A method for preparing hydroxyl-terminated dimethyldiphenylpolysiloxane

Abstract

This invention discloses a method for preparing hydroxyl-terminated dimethyldiphenylpolysiloxane, comprising the following steps: using octaphenylcyclotetrasiloxane and dimethylcyclosiloxane as polymerization monomers, a polymerization reaction is carried out under the action of a catalyst; then, hydroxyl silicone oil is added for degradation, equilibration, and condensation reactions; finally, water is added for a second degradation reaction to obtain the hydroxyl-terminated dimethyldiphenylpolysiloxane. This invention reduces the polymer viscosity by adding a small amount of hydroxyl silicone oil in the first stage of the polymerization reaction, allowing the polymer to undergo sufficient condensation and equilibration reactions at a low viscosity. The reduced polymer viscosity also alleviates the pressure on equipment operating at high viscosity. Furthermore, the raw materials used in this invention are octaphenylcyclotetrasiloxane and dimethylcyclosiloxane, which are low in cost and easy to industrialize; and the prepared hydroxyl-terminated dimethyldiphenylpolysiloxane product has high transparency.

Description

Technical Field

[0001] This invention belongs to the field of organosilicon materials, and in particular relates to a method for preparing hydroxyl-terminated dimethyldiphenylpolysiloxane. Background Technology

[0002] Phenyl polysiloxanes are produced by introducing phenylsiloxane linkages into the molecular chain of methyl polysiloxanes. Compared with methyl polysiloxanes, phenyl polysiloxanes have better resistance to high and low temperatures, radiation, damping, flame retardancy, and ablation, and are therefore widely used in aerospace, electronic equipment, new energy and other industrial fields.

[0003] Phenyl polysiloxanes include methylphenyl polysiloxanes and dimethyldiphenyl polysiloxanes. While the preparation method for methylphenyl polysiloxanes is relatively simple, the high price of the key raw material, methylphenyl mixed cyclosiloxanes, limits the application and development of methylphenyl silicone rubber. Dimethyldiphenyl polysiloxanes with the same phenyl content have comparable performance to methylphenyl polysiloxanes, but are significantly cheaper. Therefore, industrially used phenyl silicone rubbers are mainly dimethyldiphenyl polysiloxane-based. However, the ring-opening rates of octaphenylcyclotetrasiloxane and octamethylcyclotetrasiloxane, the raw materials required for the preparation of dimethyldiphenyl polysiloxane, differ greatly, and their compatibility is poor. Therefore, it is difficult to prepare dimethyldiphenyl polysiloxane using simple, traditional ring-opening polymerization methods. Thus, how to obtain polysiloxanes with randomly distributed phenyl groups has been a research hotspot, and many insurmountable technical challenges remain.

[0004] Patent document CN103709407A discloses a method for preparing phenyl silicone oil. This method first prepares dimethyl-diphenylcyclosiloxane through high-temperature pyrolysis, and then prepares diphenyl silicone oils with different phenyl contents through ring-opening copolymerization. This method can overcome the problems of poor compatibility between different rings and large differences in ring-opening rates, and can obtain uniform and transparent phenyl silicone oil. However, this method has a complex preparation process, high equipment requirements, and under alkaline conditions, prolonged high temperatures can cause the silanyl-phenyl bonds to break, leading to cross-linking, thereby reducing the yield of the final ring and causing blockage of the equipment outlet, potentially leading to safety accidents.

[0005] Patent document CN102675645A discloses an α,ω-hydroxyl-terminated diphenylsiloxane-dimethylsiloxane copolymer and its preparation method. This method uses a mixed ring of octaphenylcyclotetrasiloxane and dimethylsiloxane as raw materials, potassium silanolate as a catalyst, and a polar solvent as a promoter to prepare hydroxyl-terminated dimethyldiphenyl polysiloxanes with different viscosities and phenyl contents. While this method is simple, the polysiloxanes obtained through direct copolymerization may exhibit uneven phenyl distribution, which can affect the heat resistance of subsequent products.

[0006] Hydroxyl-terminated dimethyldiphenylpolysiloxanes (DDMs) play a crucial role in the development of specialized fields in my country as a raw material for high-temperature, room-temperature vulcanizing silicone rubber. However, existing methods for preparing DDMs still have many problems, such as complex processes and uneven phenyl distribution. Therefore, developing a simple and industrially applicable method for preparing DDMs is a critical challenge that urgently needs to be addressed. Summary of the Invention

[0007] To address the aforementioned technical problems, this invention provides a method for preparing hydroxyl-terminated dimethyldiphenyl polysiloxane, comprising the following steps:

[0008] Using octaphenylcyclotetrasiloxane and dimethylcyclosiloxane as monomers, a polymerization reaction is carried out under the action of a catalyst. Then, hydroxyl silicone oil is added to carry out degradation, equilibration, and polycondensation reactions. Finally, water is added to carry out a second step of degradation reaction to obtain the hydroxyl-terminated dimethyldiphenylpolysiloxane.

