A high degree of polymerization polyvinyl chloride resin, its preparation method and application

Abstract

This application relates to the field of polymer materials technology, specifically to an ultra-high degree of polymerization (UHDP) polyvinyl chloride (PVC) resin, its preparation method, and its applications. The UHDP PVC resin and its preparation method provided in this application employ a low-temperature suspension polymerization method and a segmented controlled process to produce PVC resin with an average degree of polymerization of 2500-4000. In the early stage of the reaction, a highly active initiator is continuously injected to improve reaction efficiency, and a high stirring speed is maintained to enhance material mixing and shearing effects. After reaching the critical conversion rate, the initiator injection is stopped, water is added, and the stirring speed is reduced. This method results in a stable reaction during production, high production efficiency, and overcomes the problem of heat transfer limitations in polymerization reactors in traditional methods. The obtained UHDP resin particles have a narrow molecular weight distribution, high porosity and oil absorption rate, few fish eyes, and excellent plasticizing and processing properties.

Description

Technical Field

[0001] This application relates to the field of polymer materials technology, specifically to an ultra-high degree of polymerization polyvinyl chloride resin, its preparation method, and its application. Background Technology

[0002] Ultra-high degree of polymerization (UHDP) polyvinyl chloride (PVC) resin (generally referring to a degree of polymerization above 2500) has a higher molecular weight, more entanglement points between molecular chains, and stronger forces compared to ordinary PVC resin. This results in better elasticity, higher heat resistance, higher tensile strength, better abrasion resistance, and stronger tear resistance. It can also absorb more plasticizers, making it suitable for producing soft rubber products as a substitute for rubber. The resulting products have better oil and weather resistance than rubber and do not require vulcanization. With the continuous development of high-end PVC products, the demand for UHDP PVC resin is increasing daily, demonstrating broad application prospects and high practical value.

[0003] The production processes for ultra-high degree of polymerization products are mainly divided into low-temperature methods and chain extender methods. However, these existing preparation methods have some inherent defects: ultra-high degree of polymerization polyvinyl chloride resins produced by the chain extender method have problems such as wide molecular weight distribution, partial cross-linking structure requiring control of gel content, a large number of fish eyes, low porosity and oil absorption rate, and poor thermal stability; the low-temperature method has problems such as excessively long reaction time and low reaction efficiency.

[0004] In view of this, there is an urgent need to develop an efficient production method for ultra-high degree of polymerization polyvinyl chloride resin with advantages such as narrow molecular weight distribution, few fish eyes, and good thermal stability. Summary of the Invention

[0005] This application provides an ultra-high degree of polymerization polyvinyl chloride resin, its preparation method, and its application, in order to solve the problems of wide molecular weight distribution, numerous fish eyes, poor thermal stability, and low production efficiency of ultra-high degree polymer polyvinyl chloride resin in the prior art.

[0006] In a first aspect, this application provides a method for preparing ultra-high degree of polymerization polyvinyl chloride resin, comprising the following steps: S1, remove air from the reaction system, mix vinyl chloride monomer, first initiator, dispersant and water, and heat to the reaction temperature; S2, at the first stirring speed, the second initiator is continuously injected to carry out the polymerization reaction. After the reaction reaches the critical conversion rate, the injection of the second initiator is stopped, water is added to the reaction system, and the reaction continues at the second stirring speed; the first stirring speed is greater than the second stirring speed. S3. When the pressure drop ΔP of the reaction system reaches the preset value, a terminator is injected, the product is separated, and ultra-high degree of polymerization polyvinyl chloride resin is obtained.

[0007] In an optional embodiment, in S1, the mass ratio of the vinyl chloride monomer, the first initiator, the dispersant, and water is 100:0.01-0.07:0.12-0.15:120-160.

[0008] As an example, the mass ratio of the vinyl chloride monomer, the first initiator, the dispersant, and water can be 100:0.01:0.15:120, 100:0.03:0.14:130, 100:0.05:0.13:140, 100:0.07:0.12:160, 100:0.07:0.15:160, 100:0.01:0.12:120, or within any of the above ranges.

