Hydrogen-terminated polydimethylsiloxane and preparation method thereof

Abstract

The invention discloses hydrogen-terminated polydimethylsiloxane and a preparation method thereof. The preparation method comprises the following steps: (1) carrying out mixed reaction on a cyclic siloxane monomer, an end-capping reagent containing a silicon-hydrogen bond and a strong acid catalyst to obtain a first reaction solution containing hydrogen-terminated polydimethylsiloxane; (2) adding ammonia water into the first reaction solution, and carrying out neutralization reaction to obtain a second reaction solution containing hydrogen-terminated polydimethylsiloxane, wherein the temperature of the neutralization reaction is 10-50 DEG C; and (3) carrying out high-temperature vacuum purification treatment on the second reaction liquid to obtain a hydrogen-terminated polydimethylsiloxane purified product, wherein the temperature of the vacuum high-temperature treatment is 100 DEG C or above. According to the preparation method disclosed by the invention, time-consuming and complicated solid-liquid separation steps (such as sedimentation and filtration) in a traditional process can be fundamentally eliminated, so that the production process is simplified, and meanwhile, the prepared hydrogen-terminated polydimethylsiloxane is high in solid content, relatively narrow in molecular weight distribution, good in structural integrity and high in yield. The performance in downstream application (such as textile after-treatment) can be effectively improved.

Description

Technical Field

[0001] This invention relates to the field of organosilicon polymer preparation technology, and in particular to a hydrogen-terminated polydimethylsiloxane and its preparation method. Background Technology

[0002] α,ω-terminated hydrogen polydimethylsiloxane (hereinafter referred to as PDMS-H) is a polymer whose main chain contains active silane-hydrogen bonds at both ends. Si PDMS-H is a specialty polydimethylsiloxane. Its unique end-group structure allows it to serve as a base polymer, enabling efficient grafting or chain extension with other compounds containing unsaturated bonds (such as vinyl groups) via hydrosilylation reactions, thereby synthesizing block, grafted, or crosslinked organosilicon polymers with specific functions. Therefore, PDMS-H plays an indispensable role in high-performance textile finishing agents, liquid silicone rubber (LSR), electronic potting compounds, leather auxiliaries, and personal care products.

[0003] Industrially, the mainstream method for preparing PDMS-H is cationic ring-opening polymerization (CROP). This technique uses cyclic siloxane monomers, typically octamethylcyclotetrasiloxane (D4), as the main raw material, and 1,1,3,3-tetramethyldisiloxane (TMDS) as a capping agent to control the molecular weight of the polymer and introduce -Si-H functional groups into the end groups. The polymerization reaction is carried out in the presence of a strong acid catalyst.

[0004] However, existing technologies suffer from a series of serious technical defects in the catalyst neutralization and product purification stages. These defects significantly limit production efficiency, increase production costs, and negatively impact product quality and the environment. Currently, the commonly used traditional process in the industry employs solid-phase inorganic bases, particularly anhydrous sodium carbonate (Na2CO3), to neutralize the strong acid catalyst remaining after the polymerization reaction. The drawbacks of this traditional process are mainly reflected in the following aspects: (1) Extremely low process efficiency: Since Na2CO3 is a solid and the polymerization product is a high-viscosity organosilicon liquid, the neutralization reaction is a typical solid-liquid heterogeneous reaction. In order to make the reaction relatively complete, vigorous mechanical stirring for up to 12 hours or even longer is required to increase the interphase contact area. Even so, the reaction rate is still slow, making the neutralization step itself a long production bottleneck.

[0005] (2) The purification process is complex and costly: The byproduct of this neutralization reaction is a solid inorganic salt (e.g., sodium triflate if triflic acid is used as catalyst). It is extremely difficult to remove these tiny solid particles completely from the highly viscous polymer. The standard work-up procedure involves a time-consuming 4-6 h settling step followed by at least one, often two or more, filtration operations. This series of physical separation units not only complicates the operation, but also requires a large investment in filtration equipment (e.g., filter press) with high maintenance costs and a high risk of filter cloth clogging, which severely affects the continuity and stability of production.

[0006] (3) The production cycle is too long: The neutralization, settling, and filtration steps alone add an additional 16-18 h to the overall production process. This lengthy production cycle significantly reduces the equipment utilization and the hourly output of the plant, directly weakening the market competitiveness of the product.

[0007] (4) Environmental burden and waste disposal issues: The filtration step generates a large amount of solid waste salt residue and waste filter material contaminated with silicone. The disposal of these solid wastes not only increases additional operating costs, but also poses a potential threat to the environment, which is inconsistent with the modern chemical industry's green and sustainable development requirements.

[0008] (5) Potential quality issues with the product: Due to the limitations of physical filtration, trace amounts of solid salt particles or residual acidic substances that have not been completely neutralized may remain in the final product. These impurities can severely affect the long-term storage stability of the product, potentially leading to slow degradation, changes in molecular weight, or crosslinking of the polymer during storage or use, thereby affecting its performance in downstream applications.

[0009] In summary, the existing PDMS-H production process based on solid-phase base neutralization has a series of technical problems that need to be solved, such as complex process, low efficiency, high cost, environmental pollution, and poor product quality. Therefore, developing a new preparation process that can fundamentally simplify the work-up process, shorten the production cycle, improve product quality, and reduce environmental impact has great technical and economic value. SUMMARY

[0010] In view of the above problems, the purpose of the present application is to provide a terminal hydrogen polydimethylsiloxane and a preparation method thereof. The preparation method of the present application can fundamentally eliminate the time-consuming and complex solid-liquid separation steps (such as settling and filtration) in traditional processes, thereby simplifying the production process, while the terminal hydrogen polydimethylsiloxane prepared has a high solid content, a narrow molecular weight distribution, a good structural regularity, and can effectively improve its performance in downstream applications (such as textile finishing).