[0009] According to an embodiment of the present invention, the amount of octaphenylcyclotetrasiloxane fed is 1 to 80% of the total mass of octaphenylcyclotetrasiloxane and dimethylcyclosiloxane, preferably 1 to 60%, and exemplary values ​​are 1%, 5%, 10%, 20%, 50%, 60%, 80%, or any value within the range of the aforementioned pairs of values.

[0010] According to an embodiment of the present invention, the catalyst may be tetramethylammonium hydroxide silanolate or potassium silanolate.

[0011] According to an embodiment of the present invention, the catalyst tetramethylammonium hydroxide silanolate is an alkaline gel prepared from tetramethylammonium hydroxide and octamethylcyclotetrasiloxane (D4), with the following chemical formula:

[0012] (CH3)4NO[Si(CH3)2O] n N(CH3)4, where n is an integer from 2 to 10, for example, n is 2, 3, 4, 5, 6, 7, 8, 9, 10.

[0013] According to an embodiment of the present invention, the catalyst potassium silanolate is an alkaline gel prepared from potassium hydroxide (KOH) and octamethylcyclotetrasiloxane (D4), with the following chemical formula: KO[Si(CH3)2O] m K and m are integers from 2 to 10, for example, n is 2, 3, 4, 5, 6, 7, 8, 9, 10.

[0014] According to an embodiment of the present invention, the amount of catalyst added is 0.01 to 0.08% of the total mass of octaphenylcyclotetrasiloxane and dimethylcyclosiloxane monomers, preferably 0.02 to 0.06%, and exemplary values ​​are 0.01%, 0.02%, 0.03%, 0.04%, 0.05%, 0.06%, 0.07%, 0.08%, or any value within the range of the aforementioned pairs. It should be noted that when the catalyst is tetramethylammonium hydroxide silanolate, the amount of catalyst added is based on tetramethylammonium hydroxide; when the catalyst is potassium silanolate, the amount of catalyst added is based on potassium hydroxide.

[0015] According to an embodiment of the present invention, when potassium silanolate is used as a catalyst, an accelerator is further added to the polymerization reaction system to carry out the polymerization reaction. Preferably, the accelerator is a polar solvent, such as at least one selected from N,N-dimethylformamide, N,N-dimethylacetamide, dimethyl sulfoxide, diethylene glycol dimethyl ether, diethylene glycol diethyl ether, and N-methylpyrrolidone.

[0016] According to an embodiment of the present invention, the amount of the promoter added is 1 to 6 times the mass of the catalyst potassium silanolate, preferably 2 to 4 times, and exemplary amounts are 1, 2, 3, 4, 5, and 6 times.

[0017] According to an embodiment of the present invention, the temperature of the polymerization reaction is 110-130°C, exemplarily 110°C, 120°C, or 130°C; the time of the polymerization reaction is 0.5-2 hours, exemplarily 0.5 hours, 1 hour, or 2 hours.

[0018] According to an embodiment of the present invention, the hydroxyl silicone oil is a short-chain hydroxyl-terminated polydimethylsiloxane, wherein the mass fraction of hydroxyl groups in the hydroxyl silicone oil is 8.5%.

[0019] According to an embodiment of the present invention, the amount of hydroxyl silicone oil added is 0.1% to 2% of the total mass of the monomers (octaphenylcyclotetrasiloxane and dimethylcyclosiloxane), preferably 0.3% to 1.5%, and exemplary values ​​are 0.1%, 0.2%, 0.3%, 0.5%, 0.8%, 1.0%, 1.2%, 1.5%, 2.0%, or any value within the range of the aforementioned pairs of values.

[0020] According to an embodiment of the present invention, the temperature of the degradation, equilibration, and polycondensation reaction is preferably the same as the temperature of the polymerization reaction, preferably 110-130°C, with examples being 110°C, 120°C, and 130°C; the time of the degradation, equilibration, and polycondensation reaction is 4-8 hours, with examples being 4 hours, 5 hours, 6 hours, 7 hours, and 8 hours.