[0009] In one alternative embodiment, the mass ratio of the vinyl chloride monomer to the second initiator is 100:0.03-0.09; as an example, the mass ratio of the vinyl chloride monomer to the second initiator can be 100:0.03, 100:0.04, 100:0.05, 100:0.06, 100:0.07, 100:0.08, 100:0.09, or within any of the above values.

[0010] In one alternative embodiment, in S1, the reaction temperature is 29-39°C; as an example, the reaction temperature can be 29°C, 30°C, 32°C, 34°C, 35°C, 37°C, 39°C, or within any range of the above values.

[0011] In an alternative embodiment, in S1, removing air from the reaction system includes evacuating to -0.08 to -0.09 MPa.

[0012] In one alternative embodiment, the first initiator and the second initiator independently comprise diisobutyryl peroxide; In one optional embodiment, the dispersant includes at least one of polyvinyl alcohol and cellulose-based dispersants; optionally, it includes at least one of polyvinyl alcohol with a degree of hydrolysis of 40%-80% (including but not limited to polyvinyl alcohol with a degree of hydrolysis of 40%, 72%, or 80%), methylcellulose, hydroxyethylcellulose, and hydroxypropyl methylcellulose.

[0013] In an optional embodiment, in S2, the first stirring speed is 120-130 rpm; as an example, the first stirring speed can be 120 rpm, 122 rpm, 124 rpm, 125 rpm, 127 rpm, 129 rpm, 130 rpm, or within any of the above values.

[0014] In one alternative embodiment, the second stirring speed is 80-100 rpm. As an example, the second stirring speed can be 80 rpm, 83 rpm, 85 rpm, 88 rpm, 90 rpm, 92 rpm, 95 rpm, 97 rpm, 100 rpm, or within any range of the above values.

[0015] In an optional embodiment, in S2, the reaction time to reach the critical conversion rate is 5-8 hours; as an example, the time to reach the critical conversion rate can be 5 hours, 5.5 hours, 6 hours, 6.5 hours, 7 hours, 7.5 hours, 8 hours, or within any of the above values.

[0016] It should be noted that the time to reach the critical conversion rate varies for products with different degrees of polymerization, and can be determined based on experimental phenomena. After reaching the critical conversion rate, the gel effect of the reaction becomes obvious, heat transfer becomes difficult, the temperature difference between the jacket water and the inside of the reactor increases, the material inside the reactor becomes viscous or even semi-solid, and the stirring current increases. The reaction time to reach the critical conversion rate is approximately 60%-80% of the total reaction time.

[0017] In one alternative embodiment, the mass ratio of the vinyl chloride monomer to the water added in S2 is 100:25-35. As examples, the mass ratio of the vinyl chloride monomer to the water added in S2 is 100:25, 100:27, 100:29, 100:30, 100:32, 100:34, 100:35, or within any range of these values.

[0018] In an optional implementation, in S3, the preset value of the pressure drop ΔP is 0.08-0.12 MPa; as an example, the preset value of the pressure drop ΔP can be 0.08 MPa, 0.09 MPa, 0.10 MPa, 0.11 MPa, 0.12 MPa, or within any of the above values.

[0019] In one alternative embodiment, the amount of the terminating agent is 100-600 ppm, optionally 200-300 ppm, based on the mass of the vinyl chloride monomer. As an example, the amount of the terminating agent, based on the mass of the vinyl chloride monomer, is 100 ppm, 200 ppm, 300 ppm, 400 ppm, 500 ppm, 600 ppm, or within any range of the above values.

