An alkoxyl-terminated polysiloxane and a method for preparing the same

Abstract

The present application relates to a kind of preparation methods of alkoxy terminated polysiloxane, comprising the following steps: (1) with low molecular weight end hydroxyl polysiloxane OX and end hydrogen polysiloxane HX, respectively, low purification is removed to D3-D10 ring body total content is less than 50 ppm, and the low ring body content DOX and DHX are prepared;(2) with DOX, DHX, condensation catalyst PNC and neutralizing agent H as raw material, end hydrogen polysiloxane PDHX with low ring body content is prepared;(3) with PDHX, alkoxy end-capping agent, platinum gold catalyst as raw material, alkoxy terminated polysiloxane with low siloxane ring body content is prepared.The present application is prepared by the synergistic innovation of "raw material rectification-controllable condensation-high efficiency end-capping", and the high molecular weight alkoxy terminated polysiloxane with viscosity of 20000-1000000 mPa.s and D3-D10 siloxane ring body total content less than 50 ppm.

Description

TECHNICAL FIELD

[0001] The present application relates to the field of silicone polymer synthesis, in particular to an alkoxy-terminated polysiloxane and a preparation method thereof. BACKGROUND

[0002] With the development of industrial technology, low odor, environmentally friendly, non-corrosive, dealcoholized room temperature curing silicone sealant, structural adhesive and other adhesive varieties have become the focus of industry research and development. The development of such silicone adhesives requires the use of high molecular weight alkoxy-terminated polysiloxane as the base polymer. In some special application scenarios, such as display panel manufacturing, microelectronics and chip packaging, sensor device sealing, etc., high-purity silicone bonding sealant is also required because the presence of a large number of small molecule siloxane rings in the sealant will slowly release during use, thereby polluting the panel and causing display quality to deteriorate, or changing the electrical properties of the switch contacts, or affecting the accuracy of the sensor device. The silicone sealant used in the microelectronics industry requires that the content of small molecule siloxane rings be as low as possible, with a total content of D3-D10 (including hexamethylcyclotrisiloxane, commonly known as D3; octamethylcyclotetrasiloxane, commonly known as D4; decamethylcyclopentasiloxane, commonly known as D5; dodecamethylcyclohexasiloxane, commonly known as D6; tetradecamethylcycloheptasiloxane, commonly known as D7; hexadecamethylcyclooctasiloxane, commonly known as D8; octadecamethylcyclononasiloxane, commonly known as D9; and eicosamethylcyclodecasiloxane, commonly known as D10) being less than 50 ppm. The small molecule siloxane ring content of the siloxane polymer used in traditional silicone sealants is generally greater than 10,000 ppm (i.e., 1%), which cannot meet the needs of the microelectronics industry. In order to produce silicone sealants for the microelectronics industry, it is necessary to develop alkoxy-terminated polysiloxane with a total content of D3-D10 of less than 50 ppm, especially high molecular weight alkoxy-terminated polysiloxane with a total content of D3-D10 of less than 50 ppm.

[0003] The prior art can use a multi-stage scraper-type short-path molecular still to directly remove low-boiling impurities from alkoxy-terminated polysiloxane to obtain low-volatility alkoxy-terminated polysiloxane. However, due to the working principle and physical structure of the scraper-type short-path molecular still, this direct low-boiling removal and purification technology can only be used for the direct low-boiling removal and purification of low molecular weight (viscosity < 20,000 mPa.s) alkoxy-terminated polysiloxane, and cannot be used for the purification of high molecular weight alkoxy-terminated polysiloxane.

[0004] Existing technologies mainly employ two synthetic processes to synthesize high molecular weight alkoxy-terminated polysiloxanes: The first process uses a mixed cyclic form of DMC siloxane as the starting material, with water as the end-capping agent. Under acidic or alkaline conditions, ring-opening polymerization, telomerization, and de-lowering purification are performed to obtain high molecular weight α,ω-dihydroxy polydimethylsiloxane. Then, using this high molecular weight α,ω-dihydroxy polydimethylsiloxane as an intermediate, and ammonium salts, carboxylic acids, organic amines, or bases as catalysts, and excess alkoxysilanes such as methyltrimethoxysilane, tetramethoxysilane, vinyltrimethoxysilane, and vinyltriethoxysilane as end-capping agents, through end-capping, neutralization, and de-lowering purification, high molecular weight alkoxy-terminated polysiloxanes with different end groups are prepared. Their molecular structure is: (R4O) a (R3) 3-a SiO[Si(CH3)2O] n (CH3)2SiOSi(R3) 3-a (OR4) a Where a = 2 or 3, R3 is methyl, ethyl, vinyl, or OR4, and R4 is methyl or ethyl. The synthesis principle is as follows:

[0005] Reaction formula (1):

[0006]

[0007] Reaction (2):

[0008]

[0009] The second process uses DMC siloxane mixed rings as the starting material and 1,3-divinyl-1,1,3,3-tetramethyldisiloxane as the end-capping agent. In the presence of an acid or alkaline catalyst, ring-opening polymerization, telomerization, and de-lowering purification processes are performed to obtain high molecular weight α,ω-divinyl polydimethylsiloxane. Then, using high molecular weight α,ω-divinyl polydimethylsiloxane as an intermediate raw material and hydrogen-containing alkoxysilanes such as trimethoxysilane, methyldimethoxysilane, methyldiethoxysilane, and triethoxysilane as end-capping agents, and with Castrol platinum as a catalyst, hydrosilylation and de-lowering purification are carried out to prepare high molecular weight alkoxy-terminated polysiloxanes with different end groups. Their molecular structure is: (R6O). b (R5) 3-b SiCH2CH2[Si(CH3)2O] n (CH3)2SiCH2CH2Si(R5) 3-b (OR6) b Where b = 2 or 3, R5 is methyl, ethyl, or OR6, and R6 is methyl or ethyl. The synthesis principle is as follows:

[0010] Reaction formula (3)

[0011]

[0012] Reaction formula (4)

[0013]

[0014] It is evident that the high molecular weight alkoxy-terminated polysiloxanes prepared using the above two processes utilize DMC siloxane mixed rings as starting materials, which are then purified through acid-base equilibrium polymerization and de-oxidation. Since the ring-opening and cyclic polymerization of DMC are essentially reversible equilibrium reactions involving both ring-opening and ring-forming reactions, the DMC conversion rate is typically only 90%. Although in-situ vacuum distillation in the reactor is used for de-oxidation purification, this process cannot completely remove the low-saturated vapor pressure and high-boiling-point siloxane rings of DMC. Existing in-situ vacuum distillation processes can only purify the intermediate to a total D3-D10 content of approximately 10,000 ppm. The high molecular weight alkoxy-terminated polysiloxanes synthesized from this intermediate have a D3-D10 content of approximately 10,000 ppm, the same as the intermediate raw material, which is far below the 50 ppm requirement for silicone sealants used in the microelectronics industry.

[0015] Furthermore, as mentioned above, a scraped short-path molecular distillation apparatus cannot be used to pre-purify high molecular weight intermediates in order to prepare high molecular weight alkoxy-terminated polysiloxanes with low siloxane cyclic content.

[0016] In view of this, this invention is hereby proposed. Summary of the Invention

[0017] To address the shortcomings of existing technologies in preparing high molecular weight alkoxy-terminated polysiloxanes with a total cyclic content of less than 50 ppm (D3-D10) and a viscosity greater than 20,000 mPa·s, this invention proposes a method for preparing high molecular weight alkoxy-terminated polysiloxanes with low siloxane cyclic content.

[0018] The second objective of this invention is to provide an alkoxy-terminated polysiloxane prepared by the above preparation method, wherein the total cyclic content of D3-D10 is less than 50 ppm and the viscosity is greater than 20000 mPa·s.

[0019] In order to achieve the above-mentioned objectives of the present invention, the following technical solution is adopted:

[0020] This invention provides a method for preparing alkoxy-terminated polysiloxanes, comprising the following steps:

[0021] S01: The hydroxyl-terminated polysiloxane (OX) and the hydrogen-terminated polysiloxane (HX) are purified separately using a multi-stage evaporator until the total D3-D10 cyclic content in the hydroxyl-terminated polysiloxane and the hydrogen-terminated polysiloxane is less than 50 ppm, thus obtaining low-cyclic-content hydroxyl-terminated polysiloxane (DOX) and low-cyclic-content hydrogen-terminated polysiloxane (DHX).

[0022] S02: Using the low-cyclic content hydroxyl-terminated polysiloxane (DOX), the low-cyclic content hydrogen-terminated polysiloxane (DHX), a condensation catalyst (PNC), and a neutralizing agent (H) as raw materials, hydrogen-terminated polysiloxane (PDHX) is prepared at a mass ratio of DOX : DHX : PNC : H = 10000 : (50-400) : 1 : 1 under certain reaction temperature, vacuum degree, and reaction time. The total content of D3-D10 rings in the hydrogen-terminated polysiloxane (PDHX) is less than 50 ppm.

[0023] S03: Using the aforementioned hydrogen-terminated polysiloxane (PDHX), alkoxy-terminant, and platinum catalyst as raw materials, and according to the mass ratio of PDHX: alkoxy-terminant: platinum catalyst = 100 : (2-8) : (0.05-0.2), under certain reaction temperature, vacuum degree, and reaction time, a high molecular weight alkoxy-terminated polysiloxane with a total D3-D10 cyclic content of less than 50 ppm is prepared.