[0021] According to an embodiment of the present invention, the preparation method further includes the following step: after the degradation, equilibration, and polycondensation reactions are completed, a dehydration condensation reaction is carried out. Preferably, the dehydration condensation reaction is carried out under vacuum.

[0022] For example, the temperature of the dehydration condensation reaction is preferably the same as the temperature of the polymerization reaction, preferably 110-130°C, with examples being 110°C, 120°C, and 130°C; the reaction time is 0.5-3 hours, with examples being 0.5 hours, 1 hour, 2 hours, and 3 hours.

[0023] Preferably, the pressure of the dehydration condensation reaction is 30-90 kPa, more preferably 40-85 kPa, and exemplary values ​​are 30 kPa, 45 kPa, 55 kPa, 60 kPa, 70 kPa, 80 kPa, 90 kPa, or any value within the range of the aforementioned pairs of values.

[0024] According to an embodiment of the present invention, when tetramethylammonium hydroxide silanolate is used as a catalyst, the catalyst is added after the dehydration condensation reaction. Preferably, the amount of the added catalyst (based on tetramethylammonium hydroxide) is 0.01 to 0.025‰ of the total mass of the monomers (octaphenylcyclotetrasiloxane and dimethylcyclosiloxane); exemplary values ​​are 0.01‰, 0.015‰, 0.02‰, 0.025‰, or any value within the range of the aforementioned pairwise values.

[0025] According to an embodiment of the present invention, when potassium silanolate is used as a catalyst, an accelerator is added after the dehydration condensation reaction. Preferably, the amount of the added accelerator is 0.5 to 1 times the mass of the potassium silanolate salt; exemplary amounts are 0.5 times, 0.8 times, and 1 times.

[0026] According to an embodiment of the present invention, the preparation method further includes the following steps: adding a catalyst or promoter after the dehydration condensation reaction, and then adding water to the reaction system to carry out the second step of degradation reaction.

[0027] Preferably, the amount of deionized water added is 0.1% to 0.8% of the total mass of the monomers (octaphenylcyclotetrasiloxane and dimethylcyclosiloxane), more preferably 0.2% to 0.6%, and exemplary values ​​are 0.1%, 0.2%, 0.3%, 0.4%, 0.5%, 0.6%, 0.7%, 0.8%, or any value within the range of the aforementioned pairs of values.

[0028] According to an embodiment of the invention, nitrogen gas is preferably introduced to bring the pressure of the reaction system back to atmospheric pressure before adding the catalyst or promoter.

[0029] According to an embodiment of the present invention, before adding deionized water to the reaction system, the reaction is stirred for 0.5 to 3 hours, preferably 1 hour.

[0030] According to an embodiment of the present invention, the addition of a catalyst or accelerator after the dehydration condensation reaction, followed by the addition of water to the reaction system for the second step of degradation reaction, is carried out under closed conditions.

[0031] According to an embodiment of the present invention, the preparation method further includes the following steps: tracking the viscosity of the degradation reaction process online; when the viscosity reaches 100-400 mPa·s (this viscosity is the viscosity displayed by an online viscometer at the reaction temperature), when tetramethylammonium hydroxide silanolate is used as a catalyst, heating the reaction system to decompose the catalyst; and when potassium silanolate is used as a catalyst, adding a neutralizing agent to terminate the reaction.

[0032] Preferably, when using tetramethylammonium hydroxide silanoate as a catalyst, the temperature of the reaction system is 145-160°C when the reaction system is heated, for example, 145°C, 150°C, and 160°C; the holding time (decomposition time) after heating is 1-3 hours, for example, 1 hour, 2 hours, and 3 hours.

[0033] According to an embodiment of the present invention, the neutralizing agent added to terminate the reaction is at least one selected from propionic acid, citric acid, tartaric acid, and phosphoric acid.

[0034] Preferably, the time for terminating the reaction is 1 to 3 hours, for example 1 hour, 2 hours, or 3 hours.

[0035] Preferably, the amount of neutralizing agent used is such that the pH of the reaction system is neutral.

[0036] According to an embodiment of the present invention, the viscosity of the online tracking degradation reaction process is monitored. When the viscosity reaches 100-400 mPa·s (this viscosity is the viscosity displayed by the online viscometer at the reaction temperature), the reaction system is heated to decompose the catalyst when tetramethylammonium hydroxide silanolate is used as the catalyst, and a neutralizing agent is added to terminate the reaction when potassium silanolate is used as the catalyst. The reaction is carried out under closed conditions.

