A process for the preparation of a medium to high viscosity vinyl terminated polydimethylsiloxane

Abstract

The application discloses a preparation method of medium-high viscosity vinyl-terminated polydimethylsiloxane, and steps of the method comprise the following: (1) linear body is heated to 35-60 DEG C, and then dehydration treatment is carried out; (2) a capping agent, linear phosphazene catalyst and end-vinyl side-chain vinyl polysiloxane are added, and then reaction is carried out under vacuum condition; (3) a terminating agent is added to obtain medium-high viscosity vinyl-terminated polydimethylsiloxane; the linear body is linear hydroxyl-terminated polydimethylsiloxane with viscosity of 40-200 mPa.s; the capping agent is vinyl-terminated polysiloxane with viscosity of 2-50 mPa.s; the structure of the terminating agent is shown in the following formula 1: wherein n1 is 30-150; the preparation method can prepare medium-high viscosity vinyl-terminated polydimethylsiloxane with viscosity of 500 mPa.s or above, and the vinyl-terminated polydimethylsiloxane has low volatile content, high vinyl retention rate and normal hardness.

Description

Technical Field

[0001] This invention belongs to the field of vinyl-terminated polysiloxane preparation technology, and particularly relates to a method for preparing medium-to-high viscosity vinyl-terminated polydimethylsiloxane. Background Technology

[0002] Vinyl-terminated polysiloxanes can serve as key raw materials for the preparation of various downstream products such as silicone rubber, silicone emulsions, and silicone release products. For example, high-temperature silicone rubber (HTV) and liquid silicone rubber (RTV) are produced by high-temperature mixing of polysiloxanes and silica. After vulcanization, they acquire their respective functions. Silicone rubber maintains good mechanical properties over a wide temperature range (-50℃ to 200℃) and can be used at high temperatures for extended periods, making it irreplaceable compared to other materials.

[0003] Currently, the industrial preparation of vinyl-terminated polysiloxanes mostly uses cyclosiloxane monomers (DMC) as raw materials and divinyltetramethyldisiloxane as a vinyl dual-terminant. A mixture of vinyl-terminated polydimethylsiloxane polymers (85-87%) and DMC (13-15%) is obtained through alkaline catalysis. Then, DMC is removed by vacuum distillation to obtain polysiloxanes with different molecular weights. However, vacuum distillation is an energy-intensive process, especially when large amounts of DMC need to be separated, resulting in a significant increase in energy consumption.

[0004] To reduce the formation of cyclosiloxane monomers, researchers explored a novel preparation method. This method uses linear polymers as raw materials and linear phosphazene chloride as a catalyst to prepare polysiloxanes via a silanol-based polycondensation reaction. The reaction process does not produce significant cyclosiloxane formation and is one of the main routes for synthesizing low-volatility polysiloxanes. For example, Chinese patent CN 117777452A discloses a method for preparing medium-to-low viscosity (1~10000 mmHg) polysiloxanes using linear phosphazene as a catalyst, linear polymers as raw materials, vinyl double-ended polymers as molecular weight regulators, and continuous nitrogen dehydration. 2A method for preparing vinyl silicone oil ( / s). It should be noted that vinyl silicone oils, typically used in liquid silicone rubber or requiring high-temperature applications, usually have viscosities exceeding 10,000 mPa·s, with raw rubber molecular weights reaching 600,000 to 800,000 Daltons. Such high viscosity makes them difficult to measure using conventional viscometers. However, the preparation method disclosed in CN 117777452 A is not suitable for preparing such high-viscosity vinyl silicone oils because continuous nitrogen purging for dehydration leads to a large accumulation of bubbles in the reactor, and at high viscosity, foam removal becomes extremely difficult, resulting in low utilization. Secondly, analysis based on the relationship between viscosity and vinyl content in CN 117777452 A reveals a certain loss of vinyl content, which undoubtedly increases production costs. Furthermore, linear phosphazenes are easily hydrolyzed and deactivated in the presence of trace amounts of water and at high temperatures (80°C and above), resulting in unsatisfactory stability.

