Low-ring-content silicone oil and preparation method thereof

Abstract

The invention belongs to the technical field of organic silicon synthesis, and particularly relates to low-ring-content silicone oil and a preparation method thereof, and the silicone oil comprises the following components in percentage by mass: 92-97% of DMC, 0.2-0.8% of crown ether, 0.5-2% of a phosphazene alkali silicon alkoxide catalyst, 0.4-2% of a phosphosilyl ester neutralizer and 0.35-3.5% of divinyl tetramethyl disiloxane. The novel phosphazene alkali silicon alkoxide catalyst and the phosphoric acid silicon ester neutralizer are adopted, so that the'back-biting 'cyclization phenomenon is greatly restrained in the polymerization process, and the reaction conversion rate and efficiency are improved; the Fe3O4-beta-cyclodextrin composite material is selected as an adsorbent of a ring body, so that the content of cyclosiloxane is reduced, the magnetic recovery rate is high, the thermal stability is high, and the biological safety is better; the volatile component content of the prepared low-ring-content silicone oil is less than 0.2% (150 DEG C / 3h), the ring content (D3-D10) is less than 200ppm, and the ring content meets the requirements of electronics, food and medical levels.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of organic silicon synthesis, and particularly relates to a low cyclic content silicone oil and a preparation method thereof. BACKGROUND

[0002] Due to high persistence and bioaccumulation of D4, D5 and D6, they may cause negative impacts on the environment and ecosystems. International medical standards (such as ISO 10993) and EU REACH regulations are now strictly controlling the residues of siloxane rings (D4-D6). Silicone oil is widely used in medical and daily chemical industries. For example, methyl silicone oil can be used in defoaming preparations, scar repair gels and medical device lubricants. Vinyl silicone oil, as the skeleton of silicone rubber material, can be used in medical catheters, breathing mask sealing pads and prosthesis filling. Since it needs to be in contact with the human body for a long time, there are higher requirements for product purity (catalyst, metal ion, organic solvent residue, etc.), biological safety (cytotoxicity, skin sensitization, implant stability, etc.), and functional adaptability.

[0003] There are still some unsolved problems in the prior art. For example, patent CN117659402A discloses a preparation process of electronic grade vinyl silicone oil with low cyclic content. The invention uses water-absorbing particles to remove water and adds piperidine adjuvants and polymerization inhibitors to reduce the cyclic content. However, the added adjuvants and polymerization inhibitors are difficult to remove and are easily decomposed at high temperatures to produce toxic substances harmful to the human body, and are not suitable for medical and daily chemical products. For example, patent CN113896893A discloses a preparation method of dimethyl silicone oil with high conversion rate and low cyclic content. The method uses linear siloxane as raw material, linear chlorophosphazene as catalyst, and hexamethyldisilazane as neutralizing agent. However, there are few domestic manufacturers of high-quality linear siloxane, the selection of raw materials is poor, and linear chlorophosphazene is volatile and easily releases hydrogen chloride, which has a great impact on equipment corrosion and limited effect on reducing the cyclic content.

[0004] In summary, there are still problems such as high toxicity of raw materials, harm to the human body, poor selection of raw materials, high degree of equipment corrosion, and limited effect on reducing the cyclic content in the preparation process of silicone oil with low cyclic content in the technical field of organic silicon synthesis. Therefore, it is of great significance to develop a low-cyclic-content silicone oil that is non-toxic and has low corrosion. SUMMARY

[0005] The present application aims to provide a low ring content silicone oil. In the silicone oil, divinyltetramethyldisiloxane is used as an end-capping agent to precisely control the vinyl functional groups at both ends of the molecular chain, crown ether complex metal ions in the phosphazene alkali silanol salt catalyst, and inhibit the rearrangement reaction that leads to the increase of ring content. The use of the phosphazene alkali silanol salt catalyst and the phosphoric acid silicate neutralizer realizes low-temperature, rapid and complete ring-opening polymerization of DMC, efficiently neutralizes the residual basic catalyst in the silicone oil system, and solves the problems of toxic raw materials and poor raw material selection.