[0037] According to an embodiment of the present invention, the preparation method further includes the following step: after heating the reaction system or adding a neutralizing agent to react, separating and purifying the reaction system. For example, the separation and purification can be carried out using methods known in the art, such as first removing low-boiling substances by vacuum heating, and then cooling to room temperature for adsorption filtration to remove solid impurities.

[0038] Preferably, the temperature for removing low-boiling substances is 160–200°C, with examples being 160°C, 180°C, and 200°C; the pressure for removing low-boiling substances is 200–1000 Pa, with examples being 200 Pa, 500 Pa, 800 Pa, and 1000 Pa; and the time for removing low-boiling substances is 1–4 hours, with examples being 1 hour, 2 hours, 3 hours, and 4 hours.

[0039] According to an embodiment of the present invention, the adsorbent used in the adsorption filtration is diatomaceous earth.

[0040] Preferably, the amount of diatomaceous earth used is 0.5% to 3% of the theoretical mass of the hydroxyl-terminated dimethyldiphenylpolysiloxane, more preferably 0.8% to 2.5%, and exemplary amounts are 0.5%, 0.8%, 1%, 1.2%, 1.7%, 2.0%, 2.5%, and 3.0%.

[0041] In a specific embodiment of the present invention, the method for preparing the hydroxyl-terminated dimethyldiphenyl polysiloxane includes the following steps:

[0042] (1) Using octaphenylcyclotetrasiloxane and dimethylcyclosiloxane as polymerization monomers, a polymerization reaction is carried out under the action of a catalyst and an optional accelerator;

[0043] (2) Add hydroxyl silicone oil to the reaction system to carry out the first step of degradation, equilibration and polycondensation reaction;

[0044] (3) Perform a vacuum dehydration condensation reaction;

[0045] (4) After purging nitrogen back to normal pressure, when tetramethylammonium hydroxide silanolate is used as the catalyst, the catalyst is added; when potassium silanolate is used as the catalyst, the promoter is added; then water is added to the reaction system to carry out the second step of degradation reaction, and the whole system is in a closed state.

[0046] (5) The viscosity of the degradation reaction process is tracked online. When the viscosity of the reaction system reaches 100-400 mPa·s, the temperature of the reaction system is increased to decompose the catalyst when tetramethylammonium hydroxide silanolate is used as the catalyst, and the whole system is kept in a closed state. When potassium silanolate is used as the catalyst, a neutralizing agent is added to terminate the reaction.

[0047] (6) After the catalyst is decomposed or the reaction is neutralized and terminated, the low-boiling substances are removed by vacuum heating, and the mixture is cooled to room temperature for adsorption filtration to remove solid impurities, thereby obtaining the hydroxyl-terminated dimethyl diphenyl polysiloxane.

[0048] The present invention also provides hydroxyl-terminated dimethyldiphenylpolysiloxane prepared by the above preparation method.

[0049] According to an embodiment of the present invention, the viscosity (25°C) of the hydroxyl-terminated dimethyldiphenylpolysiloxane is 4500–7500 mPa·s, with exemplary values ​​of 4600 mPa·s, 5200 mPa·s, 6200 mPa·s, 7000 mPa·s, and 7200 mPa·s.

[0050] According to an embodiment of the present invention, the refractive index (20°C) of the hydroxyl-terminated dimethyldiphenylpolysiloxane is 1.420 to 1.505, with exemplary values ​​of 1.423, 1.446, 1.468, 1.484, and 1.501.

[0051] According to an embodiment of the present invention, the volatile content (150°C / 3h) in the hydroxyl-terminated dimethyldiphenylpolysiloxane is 1.0-3.5%, with exemplary values ​​of 1.5%, 2.0%, 2.2%, 2.5%, and 3.1%.

[0052] According to an embodiment of the present invention, the phenyl content in the hydroxyl-terminated dimethyldiphenyl polysiloxane is 5.0% to 27%, with exemplary values ​​of 5.0%, 9.8%, 15.1%, 19.8%, and 26.8%.

[0053] The beneficial effects of this invention are:

[0054] 1. The method for preparing hydroxyl-terminated dimethyldiphenyl polysiloxane provided by the present invention can reduce the viscosity of the polymer by adding a small amount of hydroxyl silicone oil in the first stage of the polymerization reaction, so that the polymer can carry out sufficient condensation and equilibrium reaction in a low viscosity state. At the same time, the reduction of polymer viscosity also reduces the pressure on the equipment to operate at a high viscosity.

