Low viscosity, low cyclic end hydrogen-containing silicone oil and its preparation method

Abstract

This invention provides a low-viscosity, low-cyclicity end-hydrogen-containing silicone oil and its preparation method, belonging to the field of organosilicon technology. The preparation method includes: a hydroxyl-terminated polydimethylsiloxane oligomer undergoes a dehydration condensation reaction under the action of a thermosensitive polyphosphazene catalyst to generate a high-viscosity polydimethylsiloxane; the thermosensitive polyphosphazene catalyst is a linear chlorinated phosphazene with a surface grafted thermosensitive polymer; in the reaction system, hydrogen-containing dual-end caps are added in 3 to 6 batches, and a link-breaking and branching reaction is carried out according to a gradient cooling program; after the reaction, the temperature is lowered to below the LCST temperature to deactivate the thermosensitive polyphosphazene catalyst, obtaining the low-viscosity, low-cyclicity end-hydrogen-containing silicone oil. This invention uses a thermosensitive polyphosphazene catalyst, combined with a batch addition of dual hydrogen-containing dual-end caps and a gradient cooling program for a link-breaking and branching reaction, to obtain an end-hydrogen-containing silicone oil with advantages of low viscosity and low cyclicity, narrow molecular weight distribution, low polydispersity index (PDI), high uniformity, and stable performance.

Description

Technical Field

[0001] This invention belongs to the field of organosilicon technology, and specifically relates to low-viscosity, low-cyclic end hydrogen-containing silicone oil and its preparation method. Background Technology

[0002] Hydrogen-terminated silicone oils (i.e., polydimethylsiloxanes with Si-H bonds at both ends) are an important class of organosilicon intermediates, widely used in block-modified silicone oils, addition-type liquid silicone rubber crosslinking agents, and ternary copolymer block silicone oils. Currently, the traditional industrial process for preparing hydrogen-terminated silicone oils involves: octamethylcyclotetrasiloxane and tetramethyldisiloxane undergoing a ring-opening polycondensation reaction under sulfuric acid / trifluoromethanesulfonic acid catalyst conditions; sodium carbonate is added for neutralization after the reaction; and the resulting mixture of sodium carbonate and sodium sulfate is filtered. This traditional process suffers from drawbacks such as high residual ring content and the generation of large amounts of solid waste during the neutralization process.

[0003] In recent years, researchers have attempted to use linear chlorinated phosphazene catalysts to replace traditional strong acids. For example, CN111378135A discloses a method for preparing low-viscosity alkoxy-terminated polydimethylsiloxane, which involves condensing a linear polymer with an alkali to obtain hydroxyl silicone oil, and then adding hydrogen-terminated polydimethylsiloxane and a phosphazene catalyst (i.e., hexachlorocyclotriphosphazene) to react and obtain low-viscosity hydrogen-containing silicone oil. The hydrogen-containing silicone oil obtained by this method has a viscosity of 2500 mPa·s-3000 mPa·s, which is too high. CN113024808A discloses a method for preparing end-hydrogen-containing silicone oil. Using high-viscosity methyl silicone oil and hydrogen-containing double-ended polymers as raw materials, end-hydrogen-containing silicone oil is prepared in a one-step process of degradation-polymerization-end-end-capping under the action of a linear phosphazene chloride composite catalyst. This method reduces the viscosity of the silicone oil to below 400 mPa·s. While the hydrogen-containing double-ended polymers end-cap the degraded small-molecule polysiloxanes, the trimethylsilanes at both ends of the raw material methyl silicone oil also end-cap the polysiloxane chains. Therefore, the resulting product contains a certain amount of byproducts such as dimethyl silicone oil and single-ended hydrogen-containing silicone oil, and exhibits poor stability. Summary of the Invention

[0004] In view of this, the present invention provides a low-viscosity, low-cyclic-terminal hydrogen-containing silicone oil and its preparation method, aiming to solve at least one technical problem in the background art.

[0005] This invention is implemented as follows: The first aspect of this invention provides a method for preparing a low-viscosity, low-cyclic-terminal hydrogen-containing silicone oil, the method comprising the following steps: S1. A hydroxyl-terminated polydimethylsiloxane oligomer is subjected to a dehydration condensation reaction under the action of a thermosensitive polyphosphazene catalyst to generate high-viscosity polydimethylsiloxane; the thermosensitive polyphosphazene catalyst is a linear chlorinated phosphazene with a surface grafted thermosensitive polymer. S2. Without adding a passivating agent, add hydrogen-containing double-headed polymers to the reaction system obtained in S1 in 3 to 6 portions, and carry out the link-breaking and branching reaction according to a gradient cooling program; the gradient cooling program refers to T n >T n-1 ;T n T n-1 These are the temperatures at which the link-breaking and branching reactions occur after the nth and (n-1)th additions of hydrogen-containing double-headed structures, respectively. S3. After the reaction is completed, the temperature is lowered to below the LCST temperature to deactivate the temperature-sensitive polyphosphazene catalyst, thus obtaining the low-viscosity, low-cyclic end-hydrogen-containing silicone oil.