[0024] First, readily available commercially available low-molecular-weight hydroxyl-terminated polysiloxanes (OX) and hydrogen-terminated polysiloxanes (HX) were selected as starting materials. These were purified using a multi-stage evaporator until the total D3-D10 cyclic content was below 50 ppm, yielding low-cyclic-content hydroxyl-terminated polysiloxanes (DOX) and hydrogen-terminated polysiloxanes (DHX). Then, using DOX and DHX as raw materials, and employing a self-made high-efficiency condensation catalyst (PNC) under specific reaction temperatures, vacuum levels, and reaction times, high-molecular-weight hydrogen-terminated polysiloxanes (PDHX) with a total D3-D10 cyclic content below 50 ppm were prepared. Finally, using PDHX, an alkoxy-termining agent, and a platinum catalyst as raw materials, and following specific feed ratios, under specific reaction temperatures, vacuum levels, and reaction times, a product with a viscosity of 20,000-1,000,000 mPa·s and a total D3-D10 cyclic content below 50 ppm was prepared. The synthesis principle of high molecular weight alkoxy-terminated polysiloxanes (ppm) is as follows:

[0025] Reaction formula (5)

[0026]

[0027] Reaction formula (6)

[0028]

[0029] Where a = 2 or 3, R1 is methyl or OR2, and R2 is methyl or ethyl.

[0030] Preferably, the hydroxyl-terminated polysiloxane (OX) mentioned in step S01 is HOSi(CH3)2[OSi(CH3)2] x O(CH3)2SiOH, wherein x is 10-100, or the viscosity of the terminal hydroxyl polysiloxane (OX) is 20-120 mPa·s; or / and

[0031] The hydrogen-terminated polysiloxane (HX) mentioned in step S01 is HSi(CH3)2[OSi(CH3)2]. y O(CH3)2SiH, wherein the value of y is 20-50, or the viscosity of the hydrogen-terminated polysiloxane (HX) is 5-100 mPa·s.

[0032] Preferably, the multi-stage evaporator consists of a primary evaporator, a secondary evaporator, and a tertiary evaporator, wherein the multi-stage evaporator is a three-stage series evaporator, and the primary, secondary, and tertiary evaporators are thin-film evaporators or short-path molecular distillation evaporators.

[0033] Preferably, the first-stage evaporator, the second-stage evaporator, and the third-stage evaporator in step S01 are all short-path molecular distillation evaporators.

[0034] Preferably, when preparing the low-cyclic content hydroxyl-terminated polysiloxane (DOX), the material temperature of the first-stage evaporator is 140-150℃ and the vacuum degree is ≤ 10 Pa, the material temperature of the second-stage evaporator is 150-160℃ and the vacuum degree is ≤ 5 Pa, and the material temperature of the third-stage evaporator is 160-170℃ and the vacuum degree is ≤ 1 Pa.

[0035] Preferably, when preparing the low-cyclic content hydrogen-terminated polysiloxane (DHX), the material temperature of the first-stage evaporator is 130-140℃ and the vacuum degree is ≤ 10 Pa, the material temperature of the second-stage evaporator is 140-150℃ and the vacuum degree is ≤ 5 Pa, and the material temperature of the third-stage evaporator is 150-160℃ and the vacuum degree is ≤ 1 Pa.

[0036] Short-path molecular distillation evaporators are commonly used separation and purification equipment in the chemical industry, and their structure will not be described in detail here. Film formation method and speed control of the short-path molecular distillation evaporator: The short-path molecular distillation evaporator adopts a scraped film evaporation process. The film formation method and speed control are achieved by controlling the scraper motor speed between 100-450 r / min, ensuring that the feed liquid is continuously and evenly distributed on the heating surface of the short-path molecular distillation evaporator. The scraper of the short-path molecular distillation evaporator scrapes the waste liquid into an extremely thin, turbulent liquid film.

[0037] Temperature control of short-path molecular distillation evaporator: The heating temperature of the short-path molecular distillation evaporator is controlled by adjusting the temperature, flow rate and pressure of the heating medium, and the condensation temperature is controlled by adjusting the temperature, flow rate and pressure of the cooling medium. The distillation temperature is set so that DOX and DHX can just maintain thermal stability.

[0038] This application pre-purifies low molecular weight precursors (OX, HX) using a multi-stage evaporator, controlling the cyclic content from the source and achieving ultra-low siloxane cyclic content (D3-D10 < 50 ppm), breaking through the bottleneck of traditional processes (D3-D10 ≈ 10000 ppm) and meeting the stringent requirements of the microelectronics industry for high-purity sealants.

