Low-cyclic polysiloxane segmented preparation method and segmented telomerization reactor

Abstract

This invention belongs to the field of organosilicon chemical synthesis technology, and discloses a segmented preparation method for low-cyclic polysiloxanes and a segmented polymerization reactor. The method includes: raw material pretreatment, segmented polymerization reaction, termination and purification, and post-treatment. The segmented polymerization reaction is carried out in an integrated segmented polymerization reactor, and includes, in sequence: 1) initiation of polycondensation under ultrasonic action; 2) end-capping polymerization under high shear action; 3) homogenization reaction under thermal equilibrium conditions. The segmented polymerization reactor integrates an ultrasonic dispersion reaction zone, a high-shear polymerization reaction zone, and a thermal equilibrium adjustment zone from top to bottom. Compared with the prior art, this invention effectively reduces the cyclic content and metal ion residue in the product through segmented reaction and refined control, improves product purity, uniformity of molecular weight distribution, and reaction efficiency, and is suitable for the continuous production of high-quality polysiloxanes.

Description

Technical Field

[0001] This invention relates to the field of organosilicon chemical synthesis technology, and in particular to a method for the segmented preparation of low-cyclic polysiloxanes and a segmented polymerization reactor. Background Technology

[0002] Polysiloxanes are an important class of polymer materials, and the purity and quality of their base polymers—low-cyclic polysiloxanes (such as D4, D5, etc.)—directly affect the performance of downstream products. Traditional preparation methods typically employ acid-base catalytic equilibrium polymerization, which has the following drawbacks: 1. High cyclic content: There are many side reactions during the reaction process, resulting in a high cyclic content in the product, which affects the rate of subsequent ring-opening polymerization and the molecular weight distribution of the polymer.

[0003] 2. Catalyst residue: To ensure the reaction rate, the amount of catalyst added is often too large, and the subsequent neutralization and filtration steps are complicated, which can easily lead to poor product transparency and high metal ion residue, affecting the product's electrical performance.

[0004] 3. Uneven reaction: As the degree of polymerization increases, the viscosity of the material rises sharply, which makes mass and heat transfer difficult, resulting in uneven temperature and concentration in the reaction system, wide molecular weight distribution, and poor product uniformity.

[0005] 4. Difficulty in removing moisture: If the moisture generated by the condensation reaction is not removed in time, it will inhibit the forward reaction. The traditional stirring method has low water vapor removal efficiency.

[0006] Patent CN117777452A discloses a method for preparing medium-low viscosity vinyl silicone oil, which uses nitrogen to remove water. However, if the product viscosity increases, the water is difficult to remove, and the water will affect the catalyst activity, thus weakening the dehydration effect of this method. Patent CN118955911A discloses a method for preparing medium-high viscosity vinyl-terminated polydimethylsiloxane, using potassium hydroxide as a terminator, which introduces metal ions (K), failing to meet the requirements for electronic-grade polysiloxane. Furthermore, the terminator preparation processes in patents CN118955911A and CN111378135A involve the introduction of cyclic siloxanes, which will lead to an increase in the cyclic content in the final product.

[0007] Therefore, there is an urgent need in this field for a preparation method and specialized equipment that can precisely control the degree of polymerization, effectively reduce the cyclic content, reduce the amount of catalyst used, and improve the purity of the product. Summary of the Invention

[0008] To address the aforementioned technical problems, this invention provides a segmented preparation method for low-cyclic polysiloxanes and a segmented polymerization reactor. Through segmented reaction and refined post-processing, precise control of the polymerization process is achieved, ultimately yielding high-quality polysiloxane products with low cyclicity, low metal content, and uniform molecular weight distribution.