[0006] Another object of the present application is to provide a preparation method of a low ring content silicone oil. The method removes impurities from the source, removes metal ion hazards in raw materials through crown ether extraction, realizes high conversion rate polymerization by using high-performance catalysts and neutralizers, reduces the generation of rings, removes most of the volatile components and rings through vacuum dehydration and dehydration, and realizes the targeted removal and convenient separation of residual trace rings by using the adsorption of Fe3O4-β-cyclodextrin and magnetic separation technology, solving the problems of water molecules deactivating the catalyst or causing the hydrolysis of siloxane bonds, the limited effect of reducing ring content, the difficulty of filtering traditional adsorbents, product loss and secondary pollution risk.

[0007] The object of the present application is achieved by the following scheme: A low ring content silicone oil, comprising the following mass fractions: DMC 92-97%, crown ether 0.2-0.8%, phosphazene alkali silanol salt catalyst 0.5-2%, phosphoric acid silicate neutralizer 0.4-2%, and divinyltetramethyldisiloxane 0.35-3.5%.

[0008] Preferably, the silicone oil comprises the following mass fractions: DMC 95-96.5%, crown ether 0.4-0.6%, phosphazene alkali silanol salt catalyst 0.8-1.5%, phosphoric acid silicate neutralizer 0.5-1%, and divinyltetramethyldisiloxane 1-3%.

[0009] DMC is a mixture of ring bodies mainly composed of D4, D4 is an eight-membered ring structure, and the Si-O bond is easily attacked by nucleophiles to undergo ring-opening polymerization. Compared with D5, D6 linear siloxane or larger rings, D4 has the highest ring-opening activity, which can reduce the residual unreacted ring bodies; and DMC ring-opening follows the typical anionic polymerization mechanism, and the molecular weight and functional groups are controllable.

[0010] Crown ether is an inhibitor of metal ions, especially potassium ions. The cavity in the molecular structure matches the potassium ion, and a stable complex is formed by coordination bond with the potassium ion. After the reaction, the potassium ion in the cavity loses Lewis acidity and cannot catalyze the rearrangement reaction of the siloxane main chain to generate rings, thereby fundamentally inhibiting the generation of rings.

[0011] The phosphazene base silanol salt as a high-efficiency anion polymerization catalyst can quickly initiate and complete the ring-opening polymerization of DMC at low temperature. The phosphazene base is a super strong base with great steric hindrance and high activity. The phosphazene anion attacks the silicon atom on the ring of DMC, causing the ring-opening of DMC, and generating a new silanol salt active center. The newly generated silanol salt active center continues to attack another DMC molecule, so that the chain continues to grow.

[0012] The acidic functional groups of the phosphosilicate neutralizer can protonate the residual basic catalyst and the silanol salt active end. The by-product has compatibility, which can simplify the process and avoid the introduction of water and product loss.

[0013] The divinyltetramethyldisiloxane provides a vinyl group at the end of the polymerization chain, and the end-capping reaction occurs while the catalytic anion is regenerated, which can continue to initiate new chains. Each end-capping agent molecule can terminate two growing molecular chains, and the amount added determines the molecular weight of the final polymer.

[0014] Preferably, the volatile content of the silicone oil is less than 0.2% (150℃ / 3h), and the ring content (D3-D10) is less than 200ppm.

[0015] Low volatile content allows the silicone oil to be heated at high temperature for a long time, with stable performance and small weight loss. Low ring content ensures that the silicone oil will not change its performance and corrode device components due to the loss of small molecular rings.

[0016] Preferably, the mass ratio of phosphazene base to methyl silicone oil in the phosphazene base silanol salt catalyst is (0.5-2):100.

[0017] The conversion of ionic phosphazene base to silanol salt allows the catalyst to be completely dissolved in the non-polar DMC and silicone oil system, realizing homogeneous catalysis. A large amount of methyl silicone oil ensures that the reaction can form a highly diluted and good flowing catalyst solution, which is beneficial to the catalytic polymerization reaction.

[0018] Preferably, the mass ratio of phosphoric acid to methyl silicone oil in the phosphosilicate neutralizer is (0.2-1):100.