[0039] Preferably, the condensation catalyst (PNC) mentioned in step S02 is synthesized from the following raw materials in the following mass ratio: ammonium chloride: phosphorus pentachloride: phosphorus oxychloride: zinc chloride: 1,1,2,2-tetrachloroethane = (50-80): 208: 15: 1: 820.

[0040] Preferably, the synthesis step of the condensation catalyst (PNC) in step S02 includes:

[0041] a) Add 820 g of 1,1,2,2-tetrachloroethane to the reactor. Under nitrogen protection, add 50-80 g of ammonium chloride, 208 g of phosphorus pentachloride, 15 g of phosphorus oxychloride and 1 g of zinc chloride in sequence while stirring.

[0042] b) Heat to 130-150℃ and reflux for 8 hours;

[0043] c) Cool to room temperature and filter to remove undissolved solid impurities to obtain a condensation catalyst (PNC) with a solid content of 25%.

[0044] Preferably, the neutralizing agent H mentioned in step S02 is one of isononylamine, γ-glycidyl etheroxypropyltrimethoxysilane, hexamethyldisilazane, and triethylamine.

[0045] High molecular weight terminal hydrogen-based polysiloxanes (PDHX) are prepared using low-cyclic-content hydroxyl-terminated polysiloxanes (DOX), low-cyclic-content hydrogen-terminated polysiloxanes (DHX), and a condensation catalyst (PNC). The catalytic principle is as follows: PNC is a super-acid (far stronger than concentrated sulfuric acid), which promotes the dehydration condensation reaction of the silanol groups in the hydroxyl-terminated polysiloxane (DOX) to obtain a high molecular weight polysiloxane. During the polymerization process, the silane-hydrogen bonds of the hydrogen-terminated polysiloxane (DHX) also participate in the reaction, causing the condensation reaction to terminate due to end-capping, thus yielding a high molecular weight terminal hydrogen-terminated polysiloxane (PDHX). This condensation catalyst (PNC) differs from traditional acidic catalysts (such as concentrated sulfuric acid and trifluoromethanesulfonic acid) or basic catalysts (such as potassium hydroxide and tetramethylammonium hydroxide) in that it does not significantly cause the siloxane to re-ring during the condensation reaction, avoiding the formation of small molecule siloxane rings. After the condensation reaction is complete, a neutralizing agent (H) is added. The role of the neutralizing agent (H) is to neutralize and permanently eliminate the catalytic activity of PNC, ensuring that the molecular weight of the product PHDX remains stable.

[0046] Preferably, the reaction temperature in step S02 is 60-100℃, the vacuum degree is ≤ 1 KPa, and the reaction time is 1-5 hours.

[0047] This application uses a mass ratio of DOX : DHX = 10000 : (50-400) for polycondensation to obtain a higher molecular weight. Increasing DHX may result in a lower molecular weight (decreased viscosity).

[0048] This application uses a specific ratio of DOX:DHX and a self-made high-efficiency PNC condensation catalyst to achieve precise control of molecular chains and controllable high molecular weight, avoiding the problem of excessively wide molecular weight distribution caused by traditional equilibrium reactions.

[0049] The high molecular weight hydrogen-terminated polysiloxane (PDHX) obtained in step S02 has the molecular formula HSi(CH3)2[OSi(CH3)2]. n O(CH3)2SiH, n value is 500-10000, or the viscosity of the high molecular weight hydrogen-terminated polysiloxane (PDHX) is 15000-1000000 mPa.s.

[0050] Preferably, the alkoxy end-capping agent in step S03 is one of CH2=CHSi(OCH3)3, CH2=CHSi(OC2H5)3, CH2=CHSi(CH3)(OCH3)2 or CH2=CHSi(CH3)(OC2H5)2; the platinum catalyst is an isopropanol solution of chloroplatinic acid H2PtCl6 with a platinum equivalent of 3000 ppm.

[0051] Preferably, the reaction temperature in step S03 is 60-80°C, the vacuum degree is 40-60 kPa, and the reaction time is 1-5 hours.

[0052] The strategy of purifying low molecular weight raw materials before polymerization in this application solves the technical problem that scraped distillation equipment cannot directly process high molecular weight polymers. Moreover, the reaction conditions are mild (condensation temperature 60-100℃, end-capping temperature 60-80℃) and energy consumption is low.

[0053] The present invention also provides an alkoxy-terminated polysiloxane prepared according to any of the above-described methods, wherein the molecular formula of the alkoxy-terminated polysiloxane is (R₂O)a(R₁). 3-a SiCH2CH2[Si(CH3)2O] n (CH3)2SiCH2CH2Si(R1) 3-a (OR2) a Where a = 2 or 3, R1 is methyl or OR2, R2 is methyl or ethyl, and n is 500-10000.