[0009] To achieve this technical objective, the present invention adopts the following solution: In a first aspect, the present invention provides a method for the segmented preparation of low-cyclic polysiloxanes, comprising the following steps: Step 1: Raw material pretreatment

[0010] Hydroxyl-terminated polydimethylsiloxane and capping agent were added to two raw material processing vessels containing metal adsorbents, respectively. The mixture was heated to 50-60°C and stirred for 20-40 minutes. The materials were then sequentially fed into a pre-filter and a fine filter to thoroughly remove adsorbent particles and mechanical impurities. Step 2: Segmented polymerization reaction

[0011] The processed raw materials enter a segmented polymerization reactor for a three-stage reaction: A single ultrasonic-induced polycondensation reaction: The treated hydroxyl-terminated polydimethylsiloxane and the catalyst were simultaneously added to the ultrasonic dispersion reaction zone of the segmented polymerization reactor. The reaction was carried out at a temperature of 60~80℃, a vacuum degree of -0.07~-0.1 MPa, and an ultrasonic power of 100~500W / L for 8~12 minutes. The amount of catalyst added was 25~75ppm. Two-stage high-shear end-capping polymerization reaction: The material after the first stage reaction enters the second-stage high-shear polymerization reaction zone, and the treated end-capping agent and supplemented catalyst are added at the same time. Under the conditions of temperature 80~120℃, vacuum degree -0.05 ~ -0.08 MPa, rotor speed 5000~20000 RPM, and rotor tip linear velocity 20~50m / s, the reaction is carried out for 8~12 minutes, and the total amount of effective catalyst components added is controlled at 5~15ppm. Three-stage thermal equilibrium homogenization: The material after the two-stage reaction enters the three-stage thermal equilibrium homogenization zone and undergoes a polymerization equilibrium reaction at 100~120℃ for 20~40 min; Step 3: Termination and Purification

[0012] A terminator was added to the reaction product of step two, and then short-path distillation was carried out at a temperature of 150~180℃ and a vacuum of -0.095~-0.1 MPa to obtain the crude product. Step 4: Post-processing

[0013] The crude product is cooled and deeply dehydrated by passing it through a molecular sieve adsorption column to obtain a low-cyclic, high-purity polysiloxane product.

[0014] Furthermore, in step one, the metal adsorbent is two of the following: disodium EDTA, hydroxyethylidene diphosphonic acid (HEDP), and aminotrimethylene phosphonic acid (ATMP). The pre-filter uses a filter bag with a precision of 5~15μm, and the fine filter uses a filter element with a precision of 0.5~1μm.

[0015] Furthermore, the hydroxyl-terminated polydimethylsiloxane has a viscosity of 80~120 mPa·s at 25°C and a hydroxyl content of 0.8%~1.5%; the end-capping agent is MD. 10 M (dodecyl undecylsiloxane), the amount of capping agent added is 20% of the mass of hydroxyl-terminated polydimethylsiloxane.

[0016] Furthermore, the catalyst is a solution of triphosphazene chloride (NPCl2)3 ligand P4-tert-butyl or a solution of tetraphosphazene chloride (NPCl2)4 ligand P4-tert-butyl.

[0017] Furthermore, in the first, second, and third stages of the reaction in step two, inert gas is introduced and vacuum is applied to remove the water generated during the reaction from the reaction system in a timely manner.

[0018] Furthermore, in step three, the terminating agent is at least one of triethylamine or diethylamine, and the amount of terminating agent added is 15~50 ppm.

[0019] Furthermore, in step four, the molecular sieve is a 3A or 4A type molecular sieve.

[0020] Secondly, the present invention provides a segmented polymerization reactor used in the aforementioned segmented preparation method of low-cyclic polysiloxanes. The segmented polymerization reactor is an integrated, one-piece structure, divided into three functional areas from top to bottom, including: An ultrasonic dispersion reaction zone is located at the top of the reactor and includes an ultrasonic dispersion device with a sound-permeable membrane structure at its bottom. The second-stage high-shear polymerization reaction zone is located in the middle of the reactor and is directly connected to the first-stage zone. It includes a rotor-stator high-shear mixer and a gear ring installed in the cavity. The three-stage thermal equilibrium homogenization zone is located at the bottom of the reactor and is a regulating vessel equipped with a planetary stirrer.

[0021] Furthermore, a feed inlet and a vacuum port are provided at the top of the first ultrasonic dispersion reaction zone and the top of the second high-shear polymerization reaction zone; an inert gas coil is provided at the bottom of the first ultrasonic dispersion reaction zone, the second high-shear polymerization reaction zone, and the third thermal equilibrium homogenization zone.

[0022] Furthermore, a jacketed heating system is provided outside the first ultrasonic dispersion reaction zone and the third thermal equilibrium homogenization zone, with a heating steam inlet and a heating steam outlet; a jacketed cooling system is provided outside the second high-shear polymerization reaction zone, with a cooling water inlet and a cooling water outlet.