[0011] To achieve the above object, the present application provides a preparation method of terminal hydrogen polydimethylsiloxane, comprising steps of: (1) mixing and reacting cyclic siloxane monomer, silicon-hydrogen bond containing end-capping agent and strong acid catalyst to obtain first reaction liquid containing terminal hydrogen polydimethylsiloxane; (2) adding ammonia water to the first reaction liquid to carry out neutralization reaction to obtain second reaction liquid containing terminal hydrogen polydimethylsiloxane, the temperature of the neutralization reaction being 10-50℃; (3) carrying out vacuum high-temperature treatment on the second reaction liquid to obtain terminal hydrogen polydimethylsiloxane purified product, the temperature of the vacuum high-temperature treatment being 100℃ or above.

[0012] Further, the mass ratio of the cyclic siloxane monomer and the silicon-hydrogen bond containing end-capping agent of the present application is 100:1.36.

[0013] Further, the mass of the strong acid catalyst of the present application is 0.1-0.5% of the mass of the cyclic siloxane monomer.

[0014] Further, the cyclic siloxane monomer of the present application is selected from octamethylcyclotetrasiloxane.

[0015] Further, the silicon-hydrogen bond containing end-capping agent of the present application is selected from 1,1,3,3-tetramethyldisiloxane.

[0016] Further, the strong acid catalyst of the present application is selected from triflic acid.

[0017] Further, the temperature of the mixing reaction of the present application is 20-50℃, and the time is 6-10h.

[0018] Further, the mass concentration of the ammonia water of the present application is 10-28%.

[0019] Further, the mass ratio of the ammonia water and the strong acid catalyst of the present application is 5-10:1.

[0020] Further, the temperature of the high-temperature vacuum purification treatment of the present application is 120-150℃, and the time of the high-temperature vacuum purification treatment is 1-10h.

[0021] Further, the vacuum degree of the vacuum high-temperature treatment of the present application is 0.08-0.1MPa.

[0022] Further, the time of the neutralization reaction of the present application is 5-10h.

[0023] Further, the step (1), the step (2) and the step (3) of the present application are all carried out in a reaction kettle with strong acid corrosion resistant lining.

[0024] The second aspect of the present application provides a terminal hydrogen polydimethylsiloxane prepared by the above-mentioned method for preparing terminal hydrogen polydimethylsiloxane.

[0025] Compared with the prior art, the method for preparing terminal hydrogen polydimethylsiloxane has at least the following beneficial effects: (1) In the present application, ammonia is used as a neutralizing agent to neutralize the strong acid catalyst. After adding ammonia to the first reaction solution, a homogeneous or nearly homogeneous mixture is formed in the first reaction solution system, so that the neutralization reaction proceeds rapidly in the liquid phase and generates a water-soluble byproduct (such as ammonium triflate). Therefore, during the separation and purification process of the second reaction solution, there is no need to perform steps such as settling and filtering to remove the neutralization product, thus fundamentally eliminating the time-consuming and complex solid-liquid separation step in the traditional process, thereby greatly simplifying the production process. At the same time, the neutralization reaction temperature of the present application is 10-50°C. At this temperature, ammonia mainly acts as a Bronsted base and undergoes a pure acid-base neutralization reaction with the strong acid catalyst. If the temperature is higher than 50°C, the nucleophilicity of ammonia molecules will be significantly enhanced, thereby triggering a series of harmful side reactions. By precisely controlling the neutralization temperature, the present application effectively suppresses the occurrence of side reactions, resulting in a narrow molecular weight distribution of the polymer and ensuring the structural integrity and regularity of the terminal hydrogen polydimethylsiloxane polymer chain, thereby producing a product with more stable performance.

[0026] (2) The second reaction solution obtained by the neutralization reaction is directly subjected to high-temperature vacuum purification treatment without any physical separation (such as filtering and settling), and the temperature of the high-temperature vacuum purification treatment is controlled to be 100°C or higher. Under this condition, the water, excess ammonia, unreacted cyclic siloxane monomers, and water-soluble neutralization byproducts (such as ammonium triflate) dissolved in the aqueous phase in the second reaction solution are all removed by evaporation, thereby obtaining a terminal hydrogen polydimethylsiloxane purification product with high solid content. At the same time, under the conditions of high temperature and vacuum, the high temperature increases the vapor pressure of ammonia, water, and monomers, and the vacuum accelerates their removal, so that the ammonia is quickly removed before it causes significant molecular chain degradation under high-temperature conditions. Under this condition, the physical removal rate is much higher than the chemical degradation rate, thereby effectively avoiding the destructive conditions of coexistence of high temperature and high concentration of ammonia. At the same time, the water in the second reaction solution system vaporizes at high temperature and can act as an in-situ stripping agent to help remove the neutralization byproducts, achieving integrated purification, which not only ensures efficiency but also ensures the integrity of the polymer. Therefore, the present application integrates multiple post-treatment unit operations such as settling, filtering, and low-boiling removal in the traditional process into one high-temperature vacuum purification step, greatly simplifying the process flow and shortening the production cycle.

[0027] (3) The present application adopts homogeneous ammonia water neutralization and integrated vacuum purification, completely cancels the longest time-consuming solid-liquid sedimentation (mostly 4-6h) and multi-stage filtration steps in the traditional process, which means that the yield and overall production efficiency of the factory can be significantly improved in the same equipment and time. At the same time, since solid-liquid separation is not required, the present application no longer needs expensive filtration equipment such as filter press, thereby reducing the fixed asset investment and equipment maintenance cost. The reduction of operation steps also reduces the requirements and labor intensity of the operators, further saving the labor cost.