[0020] In an optional embodiment, in S3, the terminating agent includes at least one of hindered phenolic antioxidants and thioester antioxidants; Optionally, the hindered phenolic antioxidant includes triethylene glycol bis[3-(3-tert-butyl-5-methyl-4-hydroxyphenyl)propionate] (CAS: 36443-68-2), pentaerythritol tetrakis[β-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate] (CAS: 6683-19-8), octadecyl β-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate (CAS: 2082-79-3), and 1,3,5-tris(3,5-di-tert-butyl-4-hydroxybenzyl)-1,3,5-triazine-2,4,6 At least one of (1H,3H,5H)-trione (CAS: 27676-62-6); the thioester antioxidant includes at least one of didodecyl thiodipropionate (CAS: 123-28-4), dioctadecyl thiodipropionate (CAS: 693-36-7), and pentaerythritol tetra(3-lauryl thiopropionate) (CAS: 29598-76-3); Optionally, the terminating agent comprises a hindered phenolic antioxidant and a thioester antioxidant in a mass ratio of 3:2 to 4:1; as an example, the mass ratio of the hindered phenolic antioxidant to the thioester antioxidant can be 3:2, 3:1.5, 3:1, 4:1, 3.5:1, or within any range of the above values. The combined use of the two antioxidants results in better thermal stability and relatively higher whiteness over time.

[0021] In one alternative embodiment, the product separation includes the steps of stripping, centrifugation, and drying.

[0022] Secondly, this application provides an ultra-high degree of polymerization polyvinyl chloride resin, which is prepared by the above-described preparation method; Optionally, the average degree of polymerization of the ultra-high degree of polymerization polyvinyl chloride resin is 2500-4000. As an example, the average degree of polymerization of the ultra-high degree of polymerization polyvinyl chloride resin can be 2500, 2800, 3000, 3300, 3500, 3700, 3900, 4000, or within any range of the above values.

[0023] Thirdly, this application provides an application of the above-mentioned ultra-high degree of polymerization polyvinyl chloride resin in the fields of sealing materials, shoe sole materials, wires and cables (especially heat-resistant and cold-resistant cables), and medical products.

[0024] The technical solution of this application has the following advantages: This application provides an ultra-high degree of polymerization (UHDP) polyvinyl chloride (PVC) resin and its preparation method. The method employs a low-temperature suspension polymerization process and a segmented control process to produce PVC resin with an average degree of polymerization of 2500-4000. In the early stages of the reaction, a highly active initiator is continuously injected to enhance reaction efficiency, and a high stirring speed is maintained to improve material mixing and shearing effects. Once the critical conversion rate is reached, the initiator injection is stopped, water is added, and the stirring speed is reduced. This method results in a stable reaction and high production efficiency, overcoming the heat transfer limitations of traditional methods. The obtained UHDP resin particles have a narrow molecular weight distribution, high porosity and oil absorption, and few fisheyes, exhibiting excellent plasticizing and processing properties. Specifically, the UHDP PVC resin produced using the low-temperature method does not require the addition of chain extenders and features a narrow molecular weight distribution, good resin thermal stability, and few fisheyes. By employing continuous initiator injection and segmented control processes in the initial stages of the reaction, the polymerization time is shortened, resulting in better reaction safety and stability. The continuous initiator injection process allows for control of heat release by adjusting the injection flow rate, fully utilizing the cooling capacity of the unit for more uniform heat release and reducing peak heat release. This ensures timely removal of reaction heat from the production unit, guaranteeing high single-reactor utilization and production efficiency. Segmented control of stirring speed and water replenishment reduces the impact of the gelation effect, resulting in a resin with a loose structure, high porosity and oil absorption, and good plasticizing and processing properties.

[0025] The ultra-high degree of polymerization polyvinyl chloride resin and its preparation method provided in this application produce resin particles with regular morphology, moderate particle size and concentrated distribution.

[0026] Additional aspects and advantages of this application will be set forth in part in the description which follows, and in part will be obvious from the description, or may be learned by practice of this application. Attached Figure Description

[0027] To more clearly illustrate the technical solutions in the specific embodiments of this application or the prior art, the drawings used in the description of the specific embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are some embodiments of this application. For those skilled in the art, other drawings can be obtained from these drawings without creative effort.