[0023] Compared with the prior art, the beneficial effects of the present invention are as follows: 1. Extremely high product purity: Through raw material pretreatment (adsorption + filtration) and segmented precise control, the content of metal impurities and cyclic byproducts is effectively reduced.

[0024] 2. Improved reaction efficiency and controllability: Ultrasonic initiation shortens the induction period; high-shear mixing ensures the immediacy and uniformity of the end-capping reaction; planetary stirring ensures the uniformity of the equilibrium stage, resulting in a narrower molecular weight distribution.

[0025] 3. High-efficiency energy utilization: Segmented energy concentration achieves "on-demand function", avoiding ineffective energy dissipation and significantly reducing total energy consumption.

[0026] 4. Highly efficient moisture removal: All three stages of the reaction combine vacuum and physical methods (cavitation effect to generate microbubbles, shear surface renewal, and bubbling) to strongly push the reaction equilibrium to the right, thereby improving the conversion rate.

[0027] 5. Equipment integration and continuous operation: The integrated segmented reactor design reduces material transfer steps, lowers the risk of contamination, and lays the foundation for continuous and automated production. Attached Figure Description

[0028] Figure 1 This is a schematic diagram of the segmented polymerization reactor structure in an embodiment of the present invention.

[0029] Figure 2 for Figure 1 Top view of plane AA in the middle.

[0030] The diagram is labeled as follows: 1. First-stage ultrasonic dispersion reaction zone; 2. Second-stage high-shear polymerization reaction zone; 3. Third-stage thermal equilibrium homogenization zone; 4. Rotor-stator high-shear mixer; 5. Planetary agitator; 6. Vacuum port; 7. Feed inlet; 8. Heating steam inlet; 9. Heating steam outlet; 10. Cooling water inlet; 11. Cooling water outlet; 12. Acoustic membrane; 13. Ultrasonic probe; 14. Inert gas coil; 15. Gear ring. Detailed Implementation

[0031] To make the objectives, technical solutions, and advantages of the present invention clearer, the technical solutions in the embodiments of the present invention will be clearly and completely described below in conjunction with the embodiments of the present invention. Obviously, the described embodiments are some embodiments of the present invention, but not all embodiments.

[0032] Unless otherwise specified, the experimental methods used in the embodiments and comparative examples of this invention are conventional methods. Unless otherwise specified, the materials and reagents used are commercially available.

[0033] This invention provides a segmented preparation method for low-cyclic polysiloxanes, comprising the following steps: Step 1: Raw material pretreatment

[0034] Hydroxyl-terminated polydimethylsiloxane (silanol silicone oil) and the capping agent were added to two raw material processing vessels containing metal adsorbents, respectively. The mixture was heated to 50-60°C and stirred for 20-40 minutes to complex and remove trace metal impurities from the raw materials. After processing, the materials were sequentially fed into a pre-filter and a fine filter to thoroughly remove adsorbent particles and mechanical impurities.

[0035] The hydroxyl-terminated polydimethylsiloxane has a viscosity of 80~120 mPa·s at 25°C and a hydroxyl content of 0.8%~1.5%; the end-capping agent is MD. 10 M (dodecyl undecylsiloxane), the amount of capping agent added is 20% of the mass of hydroxyl-terminated polydimethylsiloxane.

[0036] The metal adsorbent is two of the following: disodium EDTA, hydroxyethylidene diphosphonic acid (HEDP), and aminotrimethylene phosphonic acid (ATMP); the pre-filter uses a filter bag with a precision of 5~15μm, and the fine filter uses a filter element with a precision of 0.5~1μm. Step 2: Segmented polymerization reaction

[0037] The processed raw materials enter a segmented polymerization reactor for a three-stage reaction: A single ultrasonic-initiated polycondensation reaction: The treated hydroxyl-terminated polydimethylsiloxane and the catalyst (a solution of triphosphazene chloride (NPCl2)3 ligand P4-tert-butyl or tetraphosphazene chloride (NPCl2)4 ligand P4-tert-butyl) are simultaneously added to a single ultrasonic dispersion reaction zone of a segmented polymerization reactor. The reaction is carried out at a temperature of 60~80℃, a vacuum degree of -0.07~-0.1 MPa, and an ultrasonic power of 100~500W / L for 8~12 min. The amount of catalyst added is 25~75ppm.