[0019] The phosphosilicate neutralizer can protonate the residual basic catalyst, and sufficient methyl silicone oil carrier ensures that the neutralizer can be quickly and uniformly dispersed in the entire reaction system after being added, avoiding the formation of a local area with too low pH (too acidic), thereby preventing the acid depolymerization of siloxane in the local area.

[0020] Preferably, the crown ether is one or both of 15-crown-5 and 18-crown-6.

[0021] K + The diameter of The cavity diameter of 18-crown-6 is Both are relatively matched, so 18-crown ether-6 is matched to K + It has higher selectivity and complexing ability, and inhibits its ability to catalyze the rearrangement of siloxane to form a ring; Na + The diameter of The cavity diameter of 15-crown ether-5 is Both are relatively matched, and the addition of 15-crown ether-5 can remove impurities in depth, removing other potential metal ion contamination sources except K +

[0022] A preparation method of a low-ring content silicone oil, comprising the following steps: S1, removing impurities from divinyltetramethyldisiloxane through a directional molecular sieve column; adding crown ether and high-purity polar solvent to the DMC for liquid separation and washing, and vacuum dehydrating; S2, respectively synthesizing a phosphazene base silanol salt catalyst and a phosphoric acid silicate neutralizer; S3, adding pretreated divinyltetramethyldisiloxane and the phosphazene base silanol salt catalyst to the dehydrated DMC, balancing the reaction at a temperature of 60-100°C for 2-6h under N2, adding the phosphoric acid silicate neutralizer, stirring and filtering, and increasing the temperature to 170-220°C under N2 at a pressure of -0.099 to -0.1MPa to remove low-molecular-weight substances for 3-8h; S4, cooling and adding Fe3O4-β-cyclodextrin to stir and adsorb the ring for 2-6h, and filtering to obtain a low-ring content silicone oil product.

[0023] Preferably, the preparation method of the phosphazene base silanol salt catalyst in step S2 is: mixing methyl silicone oil with phosphazene base and stirring, reacting at a temperature of 80-120°C under N2 protection for 4-8h until the system is clear, and vacuum removing low-molecular-weight substances at a temperature of 100-120°C for 10-60min to obtain the phosphazene base silanol salt catalyst.

[0024] As a new catalyst, phosphazene base has the advantages of ultra-high catalytic activity, no metal residue, and precise controllability compared with traditional systems. Compared with traditional catalysts that can easily cause back-biting and ring-forming side reactions, phosphazene base can effectively inhibit this side reaction and reduce the ring content. At the same time, the phosphazene base silanol salt prepared by reacting it with DMC can better dissolve siloxane, further improving the reaction efficiency. Before the reaction of phosphazene base, it is an ion pair, which has poor dispersibility in organic phase. After reacting with methylsilanol, the siloxane group is connected to the potassium ion through a covalent bond, improving the solubility and dispersion uniformity of the catalyst in DMC raw materials, so that all catalytic active centers can fully contact DMC monomers, improving the catalytic efficiency and conversion efficiency.

[0025] ​The phosphazene base and the silanol are sensitive to moisture and oxygen in the air, the moisture can cause the catalyst to be deactivated by hydrolysis, N2 provides a water-free and oxygen-free inert environment to ensure the purity of the reaction and the activity of the catalyst; the conjugate acid of the phosphazene base is a byproduct of the reaction and has a certain volatility, which can be removed together with trace amounts of water, low molecular silanol, etc. by vacuum stripping to purify the catalyst.

[0026] Preferably, the preparation method of the phosphosilicate neutralizer in step S2 is: mixing methyl silicone oil with phosphoric acid and stirring, reacting at a temperature of 100-140℃ under N2 protection for 2-6h until the system is clear, and vacuum stripping at a temperature of 100-140℃ for 10-60min to obtain the phosphosilicate neutralizer.

[0027] The hydroxyl group of phosphoric acid reacts with the silicon hydroxyl group of methyl silicone oil to generate phosphosilicate and water, N2 prevents the discoloration of the product caused by the oxidation discoloration of the raw materials, and can also inhibit hydrolysis, thereby improving the reaction conversion rate and efficiency; the temperature of 100-140℃ avoids siloxane rearrangement and excessive condensation of phosphoric acid; by vacuum stripping, trace amounts of water can be removed together with the product to purify the product and improve the stability of the neutralizer.

