, it was rinsed with an equal mass of 0.2% dilute hydrochloric acid solution and dried. The filtrates were combined and collected. The filter cake was then washed three times or more with 85°C deionized water until the conductivity of the filtrate was below 100 μS / cm. The filter cake was then dried to obtain polyphenylene sulfide resin.

[0172] The obtained resin was tested, and the data are shown in Table 1.

[0173] Comparative Example 1:

[0174] Similar to Example 1, except that after adding water, the pressure was kept constant at 260°C for 2.6 hours to obtain the final PPS reaction solution. The same post-treatment was used after the reaction was completed.

[0175] The obtained resin was tested, and the data are shown in Table 1.

[0176] Examples 2-5:

[0177] Examples 2-5 are the same as Example 1, except that when the conversion rate of p-dichlorobenzene in the system reaches 98.5%, 98.7%, 99.5%, and 99.6% respectively, the pressure reducing valve is adjusted to slowly release gas and pressure.

[0178] The obtained resin was tested, and the data are shown in Table 1.

[0179] Comparative Example 2:

[0180] Similar to Example 1, except that when the conversion rate of dichlorobenzene in the system is detected to reach 99.9%, the pressure reducing valve is adjusted to slowly release the pressure.

[0181] The obtained resin was tested, and the data are shown in Table 1.

[0182] Examples 6-9:

[0183] Examples 6-9 are the same as Example 1, except that the pressure reducing valve is adjusted to slowly release the pressure, and the pressure is reduced to 13.5 kgf / cm² over 2 hours. 2 14 kgf / cm 2 15kgf / cm 2 15.5 kgf / cm 2 .

[0184] The obtained resin was tested, and the data are shown in Table 2.

[0185] Examples 10-13:

[0186] Examples 10-13 are the same as Example 1, except that the pressure reducing valve is adjusted to slowly release the pressure, reducing it to 14.5 kgf / cm³ at a constant rate over 1 hour, 1.5 hours, 2.5 hours, and 3 hours respectively. 2 .

[0187] The obtained resin was tested, and the data are shown in Table 3.

[0188] Example 14:

[0189] The process is basically the same as in Example 1, except that the polymerization step involves adding 1.5 mol / mol sulfur in water using a high-pressure pump and continuing to heat the mixture (at a rate of 0.5°C / min) to 260°C and holding it therewhile, at which point the pressure stabilizes at 17 kgf / cm³. 2 When the conversion rate of dichlorobenzene in the system reached 99.4%, the pressure reducing valve was adjusted to slowly release the pressure, reducing it to 15 kgf / cm³ over 1.5 hours. 2 The temperature was kept constant during this period. The post-processing procedure was the same.

[0190] The obtained resin was tested, and the data are shown in Table 3.

[0191] Example 15:

[0192] The process is basically the same as in Example 1, except that the polymerization step involves adding 1.5 mol / mol sulfur in water using a high-pressure pump and continuing to heat the mixture (0.5 °C / min) to 260 °C and holding it therewhile, at which point the pressure stabilizes at 16 kgf / cm³. 2 When the conversion rate of dichlorobenzene in the system reached 99.8%, the pressure reducing valve was adjusted to slowly release the pressure, reducing it to 13 kgf / cm³ over 2.5 hours. 2 The temperature was kept constant during this period. The post-processing procedure was the same.

[0193] The obtained resin was tested, and the data are shown in Table 3.

[0194] Example for reference:

[0195] PPS resin was obtained according to the method of Example 1 in CN106633062A, wherein the chlorine content was 750ppm, the molecular weight was 45800, the resin surface was smooth, and there was no obvious rough structure.

[0196] Table 1

[0197]

[0198] Table 2

[0199]

[0200] Table 3

[0201]

[0202] As can be seen from the above embodiments and comparative examples, the present invention can obtain low-to-medium molecular weight polyphenylene sulfide while also achieving a reduced chloride ion content.

[0203] Furthermore, the comparison between the above embodiments and comparative examples also shows that the preparation method provided by the present invention can obtain polyphenylene sulfide products that meet the expectations of the present invention.

[0204] It should be noted that although the technical solution of the present invention has been described with specific examples, those skilled in the art will understand that the present invention should not be limited thereto.

[0205] The various embodiments of the present invention have been described above. These descriptions are exemplary and not exhaustive, nor are they limited to the disclosed embodiments. Many modifications and variations will be apparent to those skilled in the art without departing from the scope and spirit of the described embodiments. The terminology used herein is chosen to best explain the principles, practical application, or technical improvements to the embodiments in the market, or to enable others skilled in the art to understand the embodiments disclosed herein.

Claims

1. A low-chlorine-content polyphenylene sulfide resin, characterized in that, The polyphenylene sulfide resin has a weight-average molecular weight of 35,000 to 55,000 and a chlorine content of 100 to 900 ppm. Furthermore, the polyphenylene sulfide resin has a rough surface structure and a viscosity of 70.00–85 μm as determined by the BET test method. 2 Specific surface area per g and, The polyphenylene sulfide resin has a Na ion content of 15-35 ppm as determined by ICP. The components in the polyphenylene sulfide resin molecular chain all originate from the sulfur source and p-dichlorobenzene, which are reactants; The preparation method of the polyphenylene sulfide resin includes the following steps: The steps of the first aggregation; the steps of the second aggregation; and the post-processing steps. in, The first polymerization step includes a first polymerization of a sulfur source with p-dichlorobenzene. The second polymerization step includes reducing pressure based on the first polymerization to perform the second polymerization. The post-processing step includes cleaning the polyphenylene sulfide resin obtained in the second polymerization step.

2. The polyphenylene sulfide resin according to claim 1, characterized in that, The polyphenylene sulfide has a weight-average molecular weight of 35,000 to 50,000; the chlorine content is 500 to 800 ppm.

3. The polyphenylene sulfide resin according to claim 1 or 2, characterized in that, The polyphenylene sulfide resin also satisfies one or more of the following conditions: i. Crystallization temperature is above 240℃; ii. The rough structure is a multi-microporous structure, and the pore volume of the micropores is 0.32~0.40 cm³. 3 / g.

4. A method for preparing a low-chlorine-content polyphenylene sulfide resin according to any one of claims 1 to 3, characterized in that, The method includes the following steps: The steps of the first aggregation; the steps of the second aggregation; and the post-processing steps. in, The first polymerization step includes a first polymerization of a sulfur source with p-dichlorobenzene. The second polymerization step includes reducing pressure based on the first polymerization to perform the second polymerization. The post-processing step includes cleaning the polyphenylene sulfide resin obtained in the second polymerization step.

5. The method according to claim 4, characterized in that, The step of reducing pressure to carry out the second polymerization is performed when the conversion rate of p-dichlorobenzene in the first polymerization is 98.5% to 99.6%.

6. The method according to claim 4 or 5, characterized in that, The decompression process reduces the pressure of the reaction system to the decompression endpoint within 1 to 3 hours.

7. The method according to claim 4 or 5, characterized in that, In the second polymerization step, the temperature of the reaction system is kept substantially constant during the depressurization process; the depressurization in the second polymerization step results in a pressure reduction of 1–3 kgf / cm² in the reaction system. 2 .

8. The method according to claim 4 or 5, characterized in that, The post-processing steps include subjecting the polyphenylene sulfide resin obtained in the second polymerization step to one or more acid washings, water washings, or combinations thereof under heated conditions.

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