[0028] Figure 1 This is an electron microscope image of the particle morphology of the ultra-high degree of polymerization polyvinyl chloride resin prepared in Example 1 of this application. Detailed Implementation

[0029] The following embodiments are provided to better understand this application. However, the following embodiments do not constitute a limitation on the content and scope of protection of this application. Any product that is the same as or similar to this application, derived by anyone under the guidance of this application or by combining the features of this application with other prior art, falls within the scope of protection of this application.

[0030] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this application belongs; the terminology used herein is for the purpose of describing particular embodiments only and is not intended to limit the application; the terms “comprising” and “having” and any variations thereof in the text of this application are intended to cover non-exclusive inclusion.

[0031] In the description of the embodiments of this application, the technical terms "first", "second", etc. are used only to distinguish different objects and should not be construed as indicating or implying relative importance or implicitly indicating the number, specific order or primary and secondary relationship of the indicated technical features.

[0032] In this document, the term "embodiment" means that a particular feature, structure, or characteristic described in connection with an embodiment may be included in at least one embodiment of this application. The appearance of this phrase in various places throughout the specification does not necessarily refer to the same embodiment, nor is it a separate or alternative embodiment mutually exclusive with other embodiments. It will be explicitly and implicitly understood by those skilled in the art that the embodiments described herein can be combined with other embodiments. The "range" disclosed in this application is defined by a lower limit and an upper limit. A given range is defined by selecting a lower limit and an upper limit, which define the boundaries of the specific range. Ranges defined in this way can include or exclude endpoints and can be arbitrarily combined; that is, any lower limit can be combined with any upper limit to form a range. In this application, unless otherwise stated, the numerical range "ab" represents a shortened representation of any combination of real numbers from a to b, where a and b are real numbers. For example, the numerical range "0-5" indicates that all real numbers between "0-5" have been listed herein, and "0-5" is merely a shortened representation of these numerical combinations. Furthermore, when a parameter is described as an integer ≥ 2, it is equivalent to disclosing that the parameter can be, for example, integers 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, etc.

[0033] In the description of the embodiments in this application, the term "and / or" is merely a description of the relationship between related objects, indicating that three relationships can exist. For example, A and / or B can represent: A existing alone, A and B existing simultaneously, and B existing alone. Additionally, the character " / " in this document generally indicates that the preceding and following related objects have an "or" relationship.

[0034] In the description of the embodiments of this application, the term "at least one" refers to one or more (including two).

[0035] Unless otherwise specified, all steps of this application may be performed sequentially or randomly, but sequentially is preferred.

[0036] Unless otherwise specified, all experimental steps or conditions in the examples were performed according to conventional experimental procedures and conditions in the art. Reagents or instruments whose manufacturers are not specified are all commercially available products.

[0037] The present application will now be described with reference to specific embodiments. It should be noted that these embodiments are merely descriptive and do not limit the present application in any way.

[0038] Example 1 This embodiment provides a method for preparing ultra-high degree of polymerization polyvinyl chloride resin, and the specific steps and operating parameters are as follows: a) Clean the polymerization reactor thoroughly, spray with an anti-sticking agent, and evacuate to -0.09 MPa. First, add 120 parts by weight of deionized water, 0.12 parts by weight of dispersant (composed of polyvinyl alcohol with a degree of alcoholysis of 80%, 72%, and 40%, in a ratio of 6:8:1), 0.03 parts by weight of highly active initiator diisobutyryl peroxide, and 100 parts by weight of vinyl chloride monomer to the polymerization reactor. At the same time, start the jacketed water bath circulation to control the temperature of the system inside the polymerization reactor to quickly reach the process set value of 38.7°C, and start timing the reaction.