[0055] 2. The raw materials used in this invention are octaphenylcyclotetrasiloxane and dimethylcyclosiloxane, which are low in cost and easy to produce industrially; and the hydroxyl-terminated dimethyldiphenylpolysiloxane product prepared has high transparency. Attached Figure Description

[0056] Figure 1 The product prepared in Example 2 of this invention 1 H NMR spectrum.

[0057] Figure 2 The product prepared in Example 2 of this invention 29 Si NMR spectrum. Detailed Implementation

[0058] The technical solution of the present invention will be further described in detail below with reference to specific embodiments. It should be understood that the following embodiments are merely illustrative and explanatory of the present invention, and should not be construed as limiting the scope of protection of the present invention. All technologies implemented based on the above content of the present invention are covered within the scope of protection intended by the present invention.

[0059] Unless otherwise stated, the raw materials and reagents used in the following examples are all commercially available products.

[0060] In the following embodiments of the present invention, dimethylcyclosiloxane was purchased from Zhejiang Xin'an Chemical Group Co., Ltd.; octaphenylcyclotetrasiloxane was purchased from Dalian Yuanyong Organosilicon Plant; and hydroxyl silicone oil was purchased from Wuxi Quanli Technology Co., Ltd.

[0061] In the following embodiments of the present invention, the viscosity of hydroxyl-terminated dimethyldiphenyl polysiloxane was determined according to the viscosity measurement method of GB / T 10247.

[0062] The refractive index of hydroxyl-terminated dimethyldiphenylpolysiloxane was determined according to the GB / T 6488 method.

[0063] The volatile matter in hydroxyl-terminated dimethyldiphenylpolysiloxane was determined according to GB / T 24131, the method for determining the volatile matter content of raw rubber.

[0064] The phenyl molar content was calculated using nuclear magnetic resonance (H1N) spectroscopy.

[0065] Example 1

[0066] In a 100L mechanical reactor, 65.3 kg of dimethylcyclosiloxane, 9.2 kg of octaphenylcyclotetrasiloxane, and 750 g of tetramethylammonium hydroxide silanolate (2 wt% tetramethylammonium hydroxide) were added. After stirring until homogeneous, the reactor temperature was raised to 110℃ and reacted for 1 hour. Then, 250 g of hydroxyl silicone oil was added and the reaction was continued for another 5 hours. The system pressure was then reduced to 45 kPa, and a vacuum dehydration condensation reaction was carried out for 1 hour. Nitrogen gas was then introduced to return the pressure to atmospheric pressure, and 90 g of tetramethylammonium hydroxide silanolate was added. The tetramethylammonium hydroxide (2 wt%) was stirred for another 1 hour. 185 g of deionized water was added to the system. The viscosity of the polymerization system was tracked using an online viscometer. When the viscosity reached 230 mPa·s (110 °C), the temperature of the reactor was raised to 150 °C and the timing was started. After 2.5 hours, the temperature was raised to 165 °C and the system pressure was reduced to 800 Pa. After vacuuming for 3 hours, the temperature was reduced to room temperature. 600 g of diatomaceous earth was added and stirred evenly. The mixture was then filtered to obtain a colorless and transparent liquid.

[0067] The product obtained in this embodiment has a viscosity of 4600 mPa·s (25℃), a refractive index of 1.423 (20℃), a volatile content of 1.5% (150℃ / 3h), and a phenyl content of 5.0%.

[0068] Example 2

[0069] In a 100L mechanical reactor, 60kg of dimethylcyclosiloxane, 17.8kg of octaphenylcyclotetrasiloxane, 785g of potassium silanolate (3wt% KOH), and 1.57kg of N-methylpyrrolidone were added. After thorough stirring, the reactor temperature was raised to 120℃ and reacted for 1.5h. Then, 390g of hydroxyl silicone oil was added, and the reaction was continued for another 6h. The system pressure was then reduced to 55kPa, and a vacuum dehydration condensation reaction was carried out for 2h. Nitrogen gas was then introduced to restore the pressure to atmospheric level, and additional... 390g of N-methylpyrrolidone was stirred for 1 hour. 270g of deionized water was added to the system. The viscosity of the polymerization system was tracked using an online viscometer. When the viscosity reached 300 mPa·s (120℃), 32g of propionic acid was added to neutralize the system for 2 hours until it became neutral. The temperature was then raised to 170℃, the system pressure was reduced to 500 Pa, and vacuum was applied for 3 hours. After the temperature was reduced to room temperature, 780g of diatomaceous earth was added and stirred evenly. The mixture was then filtered to obtain a colorless and transparent liquid.

[0070] The product obtained in this embodiment has a viscosity of 6200 mPa·s (25℃), a refractive index of 1.446 (20℃), a volatile content of 2.0% (150℃ / 3h), and a phenyl content of 9.8%.