[0038] The cavitation effect of ultrasound significantly improves the dispersion efficiency of the catalyst in viscous hydroxyl-terminated polydimethylsiloxane and may form highly active ionic aggregates, thereby rapidly initiating a condensation reaction to generate an intermediate with a certain degree of polymerization. Simultaneously, by introducing inert gas through a coil and using a vacuum device to create a vacuum, the water generated during the reaction is promptly removed from the system.

[0039] Two-stage high-shear end-capping polymerization reaction: The material after the first-stage reaction enters the second-stage high-shear polymerization reaction zone, and the treated MD is added at the same time. 10 M-type end-capping agent and supplementary catalyst (total effective catalyst content controlled at 5~15ppm) are reacted from top to bottom for 8~12 minutes under the conditions of temperature 80~120℃, vacuum degree -0.05 ~ -0.08 MPa, rotor speed 5000~20000 RPM, and rotor tip linear velocity 20~50m / s.

[0040] During this stage, the material viscosity increases, and the high shear effect not only enables instantaneous and uniform mixing of the capping agent and intermediates and precise control of the chain end structure, but also the local high temperature generated further promotes the reaction and efficiently removes residual moisture under vacuum conditions.

[0041] Three-stage thermal equilibrium homogenization: The material after the second stage reaction enters the third-stage thermal equilibrium homogenization zone, where a polymerization equilibrium reaction is carried out at 100~120℃ for 20~40 minutes; the purpose of this stage is to rearrange the molecular chains to achieve thermodynamic equilibrium, thereby making the degree of polymerization more uniform. Step 3: Termination and Purification

[0042] A terminator is added to the reaction product of step two, followed by short-path distillation at a temperature of 150~180℃ and a vacuum of -0.095~-0.1 MPa to remove unreacted monomers, capping agents, and water produced in the reaction, yielding a crude product.

[0043] The terminator is at least one of triethylamine or diethylamine, and the amount of terminator added is 30-50 ppm. Step 4: Post-processing

[0044] The crude product is cooled and deeply dehydrated by passing it through a 3A or 4A type molecular sieve adsorption column to obtain a low-cyclic, high-purity polysiloxane product.

[0045] Please see Figure 1 and Figure 2 This invention provides a segmented polymerization reactor used in the aforementioned segmented preparation method of low-cyclic polysiloxanes. The segmented polymerization reactor is an integrated, one-piece structure, divided into three functional areas from top to bottom, including: An ultrasonic dispersion reaction zone 1 is located at the top of the reactor and includes an ultrasonic dispersion device. In this design, the ultrasonic dispersion device uses an ultrasonic probe 13. A sound-permeable membrane 12 and an inert gas coil 14 are installed at the bottom. The structure of the sound-permeable membrane 12 allows energy to be transferred downwards. The inert gas coil 14 is used to blow in gas to cooperate with the vacuum system to remove moisture generated during the reaction. A feed inlet 7 and a vacuum port 6 are installed at the top. The vacuum port 6 is connected to the vacuum system. An external jacketed heating system is installed, which has a heating steam inlet 8 and a heating steam outlet 9.

[0046] The second-stage high-shear polymerization reaction zone 2, located in the middle of the reactor, is directly connected to the first-stage ultrasonic dispersion reaction zone 1. It includes a rotor-stator high-shear mixer 4 and a gear ring 15 housed within the cavity. The rotor-stator high-shear mixer 4 provides shear force for the high-viscosity materials, working in conjunction with the gear ring 15 to ensure more uniform mixing and promote the reaction. A feed inlet 7 and a vacuum port 6 are located at the top, and an inert gas coil 14 is located at the bottom. An external jacketed cooling system with a cooling water inlet 10 and a cooling water outlet 11 is provided to prevent the material temperature from exceeding 150°C due to high-shear heat generation.