[0039] b) The reaction temperature of the polymerization system was stabilized at 38.7℃ by using the water bath circulation in the jacket of the polymerization reactor. The stirring speed was set to 120 rpm. During the reaction, 0.05 parts of highly active initiator diisobutyryl peroxide were continuously injected. After 5 hours of reaction (when the reaction reached the critical conversion rate), the injection of initiator was stopped and 25 parts of deionized water were added. The stirring speed was reduced to 100 rpm and the reaction continued.

[0040] c) When the polymerization reaction is maintained until the system pressure drop ΔP reaches the process set value of 0.1 MPa, 0.02 parts by weight of a terminator (composed of triethylene glycol bis[3-(3-tert-butyl-5-methyl-4-hydroxyphenyl)propionate] and didodecyl thiodipropionate in a ratio of 4:1) is injected into the polymerization reactor to terminate the polymerization reaction. The slurry is stripped, centrifuged, and dried to obtain ultra-high degree of polymerization polyvinyl chloride resin.

[0041] Figure 1The image shows an electron microscope (EM) image of the particle morphology of the product obtained in this embodiment. As can be seen from the image, the resin particles have a regular morphology, moderate particle size, and concentrated distribution. The morphological structures of other embodiments are similar to those in this embodiment and will not be shown individually.

[0042] Example 2 This embodiment provides a method for preparing ultra-high degree of polymerization polyvinyl chloride resin, and the specific steps and operating parameters are as follows: a) Clean the polymerization reactor thoroughly, spray with an anti-sticking agent, and evacuate to -0.09 MPa. First, add 140 parts by weight of deionized water, 0.13 parts by weight of dispersant (composed of polyvinyl alcohol with a degree of alcoholysis of 80%, 72%, and 40%, in a ratio of 6:8:1), 0.04 parts by weight of highly active initiator diisobutyryl peroxide, and 100 parts by weight of vinyl chloride monomer to the polymerization reactor. At the same time, start the jacketed water bath circulation to control the temperature of the system inside the polymerization reactor to quickly reach the process set value of 35.2℃, and start timing the reaction.

[0043] b) The reaction temperature of the polymerization system was stabilized at 35.2℃ by using the jacket water bath circulation of the polymerization reactor. The stirring speed was set to 125 rpm. During the reaction, 0.06 parts of highly active initiator diisobutyryl peroxide were continuously injected. After 6 hours of reaction, the injection of initiator was stopped and 30 parts of deionized water were added. The stirring speed was reduced to 95 rpm to continue the reaction.

[0044] c) When the polymerization reaction is maintained until the system pressure drop ΔP reaches the process set value of 0.1 MPa, 0.022 parts by weight of a terminator (composed of triethylene glycol bis[3-(3-tert-butyl-5-methyl-4-hydroxyphenyl)propionate] and didodecyl thiodipropionate in a ratio of 4:1) is injected into the polymerization reactor to terminate the polymerization reaction. The slurry is stripped, centrifuged, and dried to obtain ultra-high degree of polymerization polyvinyl chloride resin.

[0045] Example 3 This embodiment provides a method for preparing ultra-high degree of polymerization polyvinyl chloride resin, and the specific steps and operating parameters are as follows: a) Clean the polymerization reactor thoroughly, spray with an anti-sticking agent, and evacuate to -0.09 MPa. First, add 150 parts by weight of deionized water, 0.14 parts by weight of dispersant (composed of polyvinyl alcohol and hydroxypropyl methylcellulose with a degree of alcoholysis of 80%, 72%, and 40%, respectively, in a ratio of 4:6:1:2), 0.045 parts by weight of highly active initiator diisobutyryl peroxide, and 100 parts by weight of vinyl chloride monomer to the polymerization reactor. At the same time, start the jacketed water bath circulation to control the temperature of the system inside the polymerization reactor to quickly reach the process set value of 32.2℃, and start timing the reaction.

[0046] b) The reaction temperature of the polymerization system was stabilized at 32.2℃ using a water bath circulation system in the jacket of the polymerization reactor. The stirring speed was set to 125 rpm. During the reaction, 0.065 parts of highly active initiator diisobutyryl peroxide were continuously injected. After 6.5 h of reaction, the injection of initiator was stopped and 33 parts of deionized water were added. The stirring speed was reduced to 90 rpm and the reaction continued.