[0005] Therefore, there is an urgent need for a method to prepare medium-to-high viscosity vinyl-terminated polydimethylsiloxane to address the shortcomings of existing technologies. Summary of the Invention

[0006] In view of the above problems, the purpose of this invention is to provide a method for preparing medium-high viscosity vinyl-terminated polydimethylsiloxane. This method can produce medium-high viscosity vinyl-terminated polydimethylsiloxane with a viscosity of 500 mPa•s or higher, and the medium-high viscosity vinyl-terminated polydimethylsiloxane has low volatile content, high vinyl retention rate, and normal hardness.

[0007] To achieve the above objectives, the first aspect of the present invention provides a method for preparing medium-to-high viscosity vinyl-terminated polydimethylsiloxane, comprising the following steps: (1) Heat the linear body to 35~60℃ and then dehydrate it; (2) Add a capping agent, a linear phosphazene catalyst, and a vinyl-terminated side-chain vinyl polysiloxane to the linear body after step (1), and then react under vacuum conditions; (3) Add the terminating agent to the product after the reaction in step (2) to react and obtain a medium-high viscosity vinyl-terminated polydimethylsiloxane with a viscosity of 500 mPa•s or higher. The linear phase is a straight-chain hydroxyl-terminated polydimethylsiloxane with a viscosity of 40~200 mPa•s; The end-capping agent is a vinyl-terminated polysiloxane with a viscosity of 2~50 mPa•s; The structure of the terminator is shown in Formula 1 below:

[0008] Formula 1 The value of n1 ranges from 30 to 150.

[0009] Compared with existing technologies, this invention uses linear phosphazene (LPNC), which can catalyze both silanol condensation and polysiloxane segment rearrangement, as a catalyst. This allows the linear phase, end-capping agent, and vinyl-terminated side-chain polysiloxane to react under low-temperature vacuum conditions, ultimately yielding medium-to-high viscosity vinyl-terminated polydimethylsiloxane with a viscosity of 500 mPa•s or higher. The use of a low-viscosity vinyl-terminated polysiloxane as the end-capping agent significantly increases its boiling point, making it less prone to volatilization under vacuum and heating conditions, thus reducing end-capping agent loss and increasing vinyl retention. Simultaneously, the low-temperature vacuum reaction method gives the linear phosphazene catalyst better catalytic activity, effectively reducing the amount of volatile rings formed. Therefore, no additional vacuum ring removal operation is needed after the reaction is terminated, simplifying the entire production process. Furthermore, the terminator shown in Formula 1 can not only neutralize the linear phosphazene catalyst to stop the reaction, but also vinyl-terminate a small amount of the reaction end, so that the hardness reaches the normal level. This effectively reduces the hydroxyl value of the system and avoids the structural problems when preparing liquid rubber or high-temperature compound.

[0010] Furthermore, the dehydration treatment of the present invention includes: vacuum stirring the linear body to dehydrate it so that the linear body loses less than 0.2% of its weight after drying in an oven at 100°C for 1 hour.

[0011] Further, the raw materials for preparation of the present invention include 100 parts by weight of linear polymer, 0.1-10 parts by weight of end-capping agent, 0-10 parts by weight of vinyl-terminated side-chain vinyl polysiloxane, 0.05-2 parts by weight of terminator, and 10-80 ppm of linear phosphazene catalyst. Specifically, the content of end-capping agent may be, but is not limited to, 0.1 parts, 1 part, 3 parts, 4 parts, 6 parts, 8 parts, or 10 parts; the content of vinyl-terminated side-chain vinyl polysiloxane may be, but is not limited to, 0 parts, 1 part, 3 parts, 4 parts, 6 parts, 8 parts, or 10 parts; the content of terminator may be, but is not limited to, 0.05 parts, 1 part, 1.2 parts, 1.5 parts, 1.8 parts, or 2.0 parts; and the content of linear phosphazene catalyst may be, but is not limited to, 10 ppm, 20 ppm, 40 ppm, 60 ppm, 70 ppm, or 80 ppm.

[0012] Furthermore, when the amount of vinyl polysiloxane with terminal vinyl side chains added is 0 parts, the reaction equation for step (2) of the present invention is as follows: ; Among them, n2 takes the value of 10~100, and n3 takes the value of 170~8500.

[0013] Furthermore, when the amount of vinyl polysiloxane with terminal vinyl side chains added is greater than 0 parts, vinyl groups can be provided for the polysiloxane side chains. The reaction equation for step (2) of the present invention is as follows: .