[0028] (4) The present application fundamentally eliminates the generation of solid salt slag waste, and the neutralization byproduct is water-soluble salt, which is removed together with water vapor in the vacuum devolatilization step, and can be condensed and recovered for subsequent treatment, avoiding the pollution of solid waste to the environment and the high disposal cost, and meeting the development direction of green chemical industry; meanwhile, the raw materials (D4, TMDS, TFMSA, ammonia water) used in the present application are all conventional industrial products, and the process conditions are mild and controllable. BRIEF DESCRIPTION OF DRAWINGS

[0029] Figure 1 The product appearance diagram of the end-hydrogen polydimethylsiloxane prepared in Example 1 and Comparative Example 5 of the present application. DETAILED DESCRIPTION

[0030] The end-hydrogen polydimethylsiloxane of the present application refers to polydimethylsiloxane containing silicon-hydrogen bonds at both ends of the molecular chain. The end-hydrogen polydimethylsiloxane of the present application can be used as a basic intermediate polymer to graft or chain-extend with other compounds containing unsaturated bonds (such as vinyl groups), thereby synthesizing block, grafted or crosslinked organosilicon polymers with specific functions, and can also be directly applied in the fields of textile finishing agents, liquid silicone rubber (LSR), electronic potting glue, leather aids and personal care products, etc. More specifically, when it is applied in textile finishing agents, the finishing effect can be effectively improved.

[0031] The preparation method of the end-hydrogen polydimethylsiloxane of the present application can include the following steps: (1) mixing and reacting cyclic siloxane monomer, end-capping agent containing silicon-hydrogen bond and strong acid catalyst to obtain first reaction liquid containing end-hydrogen polydimethylsiloxane; (2) adding ammonia water to the first reaction liquid to carry out neutralization reaction to obtain second reaction liquid containing end-hydrogen polydimethylsiloxane; (3) vacuum high-temperature treatment of the second reaction liquid to obtain end-hydrogen polydimethylsiloxane purification product.

[0032] In step (1), the mixing reaction is carried out in a reaction kettle with strong acid corrosion-resistant lining. Specifically, the reaction kettle can be a enamel reaction kettle or a glass reaction kettle.

[0033] The mass ratio of the cyclic siloxane monomer and the silicon-hydrogen bond-containing capping agent of the present application is determined according to the target molecular weight, for example, taking the cyclic siloxane monomer as octamethylcyclotetrasiloxane and the silicon-hydrogen bond-containing capping agent as 1,1,3,3-tetramethyldisiloxane as an example, for a product with a target molecular weight of 10,000 g / mol, the mass ratio of the cyclic siloxane monomer and the silicon-hydrogen bond-containing capping agent can be 100:1.36.

[0034] The mass of the strong acid catalyst is 0.1% to 0.5% of the mass of the cyclic siloxane monomer, preferably, the mass of the strong acid catalyst is 0.2% to 0.3% of the mass of the cyclic siloxane monomer, more preferably, the mass of the strong acid catalyst is 0.25% of the mass of the cyclic siloxane monomer, for example, the mass of the strong acid catalyst is 0.1%, 0.15%, 0.2%, 0.25%, 0.3%, 0.35%, 0.4%, 0.45%, 0.5% of the mass of the cyclic siloxane monomer, but not limited thereto, other values not listed in the scope of the present application are also applicable.

[0035] The cyclic siloxane monomer is selected from octamethylcyclotetrasiloxane (D4). The silicon-hydrogen bond-containing capping agent is selected from 1,1,3,3-tetramethyldisiloxane (TMDS). The strong acid catalyst is selected from trifluoromethanesulfonic acid.

[0036] The temperature of the mixing reaction is 20°C to 50°C, preferably, the temperature of the mixing reaction is 30°C to 40°C, for example, the temperature of the mixing reaction is 20°C, 25°C, 30°C, 35°C, 40°C, 45°C, 50°C, but not limited thereto, other values not listed in the scope of the present application are also applicable. The time of the mixing reaction is 6h to 10h, preferably, the time of the mixing reaction is 8h, for example, the time of the mixing reaction is 6h, 7h, 8h, 9h, 10h, but not limited thereto, other values not listed in the scope of the present application are also applicable. Under this reaction condition, the polymerization reaction of the cyclic siloxane monomer and the silicon-hydrogen bond-containing capping agent under the condition of the strong acid catalyst reaches or approaches the polymerization-depolymerization equilibrium, obtaining a first reaction liquid containing hydrogen-terminated polydimethylsiloxane, in addition, the first reaction liquid also contains residual strong acid catalyst and possibly unreacted cyclic siloxane monomer, silicon-hydrogen bond-containing capping agent and other substances.

[0037] In step (2), the neutralization reaction is carried out in a reaction kettle with a strong acid corrosion-resistant lining, specifically, the reaction kettle can be a porcelain-lined reaction kettle or a glass reaction kettle.

[0038] The present application uses ammonia as a neutralizing agent to neutralize the strong acid catalyst, after adding ammonia to the first reaction liquid, a homogeneous or nearly homogeneous mixture is formed in the first reaction liquid system, so that the neutralization reaction proceeds rapidly in the liquid phase, and a water-soluble byproduct (such as ammonium triflate) is generated, therefore, no settling, filtering and other steps are required to remove the neutralization product during the separation and purification process of the second reaction liquid, fundamentally eliminating the time-consuming and complex solid-liquid separation step in the traditional process, thereby greatly simplifying the production process. Specifically, the mass concentration of ammonia is 10% to 28%, preferably, the mass concentration of ammonia is 20%, for example, the mass concentration of ammonia is 10%, 12%, 14%, 15%, 16%, 18%, 20%, 22%, 24%, 25%, 26%, 28%, but not limited to this, other values not listed in the scope of the present application are also applicable. The mass ratio of ammonia to strong acid catalyst is 5-10:1, for example, the mass ratio of ammonia to strong acid catalyst is 5:1, 5.5:1, 6:1, 6.5:1, 7:1, 7.5:1, 8:1, 8.5:1, 9:1, 9.5:1, 10:1, but not limited to this, other values not listed in the scope of the present application are also applicable. Controlling the amount of ammonia added in this range is sufficient to completely neutralize the residual strong acid catalyst in the first reaction liquid, which can ensure the complete neutralization reaction.