[0047] c) When the polymerization reaction is maintained until the system pressure drop ΔP reaches the process set value of 0.09 MPa, 0.025 parts by weight of a terminator (composed of pentaerythritol tetrakis[β-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate] and dioctadecyl thiodipropionate in a ratio of 2:1) is injected into the polymerization reactor to terminate the polymerization reaction. The slurry is stripped, centrifuged, and dried to obtain ultra-high degree of polymerization polyvinyl chloride resin.

[0048] Example 4 This embodiment provides a method for preparing ultra-high degree of polymerization polyvinyl chloride resin, and the specific steps and operating parameters are as follows: a) Clean the polymerization reactor thoroughly, spray with an anti-sticking agent, and evacuate to -0.09 MPa. First, add 160 parts by weight of deionized water, 0.15 parts by weight of dispersant (composed of polyvinyl alcohol and hydroxypropyl methylcellulose with a degree of alcoholysis of 80%, 72%, and 40%, respectively, in a ratio of 4:6:1:2), 0.05 parts by weight of highly active initiator diisobutyryl peroxide, and 100 parts by weight of vinyl chloride monomer to the polymerization reactor. At the same time, start the jacketed water bath circulation to control the temperature of the system inside the polymerization reactor to quickly reach the process set value of 29.8℃, and start timing the reaction.

[0049] b) The reaction temperature of the polymerization system was stabilized at 29.8℃ by using the jacket water bath circulation of the polymerization reactor. The stirring speed was set to 130 rpm. During the reaction, 0.07 parts of highly active initiator diisobutyryl peroxide were continuously injected. After 7 hours of reaction, the injection of initiator was stopped and 33 parts of deionized water were added. The stirring speed was reduced to 80 rpm to continue the reaction.

[0050] c) When the polymerization reaction is maintained until the system pressure drop ΔP reaches the process set value of 0.09 MPa, 0.03 parts by weight of a terminator (composed of pentaerythritol tetrakis[β-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate] and dioctadecyl thiodipropionate in a ratio of 2:1) is injected into the polymerization reactor to terminate the polymerization reaction. The slurry is stripped, centrifuged, and dried to obtain ultra-high degree of polymerization polyvinyl chloride resin.

[0051] Example 5 This embodiment provides a method for preparing ultra-high degree of polymerization polyvinyl chloride resin, and the specific steps and operating parameters are as follows: a) Clean the polymerization reactor thoroughly, spray with an anti-sticking agent, and evacuate to -0.09 MPa. First, add 140 parts by weight of deionized water, 0.13 parts by weight of dispersant (the dispersant is a compound of polyvinyl alcohol and methylcellulose with a degree of alcoholysis of 80%, 72%, and 40%, in a ratio of 4:6:1:2), 0.04 parts by weight of highly active initiator diisobutyryl peroxide, and 100 parts by weight of vinyl chloride monomer to the polymerization reactor. At the same time, start the jacketed water bath circulation to control the temperature of the system inside the polymerization reactor to quickly reach the process set value of 35.2℃, and start timing the reaction.

[0052] b) The reaction temperature of the polymerization system was stabilized at 35.2℃ by using the jacket water bath circulation of the polymerization reactor. The stirring speed was set to 125 rpm. During the reaction, 0.06 parts of highly active initiator diisobutyryl peroxide were continuously injected. After 6 hours of reaction, the injection of initiator was stopped and 30 parts of deionized water were added. The stirring speed was reduced to 95 rpm to continue the reaction.

[0053] c) When the polymerization reaction is maintained until the system pressure drop ΔP reaches the process set value of 0.1 MPa, 0.022 parts by weight of a terminator (the terminator is a single type of pentaerythritol tetrakis[β-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate]) is injected into the polymerization reactor to terminate the polymerization reaction. The slurry is stripped, centrifuged, and dried to obtain ultra-high degree of polymerization polyvinyl chloride resin.