[0014] Where n² = 10~100, m + n = 10~1200, p + q = 170~8500.

[0015] Furthermore, in step (2) of the present invention, the vacuum degree under vacuum conditions is greater than 0.08 MPa, and the reaction time is 2-10 h. The vacuum condition allows the water generated in the system to be discharged, maintains the stability of the linear phosphazene catalyst, and accelerates the reaction process. Under the catalytic action of the linear phosphazene catalyst, the molecular chains rearrange, and the reaction finally reaches equilibrium after 2-10 h.

[0016] Furthermore, the structural formula of the linear phosphazene catalyst (LPNC) of the present invention is shown below:

[0017] Linear phosphazene catalysts Furthermore, the preparation of the end-capping agent of the present invention includes: mixing vinyl dual-end-capped silicone oil (CAS: 2627-95-4), vinyl-terminated dimethyl silicone oil, and a linear phosphazene catalyst, and reacting them at 50-80°C for 2-10 hours. During the research process, the inventors of this application discovered that a reaction temperature below 50°C results in a longer reaction time, while a reaction temperature above 80°C increases the amount of volatile cyclic compounds formed in the system. Therefore, the preferred reaction temperature is 50-80°C, and the reaction temperature can be, but is not limited to, 50°C, 60°C, 70°C, or 80°C.

[0018] Furthermore, the reaction formula for preparing the end-capping agent of the present invention is as follows: ; Where n4 = 170~1200, n5 = 1~50.

[0019] Furthermore, the raw materials for preparing the end-capping agent of the present invention include 100 parts by weight of vinyl dual end-caps, 120-2000 parts by weight of vinyl-terminated dimethyl silicone oil, and 40-120 ppm of linear phosphazene catalyst. Specifically, the content of vinyl-terminated dimethyl silicone oil may be, but is not limited to, 120 parts, 250 parts, 380 parts, 500 parts, 720 parts, 950 parts, 1080 parts, 1400 parts, 1600 parts, 1800 parts, and 2000 parts; the content of linear phosphazene catalyst may be, but is not limited to, 40 ppm, 60 ppm, 80 ppm, 100 ppm, and 120 ppm. Compared with the traditional alkaline method for preparing end-capping agents, the advantages of using a linear phosphazene catalyst are: 1) no neutralization is required, and it can be directly used in the next step; 2) the cyclic content is low, and no de-lowering treatment is required, and it can be directly used in the next step.

[0020] Further, the preparation of the terminator of the present invention includes: adding a cyclic siloxane and potassium hydroxide into a reactor, introducing nitrogen gas, evacuating the reactor, introducing nitrogen gas again and heating the reactor, stopping the nitrogen gas supply after the potassium hydroxide is completely dissolved, adding a vinyl double-ended head to react, and continuing to introduce nitrogen gas after the reaction is complete. Specifically, the cyclic siloxane can be octamethylcyclotetrasiloxane (D4). Specifically, the reaction formula for preparing the terminator of the present invention is as follows: ; Where z is the molar amount of octamethylcyclotetrasiloxane, and n1 takes the value of 30~150.

[0021] Furthermore, the preparation of the terminator of the present invention includes: adding cyclic siloxane and potassium hydroxide into a reactor, bubbling with nitrogen gas, then evacuating the reactor air at a temperature below 60°C for 10 minutes to remove carbon dioxide, then purging with nitrogen gas to remove the vacuum and heating to 140~150°C; stopping the nitrogen gas flow after KOH is completely dissolved, then adding a vinyl double-ended agent and reacting for 15 minutes, and continuing to bubble with nitrogen gas for 3 hours after the reaction is completed. In addition, the inventors of the present invention discovered during the invention process that if organic amines (such as triethylamine) are simply used as terminators, the hardness of the vinyl-terminated polysiloxane obtained in step (3) does not reach the normal level.