[0054] Preferably, the alkoxy-terminated polysiloxane has a viscosity of 20,000 mPa·s to 1,000,000 mPa·s and a total D3-D10 cyclic content of less than 50 ppm.

[0055] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0056] 1. This invention pre-purifies low molecular weight precursors (OX, HX) using a multi-stage evaporator, controlling the cyclic content from the source and achieving ultra-low siloxane cyclic content (D3-D10 < 50 ppm), breaking through the bottleneck of traditional processes (D3-D10 ≈ 10000 ppm) and meeting the stringent requirements of the microelectronics industry for high-purity sealants.

[0057] 2. By using a specific ratio of DOX:DHX and a self-made high-efficiency PNC condensation catalyst, precise control of molecular chains can be achieved, and high molecular weight can be controlled, avoiding the problem of excessively wide molecular weight distribution caused by traditional equilibrium reactions.

[0058] 3. The strategy of purifying low molecular weight raw materials before polymerization solves the technical problem that scraped distillation equipment cannot directly process high molecular weight polymers. Moreover, the reaction conditions are mild, energy consumption is low, and the process compatibility is strong, making it suitable for industrial production.

[0059] 4. The raw materials for preparation of this invention are inexpensive and readily available, the production process is simple and easy to operate, the reaction temperature is mild, the total content of D3-D10 rings is less than 50 ppm, the molecular weight of the product is high, the viscosity range of the product is controllable, and it is easy to realize industrialization.

[0060] 5. The product has both low volatility and high adhesion, making it particularly suitable for fields such as display panels and chip packaging where material purity is sensitive.

[0061] 6. Through the synergistic innovation of "raw material distillation - controlled polycondensation - efficient end-capping", this invention achieves for the first time the unification of high molecular weight (high viscosity) and ultra-low cyclic content, filling the technological gap of high-purity organosilicon sealants for microelectronics. Detailed Implementation

[0062] The technical solution of the present invention will be clearly and completely described below with reference to specific embodiments. However, those skilled in the art will understand that the embodiments described below are some embodiments of the present invention, but not all embodiments, and are only used to illustrate the present invention, and should not be regarded as limiting the scope of the present invention. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0063] Unless otherwise specified in the examples, the tests were conducted under standard conditions or conditions recommended by the manufacturer. Reagents or instruments whose manufacturers are not specified are all commercially available products. An NDJ-8S rotational viscometer was used in the examples, and the testing standard adopted was GB / T 2794-1995, "Determination of Viscosity of Adhesives". The content of siloxane cyclic compounds D3-D10 in the examples was determined using headspace-GCMS gas chromatography.

[0064] Example 1

[0065] S1. Purification of terminal hydroxyl polysiloxane OX: Commercially available low molecular weight terminal hydroxyl polysiloxane OX with a viscosity of 60 mPa·s was selected. It was purified by a three-stage series scraped short-path molecular distillation evaporator. The reaction temperature / vacuum degree of the first, second and third stage distillation evaporators were set to 150℃ / 5 Pa, 160℃ / 1 Pa and 170℃ / 0.5 Pa, respectively, to obtain terminal hydroxyl polysiloxane DOX with a low cyclic content of 0 ppm (below the detection limit of 5 ppm) of D3-D10 cyclic compounds.

[0066] S2. Purification of terminal hydrogen-based polysiloxane HX: Commercially available low molecular weight terminal hydrogen-based polysiloxane HX with a viscosity of 20 mPa·s was selected. It was purified by a three-stage series scraped short-path molecular distillation evaporator. The material temperature / vacuum degree of the first, second and third stage distillation evaporators were set to 130℃ / 10 Pa, 140℃ / 5 Pa and 150℃ / 1 Pa, respectively, to obtain terminal hydrogen-based polysiloxane DHX with a total D3-D10 cyclic content of 0 ppm (below the detection limit of 5 ppm).

[0067] S3. Preparation of condensation catalyst PNC: a) Add 820 g of 1,1,2,2-tetrachloroethane to a glass reactor. Under nitrogen protection, add 50 g of ammonium chloride, 208 g of phosphorus pentachloride, 15 g of phosphorus oxychloride and 1 g of zinc chloride sequentially while stirring; b) Heat to 130-150℃ and reflux for 8 hours; c) Cool to room temperature, filter to remove undissolved solid impurities, and obtain a light yellow liquid with a solid content of 25%, which is the condensation catalyst PNC.