[0054] Comparative Example 1 This comparative example provides a method for preparing ultra-high degree of polymerization polyvinyl chloride resin. The difference from Example 1 is that the initiator is added only once, that is, the amount of initiator added in step a) is 0.08 parts by weight, and no initiator is added in step b).

[0055] Comparative Example 2 This comparative example provides a method for preparing ultra-high degree of polymerization polyvinyl chloride resin. The difference from Example 1 is that the initiator is added only once, that is, no initiator is added in step a), and the amount of initiator added in step b) is 0.08 parts by weight.

[0056] Comparative Example 3 This comparative example provides a method for preparing ultra-high degree of polymerization polyvinyl chloride resin. The difference from Example 1 is that the initiator in step a) is cumyl peroxyneodecanate, and the amount added is 0.14 parts by weight. In step b), no initiator is added.

[0057] Comparative Example 4 This comparative example provides a method for preparing ultra-high degree of polymerization polyvinyl chloride resin. The difference from Example 1 is that deionized water is not added in step b).

[0058] Comparative Example 5 This comparative example provides a method for preparing ultra-high degree of polymerization polyvinyl chloride resin. The difference from Example 1 is that the stirring speed remains unchanged, and the stirring speed in step b) is always maintained at 130 rpm.

[0059] Comparative Example 6 This comparative example provides a method for preparing ultra-high degree of polymerization polyvinyl chloride resin. The difference from Example 1 is that the stirring speed remains unchanged, and the stirring speed in step b) is always maintained at 80 rpm.

[0060] Experimental Example The ultra-high degree of polymerization polyvinyl chloride resins provided in each embodiment and comparative example were subjected to various performance tests. The specific test items and methods are as follows: the average degree of polymerization, apparent density, oil absorption rate, fish eye, and aging whiteness were all tested according to the test methods specified in the national standard GB / T5761-2006. The molecular weight distribution index was determined by gel permeation chromatography. The average particle size and particle size distribution were measured by wet injection using a laser particle size analyzer. The plasticizing time was determined by the complete roll wrap time of the two-roll mill. The porosity was determined by mercury intrusion porosimetry.

[0061] The specific test results are shown in the table below: Table 1

[0062] As shown in the table above, the continuous injection process using a highly active initiator (Example 1) resulted in the shortest reaction time and the highest production efficiency. While the initiator was added only once before the reaction (Comparative Example 1), resulting in the shortest reaction time, the polymerization rate was too fast in the early stages, making temperature control difficult and even risking explosive polymerization. The excessively fast reaction rate in the early stages also led to an excessive number of fisheyes in the product. The continuous injection of the initiator only during the reaction (Comparative Example 2) resulted in a longer reaction time, while the reaction time was even longer when using a lower-activity initiator (Comparative Example 3). In Comparative Example 4, the lack of deionized water replenishment in the later stages of the reaction led to a severe gel effect, a decrease in the heat transfer coefficient, and large temperature fluctuations, resulting in a wider molecular weight distribution and more fisheyes. From the test results of Example 1 and Comparative Examples 5 and 6, the particle morphology and particle size distribution were the best with the variable stirring speed process. A consistently low stirring speed resulted in poor shear dispersion and larger particle sizes, while a consistently high stirring speed led to higher aggregation and fusion of primary particles, resulting in lower oil absorption and more fisheyes.

[0063] Obviously, the above embodiments are merely illustrative examples for clear explanation and are not intended to limit the implementation. Those skilled in the art will recognize that other variations or modifications can be made based on the above description. It is neither necessary nor possible to exhaustively list all possible implementations here. However, obvious variations or modifications derived therefrom are still within the scope of protection of this invention.