[0022] Furthermore, the raw materials for preparing the terminator of the present invention include 100 parts by weight of cyclic siloxane, 1.5 to 3.5 parts by weight of potassium hydroxide, and 2.5 to 5.83 parts by weight of vinyl bis-terminated resin. Specifically, the content of potassium hydroxide (KOH) may be, but is not limited to, 1.5 parts, 2 parts, 2.5 parts, 3 parts, or 3.5 parts; the content of vinyl bis-terminated resin may be, but is not limited to, 2.5 parts, 3 parts, 3.5 parts, 4 parts, 4.5 parts, 5.0 parts, 5.5 parts, or 5.83 parts.

[0023] Furthermore, the molar ratio of potassium hydroxide to the vinyl double-ended head in this invention is 1.9 to 2.1:1. Specifically, the molar ratio of potassium hydroxide to the vinyl double-ended head can be, but is not limited to, 1.9:1, 2.0:1, or 2.1:1.

[0024] Furthermore, the reaction time in step (3) of the present invention is 2 to 5 hours. Specifically, the reaction time in step (3) can be, but is not limited to, 2 hours, 3 hours, 4 hours, or 5 hours.

[0025] Furthermore, the reaction formula for step (3) of the present invention is as follows: ; The value of n1 is 30 to 150. Detailed Implementation

[0026] To better illustrate the purpose, technical solution, and beneficial effects of this invention, the invention will be further described below with reference to specific embodiments. It should be noted that the methods described below are further explanations of this invention and should not be construed as limiting it.

[0027] The capping agent, linear phosphazene catalyst, and terminator used in the examples and comparative examples can be prepared by the following method: The preparation of the end-capping agent includes: mixing 100 parts by weight of vinyl double end-caps, 240 parts by weight of vinyl-terminated dimethyl silicone oil with a viscosity of 2000 mPa•s, and 120 ppm of linear phosphazene catalyst, and reacting at 80°C for 2 h. After testing, a vinyl-terminated polysiloxane end-capping agent with a viscosity of 4 mPa•s is obtained, wherein the vinyl content is 8.54 wt%.

[0028] The preparation of the linear phosphazene catalyst includes: mixing 22.69g PCl5, 2.912g NH4Cl and 73.42g C2H2Cl4, heating to reflux temperature and reacting for 12h to obtain a transparent liquid. The effective content of the catalyst was found to be 30%. Since the linear phosphazene catalyst is hygroscopic, it needs to be stored in an N2 atmosphere.

[0029] The preparation of the terminator included: adding 100g of octamethylcyclotetrasiloxane and 2.1g of KOH into a reactor, bubbling with nitrogen gas, evacuating the reactor for 10 minutes at a temperature below 60℃ to remove carbon dioxide from the air, then evacuating with nitrogen gas and heating to 145℃; stopping the nitrogen bubbling after the KOH was completely dissolved, then adding 3.5g of vinyl double-ended head (the molar ratio of potassium hydroxide to vinyl double-ended head was 2:1) and reacting for 15 minutes. After the reaction was completed, the reaction was continued with nitrogen bubbling for 3 hours to obtain the terminator. The alkali content in the terminator was measured to be 0.3743 mmol / g.

[0030] Example 1 This embodiment provides a method for preparing medium-to-high viscosity vinyl-terminated polydimethylsiloxane, the steps of which include: (1) 100 parts by mass of linear body with a viscosity of 100 mPa·s were heated to 40°C and then vacuum stirred to dehydrate the linear body so that the weight loss was less than 0.2% after drying in an oven at 100°C for 1 h; (2) Add 1.54 parts by mass of capping agent and 40 ppm of linear phosphazene catalyst to the linear body after step (1), and then react for 5 h under vacuum at 0.09 MPa; (3) Add 0.23 parts by mass of the terminator to the product after the reaction in step (2) and react for 3 hours. After filtration, the product has a viscosity of 1×10⁻⁶. 4 Vinyl-terminated polydimethylsiloxane at mPa•s, wherein the vinyl-terminated content is 0.13wt%.