[0071] Figure 1 The product in Embodiment 2 of the present invention 1 H NMR spectrum. 1 In the 1H NMR spectrum, the chemical shifts near 0 ppm represent the methyl hydrogen atoms bonded to silicon atoms, and the chemical shifts of hydrogen atoms on the benzene ring are between 7 and 8 ppm. This demonstrates that the method of this invention successfully prepared hydroxyl-terminated dimethyldiphenyl polysiloxane.

[0072] Figure 2 The product in Embodiment 2 of the present invention 29 Si NMR spectrum. 29 In the Si NMR spectrum, the chemical shift of silanols is around -12 ppm, -19 to 22 ppm corresponds to the chemical shift of (CH3)2SiO, and -45 to 48 ppm corresponds to the chemical shift of (C6H5)2SiO. This further proves that the method of the present invention has successfully prepared hydroxyl-terminated dimethyldiphenylpolysiloxane.

[0073] Example 3

[0074] In a 100L mechanical reactor, 53kg of dimethylcyclosiloxane, 25kg of octaphenylcyclotetrasiloxane, 1170g of potassium silanolate (3wt% KOH content), and 3.5kg of diethylene glycol dimethyl ether were added. After stirring until homogeneous, the reactor temperature was raised to 130℃ and reacted for 2 hours. Then, 470g of hydroxyl silicone oil was added and the reaction was continued for another 8 hours. The system pressure was then reduced to 70kPa, and a vacuum dehydration condensation reaction was carried out for 2 hours. Nitrogen gas was then introduced to restore the pressure to atmospheric level, and diethylene glycol was added as a supplement. 650g of dimethyl ether was added and stirred for 1 hour. 310g of deionized water was added to the system. The viscosity of the polymerization system was tracked using an online viscometer. When the viscosity reached 330mPa·s (130℃), 20.52g of phosphoric acid was added to neutralize the system for 2 hours until it became neutral. The temperature was then raised to 180℃, the system pressure was reduced to 400Pa, and the system was evacuated for 4 hours. After the temperature was reduced to room temperature, 800g of diatomaceous earth was added and stirred evenly. The mixture was then filtered to obtain a colorless and transparent liquid.

[0075] The product obtained in this embodiment has a viscosity of 7000 mPa·s (25℃), a refractive index of 1.468 (20℃), a volatile content of 2.2% (150℃ / 3h), and a phenyl content of 15.1%.

[0076] Example 4

[0077] In a 100L mechanical reactor, 46kg of dimethylcyclosiloxane, 31kg of octaphenylcyclotetrasiloxane, and 2100g of tetramethylammonium hydroxide silanolate (2wt% tetramethylammonium hydroxide) were added. After stirring until homogeneous, the reactor temperature was raised to 120℃ and reacted for 2 hours. Then, 770g of hydroxyl silicone oil was added and the reaction was continued for another 8 hours. The system pressure was then reduced to 60KPa, and a vacuum dehydration condensation reaction was carried out for 2 hours. Nitrogen gas was then introduced to return the pressure to atmospheric pressure, and 80g of tetramethylammonium hydroxide silanolate (2wt% tetramethylammonium hydroxide) was added. The ammonium hydroxide content was 2 wt%, and the reaction was stirred for 1 hour. 400 g of deionized water was added to the system. The viscosity change of the polymerization system was tracked by an online viscometer. When the viscosity reached 220 mPa·s (120℃), the temperature of the reactor was raised to 160℃ and the timing was started. After 1.5 hours, the temperature was raised to 180℃ and the system pressure was reduced to 300 Pa. After vacuuming for 3 hours, the temperature was reduced to room temperature. 1000 g of diatomaceous earth was added and stirred evenly. After pressure filtration, a colorless and transparent liquid was obtained.

[0078] The product obtained in this embodiment has a viscosity of 5200 mPa·s (25℃), a refractive index of 1.484 (20℃), a volatile content of 2.5% (150℃ / 3h), and a phenyl content of 19.8%.