[0047] The three-stage thermal equilibrium homogenization zone 3, located at the bottom of the reactor, is a regulating vessel equipped with a planetary stirrer 5 to ensure uniform mixing and heat transfer of high-viscosity materials without dead zones. An inert gas coil 14 is installed at the bottom to provide an inert atmosphere during the reaction and to assist in material bubbling, further aiding in the removal of low-boiling-point substances. An external jacketed heating system is provided, with a heating steam inlet 8 and a heating steam outlet 9. Example 1

[0048] Step 1: Mix 1000g of hydroxyl-terminated polydimethylsiloxane (viscosity 95 mPa·s, hydroxyl content 1.2%) with 200g of MD 10 M-type end-capping agent was added to two raw material processing reactors containing disodium EDTA and hydroxyethylidene diphosphonic acid, respectively. The mixture was heated to 60°C and stirred for 20 minutes. Subsequently, it was filtered sequentially through a 15μm filter bag and a 1μm absolute precision polypropylene filter cartridge.

[0049] Step 2: The processed raw materials enter the segmented polymerization reactor for a three-stage reaction: A single ultrasonic-induced polycondensation reaction was performed: the treated hydroxyl-terminated polydimethylsiloxane and a 35 ppm solution of triphosphazene chloride (NPCl2)3 ligand P4-tert-butyl were added to the ultrasonic dispersion reaction zone of the segmented reactor and ultrasonically treated (power 100W / L) for 10 min at 70℃ and -0.07 MPa.

[0050] Two-stage high-shear end-capping polymerization reaction: The material enters the two-stage high-shear polymerization reaction zone, and the remaining 15ppm of triphosphazene chloride (NPCl2)3 ligand P4-tert-butyl solution and MD are added. 10 M sealing agent, ensure temperature does not exceed 120℃, vacuum -0.05MPa, high shear machine speed 5000RPM (linear speed about 25m / s), reaction time about 10min.

[0051] Three-stage thermal equilibrium homogenization: The material enters the three-stage thermal equilibrium homogenization zone, is heated to 110℃, and reacted by planetary stirring for 30 minutes.

[0052] Step 3: Add 25 ppm of diethylamine to terminate the reaction, then heat to 160°C and perform short-path distillation at -0.096 MPa.

[0053] Step 4: After distillation, the product is cooled to room temperature by passing it through a 4A molecular sieve column to obtain the target product. Example 2

[0054] Step 1: Mix 1000g of hydroxyl-terminated polydimethylsiloxane (viscosity 100 mPa·s, hydroxyl content 1.1%) with 200g of MD 10 M-type end-capping agent was added to two raw material processing reactors containing hydroxyethylidene diphosphonic acid and aminotrimethylene phosphonic acid, respectively. The mixture was heated to 70°C and stirred for 30 minutes. Subsequently, it was filtered sequentially through a 10μm filter bag and a 0.8μm absolute precision polypropylene filter element.

[0055] Step 2: The processed raw materials enter the segmented polymerization reactor for a three-stage reaction: A single ultrasonic-induced polycondensation reaction was carried out: the treated hydroxyl-terminated polydimethylsiloxane and 50 ppm triphosphazene chloride (NPCl2)3 ligand P4-tert-butyl solution were added to the ultrasonic dispersion reaction zone of the segmented reactor and ultrasonically treated (power 100W / L) for 10 min at 70℃ and -0.08 MPa.

[0056] Two-stage high-shear end-capping polymerization reaction: The material enters the two-stage high-shear polymerization reaction zone, and the remaining 10 ppm of triphosphazene chloride (NPCl2)3 ligand P4-tert-butyl solution and MD are added. 10 M sealing agent, ensure temperature does not exceed 120℃, vacuum -0.05MPa, high shear machine speed 5000RPM (linear speed about 25m / s), reaction time about 10min.

[0057] Three-stage thermal equilibrium homogenization: The material enters the three-stage thermal equilibrium homogenization zone, is heated to 110℃, and reacted by planetary stirring for 30 minutes.

[0058] Step 3: Add 30 ppm of triethylamine to terminate the reaction, then heat to 170°C and perform short-path distillation at -0.098 MPa.