[0068] Example 2

[0069] Preparation of PDHX: In an enamel reactor equipped with heating, vacuuming, and reduced pressure distillation functions, 10,000 g of DOX prepared in step S1 and 50 g of DHX prepared in step S2 were added and stirred evenly. The material temperature was raised to 60°C, and 1 g of the condensation catalyst PNC prepared in step S3 was added. Then, the vacuum was drawn to 500 Pa, and the material temperature was maintained at 60°C. The dehydration condensation reaction was carried out for 2 hours until the viscosity of the material no longer changed. Then, 1 g of γ-glycidyl etheroxypropyltrimethoxysilane was added and stirred evenly to prepare a colorless, transparent, viscous, high molecular weight hydrogen-terminated polysiloxane PDHX with low siloxane cyclic content. Its viscosity was 960,000 mPa·s, and the total D3-D10 siloxane cyclic content was 15 ppm.

[0070] Example 3

[0071] Preparation of PDHX: In an enamel reactor equipped with heating, vacuuming, and reduced pressure distillation functions, 10,000 g of DOX and 200 g of DHX were added and stirred evenly. The material temperature was raised to 60°C, and 1 g of PNC was added. Then, the vacuum was drawn to 500 Pa, and the material temperature was maintained at 60°C. The dehydration condensation reaction was carried out for 2 hours until the viscosity of the material no longer changed. Then, 1 g of γ-glycidyl etheroxypropyltrimethoxysilane was added and stirred evenly to prepare a colorless, transparent, viscous, high molecular weight hydrogen-terminated polysiloxane PDHX with low siloxane cyclic content. Its viscosity was 165,000 mPa·s, and the total D3-D10 siloxane cyclic content was 28 ppm.

[0072] Example 4

[0073] Preparation of PDHX: In an enamel reactor equipped with heating, vacuuming, and reduced pressure distillation functions, 10,000 g of DOX and 400 g of DHX were added and stirred evenly. The material temperature was raised to 60°C, and 1 g of PNC was added. Then, the vacuum was drawn to 500 Pa, and the material temperature was maintained at 60°C. The dehydration condensation reaction was carried out for 2 hours until the viscosity of the material no longer changed. Then, 1 g of hexamethyldisilazane was added and stirred evenly to prepare a colorless, transparent, viscous, high molecular weight hydrogen-terminated polysiloxane PDHX with low siloxane cyclic content. Its viscosity was 15,500 mPa·s, and the total D3-D10 siloxane cyclic content was 39 ppm.

[0074] Example 5

[0075] Preparation of high molecular weight alkoxy-terminated polysiloxane with low siloxane cyclic content: In a stainless steel reactor equipped with heating, stirring and vacuum functions, 100 g of PDHX prepared in Example 2 and 2 g of vinyltrimethoxysilane were added and stirred evenly. Then, 0.05 g of 3000 ppm platinum equivalent isopropanol chloroplatinate solution was added and stirred evenly. The temperature was raised to 80°C and the vacuum was maintained at 50 kPa. The reaction was carried out for 5 hours and then cooled to room temperature to obtain a colorless, transparent and viscous high molecular weight trimethoxy-terminated polysiloxane with low siloxane cyclic content. Its viscosity was 1,000,000 mPa·s and the total D3-D10 siloxane cyclic content was 15 ppm.

[0076] Example 6

[0077] Preparation of high molecular weight alkoxy-terminated polysiloxane with low siloxane cyclic content: In a stainless steel reactor equipped with heating, stirring, and vacuum functions, 100 g of PDHX intermediate with a viscosity of 165000 mPa·s and a total D3-D10 siloxane cyclic content of 28 ppm, prepared in Example 3, was added. Then, 5 g of methyl vinyl dimethoxysilane was added, and after stirring evenly, 0.1 g of a 3000 ppm platinum equivalent isopropanol chloroplatinate solution was added. After stirring evenly, the temperature was raised to 100°C, and a vacuum of 50 kPa was maintained. The reaction was carried out for 5 hours, and then cooled to room temperature to obtain a colorless, transparent, viscous high molecular weight dimethoxy-terminated polysiloxane with a low siloxane cyclic content, a viscosity of 183000 mPa·s, and a total D3-D10 siloxane cyclic content of 28 ppm.

[0078] Example 7

[0079] Preparation of high molecular weight alkoxy-terminated polysiloxane with low siloxane cyclic content: In a stainless steel reactor equipped with heating, stirring, and vacuum functions, 100 g of PDHX intermediate with a viscosity of 15500 mPa·s and a total D3-D10 siloxane cyclic content of 39 ppm, prepared in Example 4, was added. Then, 8 g of vinyltriethoxysilane was added, and after stirring evenly, 0.2 g of 3000 ppm platinum equivalent isopropanol chloroplatinate solution was added. After stirring evenly, the temperature was raised to 100°C, and a vacuum of 50 kPa was maintained. The reaction was carried out for 5 hours, and then cooled to room temperature to obtain a colorless, transparent, viscous high molecular weight triethoxy-terminated polysiloxane with a low siloxane cyclic content, a viscosity of 21000 mPa·s, and a total D3-D10 siloxane cyclic content of 39 ppm.