[0039] The temperature of the neutralization reaction is 10°C to 50°C, preferably, the temperature of the neutralization reaction is 20°C to 35°C, more preferably, the temperature of the neutralization reaction is 25°C to 32°C, as an example, the temperature of the neutralization reaction is 10°C, 12°C, 15°C, 18°C, 20°C, 21°C, 22°C, 23°C, 24°C, 25°C, 26°C, 27°C, 28°C, 29°C, 30°C, 31°C, 32°C, 33°C, 34°C, 35°C, 40°C, 45°C, 50°C, but not limited to, other values not listed in the scope of the present application are also applicable. At this temperature, ammonia mainly acts as a Bronsted base and reacts with the strong acid catalyst to generate a pure acid-base neutralization reaction, and the active ester group (such as -Si-O-SO2CF3) at the end of the polymer chain is hydrolyzed to generate a terminal silicon hydroxyl group (-SiOH), which is then effectively capped by the capping agent in the system, thereby ensuring the structural integrity of the polymer. If the temperature is higher than 50°C (for example, 55°C to 60°C or higher), the nucleophilicity of ammonia molecules will be significantly enhanced, thereby initiating a series of harmful side reactions. These side reactions include but are not limited to: ammonia as a nucleophile attacking silicon atoms, or as a base catalyst catalyzing condensation reactions between terminal silicon hydroxyl groups, resulting in undesirable chain extension, branching, and even slight crosslinking. These defects in the microstructure will destroy the regularity of the polymer molecular structure, change its molecular weight distribution, and ultimately lead to a sharp decline in its performance in downstream applications. The time of the neutralization reaction is 5h to 10h, as an example, the time of the neutralization reaction is 5h, 6h, 7h, 8h, 9h, 10h, but not limited to, other values not listed in the scope of the present application are also applicable.

[0040] The second reaction solution obtained by step (2) of the present application contains hydrogen-terminated polydimethylsiloxane, in addition to water, unreacted cyclic siloxane monomers, capping agents, excess ammonia, water-soluble neutralization products dissolved in the aqueous phase, other low molecular weight by-products, and the like.

[0041] In step (3), the high-temperature vacuum purification treatment is carried out in a reaction kettle with a strong acid-resistant lining, specifically, the reaction kettle can be a porcelain reaction kettle or a glass reaction kettle.

[0042] The second reaction liquid after the homogeneous neutralization reaction is directly subjected to high-temperature vacuum purification treatment without any physical separation (such as filtration or sedimentation). The temperature of the high-temperature vacuum purification treatment is 100°C or higher, preferably 120°C to 150°C, for example, 100°C, 110°C, 120°C, 130°C, 140°C, or 150°C, but is not limited thereto, and other values not listed in the present application are also applicable. The time of the high-temperature vacuum purification treatment is 1h to 10h, for example, 1h, 2h, 3h, 4h, 5h, 6h, 7h, 8h, 9h, or 10h, but is not limited thereto, and other values not listed in the present application are also applicable. The vacuum degree of the high-temperature vacuum purification treatment is 0.08MPa to 0.1MPa, for example, 0.08MPa, 0.09MPa, or 0.1MPa, but is not limited thereto, and other values not listed in the present application are also applicable. Under the above conditions, the water, excess ammonia, unreacted cyclic siloxane monomers, and water-soluble neutralization byproducts (such as ammonium triflate) dissolved in the aqueous phase in the second reaction liquid are all removed by evaporation, thereby obtaining a purified product of hydrogen-terminated polydimethylsiloxane. At the same time, under the conditions of high temperature and vacuum, the high temperature increases the vapor pressure of ammonia, water, and monomers, and the vacuum accelerates the removal of these substances, so that the ammonia is quickly removed before it causes significant molecular chain degradation under high-temperature conditions. Under the above conditions, the physical removal rate is much higher than the chemical degradation rate, thereby effectively avoiding the destructive conditions of coexistence of high temperature and high concentration of ammonia. At the same time, the water in the system is vaporized at high temperature and can be used as an in-situ stripping agent to help remove the neutralization byproducts, thereby achieving integrated purification, ensuring the efficiency and the integrity of the polymer. Therefore, the present application integrates the multiple post-processing unit operations such as sedimentation, filtration, and low-boiling removal in the traditional process into one high-temperature vacuum purification treatment step, greatly simplifying the process flow and shortening the production cycle.

[0043] To better illustrate the purpose, technical solutions, and beneficial effects of the present application, the present application will be further described below in conjunction with specific examples. It should be noted that the following description of the method is a further explanation and description of the present application and should not be considered as a limitation of the present application.

[0044] The monomers, capping agents, catalysts, neutralizing agents, and other raw materials involved in the examples and comparative examples of the present application are all industrial grade and are obtained through conventional commercial channels.

[0045] Example 1 This example is a method for preparing hydrogen-terminated polydimethylsiloxane, which comprises the following steps: (1) Place 1000g of octamethylcyclotetrasiloxane, 13.6g of 1,1,3,3-tetramethyldisiloxane and 2.5g of trifluoromethanesulfonic acid in a 2L enamel reactor and stir at 35°C for 8h to obtain a first reaction solution containing a crude product of terminal hydrogen polydimethylsiloxane. (2) Under the condition of maintaining the temperature at 30°C, 14g of ammonia water with a mass concentration of 20% was added dropwise to the first reaction solution, and the mixture was stirred at 30°C for 10h to obtain a second reaction solution containing the crude product of terminal hydrogen polydimethylsiloxane. (3) The temperature of the second reaction liquid was raised to 150°C and subjected to devolatilization treatment for 6 hours under a vacuum of 0.08 MPa. The temperature was then lowered to below 80°C, and the purified terminal hydrogen polydimethylsiloxane was obtained.