[0079] Example 5

[0080] In a 100L mechanical reactor, 35kg of dimethylcyclosiloxane, 35kg of octaphenylcyclotetrasiloxane, 1280g of potassium silanolate (KOH content 3wt%), and 4.48kg of N,N-dimethylformamide were added. After stirring until homogeneous, the reactor temperature was raised to 130℃ and reacted for 2 hours. Then, 820g of hydroxyl silicone oil was added and the reaction was continued for another 8 hours. The system pressure was then reduced to 80kPa, and a vacuum dehydration condensation reaction was carried out for 2 hours. Nitrogen gas was then introduced to return the pressure to atmospheric pressure, and N,N-dimethylformamide was added as needed. 1000g of dimethylformamide was added and stirred for 1 hour. 400g of deionized water was added to the system. The viscosity of the polymerization system was tracked using an online viscometer. When the viscosity reached 350mPa·s (130℃), 44.8g of citric acid was added to neutralize the system for 2 hours until it became neutral. The temperature was then raised to 190℃, the system pressure was reduced to 220Pa, and the system was evacuated for 4 hours. After the temperature was reduced to room temperature, 1200g of diatomaceous earth was added and stirred evenly. The mixture was then filtered to obtain a colorless and transparent liquid.

[0081] The product obtained in this embodiment has a viscosity of 7200 mPa·s (25℃), a refractive index of 1.501 (20℃), a volatile content of 3.1% (150℃ / 3h), and a phenyl content of 26.8%.

[0082] Comparative Example 1

[0083] In a 100L mechanical reactor, 65.3 kg of dimethylcyclosiloxane, 9.2 kg of octaphenylcyclotetrasiloxane, and 750 g of tetramethylammonium hydroxide silanolate (2 wt% tetramethylammonium hydroxide) were added. After thorough stirring, the reactor temperature was raised to 110℃ and the reaction was carried out for 2 hours. (At this point, the viscosity reached 5.0 × 10⁻⁶). 5 (The stirring paddle was subjected to excessive force, so stirring had to be stopped.) After continuing the reaction for 5 hours, 185g of deionized water was added to the system. Initially, it was difficult for water to enter the reaction system. After continuing the reaction for 10 hours, when the viscosity reached 300mPa·s (110℃), the temperature of the reactor was raised to 150℃ and the timing was started. After 2.5 hours, the temperature was raised to 165℃ and the system pressure was reduced to 800Pa. After vacuuming for 3 hours, the temperature was reduced to room temperature. 600g of diatomaceous earth was added and stirred evenly. After pressure filtration, a turbid, whitish liquid was obtained.

[0084] The product obtained in this comparative example has a viscosity of 6900 mPa·s (25℃), a refractive index of 1.422 (20℃), a volatile content of 4.1% (150℃ / 3h), and a phenyl content of 5.0%.

[0085] The viscosity, refractive index, phenyl content, volatile matter, and transparency properties of the hydroxyl-terminated dimethyldiphenyl polysiloxanes prepared in Examples 1-5 and Comparative Example 1 are shown in Table 1 below.

[0086] Table 1

[0087] Example 1 4600 1.423 5.0％ 1.5％ Colorless and transparent Example 2 6200 1.446 9.8％ 2.0％ Colorless and transparent Example 3 7000 1.468 15.1％ 2.2％ Colorless and transparent Example 4 5200 1.484 19.8％ 2.5％ Colorless and transparent Example 5 7200 1.501 26.8％ 3.1％ Colorless and transparent Comparative Example 1 6900 1.422 5.0％ 4.1％ turbid, whitish