[0031] Example 2 This embodiment provides a method for preparing medium-to-high viscosity vinyl-terminated polydimethylsiloxane, the steps of which include: (1) 100 parts by mass of linear body with a viscosity of 100 mPa·s were heated to 60°C and then vacuum stirred to dehydrate the linear body so that the weight loss was less than 0.2% after drying in an oven at 100°C for 1 h; (2) Add 1.5 parts by mass of end-capping agent, 40 ppm of linear phosphazene catalyst, and 1 part by mass of end-vinyl side-chain vinyl polysiloxane (viscosity 3×10) to the linear body after step (1). 4 (mPa•s, vinyl content 4wt%), and then reacted under a vacuum of 0.09MPa for 8h; (3) Add 0.23 parts by mass of the terminator to the product after the reaction in step (2) and react for 3 hours. After filtration, the product has a viscosity of 1×10⁻⁶. 4 The terminal vinyl and side vinyl polydimethylsiloxane has a content of 0.13 wt% and a side vinyl content of 0.04 wt% per mPa•s, and a total vinyl content of 0.17 wt%.

[0032] Example 3 This embodiment provides a method for preparing medium-to-high viscosity vinyl-terminated polydimethylsiloxane, the steps of which include: (1) 100 parts by mass of linear body with a viscosity of 100 mPa·s were heated to 40°C and then vacuum stirred to dehydrate the linear body so that the weight loss was less than 0.2% after drying in an oven at 100°C for 1 h; (2) Add 0.7 parts by mass of capping agent and 40 ppm of linear phosphazene catalyst to the linear body after step (1), and then react under vacuum of 0.095 MPa for 5 h; (3) Add 0.23 parts by mass of the terminator to the product after the reaction in step (2) and react for 3 hours. After filtration, the product has a viscosity of 1×10⁻⁶. 5 Vinyl-terminated polydimethylsiloxane at mPa•s, wherein the vinyl-terminated content is 0.06wt%.

[0033] Example 4 This embodiment provides a method for preparing medium-to-high viscosity vinyl-terminated polydimethylsiloxane, the steps of which include: (1) 100 parts by mass of linear body with a viscosity of 100 mPa·s were heated to 60°C and then vacuum stirred to dehydrate the linear body so that the weight loss was less than 0.2% after drying in an oven at 100°C for 1 h; (2) Add 0.7 parts by mass of end-capping agent, 40 ppm of linear phosphazene catalyst, and 0.5 parts by mass of vinyl-terminated side-chain vinyl polysiloxane (viscosity 3×10) to the linear body after step (1). 4 (mPa•s, vinyl content 4wt%), and then reacted under a vacuum of 0.095MPa for 8h; (3) Add 0.23 parts by mass of the terminator to the product after the reaction in step (2) and react for 3 hours. After filtration, the product has a viscosity of 1×10⁻⁶. 5 The terminal vinyl and side vinyl polydimethylsiloxane has a content of 0.06 wt% and a side vinyl content of 0.02 wt% in mPa•s, and a total vinyl content of 0.08 wt%.

[0034] Example 5 This embodiment provides a method for preparing medium-to-high viscosity vinyl-terminated polydimethylsiloxane, the steps of which include: (1) 100 parts by mass of linear body with a viscosity of 200 mPa·s were heated to 40°C, and then vacuum stirred to dehydrate the linear body so that the weight loss was less than 0.2% after drying in an oven at 100°C for 1 h; (2) Add 0.17 parts by mass of capping agent and 10 ppm of linear phosphazene catalyst to the linear body after step (1), and then react for 10 h under vacuum at 0.095 MPa; (3) Add 0.05 parts by mass of the terminator to the product after the reaction in step (2) and react for 3 hours. After filtration, obtain semi-fluid vinyl-terminated polydimethylsiloxane (i.e. raw rubber with the trade name 110-0) with a vinyl mass fraction of 0.015%.

[0035] Example 6 This embodiment provides a method for preparing medium-to-high viscosity vinyl-terminated polydimethylsiloxane, the steps of which include: (1) 100 parts by mass of linear body with a viscosity of 200 mPa·s were heated to 40°C, and then vacuum stirred to dehydrate the linear body so that the weight loss was less than 0.2% after drying in an oven at 100°C for 1 h; (2) Add 0.17 parts by weight of end-capping agent, 10 ppm of linear phosphazene catalyst, and 0.7 parts by weight of vinyl-terminated side-chain vinyl polysiloxane (viscosity 1×10⁻⁶) to the linear body after step (1). 5 (mPa•s, vinyl content 10wt%), and then reacted under vacuum of 0.095MPa for 8h; (3) Add 0.05 parts by mass of the terminator to the product after the reaction in step (2) and react for 3 hours. After filtration, a semi-fluid vinyl-terminated polydimethylsiloxane (i.e., raw rubber with the trade name 110-3) is obtained. The mass fraction of the terminal vinyl group is 0.014%, the mass fraction of the side vinyl group is 0.069%, and the mass fraction of the total vinyl group is 0.083%.