[0006] Furthermore, S3 also includes: after the thermosensitive polyphosphazene catalyst is deactivated, a quencher is added, and after stirring, a thin-film evaporation process is carried out to remove the low-temperature effect.

[0007] Furthermore, the preparation method of the thermosensitive polyphosphazene catalyst is as follows: Linear polydichlorophosphazene is available; Linear polydichlorophosphazene was subjected to a nucleophilic substitution reaction with poly(N-isopropylacrylamide)-hydroxyl groups in the presence of an inert atmosphere and an acid-binding agent, so that poly(N-isopropylacrylamide) was chemically grafted onto the phosphorus atoms of the linear polydichlorophosphazene. After purification, the thermosensitive polyphosphazene catalyst was obtained.

[0008] Furthermore, the acid-binding agent is triethylamine, and its molar ratio with poly(N-isopropylacrylamide)-hydroxyl is 1.2~1.5:1.

[0009] Further, the purification step includes: The reaction solvent was removed by vacuum distillation and solid impurities were removed by filtration to obtain the concentrated crude product. The crude product is dissolved, precipitated, and separated, and this process is repeated 2 to 3 times, with the precipitate collected. The precipitate was dried to obtain the thermosensitive polyphosphazene catalyst.

[0010] Furthermore, the mass concentration of the thermosensitive polyphosphazene catalyst in S1 is 0.5 ppm to 5 ppm; The conditions for the dehydration polycondensation reaction are: stirring at 130℃~160℃ for 1h~3h under normal pressure, or stirring at 60℃~90℃ for 1h~3h under vacuum.

[0011] Furthermore, in S2, the temperature of the first branch-breaking reaction is T1 = 70℃~90℃, and the temperature of the last branch-breaking reaction is T... N =45℃~50℃; T n T n-1 The temperature difference is 5℃~10℃; Once the viscosity of the system stabilizes after each branch breaking reaction, a hydrogen-containing double-ended head is added to initiate the next branch breaking reaction.

[0012] Furthermore, the total amount of hydrogen-containing double-ended polymer in S2 is 2% to 15% of the hydroxyl-terminated polydimethylsiloxane oligomer; During the first branch-breaking reaction, the amount of hydrogen-containing double-ended head added is 15% to 30% of the total amount; During the final branching reaction, the amount of hydrogen-containing double-ended head added is 5% to 20% of the total amount.

[0013] Furthermore, hydrogen-containing double-heading caps are added to S2 in four or five separate steps.

[0014] A second aspect of the present invention provides a low-viscosity, low-cyclic-terminal hydrogen-containing silicone oil, which is prepared by the above-described method for preparing low-viscosity, low-cyclic-terminal hydrogen-containing silicone oil.

[0015] Compared with the prior art, the present invention has the following beneficial effects: 1. This invention uses a thermosensitive polyphosphazene catalyst, combined with a branching reaction involving the batch addition of a dual hydrogen-containing double-header and a gradient cooling program, to produce an end-hydrogen-containing silicone oil with advantages of low viscosity and low cyclicity, as well as a narrow molecular weight distribution, a small polydispersity index (PDI), high uniformity, and stable performance.

[0016] 2. The present invention grafts poly(N-isopropylacrylamide) onto the surface of linear polydichlorophosphazene, which has a minimum critical solution temperature (LCST). It exhibits a catalytically active conformation at temperatures above the LCST and a catalytically deactivated conformation at temperatures below the LCST. The catalytic activity is reversibly switched on and off by temperature change. The activity of the catalyst can be controlled by temperature control. In subsequent stages, deactivation can be directly achieved by cooling, reducing the amount of quencher required.

[0017] 3. This invention employs gradient cooling to effectively suppress cyclization side reactions. Initially, a higher temperature accelerates the chain scission and end-capping reaction rates; as the temperature gradually decreases, the molecular chain mobility declines, effectively reducing the probability of cyclic formation through the bite-back reaction. The batch-added hydrogen-containing double end-capsules can promptly capture the active end groups generated by chain scission, preventing them from undergoing intramolecular cyclization, achieving chain scission-immediate end-capping, thereby suppressing cyclization side reactions. Detailed Implementation

[0018] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below with reference to embodiments. It should be understood that the specific embodiments described herein are merely illustrative and not intended to limit the invention.

[0019] A method for preparing low-viscosity, low-cyclic-terminated hydrogen-containing silicone oil includes the following steps: S1. The terminal hydroxyl polydimethylsiloxane oligomer is subjected to a dehydration condensation reaction under the action of a thermosensitive polyphosphazene catalyst to generate high-viscosity polydimethylsiloxane; the thermosensitive polyphosphazene catalyst is a linear chlorinated phosphazene with a surface grafted thermosensitive polymer.