[0028] Preferably, the Fe3O4-β-cyclodextrin addition amount in step S4 is 0.5-2% of the product.

[0029] The Fe3O4-β-cyclodextrin composite material is composed of ferroferric oxide magnetic nanoparticles and a β-cyclodextrin (β-CD) molecular shell. There is a size matching effect and hydrophobic interaction between the hydrophobic cavity of β-CD and cyclotrisiloxane (D4 is the most typical), which can form a stable inclusion compound. The Fe3O4 nanoparticles provide the convenience of magnetic separation, and the adsorbent can be recycled for 10-20 times with high recovery efficiency. Compared with other adsorbents, the adsorbent does not cause the generation or residual of toxic substances.

[0030] The beneficial effects of the present application are: (1) The obtained low ring content silicone oil has a volatile content of <0.2% (150℃ for 3h), and a ring content (D3-D10) of <200ppm, which meets the requirements of electronic, food and medical grades; (2) The new phosphazene base silanol salt catalyst and phosphosilicate neutralizer are used, compared with the conventional catalytic process, the reaction temperature is low, the reaction time is short, the efficiency is greatly improved, and the "backbite" ring formation phenomenon can be greatly suppressed during polymerization. Compared with direct use of phosphazene base catalysis and phosphoric acid neutralization, the silanol salt structure can make it better contact with the system, improve the reaction conversion rate, the product molecular weight distribution is narrower, and the product quality is improved; (3) The Fe3O4-β-cyclodextrin composite material is selected as the adsorbent of the ring to reduce the content of cyclotrisiloxane, has high magnetic recovery rate, high thermal stability and better biological safety, and is more suitable for use in medical and daily chemical products. DETAILED DESCRIPTION

[0031] Example 1 The embodiment provides a low cyclic content silicone oil, which specifically comprises the following components in mass fraction: DMC 95.4%, crown ether 0.5%, phosphazene base silanol salt catalyst 1%, phosphosilicate neutralizer 0.8%, and divinyltetramethyldisiloxane 1.6%; the mass ratio of phosphazene base and methyl silicone oil in the phosphazene base silanol salt catalyst is (1.8):100; and the mass ratio of phosphoric acid and methyl silicone oil in the phosphosilicate neutralizer is (0.8):100.

[0032] The embodiment further provides a preparation method of the low cyclic content silicone oil, which specifically comprises the following steps. S1, DMC pretreatment: adding analytical grade isopropyl alcohol and 18-crown-6 ether to DMC, and stirring and adsorbing for 3h, and then standing, washing and filtering; adding the washed DMC into a reaction kettle, stirring and heating, and performing dehydration at 80°C by using a vacuum device, and the dehydration amount is 10%; divinyltetramethyldisiloxane pretreatment: passing the divinyltetramethyldisiloxane through a directional molecular sieve column to remove metal impurities in the raw material; S2, synthesis of the phosphazene base silanol salt catalyst: mixing and stirring methyl silicone oil and phosphazene base, and reacting at 100°C under N2 protection for 6h until the system is clear, and then performing low-temperature vacuum removal at 120°C for 30min to obtain the phosphazene base silanol salt catalyst; synthesis of the phosphosilicate neutralizer: mixing and stirring methyl silicone oil and phosphoric acid, and reacting at 130°C under N2 protection for 4h until the system is clear, and then performing low-temperature vacuum removal at 120°C for 30min to obtain the phosphosilicate neutralizer; S3, polymerization and low-temperature removal: adding the pretreated DMC into a reaction kettle, heating to 70°C, adding the pretreated divinyltetramethyldisiloxane, adding the phosphazene base silanol salt, stirring and reacting for 3h, and then adding the phosphosilicate and neutralizing for 2h; after filtration, performing nitrogen removal at 180°C for 4h; S4, adsorption: cooling to 100°C, adding 1% of Fe3O4-β-cyclodextrin of the product mass, stirring and adsorbing for 2h, magnetically recovering the adsorbent, and then filtering to obtain the finished product.