[0036] Comparative Example 1 This comparative example provides a method for preparing vinyl-terminated polydimethylsiloxane, the steps of which include: (1) Heat 100 parts by weight of octamethylcyclotetrasiloxane to 100°C; (2) Add 1.54 parts by mass of capping agent and 100 ppm of tetramethylammonium hydroxide catalyst to the octamethylcyclotetrasiloxane after step (1), and then react for 5 h; (3) After step (2), the temperature is raised to 140℃ to degrade the tetramethylammonium hydroxide catalyst, yielding a product with a viscosity of 7.0 × 10⁻⁶. 3 Vinyl-terminated polydimethylsiloxane at mPa·s.

[0037] Comparative Example 2 This comparative example provides a method for preparing vinyl-terminated polydimethylsiloxane, the steps of which include: (1) Heat 100 parts by mass of 100 mPa•s linear body to 100℃; (2) Add 1.54 parts by mass of capping agent and 100 ppm of tetramethylammonium hydroxide to the linear body after step (1), react for 5 h, and then dehydrate under vacuum of 0.05 MPa; (3) After step (2), the temperature is raised to 140℃ to degrade the tetramethylammonium hydroxide catalyst, yielding a product with a viscosity of 6.5*10. 3 Vinyl-terminated polydimethylsiloxane at mPa•s.

[0038] Comparative Example 3 This comparative example provides a method for preparing medium-to-high viscosity vinyl-terminated polydimethylsiloxane, the steps of which include: (1) 100 parts by mass of linear body with a viscosity of 100 mPa·s were heated to 40°C and then vacuum stirred to dehydrate the linear body so that the weight loss was less than 0.2% after drying in an oven at 100°C for 1 h; (2) Add 1.54 parts by mass of capping agent and 40 ppm of linear phosphazene catalyst to the linear body after step (1), and then react for 5 h under vacuum at 0.09 MPa; (3) Add 50 ppm KOH (50% aqueous solution) to the product after the reaction in step (2) and react for 3 hours. After filtration, the product has a viscosity of 1×10⁻⁶. 4Vinyl-terminated polydimethylsiloxane at mPa•s, wherein the vinyl-terminated content is 0.13wt%.

[0039] Comparative Example 4 This comparative example provides a method for preparing medium-to-high viscosity vinyl-terminated polydimethylsiloxane, the steps of which include: (1) 100 parts by mass of linear body with a viscosity of 100 mPa·s were heated to 40°C and then vacuum stirred to dehydrate the linear body so that the weight loss was less than 0.2% after drying in an oven at 100°C for 1 h; (2) Add 0.45 parts by mass of vinyl double-ended (CAS: 2627-95-4) and 40 ppm of linear phosphazene catalyst to the linear body after step (1), and then react for 5 h under vacuum at 0.09 MPa; (3) Add 0.073 parts by mass of the terminator to the product after the reaction in step (2) and react for 3 hours. After filtration, the product has a viscosity of 2.5 × 10⁻⁶. 4 Vinyl-terminated polydimethylsiloxane at mPa•s, wherein the vinyl-terminated content is 0.09wt%.

[0040] It is important to note that in Examples 1-6, only a small portion of the terminator was used to cap the polysiloxane backbone; the majority served to neutralize the catalyst, rendering it ineffective. Therefore, the amount of vinyl groups introduced by the terminator was very small, and can be ignored when calculating the end-vinyl content of the finished silicone oil. Furthermore, since the amount of end-vinyl groups in the vinyl-terminated side-chain polysiloxanes is relatively small, the end-vinyl groups introduced by the vinyl-terminated side-chain polysiloxanes can be ignored when calculating the end-vinyl content of the finished silicone oil in Examples 2, 4, and 6.

[0041] The vinyl-terminated polydimethylsiloxanes prepared in Examples 1-6 and Comparative Examples 1-4 were subjected to hardness testing, volatile matter testing, and vinyl retention rate testing according to the following testing methods. The test results are shown in Table 1.