[0080] Comparative Example 1

[0081] Preparation of PDHX: In an enamel reactor equipped with heating, vacuuming, and reduced pressure distillation functions, 10,000 g of DOX and 600 g of DHX were added and stirred evenly. The material temperature was raised to 60°C, and 1 g of PNC was added. Then, the vacuum was drawn to 500 Pa, and the material temperature was maintained at 60°C. The dehydration condensation reaction was carried out for 2 hours until the viscosity of the material no longer changed. A colorless, transparent, viscous high molecular weight hydrogen-terminated polysiloxane PDHX with low siloxane cyclic content was prepared, with a viscosity of 1550 mPa·s and a total D3-D10 siloxane cyclic content of 45 ppm.

[0082] Comparative Example 2

[0083] Preparation of PDHX: In an enamel reactor equipped with heating, vacuuming, and reduced pressure distillation functions, 10,000 g of DOX and 400 g of DHX were added and stirred evenly. The material temperature was raised to 60°C, and 1 g of trifluoromethanesulfonic acid was added. Then, the vacuum was drawn to 500 Pa, and the material temperature was maintained at 60°C. The dehydration condensation reaction was carried out for 2 hours until the viscosity of the material no longer changed. A colorless, transparent, viscous high molecular weight hydrogen-terminated polysiloxane PDHX with low siloxane cyclic content was prepared, with a viscosity of 8380 mPa·s and a total D3-D10 siloxane cyclic content of 5682 ppm.

[0084] Comparative Example 3

[0085] Preparation of alkoxy-terminated polysiloxane: In a stainless steel reactor equipped with heating, stirring and vacuum functions, 100 g of PDHX prepared in Comparative Example 2 above and 2 g of vinyltrimethoxysilane were added and stirred evenly. Then, 0.05 g of 3000 ppm platinum equivalent isopropanol chloroplatinate solution was added and stirred evenly. The temperature was raised to 80 °C and the vacuum was maintained at 50 kPa. The reaction was carried out for 5 hours and then cooled to room temperature to obtain a colorless and transparent trimethoxy-terminated polysiloxane with a viscosity of 9450 mPa·s and a total D3-D10 siloxane cyclic content of 5643 ppm.

[0086] Comparative Example 4

[0087] Preparation of high molecular weight alkoxy-terminated polysiloxane with low siloxane cyclic content: In a stainless steel reactor equipped with heating, stirring, and vacuum functions, 100 g of PDHX intermediate with a viscosity of 15500 mPa·s and a total D3-D10 siloxane cyclic content of 39 ppm, prepared in Example 4, was added. Then, 12 g of vinyltriethoxysilane was added, and after stirring evenly, 0.2 g of 3000 ppm platinum equivalent isopropanol chloroplatinate solution was added. After stirring evenly, the temperature was raised to 100°C, and a vacuum of 50 kPa was maintained. The reaction was carried out for 5 hours, and then cooled to room temperature to obtain a colorless, transparent, viscous high molecular weight triethoxy-terminated polysiloxane with a low siloxane cyclic content, a viscosity of 16100 mPa·s, and a total D3-D10 siloxane cyclic content of 39 ppm.

[0088] This description is intended to illustrate the technical solutions of the present invention, and not to limit them. Although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some or all of the technical features therein. Such modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of the present invention.