[0046] like Figure 1 As shown in the product appearance diagram of the glass bottle on the right, the hydrogen-terminated polydimethylsiloxane prepared in this embodiment is a colorless, transparent, odorless viscous liquid. Its viscosity was measured to be 260 cP using an NDJ-8S rotational viscometer at 25°C. The total process time for this embodiment is approximately 24 to 30 hours.

[0047] Example 2 This embodiment describes a method for preparing hydrogen-terminated polydimethylsiloxane, comprising the following steps: (1) Place 1000g of octamethylcyclotetrasiloxane, 13.6g of 1,1,3,3-tetramethyldisiloxane and 3.5g of trifluoromethanesulfonic acid in a 2L enamel reactor and stir at 35°C for 8h to obtain a first reaction solution containing a crude product of terminal hydrogen polydimethylsiloxane. (2) Under the condition of maintaining the temperature at 30°C, 19.6g of ammonia water with a mass concentration of 20% was added dropwise to the first reaction solution, and the mixture was stirred at 30°C for 10h to obtain a second reaction solution containing crude product of terminal hydrogen polydimethylsiloxane. (3) The temperature of the second reaction liquid was raised to 150°C and subjected to devolatilization treatment for 6 hours under a vacuum of 0.08 MPa. The temperature was then lowered to below 80°C, and the purified terminal hydrogen polydimethylsiloxane was obtained.

[0048] The hydrogen-terminated polydimethylsiloxane prepared in this embodiment is a colorless, transparent, and odorless viscous liquid. Its viscosity was measured to be 265 cP at 25°C using an NDJ-8S rotational viscometer.

[0049] Example 3 This embodiment describes a method for preparing hydrogen-terminated polydimethylsiloxane, comprising the following steps: (1) 1000 g octamethylcyclotetrasiloxane, 13.6 g 1,1,3,3-tetramethyldisiloxane and 1.5 g trifluoromethanesulfonic acid were placed in a 2 L porcelain reaction kettle, and stirred at 35 °C for 8 h to obtain a first reaction liquid containing crude product of terminal hydrogen polydimethylsiloxane; (2) 8.4 g of 20% ammonia water was added dropwise into the first reaction liquid while maintaining the temperature at 30 °C, and stirred at 30 °C for 10 h to obtain a second reaction liquid containing crude product of terminal hydrogen polydimethylsiloxane; (3) The temperature of the second reaction liquid was raised to 150 °C, and vacuum treatment was carried out at a vacuum degree of 0.08 MPa for 6 h, and then the temperature was lowered to below 80 °C to obtain purified product of terminal hydrogen polydimethylsiloxane.

[0050] The terminal hydrogen polydimethylsiloxane prepared in this example was a colorless, transparent, odorless viscous liquid, and its viscosity was 250 cP at 25 °C as tested by using an NDJ-8S rotary viscometer.

[0051] Example 4 This example is a preparation method of terminal hydrogen polydimethylsiloxane, comprising the following steps: (1) 1000 g octamethylcyclotetrasiloxane, 13.6 g 1,1,3,3-tetramethyldisiloxane and 2.5 g trifluoromethanesulfonic acid were placed in a 2 L porcelain reaction kettle, and stirred at 35 °C for 8 h to obtain a first reaction liquid containing crude product of terminal hydrogen polydimethylsiloxane; (2) 14 g of 20% ammonia water was added dropwise into the first reaction liquid while maintaining the temperature at 25 °C, and stirred at 25 °C for 10 h to obtain a second reaction liquid containing crude product of terminal hydrogen polydimethylsiloxane; (3) The temperature of the second reaction liquid was raised to 150 °C, and vacuum treatment was carried out at a vacuum degree of 0.08 MPa for 6 h to remove water, excess ammonia, unreacted monomers and water-soluble ammonium trifluoromethanesulfonate byproduct and other substances, and then the temperature was lowered to below 80 °C to obtain purified product of terminal hydrogen polydimethylsiloxane.

[0052] The terminal hydrogen polydimethylsiloxane prepared in this example was a colorless, transparent, odorless viscous liquid, and its viscosity was 260 cP at 25 °C as tested by using an NDJ-8S rotary viscometer.

[0053] Example 5 This example is a preparation method of terminal hydrogen polydimethylsiloxane, comprising the following steps: (1) 1000 g octamethylcyclotetrasiloxane, 13.6 g 1,1,3,3-tetramethyldisiloxane and 2.5 g trifluoromethanesulfonic acid were placed in a 2 L enamel reaction kettle, and stirred at 35 °C for 8 h to obtain a first reaction liquid containing crude end-hydrogen polydimethylsiloxane; (2) 14 g of 20% ammonia water was added dropwise into the first reaction liquid while maintaining the temperature at 35 °C, and stirred at 35 °C for 10 h to obtain a second reaction liquid containing crude end-hydrogen polydimethylsiloxane; (3) The temperature of the second reaction liquid was raised to 150 °C, and vacuum devolatilization was performed at a vacuum degree of 0.08 MPa for 6 h, and then the temperature was lowered to below 80 °C, and the end-hydrogen polydimethylsiloxane purified product was discharged.

[0054] The end-hydrogen polydimethylsiloxane prepared in this example was a colorless, transparent, odorless viscous liquid, and its viscosity was 255 cP tested using an NDJ-8S rotary viscometer at 25 °C.