[0020] The preparation method of the thermosensitive polyphosphazene catalyst is as follows: S11. Provide linear polydichlorophosphazene; linear polydichlorophosphazene can be commercially available or synthesized in-house, for example: using hexachlorocyclotriphosphazene as raw material, thermally induced ring-opening polymerization is carried out at 200℃~280℃ under vacuum conditions to obtain linear polydichlorophosphazene; to improve polymerization efficiency, product yield and purity, raw material pretreatment and catalyst can be added according to actual needs. In the following examples, the method for synthesizing linear polydichlorophosphazene in-house is as follows: the hexachlorocyclotriphosphazene raw material is purified and pretreated by recrystallization and vacuum sublimation, and then placed in a sealed glass tube for storage; under a nitrogen protective atmosphere, the sealed glass tube is placed in a muffle furnace and a catalyst (about 1.0 wt% anhydrous aluminum trichloride) is added, and heated at a certain temperature (e.g., 250℃~260℃) for a period of time (e.g., 15h), and the product is taken out when the transparent liquid in the glass tube no longer flows obviously, and the product is dissolved in a dry THF solution, filtered and collected, and dried under vacuum at 70℃ to obtain linear polydichlorophosphazene.

[0021] S12. Linear polydichlorophosphazene (PDCP) and poly(N-isopropylacrylamide)-hydroxyl (PNIPAM-OH) undergo a nucleophilic substitution reaction in the presence of an inert atmosphere and an acid-binding agent, causing poly(N-isopropylacrylamide) to be chemically grafted onto the phosphorus atoms of the linear polydichlorophosphazene. After purification, the thermosensitive polyphosphazene catalyst is obtained. Specifically, the molar ratio of poly(N-isopropylacrylamide)-hydroxyl to phosphorus atoms in the linear polydichlorophosphazene is 0.05~0.30:1, which is adjusted according to the grafting density; the acid-binding agent is triethylamine, and its molar ratio with poly(N-isopropylacrylamide)-hydroxyl is 1.2~1.5:1. In the presence of an acid-binding agent (such as triethylamine), the hydroxyl group (-OH) of PNIPAM attacks the phosphorus atom (P) with a lower electron density on the PDCP backbone, causing a P-Cl bond to break. The chlorine atom combines with the hydrogen on the hydroxyl group, removing one molecule of hydrogen chloride (HCl). The oxygen atom of PNIPAM forms a new POC covalent bond with the phosphorus atom, thereby linking PNIPAM to the PDCP backbone.

[0022] To remove byproducts generated during the nucleophilic substitution reaction, the present invention includes the following purification steps for the post-reaction system: removing the reaction solvent by vacuum distillation and removing solid impurities (mainly triethylamine hydrochloride precipitated from the reaction system) by filtration to obtain a concentrated crude product; dissolving the crude product in a good solvent (such as tetrahydrofuran THF), and then slowly adding the solution dropwise to a precipitant (such as the poor solvent n-hexane) under vigorous stirring. During this process, the target product will precipitate due to a sharp decrease in solubility, while most small molecule impurities (such as unreacted PNIPAM, acid-binding agents, salts, etc.) will remain in the solution; collecting the solid through solid-liquid separation, and repeating the above dissolution-precipitation-separation steps 2 to 3 times to collect the precipitate; drying the precipitate to obtain a thermosensitive polyphosphazene catalyst.

[0023] Compared to conventional linear chlorophosphazene, this invention grafts poly(N-isopropylacrylamide) onto the surface of linear polydichlorophosphazene. This poly(N-isopropylacrylamide) has a minimum critical solution temperature (LCST). It exhibits a catalytically active conformation at temperatures above the LCST and a catalytically deactivated conformation at temperatures below the LCST. The catalytic activity can be reversibly switched on and off by temperature changes. In this way, the activity of the catalyst can be controlled by temperature control. In subsequent stages, deactivation can be directly achieved by cooling, reducing the amount of quencher required.

[0024] Specifically, under low-temperature conditions, the poly(N-isopropylacrylamide) chains extend and swell, becoming hydrophilic; they cover the surface of linear polydichlorophosphazene, creating strong steric hindrance to substrate molecules approaching the active center, thus ineffectively causing subsequent chain-breaking and branching reactions. Under high-temperature conditions, the poly(N-isopropylacrylamide) chains collapse and aggregate, becoming hydrophobic; the collapsed chain segments are significantly reduced in volume, exposing the underlying linear polydichlorophosphazene active center, allowing the substrate to freely approach and activating the chain-breaking and branching reaction.

[0025] In specific implementation, the mass concentration of the thermosensitive polyphosphazene catalyst is 0.5ppm~5ppm, preferably 1ppm~4ppm; the conditions for the dehydration polycondensation reaction are: stirring at 130℃~160℃ under normal pressure for 1h~3h, or stirring at 60℃~90℃ under vacuum for 1h~3h.