[0088] The embodiments of the present invention have been described above. However, the present invention is not limited to the above embodiments. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A method for preparing a hydroxyl-terminated dimethyldiphenyl polysiloxane, characterized in that, Includes the following steps: (1) Using octaphenylcyclotetrasiloxane and dimethylcyclosiloxane as monomers for polymerization, a polymerization reaction is carried out under the action of a catalyst and an optional accelerator; The amount of octaphenylcyclotetrasiloxane fed into the feed is 1-80% of the total mass of octaphenylcyclotetrasiloxane and dimethylcyclosiloxane; The catalyst is tetramethylammonium hydroxide silanoate or potassium silanoate; The catalyst is added in an amount of 0.01–0.08% of the total mass of octaphenylcyclotetrasiloxane and dimethylcyclosiloxane monomers; When potassium silanolate is used as a catalyst, an accelerator is further added to the polymerization reaction system to carry out the polymerization reaction; The accelerator is a polar solvent selected from at least one of N,N-dimethylformamide, N,N-dimethylacetamide, dimethyl sulfoxide, diethylene glycol dimethyl ether, diethylene glycol diethyl ether, and N-methylpyrrolidone. The amount of the accelerator added is 1 to 6 times the mass of the potassium silanolate catalyst; The polymerization reaction is carried out at a temperature of 110–130°C and for a duration of 0.5–2 hours. (2) Add hydroxyl silicone oil to the reaction system to carry out the first step of degradation, equilibration and polycondensation reaction; The amount of hydroxyl silicone oil added is 0.1% to 2% of the total mass of the monomers octaphenylcyclotetrasiloxane and dimethylcyclosiloxane; The temperature of the degradation, equilibration, and polycondensation reactions is the same as that of the polymerization reaction, which is 110–130°C; the time of the degradation, equilibration, and polycondensation reactions is 4–8 hours. (3) Perform a vacuum dehydration condensation reaction; (4) After returning to normal pressure with nitrogen, when using tetramethylammonium hydroxide siloxane as catalyst, add catalyst. The amount of catalyst added is 0.01 to 0.025‰ of the total mass of the monomers octaphenylcyclotetrasiloxane and dimethylcyclosiloxane, calculated as tetramethylammonium hydroxide. When potassium silanolate is used as a catalyst, an accelerator is added, wherein the amount of the added accelerator is 0.5 to 1 times the mass of potassium silanolate; Then water is added to the reaction system to carry out the second step of the degradation reaction, and the entire system is in a closed state; (5) The viscosity of the degradation reaction process is tracked online. When the viscosity of the reaction system reaches 100~400 mPa·s, the temperature of the reaction system is increased to decompose the catalyst when tetramethylammonium hydroxide silanoate is used as the catalyst. The whole system is kept in a closed state. When potassium silanolate is used as a catalyst, a neutralizing agent is added to terminate the reaction, and the entire system is kept in a closed state. (6) After the catalyst is decomposed or the reaction is neutralized and terminated, the low-boiling substances are removed by vacuum heating, and the mixture is cooled to room temperature for adsorption filtration to remove solid impurities, thereby obtaining the hydroxyl-terminated dimethyl diphenyl polysiloxane.

2. The preparation method according to claim 1, characterized in that, The hydroxyl silicone oil is a short-chain hydroxyl-terminated polydimethylsiloxane, wherein the mass fraction of hydroxyl groups in the hydroxyl silicone oil is 8.5%.

3. The preparation method according to claim 1, characterized in that, The pressure of the dehydration condensation reaction is 30–90 kPa.

4. The preparation method according to any one of claims 1-3, characterized in that, The water is deionized water, and the amount of deionized water added is 0.1 to 0.8% of the total mass of the monomers octaphenylcyclotetrasiloxane and dimethylcyclosiloxane.

5. The preparation method according to claim 1, characterized in that, When using tetramethylammonium hydroxide silanoate as a catalyst, the temperature of the reaction system is raised to 145–160 °C; the holding time after the temperature is raised is 1–3 h.

6. The preparation method according to any one of claims 1-3, characterized in that, The neutralizing agent added to terminate the reaction is at least one selected from propionic acid, citric acid, tartaric acid, and phosphoric acid.

7. The preparation method according to any one of claims 1-3, characterized in that, The time for terminating the reaction is 1 to 3 hours.

8. The preparation method according to any one of claims 1-3, characterized in that, The temperature for removing low-boiling substances is 160–200°C; the pressure for removing low-boiling substances is 200–1000 Pa; and the time for removing low-boiling substances is 1–4 hours.

9. The preparation method according to any one of claims 1-3, characterized in that, The adsorbent used in the adsorption filtration is diatomaceous earth.

10. The preparation method according to claim 9, characterized in that, The amount of diatomaceous earth used is 0.5% to 3% of the theoretical mass of the hydroxyl-terminated dimethyldiphenylpolysiloxane.

11. The hydroxyl-terminated dimethyldiphenylpolysiloxane prepared by the preparation method according to any one of claims 1-10.

12. The hydroxyl-terminated dimethyldiphenyl polysiloxane as described in claim 11, characterized in that, The viscosity of the hydroxyl-terminated dimethyldiphenylpolysiloxane is 4500~7500 mPa·s at 25°C.

13. The hydroxyl-terminated dimethyldiphenyl polysiloxane as described in claim 11, characterized in that, The refractive index of the hydroxyl-terminated dimethyldiphenylpolysiloxane is 1.420~1.505 at 20°C.

14. The hydroxyl-terminated dimethyldiphenyl polysiloxane as described in claim 11, characterized in that, The volatile content in the hydroxyl-terminated dimethyldiphenylpolysiloxane is 1.0~3.5% at 150℃ / 3h.

15. The hydroxyl-terminated dimethyldiphenyl polysiloxane as described in claim 11, characterized in that, The phenyl content in the hydroxyl-terminated dimethyldiphenyl polysiloxane is 5.0-27%.

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