[0055] Example 6 This example is a preparation method of end-hydrogen polydimethylsiloxane, comprising the following steps: (1) 1000 g octamethylcyclotetrasiloxane, 13.6 g 1,1,3,3-tetramethyldisiloxane and 2.5 g trifluoromethanesulfonic acid were placed in a 2 L enamel reaction kettle, and stirred at 35 °C for 8 h to obtain a first reaction liquid containing crude end-hydrogen polydimethylsiloxane; (2) 15 g of 25% ammonia water was added dropwise into the first reaction liquid while maintaining the temperature at 30 °C, and stirred at 30 °C for 10 h to obtain a second reaction liquid containing crude end-hydrogen polydimethylsiloxane; (3) The temperature of the second reaction liquid was raised to 150 °C, and vacuum devolatilization was performed at a vacuum degree of 0.08 MPa for 6 h, and then the temperature was lowered to below 80 °C, and the end-hydrogen polydimethylsiloxane purified product was discharged.

[0056] The end-hydrogen polydimethylsiloxane prepared in this example was a colorless, transparent, odorless viscous liquid, and its viscosity was 260 cP tested using an NDJ-8S rotary viscometer at 25 °C.

[0057] Example 7 This example is a preparation method of end-hydrogen polydimethylsiloxane, comprising the following steps: (1) 1000 g octamethylcyclotetrasiloxane, 13.6 g 1,1,3,3-tetramethyldisiloxane and 2.5 g trifluoromethanesulfonic acid were placed in a 2 L enamel reaction kettle, and stirred at 35 °C for 8 h to obtain a first reaction liquid containing crude end-hydrogen polydimethylsiloxane; (2) Under the condition of maintaining the temperature at 30°C, 14g of ammonia water with a mass concentration of 20% was added dropwise to the first reaction solution, and the mixture was stirred at 30°C for 10h to obtain a second reaction solution containing the crude product of terminal hydrogen polydimethylsiloxane. (3) The temperature of the second reaction liquid is raised to 120°C and subjected to devolatilization treatment for 8 hours under a vacuum of 0.08 MPa. The temperature is then lowered to below 80°C, and the purified terminal hydrogen polydimethylsiloxane is obtained.

[0058] The hydrogen-terminated polydimethylsiloxane prepared in this embodiment is a colorless, transparent, and odorless viscous liquid. Its viscosity was measured to be 255 cP using an NDJ-8S rotational viscometer at 25°C.

[0059] Example 8 This embodiment describes a method for preparing hydrogen-terminated polydimethylsiloxane, comprising the following steps: (1) Place 1000g of octamethylcyclotetrasiloxane, 13.6g of 1,1,3,3-tetramethyldisiloxane and 2.5g of trifluoromethanesulfonic acid in a 2L enamel reactor and stir at 35°C for 8h to obtain a first reaction solution containing a crude product of terminal hydrogen polydimethylsiloxane. (2) Under the condition of maintaining the temperature at 30°C, 14g of ammonia water with a mass concentration of 20% was added dropwise to the first reaction solution, and the mixture was stirred at 30°C for 10h to obtain a second reaction solution containing the crude product of terminal hydrogen polydimethylsiloxane. (3) The temperature of the second reaction liquid was raised to 135°C and subjected to devolatilization treatment under a vacuum of 0.08 MPa for 7 hours. The temperature was then lowered to below 80°C, and the purified terminal hydrogen polydimethylsiloxane was obtained.

[0060] The hydrogen-terminated polydimethylsiloxane prepared in this embodiment is a colorless, transparent, and odorless viscous liquid. Its viscosity was measured to be 290 cP using an NDJ-8S rotational viscometer at 25°C.

[0061] Comparative Example 1 This comparative example illustrates a method for preparing a hydrogen-terminated polydimethylsiloxane, comprising the following steps: (1) Place 1000g of octamethylcyclotetrasiloxane, 13.6g of 1,1,3,3-tetramethyldisiloxane and 2.5g of trifluoromethanesulfonic acid in a 2L enamel reactor and stir at 35°C for 8h to obtain a first reaction solution containing a crude product of terminal hydrogen polydimethylsiloxane. (2) Under the condition of maintaining the temperature at 30°C, 3.6g of anhydrous sodium carbonate was added to the first reaction solution and stirred at 30°C for 12h to obtain a second reaction solution containing the crude product of terminal hydrogen polydimethylsiloxane. (3) The second reaction liquid was allowed to stand and settle for 6 h, and white solid precipitates were observed at the bottom of the reactor. The supernatant was filtered by a filter press to remove the solid sodium triflate, the temperature of the filtrate was raised to 150°C, and the temperature was lowered to below 80°C after devolatilization treatment under a vacuum of 0.08 MPa for 6 h, and the product was discharged.

[0062] The end-hydrogen polydimethylsiloxane obtained by the preparation method of the present comparative example was a colorless, transparent, odorless viscous liquid, and its viscosity was 255 cP when tested by an NDJ-8S rotary viscometer at 25°C. The total process time of the preparation method was about 34 h to 40 h, which was much longer than that of Example 1.

[0063] Comparative Example 2 The present comparative example was a preparation method of an end-hydrogen polydimethylsiloxane, comprising the following steps: (1) 1000 g of octamethylcyclotetrasiloxane, 13.6 g of 1,1,3,3-tetramethyldisiloxane, and 2.5 g of trifluoromethanesulfonic acid were placed in a 2L enamel reactor, and stirred at 35°C for 8 h to obtain a first reaction liquid containing a crude product of end-hydrogen polydimethylsiloxane; (2) 14 g of 20% ammonia water was added dropwise to the first reaction liquid while maintaining the temperature at 55°C, and stirred at 55°C for 10 h to obtain a second reaction liquid containing a crude product of end-hydrogen polydimethylsiloxane; (3) The temperature of the second reaction liquid was raised to 150°C, and the temperature was lowered to below 80°C after devolatilization treatment under a vacuum of 0.08 MPa for 6 h, and the product was discharged.