[0026] S2. Without adding a passivating agent, add hydrogen-containing double-ended heads to the reaction system obtained in S1 in 3 to 6 batches (preferably 4 to 5 batches) and carry out the branching reaction according to a gradient cooling program; the gradient cooling program refers to T n >T n-1 ;T n T n-1 These are the temperatures at which the branching reaction occurs after the nth and (n-1)th additions of hydrogen-containing double-headed tubes, respectively.

[0027] Hydrogen-containing double-ended polymers (tetramethyldisiloxane) function as both chain scissors and end-capping agents. They cleave existing high-molecular-weight polysiloxane chains, and simultaneously, the Si-H bonds at both ends of the molecule immediately connect to the chain-breaking point, forming new, shorter molecular chain ends. The more the molecular chain is cleaved, the lower the molecular weight and viscosity of the final product. If all hydrogen-containing double-ended polymers are added at once, the instantaneous concentration in the system becomes too high, leading to excessive chain cleavage. This causes the trimethylsilane at both ends of the methyl silicone oil to also end-cap the polysiloxane chains, resulting in excessive byproducts. The batch addition of this invention makes the chain cleavage more balanced and controllable; gradient cooling can gradually reduce the reactivity, making each chain cleavage reaction more stable and controllable. Furthermore, the formation of cyclic compounds (such as D3 and D4 cyclic siloxanes) is an unavoidable side reaction in traditional silicone oil preparation methods. Cyclic compounds are essentially stable cyclic impurities formed by the back-biting reaction of linear molecular chains. Gradient cooling effectively suppresses cyclization side reactions because: at higher temperatures, the chain breaking and end-capping reaction rates are rapid; as the temperature gradually decreases, the mobility of the molecular chains decreases, thus effectively reducing the probability of back-biting reactions forming cyclic structures. The batch-added hydrogen-containing double end caps can promptly capture the active end groups generated by chain breaking, preventing them from undergoing intramolecular cyclization, achieving chain breaking-immediate end-capping.

[0028] The total amount of hydrogen-containing dual-end terminator is 2%~15% of the hydroxyl-terminated polydimethylsiloxane oligomer; during the first branch-breaking reaction, the amount of hydrogen-containing dual-end terminator added is 15%~30% of the total amount; during the last branch-breaking reaction, the amount of hydrogen-containing dual-end terminator added is 5%~20% of the total amount. The temperature of the first branch-breaking reaction is T1 = 70℃~90℃, and the temperature of the last branch-breaking reaction is T... N =45℃~50℃. The time for a single branch breaking reaction is 5min~70min, which can be adjusted according to the time it takes for the viscosity of the system to stabilize after the branch breaking reaction. After the system stabilizes, add the hydrogen-containing double end cap to carry out the next branch breaking reaction.

[0029] S3. After the reaction is completed, the temperature is lowered to below the LCST temperature (generally 20℃~40℃) and then kept at that temperature to deactivate the temperature-sensitive polyphosphazene catalyst. Then a small amount of quencher is added (a nitrogen-based quencher, such as silazane, ammonia, organic amine, etc. The following examples use hexamethyldisilazane (HMDS) as an example. The amount used is generally 1 to 2 times the mass of the catalyst). Thin-film evaporation is then performed to remove low-boiling substances, resulting in the low-viscosity, low-cyclic end hydrogen-containing silicone oil.

[0030] This invention employs a combination of cooling deactivation and chemical quenching to deactivate temperature-sensitive catalysts, which significantly reduces the amount of quenching agent required compared to conventional chemical quenching of catalysts.

[0031] Although the product obtained by S2 of this invention has a low cyclic content, it still contains small amounts of low-boiling-point components, such as unreacted tetramethyldisiloxane and short-chain linear compounds. To obtain high-quality hydrogen-containing silicone oil, further de-boiling treatment is necessary. The conditions for thin-film evaporation are: temperature 120℃~160℃, vacuum degree -0.095MPa~-0.099MPa. Furthermore, because the hydrogen-containing silicone oil obtained by this invention has extremely low cyclic and low-boiling-point content, the thin-film evaporation de-boiling can be completed at a lower temperature and in a shorter time, significantly reducing energy consumption and the risk of product thermal damage compared to traditional processes (which typically require above 170℃ and 3-5 hours). Example 1 A method for preparing low-viscosity, low-cyclic-terminated hydrogen-containing silicone oil includes the following steps: S0, Thermosensitive Polyphosphazene Catalyst: In a reactor equipped with a stirrer, thermometer, and condenser, approximately 2.5 parts by mass of linear polydichlorophosphazene (degree of polymerization 50), 20 parts by mass of poly(N-isopropylacrylamide)-hydroxy (PNIPAM-OH, number average molecular weight approximately 5000 g / mol Mn), and 0.53 parts by mass of triethylamine were added. The temperature was raised to 60°C and maintained for 24 hours. After the reaction, the reaction solvent was removed by vacuum distillation and solid impurities were removed by filtration to obtain a concentrated crude product. The crude product was dissolved in tetrahydrofuran (THF), and the solution was slowly added dropwise to n-hexane under vigorous stirring. The solid was collected by solid-liquid separation. The above dissolution-precipitation-separation steps were repeated three times to collect the precipitate. The precipitate was dried to obtain the thermosensitive polyphosphazene catalyst.