Claims

1. A method for preparing an alkoxy-terminated polysiloxane, characterized in that, Includes the following steps: S01: The hydroxyl-terminated polysiloxane OX and the hydrogen-terminated polysiloxane HX are purified using a multi-stage evaporator until the total content of D3-D10 cyclic compounds in the hydroxyl-terminated polysiloxane and the hydrogen-terminated polysiloxane is less than 50 ppm, thus obtaining hydroxyl-terminated polysiloxane DOX and hydrogen-terminated polysiloxane DHX with low cyclic compound content. S02: Using the low-cyclic content terminal hydroxyl polysiloxane DOX, the low-cyclic content terminal hydrogen polysiloxane DHX, condensation catalyst PNC and neutralizing agent H as raw materials, according to the mass ratio of DOX : DHX : PNC : H = 10000 : (50-400) : 1 : 1, under certain reaction temperature, vacuum degree and reaction time, terminal hydrogen polysiloxane PDHX is prepared, wherein the total content of D3-D10 rings in the terminal hydrogen polysiloxane PDHX is less than 50 ppm; S03: Using the aforementioned hydrogen-terminated polysiloxane PDHX, alkoxy-terminant, and platinum catalyst as raw materials, and according to the mass ratio of PDHX : alkoxy-terminant : platinum catalyst = 100 : (2-8) : (0.05-0.2), under certain reaction temperature, vacuum degree, and reaction time, a high molecular weight alkoxy-terminated polysiloxane with a total D3-D10 cyclic content of less than 50 ppm is prepared. The condensation catalyst PNC mentioned in step S02 is synthesized from the following raw materials in the following mass ratio: ammonium chloride: phosphorus pentachloride: phosphorus oxychloride: zinc chloride: 1,1,2,2-tetrachloroethane = (50-80): 208: 15: 1: 820; The synthesis steps of the condensation catalyst PNC described in step S02 include: a) Add 820 g of 1,1,2,2-tetrachloroethane to the reactor. Under nitrogen protection, add 50-80 g of ammonium chloride, 208 g of phosphorus pentachloride, 15 g of phosphorus oxychloride and 1 g of zinc chloride in sequence while stirring. b) Heat to 130-150℃ and reflux for 8 hours; c) Cool to room temperature, filter to remove undissolved solid impurities, and obtain condensation catalyst PNC with a solid content of 25%.

2. The method for preparing alkoxy-terminated polysiloxane according to claim 1, characterized in that, The hydroxyl-terminated polysiloxane OX mentioned in step S01 is HOSi(CH3)2[OSi(CH3)2] x O(CH3)2SiOH, wherein the value of x is 10-100, or the viscosity of the terminal hydroxyl polysiloxane OX is 20-120 mPa.s; The hydrogen-terminated polysiloxane HX mentioned in step S01 is HSi(CH3)2[OSi(CH3)2]. y O(CH3)2SiH, where the y value is 20-50, or the viscosity of the terminal hydrogen-based polysiloxane HX is 5-100 mPa·s.

3. The method for preparing alkoxy-terminated polysiloxane according to claim 1, characterized in that, The multi-stage evaporator consists of a first-stage evaporator, a second-stage evaporator, and a third-stage evaporator, which are three stages connected in series. The first-stage, second-stage, and third-stage evaporators are all short-path molecular distillation evaporators. When preparing the low-cyclic content terminal hydroxyl polysiloxane DOX, the material temperature in the first-stage evaporator is 140-150℃ and the vacuum degree is ≤ 10 Pa; the material temperature in the second-stage evaporator is 150-160℃ and the vacuum degree is ≤ 5 Pa; and the material temperature in the third-stage evaporator is 160-170℃ and the vacuum degree is ≤ 1 Pa. When preparing the low-cyclic content terminal hydrogen polysiloxane DHX, the material temperature in the first-stage evaporator is 130-140℃ and the vacuum degree is ≤ 10 Pa; the material temperature in the second-stage evaporator is 140-150℃ and the vacuum degree is ≤ 5 Pa; and the material temperature in the third-stage evaporator is 150-160℃ and the vacuum degree is ≤ 1 Pa.

4. The method for preparing alkoxy-terminated polysiloxane according to claim 1, characterized in that, The reaction temperature in step S02 is 60-100℃, the vacuum degree is ≤ 1 KPa, and the reaction time is 1-5 hours.

5. The method for preparing alkoxy-terminated polysiloxane according to claim 1, characterized in that, The alkoxy end-capping agent mentioned in step S03 is one of CH2=CHSi(OCH3)3, CH2=CHSi(OC2H5)3, CH2=CHSi(CH3)(OCH3)2 or CH2=CHSi(CH3)(OC2H5)2; the platinum catalyst is an isopropanol solution of chloroplatinic acid H2PtCl6 with a platinum equivalent of 3000 ppm.

6. The method for preparing alkoxy-terminated polysiloxane according to claim 1, characterized in that, The reaction temperature in step S03 is 60-80℃, the vacuum degree is 40-60 KPa, and the reaction time is 1-5 hours.

7. An alkoxy-terminated polysiloxane prepared by the preparation method according to any one of claims 1-6, characterized in that: The molecular formula of the alkoxy-terminated polysiloxane is (R₂O)a(R₁). 3-a SiCH2CH2[Si(CH3)2O] n (CH3)2SiCH2CH2Si(R1) 3-a (OR2) a Where a = 2 or 3, R1 is methyl or OR2, R2 is methyl or ethyl, and n is 500-10000.

8. The alkoxy-terminated polysiloxane according to claim 7, characterized in that, The alkoxy-terminated polysiloxane has a viscosity of 20,000 mPa·s to 1,000,000 mPa·s and a total D3-D10 cyclic content of less than 50 ppm.

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