[0059] Step 4: After distillation, the product is cooled to room temperature by passing it through a 3A molecular sieve column to obtain the target product. Example 3

[0060] Step 1: Mix 1000g of hydroxyl-terminated polydimethylsiloxane (viscosity 108 mPa·s, hydroxyl content 0.9%) with 200g of MD 10M-type end-capping agent was added to two raw material processing reactors containing disodium EDTA and aminotrimethylenephosphonic acid, respectively. The mixture was heated to 80°C and stirred for 40 minutes. Subsequently, it was filtered sequentially through an 8μm filter bag and a 0.7μm absolute precision polypropylene filter element.

[0061] Step 2: The processed raw materials enter the segmented polymerization reactor for a three-stage reaction: A single ultrasonic-induced polycondensation reaction was performed: the treated hydroxyl-terminated polydimethylsiloxane and 55 ppm tetraphosphonon chloride (NPCl2)4 ligand P4-tert-butyl solution were added to the ultrasonic dispersion reaction zone of the segmented reactor and ultrasonically treated (power 100W / L) for 10 min at 70℃ and -0.09 MPa.

[0062] Two-stage high-shear end-capping polymerization reaction: The material enters the two-stage high-shear polymerization reaction zone, and the remaining 15ppm tetraphosphonon chloride (NPCl2)4 ligand P4-tert-butyl solution and MD are added. 10 M sealing agent, ensure temperature does not exceed 120℃, vacuum -0.05MPa, high shear machine speed 5000RPM (linear speed about 25m / s), reaction time about 10min.

[0063] Three-stage thermal equilibrium homogenization: The material enters the three-stage thermal equilibrium homogenization zone, is heated to 110℃, and reacted by planetary stirring for 30 minutes.

[0064] Step 3: Add 35 ppm of triethylamine to terminate the reaction, then heat to 170°C and perform short-path distillation at -0.099 MPa.

[0065] Step 4: After distillation, the product is cooled to room temperature by passing it through a 3A molecular sieve column to obtain the target product. Example 4

[0066] Step 1: Mix 1000g of hydroxyl-terminated polydimethylsiloxane (viscosity 100 mPa·s, hydroxyl content 1.1%) with 200g of MD 10 M-type end-capping agent was added to two raw material processing reactors containing disodium EDTA and hydroxyethylidene diphosphonic acid, respectively. The mixture was heated to 60°C and stirred for 40 minutes. Subsequently, it was filtered sequentially through a 5μm filter bag and a 0.5μm absolute precision polypropylene filter cartridge.

[0067] Step 2: The processed raw materials enter the segmented polymerization reactor for a three-stage reaction: A single ultrasonic-induced polycondensation reaction was performed: the treated hydroxyl-terminated polydimethylsiloxane and 75 ppm triphosphazene chloride (NPCl2)3 ligand P4-tert-butyl solution were added to the ultrasonic dispersion reaction zone of the segmented reactor and ultrasonically treated (power 500W / L) for 10 min at 70℃ and -0.1 MPa.

[0068] Two-stage high-shear end-capping polymerization reaction: The material enters the two-stage high-shear polymerization reaction zone, and the remaining 5ppm triphosphazene chloride (NPCl2)3 ligand P4-tert-butyl solution and MD are added. 10 M sealing agent, ensure temperature does not exceed 120℃, vacuum -0.05MPa, high shear machine speed 15000RPM (linear speed about 45m / s), reaction time about 10min.

[0069] Three-stage thermal equilibrium homogenization: The material enters the three-stage thermal equilibrium homogenization zone, is heated to 110℃, and reacted by planetary stirring for 30 minutes.

[0070] Step 3: Add 40 ppm of triethylamine to terminate the reaction, then heat to 180°C and perform short-path distillation at -0.1 MPa.

[0071] Step 4: After distillation, the product is cooled to room temperature by passing it through a 3A molecular sieve column to obtain the target product. Comparative Example 1

[0072] Using DMC (octamethylcyclotetrasiloxane) as a raw material, a small amount of water molecules (approximately 3-5%) were removed from the DMC by vacuum distillation under conditions of T=70℃ and P=-0.1MPa; then MD was added. 10 M capping agent, DMC and capping agent in a mass ratio of 5:1, are mixed evenly, then nitrogen gas is introduced, and the mixture is heated to 105~110℃. Then 100ppm tetramethylammonium hydroxide alkaline gel is added as a catalyst, and the polymerization reaction is carried out for 4 hours. The temperature is raised to 150℃ (higher than its decomposition temperature of 134℃) to decompose the catalyst, generating methanol and trimethylamine. At the same time, the amount of nitrogen gas is increased to terminate its catalytic effect. After the catalyst is completely decomposed, the temperature is raised to 175℃~185℃, and the pressure is controlled at about -0.1MPa for descaling. After descaling is completed, the target product is obtained. Comparative Example 2