[0032] S1. Add 932 parts by mass of hydroxyl-terminated polydimethylsiloxane oligomer (linear) to a reactor equipped with a stirrer, thermometer, condenser, and vacuum system. Add 2 ppm of thermosensitive polyphosphazene catalyst (pre-diluted with dichloromethane to an effective content of 4 wt%). Start stirring, heat to 75°C, and evacuate to -85 kPa. React for 2 hours. During this period, the viscosity of the system gradually increases, and polycondensation forms high-viscosity polydimethylsiloxane.

[0033] S2. Remove the vacuum environment from the reactor, weigh 68 parts by mass of the hydrogen-containing double-headed compound (tetramethyldisiloxane), and add it to the reactor in 5 batches. Perform the branching reaction according to a gradient cooling program; the specific gradient cooling program is as follows: First reaction: Add 12 parts by weight of hydrogen-containing double-ended head, stir and keep warm at 80°C for 20 min; Second step: Switch the jacket of the reaction system to cooling water to quickly cool down to 70°C, then add 14 parts by mass of hydrogen-containing double-ended head, stir and keep the reaction at the temperature for 25 minutes; Third time: Switch the jacket of the reaction system to cooling water to quickly cool down to 60°C, then add 20 parts by mass of hydrogen-containing double-ended head, stir and keep the reaction at the temperature for 30 minutes; Fourth step: Switch the jacket of the reaction system to cooling water to quickly cool down to 55°C, then add 16 parts by mass of hydrogen-containing double-ended head, stir and keep the reaction at the temperature for 30 minutes. Fifth step: Switch the jacket of the reaction system to cooling water to quickly cool down to 50°C, add 6 parts by mass of hydrogen-containing double-ended head, stir and keep the reaction at the temperature for 10 minutes.

[0034] S3. After the reaction was completed, no solid was observed to be produced. The jacket of the reaction system was switched to cooling water to quickly cool down to 25°C, which deactivated the temperature-sensitive polyphosphazene catalyst. Then, a trace amount of silazane (2.5 ppm) was added and stirred for 15 min to quench it. Finally, thin film evaporation (temperature 135°C, vacuum degree -0.097 MPa) was performed to remove low-boiling substances. After cooling, a low-viscosity, low-cyclic end hydrogen-containing silicone oil was obtained.

[0035] Example 2 The difference between this embodiment and Embodiment 1 is that, in S2, 68 parts by mass of the hydrogen-containing double-headed compound are added to the reactor in four batches, and the branching reaction is carried out according to the gradient cooling procedure; other conditions and steps are the same as in Embodiment 1.

[0036] The gradient cooling procedure in this embodiment is as follows: First reaction: Add 14 parts by weight of hydrogen-containing double-ended head, stir and keep warm at 80°C for 25 min; Second step: Switch the jacket of the reaction system to cooling water to quickly cool down to 70°C, then add 23 parts by mass of hydrogen-containing double-ended head, stir and keep the reaction at the temperature for 35 minutes; Third time: Switch the jacket of the reaction system to cooling water to quickly cool down to 60°C, then add 23 parts by mass of hydrogen-containing double-ended head, stir and keep the reaction at the temperature for 35 minutes; Fourth step: Switch the jacket of the reaction system to cooling water to quickly cool down to 45°C, add 8 parts by mass of hydrogen-containing double-ended head, stir and keep the reaction at the temperature for 10 minutes.

[0037] Example 3 The difference between this embodiment and Embodiment 1 is that, in S2, 68 parts by mass of the hydrogen-containing double-headed compound are added to the reactor in three batches, and the branching reaction is carried out according to a gradient cooling procedure; all other conditions and steps are the same as in Embodiment 1. The gradient cooling procedure in this embodiment is as follows: First reaction: Add 14 parts by weight of hydrogen-containing double-ended head, stir and keep warm at 80°C for 25 min; Second step: Switch the jacket of the reaction system to cooling water to quickly cool down to 70°C, then add 40 parts by mass of hydrogen-containing double-ended head, stir and keep the reaction at the temperature for 70 minutes; Third time: Switch the jacket of the reaction system to cooling water to quickly cool down to 50°C, add 14 parts by mass of hydrogen-containing double-ended head, stir and keep the reaction at the temperature for 25 minutes.