[0064] During the neutralization reaction, a small amount of gel-like particles were observed in the reaction system, and its viscosity was 285 cP when tested by an NDJ-8S rotary viscometer at 25°C, indicating that an undesirable chain extension or branching side reaction occurred.

[0065] Comparative Example 3 (1) 1000 g of octamethylcyclotetrasiloxane, 13.6 g of 1,1,3,3-tetramethyldisiloxane, and 2.5 g of trifluoromethanesulfonic acid were placed in a 2L enamel reactor, and stirred at 35°C for 8 h to obtain a first reaction liquid containing a crude product of end-hydrogen polydimethylsiloxane; (2) 14 g of 20% ammonia water was added dropwise to the first reaction liquid while maintaining the temperature at 60°C, and stirred at 60°C for 10 h to obtain a second reaction liquid containing a crude product of end-hydrogen polydimethylsiloxane; (3) The temperature of the second reaction liquid was raised to 150°C and subjected to devolatilization treatment for 6 hours under a vacuum of 0.08 MPa. The temperature was then lowered to below 80°C, and the purified terminal hydrogen polydimethylsiloxane was obtained.

[0066] During the neutralization reaction, a small amount of crosslinked material was observed to adhere to the reactor wall and the agitator. The viscosity was measured at 25°C using an NDJ-8S rotational viscometer and found to be 310 cP, which is significantly higher than that of Example 1, indicating that an undesirable chain extension or branching side reaction occurred.

[0067] Comparative Example 4 (1) Place 1000g of octamethylcyclotetrasiloxane, 13.6g of 1,1,3,3-tetramethyldisiloxane and 2.5g of trifluoromethanesulfonic acid in a 2L enamel reactor and stir at 35°C for 8h to obtain a first reaction solution containing a crude product of terminal hydrogen polydimethylsiloxane. (2) Under the condition of maintaining the temperature at 30°C, 14g of ammonia water with a mass concentration of 20% was added dropwise to the first reaction solution, and the mixture was stirred at 30°C for 10h to obtain a second reaction solution containing the crude product of terminal hydrogen polydimethylsiloxane. (3) The temperature of the second reaction liquid is raised to 90°C and subjected to devolatilization treatment for 6 hours under a vacuum of 0.08 MPa. The temperature is then lowered to below 80°C, and the purified terminal hydrogen polydimethylsiloxane is obtained.

[0068] The viscosity of the hydrogen-terminated polydimethylsiloxane prepared in this comparative example was measured to be 280 cP using an NDJ-8S rotational viscometer at 25°C.

[0069] Comparative Example 5 (1) Place 1000g of octamethylcyclotetrasiloxane, 13.6g of 1,1,3,3-tetramethyldisiloxane and 2.5g of trifluoromethanesulfonic acid in a 2L SS316 stainless steel reactor and stir at 35℃ for 8h to obtain the first reaction solution containing the crude product of terminal hydrogen polydimethylsiloxane. (2) Under the condition of maintaining the temperature at 30°C, 14g of ammonia water with a mass concentration of 20% was added dropwise to the first reaction solution, and the mixture was stirred at 30°C for 10h to obtain a second reaction solution containing the crude product of terminal hydrogen polydimethylsiloxane. (3) The temperature of the second reaction liquid was raised to 150°C and subjected to devolatilization treatment for 6 hours under a vacuum of 0.08 MPa. The temperature was then lowered to below 80°C, and the purified terminal hydrogen polydimethylsiloxane was obtained.

[0070] like Figure 1As shown in the left glass bottle product appearance diagram, the end-hydrogen polydimethylsiloxane prepared by the comparative example is in a milky white, turbid state, and is accompanied by a putrefactive odor. At the same time, green precipitate is found at the bottom of the SS316 stainless steel reaction kettle, which may be due to the reaction of trifluoromethanesulfonic acid (TFMSA) in the system with the metal (iron, nickel, chromium, etc.) of the stainless steel kettle wall, on the one hand causing corrosion of the kettle body, on the other hand the generated metal salt can cause the catalyst to be poisoned and ineffective, and catalyze the degradation of the polymer and other side reactions, ultimately leading to uncontrolled viscosity, turbidity and odor of the product, resulting in production failure. At the same time, the polymer reaction sticking time is extended from normal (Example 1) 2-3h to 4h, and the viscosity of the end-hydrogen polydimethylsiloxane prepared by the comparative example is 208 cP, which is far lower than the target value, indicating that the polymerization reaction is incomplete.

[0071] The number average molecular weight and molecular weight distribution of the end-hydrogen polydimethylsiloxane prepared in Examples 1-8 and Comparative Examples 1-5 were measured by gel permeation chromatography, and the test results are shown in Table 1. Solid content test: 100g of the end-hydrogen polydimethylsiloxane prepared in Examples 1-8 and Comparative Examples 1-5 was placed in an oven at 105°C for 4h, and then the mass was measured. The ratio of the mass after baking to the initial mass is the solid content. If the low-boiling-point components are not removed completely, the solid content will be too low (containing water or low-boiling-point components).