[0073] Using DMC as raw material, a small amount of water molecules (approximately 3-5%) were removed from the DMC by vacuum distillation under conditions of T=70℃ and P=-0.1MPa; then MD was added. 10 M capping agent, DMC and capping agent in a mass ratio of 5:1, are mixed evenly, heated to 80℃~90℃, 5% concentrated sulfuric acid is added, and the polymerization reaction is carried out for about 2 hours; then acetic acid is added to neutralize for 0.5 hours, filtered, and then heated to 165~170℃, nitrogen bubbling, vacuum -0.1MPa, to remove the low-density, and the target product is obtained after the removal is completed. Comparative Example 3

[0074] Hydroxyl-terminated polydimethylsiloxane silanol silicone oil was used as raw material. A capping agent was added, with a mass ratio of silanol silicone oil to capping agent of 5:1. The mixture was stirred evenly, heated to 100℃~120℃, and 30ppm potassium hydroxide alkaline colloid was added. The polymerization reaction was carried out for about 2 hours. Then, phosphoric acid was added for neutralization for 0.5 hours. After filtration, the temperature was raised to 165~170℃, nitrogen was bubbled, and a vacuum of -0.1MPa was applied for de-lowering. After the de-lowering was completed, the target product was obtained. Comparative Example 4

[0075] The selected polysiloxane is a commercially available low-cyclic silicone oil, such as Anhui Aiyota IOTa-MX.

[0076] The products of each embodiment and comparative example were subjected to performance testing, and the test results are shown in Table 1.

[0077] Cyclic content: Refer to HG / T 6395-2025 "Determination of Volatile Methylcyclosiloxane Content in Silicone Oil"; Metal ion content: Inductively coupled plasma atomic emission spectrometry (ICP-AES) was used according to NB / SH / T 0864-2013. Viscosity: Refer to HG / T 2363-1992 "Test Method for Kinematic Viscosity of Silicone Oil"; Volatile matter: Oven drying method: Weigh a certain amount of sample and heat it in an oven at 150℃ for a certain time (e.g., 2-3 hours). Calculate the volatile matter content by the mass difference before and after heating. Yield: This usually refers to the percentage of the actual mass of the polysiloxane obtained relative to the total mass of the reactants. Molecular weight distribution: Refer to GB / T 36214.1-2018 (Determination of average molecular weight and distribution of polymers by volume exclusion chromatography for plastics - Part 1: General rules).

[0078] Table 1. Performance test results of the products of each embodiment and comparative example.

[0079] As can be seen from Table 1, the polysiloxanes prepared by the method of the present invention have significant advantages in cyclic content, metal ion content and yield, while other performance parameters do not change significantly.

[0080] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, and not to limit them; although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some or all of the technical features; if these modifications and variations fall within the scope of the claims of the present invention and their equivalents, they should all be considered to be within the protection scope of the present invention.