[0038] Example 4 The difference between this embodiment and Embodiment 1 is that, in S2, 68 parts by mass of the hydrogen-containing double-headed compound are added to the reactor in 6 batches, and the branching reaction is carried out according to a gradient cooling procedure; all other conditions and steps are the same as in Embodiment 1. The gradient cooling procedure in this embodiment is as follows: First reaction: Add 11 parts by weight of hydrogen-containing double-ended head, stir and keep warm at 80°C for 15 min; Second step: Switch the jacket of the reaction system to cooling water to quickly cool down to 75°C, then add 13 parts by mass of hydrogen-containing double-ended head, stir and keep the reaction at the temperature for 25 minutes; Third time: Switch the jacket of the reaction system to cooling water to quickly cool down to 65°C, then add 14 parts by mass of hydrogen-containing double-ended head, stir and keep the reaction at the temperature for 25 minutes; Fourth step: Switch the jacket of the reaction system to cooling water to quickly cool down to 60°C, then add 13 parts by mass of hydrogen-containing double-ended head, stir and keep the reaction at the temperature for 25 minutes; 5th step: Switch the jacket of the reaction system to cooling water to quickly cool down to 55°C, add 13 parts by mass of hydrogen-containing double-ended head, stir and keep the reaction at the temperature for 25 minutes; 6th step: Switch the jacket of the reaction system to cooling water to quickly cool down to 45°C, add 4 parts by mass of hydrogen-containing double-ended head, stir and keep the reaction at the temperature for 5 minutes.

[0039] Example 5 The difference between this embodiment and Example 1 is that the amount of thermosensitive polyphosphazene catalyst used in S1 is 0.5 ppm, and the amount of quencher silazane used in S3 is adjusted to 0.625 ppm; other conditions and steps are the same as in Example 1.

[0040] Example 6 The difference between this embodiment and Example 1 is that the amount of thermosensitive polyphosphazene catalyst used in S1 is 4 ppm, and the amount of quencher silazane used in S3 is adjusted to 5 ppm; other conditions and steps are the same as in Example 1.

[0041] Example 7 The difference between this embodiment and Example 1 is that the amount of thermosensitive polyphosphazene catalyst used in S1 is 5 ppm, and the amount of quencher silazane used in S3 is adjusted to 6.25 ppm; other conditions and steps are the same as in Example 1.

[0042] Comparative Example 1 This comparative example uses the traditional D4 ring-opening polymerization method to prepare end-hydrogen-containing silicone oil. The steps are as follows: 932 parts by mass of octamethylcyclotetrasiloxane (D4) and 68 parts by mass of tetramethyldisiloxane are weighed as raw materials and subjected to ring-opening equilibrium polymerization catalyzed by 20 parts by mass of sulfuric acid; the reaction temperature is 60℃ and the reaction time is 6 h. After the reaction is completed, 40 parts by mass of sodium carbonate are added to neutralize to neutral, the neutralized salt is removed by filtration, and then the oil is dehydrogenated by thin-film evaporation (temperature 135℃, vacuum degree -0.097MPa) to obtain end-hydrogen-containing silicone oil.

[0043] Comparative Example 2 The difference between this comparative example and Example 1 is that the hydrogen-containing dual-header in S2 is added all at once, while the other conditions and steps are the same as in Example 1.

[0044] Specifically, in Comparative Example S2, the vacuum environment of the reactor was removed, and 68 parts by mass of hydrogen-containing double-headed (tetramethyldisiloxane) were weighed and added to the reactor. The reaction was carried out according to the gradient program of 80℃ / 20min→70℃ / 25min→60℃ / 30min→55℃ / 30min→50℃ / 10min.

[0045] Comparative Example 3 The difference between this comparative example and Example 1 is that the gradient cooling procedure in S2 is modified to be constant temperature, that is, the reaction temperature is 80°C after each addition of the hydrogen-containing double-headed head. Other conditions and steps are the same as in Example 1.

[0046] Comparative Example 4 The difference between this comparative example and Example 1 is that the catalyst in S2 is replaced with a conventional phosphazene catalyst (ungrafted linear polydichlorophosphazene), that is, the reaction temperature is 80°C after each addition of the hydrogen-containing double-headed catalyst, and silazane (HMDS) is directly added in S3 to terminate the reaction (conventional dosage 20 ppm). Other conditions and steps are the same as in Example 1.

[0047] The viscosity, hydrogen content, and PDI of the hydrogen-containing silicone oils obtained in Examples 1 to 7 and Comparative Examples 1 to 4 were tested, and the results are shown in Table 1 below.

[0048] Viscosity was determined according to industry standard HG / T2363-1992 "Test Method for Kinematic Viscosity of Silicone Oil"; hydrogen content was measured according to industry standard HG / T 4658-2014 "Determination of Active Hydrogen Content in Hydrogen-Containing Silicone Oil for Textile Dyeing and Finishing Auxiliaries", and the hydrogen content is the content of terminal hydrogen (active hydrogen); molecular weight distribution was determined by gel permeation chromatography, and the average molecular weight (Mn) and weight average molecular weight (Mw) were calculated. The polydispersity index PDI = Mw / Mn.