[0033] Example 2 The embodiment provides a low cyclic content silicone oil, which specifically comprises the following components in mass fraction: DMC 95.4%, crown ether 0.5%, phosphazene base silanol salt catalyst 0.5%, phosphosilicate neutralizer 0.4%, and divinyltetramethyldisiloxane 1.6%; the mass ratio of phosphazene base and methyl silicone oil in the phosphazene base silanol salt catalyst is (1.8):100; and the mass ratio of phosphoric acid and methyl silicone oil in the phosphosilicate neutralizer is (0.8):100.

[0034] The method and steps for preparing the low ring content silicone oil are the same as those in Example 1.

[0035] Example 3: The low ring content silicone oil provided in this example specifically comprises the following components in mass fraction: DMC 95.4%, crown ether 0.5%, phosphazene base silanol salt catalyst 2%, phosphoric acid silicon ester neutralizer 2%, and divinyl tetramethyl disiloxane 1.6%. The mass ratio of phosphazene base to methyl silicone oil in the phosphazene base silanol salt catalyst is (1.8):100; and the mass ratio of phosphoric acid to methyl silicone oil in the phosphoric acid silicon ester neutralizer is (0.8):100.

[0036] The method and steps for preparing the low ring content silicone oil are the same as those in Example 1.

[0037] Example 4: The low ring content silicone oil provided in this example specifically comprises the following components in mass fraction: DMC 92%, crown ether 0.2%, phosphazene base silanol salt catalyst 1%, phosphoric acid silicon ester neutralizer 0.8%, and divinyl tetramethyl disiloxane 3.5%. The mass ratio of phosphazene base to methyl silicone oil in the phosphazene base silanol salt catalyst is (1.8):100; and the mass ratio of phosphoric acid to methyl silicone oil in the phosphoric acid silicon ester neutralizer is (0.8):100.

[0038] The method and steps for preparing the low ring content silicone oil are the same as those in Example 1.

[0039] Example 5: The low ring content silicone oil provided in this example specifically comprises the following components in mass fraction: DMC 97%, crown ether 0.8%, phosphazene base silanol salt catalyst 1%, phosphoric acid silicon ester neutralizer 0.8%, and divinyl tetramethyl disiloxane 0.35%. The mass ratio of phosphazene base to methyl silicone oil in the phosphazene base silanol salt catalyst is (1.8):100; and the mass ratio of phosphoric acid to methyl silicone oil in the phosphoric acid silicon ester neutralizer is (0.8):100.

[0040] The method and steps for preparing the low ring content silicone oil are the same as those in Example 1.

[0041] Example 6: The low ring content silicone oil provided in this example specifically comprises the following components in mass fraction: DMC 95.4%, crown ether 0.5%, phosphazene base silanol salt catalyst 2%, phosphoric acid silicon ester neutralizer 2%, and divinyl tetramethyl disiloxane 1.6%.

[0042] Example 7: The low ring content silicone oil provided in this example specifically comprises the following components in mass fraction: DMC 95.4%, crown ether 0.5%, phosphazene base silanol salt catalyst 2%, phosphoric acid silicon ester neutralizer 2%, and divinyl tetramethyl disiloxane 1.6%.

[0043] Example 8: The low-cyclosiloxane content silicone oil contains the same mass fraction components, methods and steps as in Example 1; the amount of Fe3O4-β-cyclodextrin added in step S4 is 0.5% of the mass of the product.

[0044] Example 9: The low-cyclosiloxane content silicone oil contains the same mass fraction components, methods and steps as in Example 1; the amount of Fe3O4-β-cyclodextrin added in step S4 is 2% of the mass of the product.

[0045] Comparative Example 1: The low-cyclosiloxane content silicone oil contains the same mass fraction components as in Example 1.