Claims

1. A method for preparing ultra-high degree of polymerization polyvinyl chloride resin, characterized in that, Includes the following steps: S1, remove air from the reaction system, mix vinyl chloride monomer, first initiator, dispersant and water, and heat to the reaction temperature; S2, at the first stirring speed, the second initiator is continuously injected to carry out the polymerization reaction. After the reaction reaches the critical conversion rate, the injection of the second initiator is stopped, water is added to the reaction system, and the reaction continues at the second stirring speed; the first stirring speed is greater than the second stirring speed. S3. When the pressure drop ΔP of the reaction system reaches the preset value, a terminator is injected, the product is separated, and ultra-high degree of polymerization polyvinyl chloride resin is obtained.

2. The method for preparing ultra-high degree of polymerization polyvinyl chloride resin according to claim 1, characterized in that, In S1, the mass ratio of the vinyl chloride monomer, the first initiator, the dispersant, and water is 100:0.01-0.07:0.12-0.15:120-160.

3. The method for preparing ultra-high degree of polymerization polyvinyl chloride resin according to claim 1, characterized in that, The mass ratio of the vinyl chloride monomer to the second initiator is 100:0.03-0.09; And / or, in S1, the reaction temperature is 29-39°C; And / or, in S1, the removal of air from the reaction system includes evacuating to -0.08 to -0.09 MPa.

4. The method for preparing ultra-high degree of polymerization polyvinyl chloride resin according to claim 1, characterized in that, The first initiator and the second initiator independently include diisobutyryl peroxide; And / or, the dispersant includes at least one of polyvinyl alcohol and cellulose dispersants; optionally, it includes at least one of polyvinyl alcohol, methylcellulose, hydroxyethylcellulose, and hydroxypropyl methylcellulose with a degree of hydrolysis of 40%-80%.

5. The method for preparing ultra-high degree of polymerization polyvinyl chloride resin according to claim 1, characterized in that, In S2, the first stirring speed is 120-130 rpm; And / or, the second stirring speed is 80-100 rpm.

6. The method for preparing ultra-high degree of polymerization polyvinyl chloride resin according to claim 1, characterized in that, In S2, the reaction time to reach the critical conversion rate is 5-8 hours; And / or, the mass ratio of the vinyl chloride monomer to the water added in S2 is 100:25-35.

7. The method for preparing ultra-high degree of polymerization polyvinyl chloride resin according to claim 1, characterized in that, In S3, the preset value for pressure drop ΔP is 0.08-0.12 MPa; And / or, based on the mass of the vinyl chloride monomer, the amount of the terminating agent is 100-600 ppm, optionally 200-300 ppm.

8. The method for preparing ultra-high degree of polymerization polyvinyl chloride resin according to any one of claims 1-7, characterized in that, In S3, the terminating agent includes at least one of hindered phenolic antioxidants and thioester antioxidants; Optionally, the hindered phenolic antioxidant includes at least one of triethylene glycol bis[3-(3-tert-butyl-5-methyl-4-hydroxyphenyl)propionate], pentaerythritol tetrakis[β-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate], octadecyl β-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate, and 1,3,5-tris(3,5-di-tert-butyl-4-hydroxybenzyl)-1,3,5-triazine-2,4,6(1H,3H,5H)-trione; the thioester antioxidant includes at least one of didodecyl thiodipropionate, dioctadecyl thiodipropionate, and pentaerythritol tetra(3-lauryl thiopropionate). Optionally, the terminating agent comprises a hindered phenolic antioxidant and a thioester antioxidant in a mass ratio of 3:2 to 4:1; And / or, the product separation includes the steps of stripping, centrifugation, and drying.

9. A polyvinyl chloride resin with ultra-high degree of polymerization, characterized in that, Prepared by the preparation method according to any one of claims 1-8; Optionally, the average degree of polymerization of the ultra-high degree of polymerization polyvinyl chloride resin is 2500-4000.

10. The application of the ultra-high degree of polymerization polyvinyl chloride resin according to claim 9 in the fields of sealing materials, shoe sole materials, wires and cables, and medical products.

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