[0042] Hardness testing: Take the silicone oil after the reaction is completed and determine the vinyl content by hydrogen spectroscopy. Use Si-H / Si-Vi=2 times hydrogen-containing silicone oil for sulfidation. The hydrogen content in the hydrogen-containing silicone oil is 0.75%, and the amount of platinum catalyst used is 3 ppm.

[0043] Volatile content detection: Accurately weigh approximately 5g of polysiloxane (m1), place it in an aluminum box, and bake at 200℃ for 4 hours. The residual mass is m2. Volatile content = (m1-m2) / m1. Take the average value after 3 measurements.

[0044] Vinyl retention rate: The ratio of actual content to vinyl content was determined by 1H NMR spectroscopy.

[0045] Table 1 Performance Test Results

[0046] As demonstrated in Examples 1-6, the method for preparing medium-high viscosity vinyl-terminated polydimethylsiloxanes according to the present invention can produce medium-high viscosity vinyl-terminated polydimethylsiloxanes with a viscosity of 500 mPa•s or higher. Furthermore, these medium-high viscosity vinyl-terminated polydimethylsiloxanes exhibit low low-volatile content, high vinyl retention rate, and normal hardness. This is because the present invention uses low-viscosity vinyl-terminated polysiloxanes as end-capping agents, which significantly increases the boiling point of the end-capping agent, making it less prone to volatilization under vacuum and heating conditions, thereby reducing end-capping agent loss and increasing vinyl retention rate. Simultaneously, the low-temperature vacuum reaction mode allows the linear phosphazene catalyst to exhibit better catalytic activity, effectively reducing the amount of low-volatile ring formation. This eliminates the need for additional vacuum ring removal after the reaction is terminated, simplifying the entire production process. Moreover, the terminator shown in Formula 1 not only neutralizes the linear phosphazene catalyst to stop the reaction but also vinyl-terminates a small amount of the reaction end, achieving normal hardness.

[0047] Comparing Example 1 and Comparative Examples 1-2, it can be seen that the volatile content of vinyl-terminated polydimethylsiloxane obtained by catalyzing octamethylcyclotetrasiloxane or linear form using an alkaline catalyst is relatively high (above 12%). Therefore, vacuum de-oxidation is required for industrial use. Thus, this invention uses linear phosphazene as a catalyst to react the linear form and the end-capping agent to prepare medium-high viscosity vinyl-terminated polydimethylsiloxane. After the reaction, it can be used directly in industry without post-processing. This effectively avoids the ring-opening-ring-back balance problem existing in the alkaline method, avoids ring production, eliminates the neutralization step and vacuum de-ring operation, and avoids the poisoning effect of trace amounts of alkali on the linear phosphazene catalyst.

[0048] Comparing Example 1 and Comparative Example 3, it can be seen that although the viscosity, volatile matter, and vinyl retention rate of the vinyl-terminated polydimethylsiloxanes prepared in Example 1 and Comparative Example 3 are similar, their hardness differs greatly. This indicates that conventional alkalis (such as potassium hydroxide) can only neutralize linear phosphazenes and stop the reaction, but cannot vinyl-terminate a small amount of the reaction end. This also shows that a small amount of unvinyl-terminated polysiloxane has a significant impact on the hardness of the compound.

[0049] Comparing Example 1 and Comparative Example 4, it can be seen that the vinyl retention rate of the vinyl-terminated polydimethylsiloxane prepared in Comparative Example 4 is only 69%. This indicates that conventional end-capping agents (such as vinyl bi-end-caps) are not suitable for linear condensation systems under vacuum heating. This is because in the LPNC catalysis process, the condensation rate is greater than the rearrangement rate, resulting in a slow breaking of the vinyl bi-end-caps, leading to significant losses under vacuum heating conditions. Furthermore, the inventors of this application have also found that low-viscosity end-capping agents prepared using the alkali method are also unsuitable for this system, as residual alkali affects the catalytic activity of linear phosphazene catalysis, and may even deactivate it.

[0050] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and are not intended to limit the scope of protection of the present invention. Although the present invention has been described in detail with reference to preferred embodiments, those skilled in the art should understand that modifications or equivalent substitutions can be made to the technical solutions of the present invention without departing from the essence and scope of the technical solutions of the present invention.