Claims

1. A segmented preparation method for low-cyclic polysiloxanes, characterized in that, Follow these steps: Step 1: Raw material pretreatment Hydroxyl-terminated polydimethylsiloxane and capping agent were added to two raw material processing vessels containing metal adsorbents, respectively. The mixture was heated to 50-60°C and stirred for 20-40 minutes. The materials were then sequentially fed into a pre-filter and a fine filter to thoroughly remove adsorbent particles and mechanical impurities. Step 2: Segmented polymerization reaction The processed raw materials enter a segmented polymerization reactor for a three-stage reaction: A single ultrasonic-induced polycondensation reaction: The treated hydroxyl-terminated polydimethylsiloxane and the catalyst were simultaneously added to the ultrasonic dispersion reaction zone of the segmented polymerization reactor. The reaction was carried out at a temperature of 60~80℃, a vacuum degree of -0.07~-0.1 MPa, and an ultrasonic power of 100~500W / L for 8~12 minutes. The amount of catalyst added was 25~75ppm. Two-stage high-shear end-capping polymerization reaction: The material after the first stage reaction enters the second-stage high-shear polymerization reaction zone, and the treated end-capping agent and supplemented catalyst are added at the same time. Under the conditions of temperature 80~120℃, vacuum degree -0.05 ~ -0.08 MPa, rotor speed 5000~20000 RPM, and rotor tip linear velocity 20~50m / s, the reaction is carried out for 8~12 minutes, and the total amount of effective catalyst components added is controlled at 5~15ppm. Three-stage thermal equilibrium homogenization: The material after the two-stage reaction enters the three-stage thermal equilibrium homogenization zone and undergoes a polymerization equilibrium reaction at 100~120℃ for 20~40 min; Step 3: Termination and Purification A terminator was added to the reaction product of step two, and then short-path distillation was carried out at a temperature of 150~180℃ and a vacuum of -0.095~-0.1MPa to obtain the crude product. Step 4: Post-processing The crude product is cooled and deeply dehydrated by passing it through a molecular sieve adsorption column to obtain a low-cyclic, high-purity polysiloxane product.

2. The method for segmented preparation of low-cyclic polysiloxane according to claim 1, characterized in that, In step one, the metal adsorbent is two of the following: disodium EDTA, hydroxyethylidene diphosphonic acid, and aminotrimethylene phosphonic acid. The pre-filter uses a filter bag with a precision of 5~15μm, and the fine filter uses a filter element with a precision of 0.5~1μm.

3. The method for segmented preparation of low-cyclic polysiloxane according to claim 1, characterized in that, The hydroxyl-terminated polydimethylsiloxane has a viscosity of 80~120 mPa·s at 25℃ and a hydroxyl content of 0.8%~1.5%; the end-capping agent is MD. 10 M, the amount of capping agent added is 20% of the mass of hydroxyl-terminated polydimethylsiloxane.

4. The method for segmented preparation of low-cyclic polysiloxane according to claim 1, characterized in that, The catalyst is a solution of triphosphazene chloride (NPCl2)3 ligand P4-tert-butyl or tetraphosphazene chloride (NPCl2)4 ligand P4-tert-butyl.

5. The method for segmented preparation of low-cyclic polysiloxane according to claim 1, characterized in that, In the first, second, and third stages of the reaction in step two, the water generated during the reaction is promptly removed from the reaction system by introducing inert gas and drawing a vacuum.

6. The method for segmented preparation of low-cyclic polysiloxane according to claim 1, characterized in that, In step three, the terminator is at least one of triethylamine or diethylamine, and the amount of terminator added is 15-50 ppm.

7. The method for segmented preparation of low-cyclic polysiloxane according to claim 1, characterized in that, In step four, the molecular sieve is a 3A or 4A type molecular sieve.

8. A segmented polymerization reactor used in the segmented preparation method of low-cyclic polysiloxane according to any one of claims 1-7, characterized in that, The segmented polymerization reactor is an integrated, one-piece structure, divided into three functional zones from top to bottom, including: An ultrasonic dispersion reaction zone is located at the top of the reactor and includes an ultrasonic dispersion device with a sound-permeable membrane structure at its bottom. The second-stage high-shear polymerization reaction zone is located in the middle of the reactor and is directly connected to the first-stage zone. It includes a rotor-stator high-shear mixer and a gear ring installed in the cavity. The three-stage thermal equilibrium homogenization zone is located at the bottom of the reactor and is a regulating vessel equipped with a planetary stirrer.

9. The segmented polymerization reactor according to claim 8, characterized in that, The top of the first ultrasonic dispersion reaction zone and the top of the second high-shear polymerization reaction zone are equipped with feed inlets and vacuum ports; the bottom of the first ultrasonic dispersion reaction zone, the second high-shear polymerization reaction zone and the third thermal equilibrium homogenization zone are equipped with inert gas coils.

10. The segmented polymerization reactor according to claim 8, characterized in that, The ultrasonic dispersion reaction zone and the three thermal equilibrium homogenization zones are equipped with jacketed heating systems, which have heating steam inlets and heating steam outlets. The high-shear polymerization reaction zone is equipped with a jacketed cooling system, which has cooling water inlets and cooling water outlets.

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