[0049] In addition, referring to the industry standard HG / T 6395-2025 "Determination of Volatile Methylcyclosiloxane Content in Silicone Oil", the contents of hexamethylcyclotrisiloxane (D3), octamethylcyclotetrasiloxane (D4), decamethylcyclopentasiloxane (D5), dodecylcyclohexasiloxane (D6), tetradecylcycloheptasiloxane (D7), hexadecylcyclooctasiloxane (D8), and octadecylcyclononasiloxane (D9) in the terminal hydrogen silicone oil before and after the thin film evaporation and de-lowering in step S3 were determined. The sum of the contents of each component is the total cyclic content. The results are shown in Table 1 below.

[0050] Table 1

[0051] Table 1 shows that the hydrogen-containing silicone oil prepared in the embodiments of the present invention has the advantages of low viscosity and low cyclicity, with a total cyclic content of less than 700 ppm and a polydispersity index (PDI) of less than 1.5. This indicates that the hydrogen-containing silicone oil prepared in the embodiments of the present invention has a narrow molecular weight distribution, high uniformity, and stable performance.

[0052] Examples 1 to 4 involved adding hydrogen-containing double-ended caps to the reactor for chain breaking and branching reactions in 5, 4, 3, and 6 cycles, respectively. The results showed that more cycles resulted in more uniform chain breaking and end-capping, a narrower molecular weight distribution (lower PDI), and lower cyclic content, but also more cumbersome operation and a slightly longer total reaction time. Fewer batches (such as the 3 batches in Example 3) resulted in simpler operation and higher efficiency, but a slight increase in PDI and cyclic content; therefore, 4-5 cycles were preferred.

[0053] In Examples 1, 5 to 7, the catalyst dosages were 2 ppm, 0.5 ppm, 4 ppm, and 5 ppm, respectively. The results showed that when the catalyst dosage was low, the number of active centers was insufficient, resulting in a slow reaction rate and incomplete reaction, leading to higher viscosity, a wider PDI band, and an increased ring size. Within a certain range, as the catalyst dosage increased, the number of active centers increased, the reaction became more efficient, and the PDI decreased and the ring size decreased. However, when the catalyst dosage was too high, the reaction became too vigorous, and the increased side reactions caused the PDI band to widen and the ring size to increase.

[0054] Comparative Example 1 uses the traditional D4 ring-opening polymerization method. Although the resulting hydrogen-terminated silicone oil has low viscosity, the D4 ring-opening polymerization is an equilibrium reaction, and a large number of rings (including unreacted D4 and other rings generated at equilibrium) always exist in the system. Even after thin-film evaporation to reduce the rings, the residual amount is still as high as 2000 ppm, requiring longer and higher-temperature removal processes. In addition, the equilibrium polymerization reaction results in a wide molecular weight distribution of the product and uncontrollable stability; moreover, the neutralization process generates a large amount of sodium carbonate solid waste, which requires filtration treatment, making the process cumbersome and environmentally unfriendly.

[0055] Comparative Example 2 used a one-time addition of hydrogen-containing dual-heading agents, resulting in an instantaneously high local concentration of the end-capping agent in the system. This led to extremely uneven chain scission reactions: some molecular chains were excessively scissioned (too small molecular weight), while others were insufficiently scissioned (too large molecular weight), ultimately causing a broad molecular weight distribution. Furthermore, the local high concentration environment during the one-time addition promoted cyclization side reactions, which in turn led to an increase in the cyclic mass.

[0056] Comparative Example 3, by modifying the gradient cooling program to an isothermal process, resulted in a significant increase in the total cyclic content. This is because cyclization side reactions are more likely to occur at high temperatures. To ensure reactivity, chain breaking and branching reactions must be carried out at a specific temperature. In Comparative Example 3, the entire reaction process was conducted at a relatively high temperature, resulting in strong molecular chain mobility and a much higher probability of cyclization re-entry compared to the gradient cooling process. Furthermore, the high temperature of the isothermal process kept the catalyst in an active state. Since the hydrogen-containing dual-heading system functions as both a chain scissor and end-capping agent, chain breaking and end-capping were uncontrollable throughout the reaction, leading to a wider PDI and poorer uniformity in the product. At high temperatures, the chain breaking reaction rate is fast. As end-capping proceeds and the system viscosity decreases, gradual cooling can suppress cyclization side reactions (molecules re-entering to form D3~D10), while also making each batch of reactions more mild and controllable.

[0057] Comparative Example 4 replaced the catalyst with conventional linear phosphazene chloride. The comparison showed that its viscosity, hydrogen content, and PDI were not much different from those of Comparative Example 2. The reason is that conventional linear phosphazene chloride is not temperature sensitive. Even if hydrogen-containing double-headed catalysts are added in batches and the temperature is reduced in a gradient, its activity will not decrease significantly as the temperature decreases. Therefore, the S2 reaction activity in Comparative Example 4 is relatively active. In addition, there are some side reactions, which lead to an increase in the cyclic content, but it is lower than that in Comparative Example 2.