Claims

1. A method for preparing medium-to-high viscosity vinyl-terminated polydimethylsiloxane, characterized in that the steps include... include: (1) Heat the linear body to 35~60℃ and then dehydrate it; (2) Add a capping agent, a linear phosphazene catalyst, and a vinyl-terminated side-chain vinyl polysiloxane to the linear body after step (1), and then react under vacuum conditions; or add a capping agent and a linear phosphazene catalyst to the linear body after step (1), and then react under vacuum conditions. (3) Add the terminating agent to the product after the reaction in step (2) to react and obtain a medium-high viscosity vinyl-terminated polydimethylsiloxane with a viscosity of 500 mPa•s or higher. The linear body is a straight-chain hydroxyl-terminated polydimethylsiloxane with a viscosity of 40~200 mPa•s; The end-capping agent is a vinyl-terminated polysiloxane with a viscosity of 2~50 mPa•s; The structure of the terminator is shown in Formula 1 below: Formula 1 The value of n1 ranges from 30 to 150; The raw materials for preparing the linear phosphazene catalyst include PCl5 and NH4Cl; The structural formula of the sealing agent is shown below: Where n5 = 1~50.

2. The method for preparing medium-to-high viscosity vinyl-terminated polydimethylsiloxane as described in claim 1, characterized in that, The dehydration process includes: vacuum stirring the linear body to dehydrate it, so that the linear body loses less than 0.2% of its weight after drying in an oven at 100°C for 1 hour.

3. The method for preparing medium-to-high viscosity vinyl-terminated polydimethylsiloxane as described in claim 1, characterized in that, The raw materials for preparation include 100 parts by mass of the linear body, 0.1 to 10 parts by mass of the end-capping agent, 0 to 10 parts by mass of the vinyl-terminated side-chain vinyl polysiloxane, 0.05 to 2 parts by mass of the terminator, and 10 to 80 ppm of the linear phosphazene catalyst.

4. The method for preparing medium-to-high viscosity vinyl-terminated polydimethylsiloxane as described in claim 1, characterized in that, The vacuum degree under the vacuum conditions described in step (2) is greater than 0.08 MPa, and the reaction time is 2 to 10 h.

5. The method for preparing medium-to-high viscosity vinyl-terminated polydimethylsiloxane as described in claim 1, characterized in that, The preparation of the end-capping agent includes: mixing vinyl double end-caps, vinyl-terminated dimethyl silicone oil, and linear phosphazene catalyst, and reacting them at 50-80°C for 2-10 hours.

6. The method for preparing medium-to-high viscosity vinyl-terminated polydimethylsiloxane as described in claim 5, characterized in that, The raw materials for preparing the end-capping agent include 100 parts by weight of the vinyl double end-capping agent, 120-2000 parts by weight of the vinyl-terminated dimethyl silicone oil, and 40-120 ppm of the linear phosphazene catalyst.

7. The method for preparing medium-to-high viscosity vinyl-terminated polydimethylsiloxane as described in claim 1, characterized in that, The preparation of the terminator includes: adding cyclic siloxane and potassium hydroxide into a reactor, introducing nitrogen gas, evacuating the reactor, introducing nitrogen gas again and heating the reactor, stopping the introduction of nitrogen gas after the potassium hydroxide has completely dissolved, adding a vinyl double-ended head to react, and continuing to introduce nitrogen gas after the reaction is completed.

8. The method for preparing medium-to-high viscosity vinyl-terminated polydimethylsiloxane as described in claim 7, characterized in that, The raw materials for preparing the terminator include 100 parts by weight of the cyclic siloxane, 1.5 to 3.5 parts by weight of the potassium hydroxide, and 2.5 to 5.83 parts by weight of the vinyl double end cap.

9. The method for preparing medium-to-high viscosity vinyl-terminated polydimethylsiloxane as described in claim 8, characterized in that, The molar ratio of potassium hydroxide to the vinyl double end cap is 1.9~2.1:

1.

10. The method for preparing medium-to-high viscosity vinyl-terminated polydimethylsiloxane as described in claim 1, characterized in that, The reaction time in step (3) is 2 to 5 hours.

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