[0072] The end-hydrogen polydimethylsiloxane prepared in Examples 1-8 and Comparative Examples 1-5 was prepared into a silicone emulsion according to the following formulation: 100 parts by weight of end-hydrogen polydimethylsiloxane (one of Examples 1-8 and Comparative Examples 1-5), 20 parts by weight of polyetheramine D230 and 60 parts by weight of isopropyl alcohol were prepared into a ternary block silicone oil according to a conventional synthesis method, and then the ternary block silicone oil was emulsified with TO-9 emulsifier at a weight ratio of 5:1 to obtain a silicone emulsion. The silicone emulsion (100g / L) was used in a "one dip and one roll" process, and pure cotton fabric was dipped in the finishing liquid, and the roll-up rate was controlled at 70-80% by a mangle. The dipped and rolled fabric was pre-dried at 100°C, and then cured at 150°C for 3 minutes. The finished fabric was equilibrated at standard temperature and humidity (20±2°C, 65±5%RH) for 24h. The finished pure cotton fabric was subjected to subjective hand feel evaluation of fabric softness by 5 experienced technicians, and the score range was 1-10, and the average value was taken. The higher the score, the better the hand feel. Among them, the hand feel score of 10-9 is excellent; 9-8 (not including 9) is good; 8-7 (not including 8) is good; 7-6 (not including 7) is general; 6-5 (not including 6) is poor; 5-4 (not including 5) is poor, and below 4 is very poor. The test results are shown in Table 1.

[0073] Table 1 Performance test results of examples and comparative examples

[0074] As shown in the test results in Table 1, the end-hydrogen polydimethylsiloxane prepared by the preparation method of the present application has substantially the same performance as the product prepared by the traditional preparation method, but the preparation process of the present application is significantly shortened compared with the traditional preparation process. Further, as shown by the comparison between Examples 1-8 and Comparative Examples 2-5, the end-hydrogen polydimethylsiloxane prepared by the preparation method of the present application has a narrower molecular weight distribution, meaning that the molecular chain length in the polymer is relatively consistent, and the side reaction is less, which indirectly indicates that the polymer structure regularity may be higher, the purity is higher, and the structural integrity is better. At the same time, when applied to textile finishing agents, the pure cotton fabric finished by the end-hydrogen polydimethylsiloxane has a more excellent hand feeling.

[0075] Further, as shown by the comparison between Example 1 and Comparative Examples 2-3, when the neutralization temperature exceeds 50℃, the side reaction between the residual ammonia in the system and the polymer chain segment may occur, which destroys the regularity of the polymer molecular structure, widens the molecular weight distribution, and deteriorates the fabric finishing performance. As shown by the comparison between Example 1 and Comparative Example 4, when the temperature of high-temperature vacuum purification treatment is lower than 100℃, the low-boiling impurities existing in the system are difficult to remove, which causes the product to have a wide molecular weight distribution, insufficient purity, and low solid content.

[0076] Finally, it should be noted that the above examples are only used to illustrate the technical solutions of the present application and not to limit the protection scope of the present application. Although the present application has been described in detail with reference to the preferred embodiments, it is not limited to the examples listed in the embodiments. Those skilled in the art should understand that the technical solutions of the present application can be modified or replaced by equivalents without departing from the essence and scope of the technical solutions of the present application.

Claims

1. A method for preparing a hydrogen-terminated polydimethylsiloxane, characterized in that, Including the following steps: (1) A first reaction solution containing terminal hydrogen polydimethylsiloxane is obtained by mixing and reacting cyclic siloxane monomers, end-capping agents containing silane-hydrogen bonds and strong acid catalysts. (2) Add ammonia to the first reaction solution to carry out a neutralization reaction to obtain a second reaction solution containing the terminal hydrogen polydimethylsiloxane, wherein the temperature of the neutralization reaction is 10℃~50℃; (3) The second reaction solution is subjected to high-temperature vacuum purification treatment to obtain a purified product of terminal hydrogen polydimethylsiloxane, wherein the temperature of the vacuum high-temperature treatment is 100°C or above.

2. The method for preparing hydrogen-terminated polydimethylsiloxane according to claim 1, characterized in that, The mass ratio of the cyclic siloxane monomer to the silane-hydrogen bond-containing end-capping agent is 100:1.

36.

3. The method for preparing hydrogen-terminated polydimethylsiloxane according to claim 1, characterized in that, The mass of the strong acid catalyst is 0.1% to 0.5% of the mass of the cyclic siloxane monomer.

4. The method for preparing hydrogen-terminated polydimethylsiloxane according to claim 1, characterized in that, The cyclic siloxane monomer is selected from octamethylcyclotetrasiloxane, the end-capping agent containing silane-hydrogen bonds is selected from 1,1,3,3-tetramethyldisiloxane, and the strong acid catalyst is selected from trifluoromethanesulfonic acid.

5. The method for preparing hydrogen-terminated polydimethylsiloxane according to claim 1, characterized in that, The mixing reaction is carried out at a temperature of 20℃ to 50℃ for a time of 6h to 10h.

6. The method for preparing hydrogen-terminated polydimethylsiloxane according to claim 1, characterized in that, The mass concentration of the ammonia water is 10% to 28%, and the mass ratio of the ammonia water to the strong acid catalyst is 5 to 10:

1.

7. The method for preparing hydrogen-terminated polydimethylsiloxane according to claim 1, characterized in that, The temperature of the high-temperature vacuum purification process is 120℃~150℃, and the time of the high-temperature vacuum purification process is 1h~10h.

8. The method for preparing hydrogen-terminated polydimethylsiloxane according to claim 1, characterized in that, The neutralization reaction takes 5 to 10 hours. The vacuum level during the high-temperature vacuum treatment is 0.08 MPa to 0.1 MPa.

9. The method for preparing hydrogen-terminated polydimethylsiloxane according to claim 1, characterized in that, Steps (1), (2), and (3) are all carried out in a reactor with a lining resistant to strong acid corrosion.

10. A hydrogen-terminated polydimethylsiloxane, characterized in that, It is prepared by the method for preparing hydrogen-terminated polydimethylsiloxane according to any one of claims 1 to 9.

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