[0058] The embodiments described above are merely illustrative of several implementations of the present invention, and while the descriptions are specific and detailed, they should not be construed as limiting the scope of the present invention. It should be noted that those skilled in the art can make various modifications and improvements without departing from the concept of the present invention, and these modifications and improvements all fall within the scope of protection of the present invention. Therefore, the scope of protection of this patent should be determined by the appended claims.

Claims

1. A method for preparing low-viscosity, low-cyclic-terminal hydrogen-containing silicone oil, characterized in that, The preparation method includes the following steps: S1. A hydroxyl-terminated polydimethylsiloxane oligomer is subjected to a dehydration condensation reaction under the action of a thermosensitive polyphosphazene catalyst to generate high-viscosity polydimethylsiloxane; the thermosensitive polyphosphazene catalyst is a linear chlorinated phosphazene with a surface grafted thermosensitive polymer. S2. Without adding a passivating agent, add hydrogen-containing double-headed polymers to the reaction system obtained in S1 in 3 to 6 portions, and carry out the link-breaking and branching reaction according to a gradient cooling program; the gradient cooling program refers to T n >T n-1 ;T n T n-1 These are the temperatures at which the link-breaking and branching reactions occur after the nth and (n-1)th additions of hydrogen-containing double-headed structures, respectively. S3. After the reaction is completed, the temperature is lowered to below the LCST temperature to deactivate the temperature-sensitive polyphosphazene catalyst, thus obtaining the low-viscosity, low-cyclic end-hydrogen-containing silicone oil.

2. The method for preparing low-viscosity, low-cyclic-terminal hydrogen-containing silicone oil according to claim 1, characterized in that, S3 also includes: after the thermosensitive polyphosphazene catalyst is deactivated, a quencher is added, and after stirring, a thin film evaporation is carried out for de-lowering treatment.

3. The method for preparing low-viscosity, low-cyclic-terminal hydrogen-containing silicone oil according to claim 1, characterized in that, The preparation method of the thermosensitive polyphosphazene catalyst is as follows: Linear polydichlorophosphazene is available; Linear polydichlorophosphazene was subjected to a nucleophilic substitution reaction with poly(N-isopropylacrylamide)-hydroxyl groups in the presence of an inert atmosphere and an acid-binding agent, so that poly(N-isopropylacrylamide) was chemically grafted onto the phosphorus atoms of the linear polydichlorophosphazene. After purification, the thermosensitive polyphosphazene catalyst was obtained.

4. The method for preparing low-viscosity, low-cyclic-terminal hydrogen-containing silicone oil according to claim 3, characterized in that, The acid-binding agent is triethylamine, and its molar ratio with poly(N-isopropylacrylamide)-hydroxyl is 1.2~1.5:

1.

5. The method for preparing low-viscosity, low-cyclic-terminal hydrogen-containing silicone oil according to claim 3, characterized in that, The purification steps include: The reaction solvent was removed by vacuum distillation and solid impurities were removed by filtration to obtain the concentrated crude product. The crude product is dissolved, precipitated, and separated, and this process is repeated 2 to 3 times, with the precipitate collected. The precipitate was dried to obtain the thermosensitive polyphosphazene catalyst.

6. The method for preparing low-viscosity, low-cyclic-terminal hydrogen-containing silicone oil according to claim 1, characterized in that, The mass concentration of the thermosensitive polyphosphazene catalyst in S1 is 0.5 ppm to 5 ppm; The conditions for the dehydration polycondensation reaction are: stirring at 130℃~160℃ for 1h~3h under normal pressure, or stirring at 60℃~90℃ for 1h~3h under vacuum.

7. The method for preparing low-viscosity, low-cyclic-terminal hydrogen-containing silicone oil according to claim 1, characterized in that, In S2, the temperature of the first branch-breaking reaction is T1 = 70℃~90℃, and the temperature of the last branch-breaking reaction is T... N =45℃~50℃; T n T n-1 The temperature difference is 5℃~10℃; Once the viscosity of the system stabilizes after each branch breaking reaction, a hydrogen-containing double-ended head is added to initiate the next branch breaking reaction.

8. The method for preparing low-viscosity, low-cyclic-terminal hydrogen-containing silicone oil according to claim 1, characterized in that, The total amount of hydrogen-containing double-ended polymer in S2 is 2% to 15% of the hydroxyl-terminated polydimethylsiloxane oligomer. During the first branch-breaking reaction, the amount of hydrogen-containing double-ended head added is 15% to 30% of the total amount; During the final branching reaction, the amount of hydrogen-containing double-ended head added is 5% to 20% of the total amount.

9. The method for preparing low-viscosity, low-cyclic-terminal hydrogen-containing silicone oil according to claim 7, characterized in that, The hydrogen-containing double-heading unit is added in 4 or 5 stages in S2.

10. A low-viscosity, low-cyclic-terminal hydrogen-containing silicone oil, characterized in that: The hydrogen-containing silicone oil is prepared by the method for preparing low-viscosity, low-cyclic hydrogen-containing silicone oil according to any one of claims 1 to 9.

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