[0046] The comparative example also provides a preparation method of a low-cyclosiloxane content silicone oil, specifically comprising the following steps: S1, divinyltetramethyldisiloxane pretreatment: passing divinyltetramethyldisiloxane through a directional molecular sieve column to remove metal impurities in the raw material; S2, synthesis of phosphazene base silanol salt catalyst: mixing methyl silicone oil with phosphazene base and stirring, reacting at 100°C under N2 protection for 6h until the system is clear, and vacuum stripping at 120°C for 30min to obtain a phosphazene base silanol salt catalyst; synthesis of phosphoric acid ester neutralizer: mixing methyl silicone oil with phosphoric acid and stirring, reacting at 130°C under N2 protection for 4h until the system is clear, and vacuum stripping at 120°C for 30min to obtain a phosphoric acid ester neutralizer; S3, polymerization and low boiling point removal: adding pretreated DMC to a reaction kettle and heating to 70°C, adding pretreated divinyltetramethyldisiloxane, adding phosphazene base silanol salt, stirring and reacting for 3h, adding phosphoric acid ester, and neutralizing for 2h. After filtration, nitrogen is passed at 180°C for 4h to remove low boiling point substances; S4, adsorption: cooling to 100°C, adding 1% of the mass of the product Fe3O4-β-cyclodextrin, stirring and adsorbing for 2h, magnetically recovering the adsorbent, and filtering to obtain the finished product.

[0047] The difference between the comparative example and Example 1 is that step S1 does not pretreat the DMC.

[0048] Comparative Example 2: The low-cyclosiloxane content silicone oil contains the same mass fraction components as in Example 1.

[0049] The comparative example also provides a preparation method of a low-cyclosiloxane content silicone oil, specifically comprising the following steps: S1, DMC pretreatment: add analytical pure isopropyl alcohol and 18-crown-6 ether-6 to DMC, the mass ratio of the three is 10:5:0.05, stir and adsorb for 3h, then stand and separate and wash. Add the washed DMC to the reaction kettle, stir and heat, and use a vacuum device to dehydrate at 80°C, with a 10% loss; divinyltetramethyldisiloxane pretreatment: pass the divinyltetramethyldisiloxane through a directional molecular sieve column to remove metal impurities in the raw material; S2, synthesis of phosphazene base silanol salt catalyst: mix methyl silicone oil with phosphazene base and stir, react at 100°C under N2 protection for 6h until the system is clear, and then dehydrate at 120°C under vacuum for 30min to obtain the phosphazene base silanol salt catalyst; synthesis of phosphoric acid silicate neutralizer: mix methyl silicone oil with phosphoric acid and stir, react at 130°C under N2 protection for 4h until the system is clear, and then dehydrate at 120°C under vacuum for 30min to obtain the phosphoric acid silicate neutralizer; S3, polymerization and dehydrogenation: add pretreated DMC to the reaction kettle and heat to 70°C, add pretreated divinyltetramethyldisiloxane, add phosphazene base silanol salt, stir and react for 3h, and then add phosphoric acid silicate and neutralize for 2h. After filtration, pass nitrogen gas at 150°C for 6h to dehydrogenate; S4, adsorption: cool to 100°C, add 1% of the product mass of Fe3O4-β-cyclodextrin, stir and adsorb for 2h, magnetically recover the adsorbent, and then filter to obtain the finished product.

[0050] The difference between this comparative example and example 1 is that the dehydrogenation temperature after neutralization and filtration in step S3 is 150°C.

[0051] Comparative example 3: The low-cyclodextrin content silicone oil contains the same mass fraction as example 1.

[0052] This comparative example also provides a method for preparing a low-cyclodextrin content silicone oil, which specifically includes the following steps: S1, DMC pretreatment: add analytical pure isopropyl alcohol and 18-crown-6 ether-6 to DMC, the mass ratio of the three is 10:5:0.05, stir and adsorb for 3h, then stand and separate and wash. Add the washed DMC to the reaction kettle, stir and heat, and use a vacuum device to dehydrate at 80°C, with a 10% loss; divinyltetramethyldisiloxane pretreatment: pass the divinyltetramethyldisiloxane through a directional molecular sieve column to remove metal impurities in the raw material; S2, polymerization and dehydrogenation: add pretreated DMC to the reaction kettle and heat to 70°C, add pretreated divinyltetramethyldisiloxane, add 30ppm of phosphazene base catalyst, stir and react for 3h, and then add 20ppm of phosphoric acid and neutralize for 2h. After filtration, pass nitrogen gas at 180°C for 4h to dehydrogenate; S3, adsorption: add 1% of product mass of Fe3O4-β-cyclodextrin, stir and adsorb for 2h, then recover the adsorbent by magnetic attraction, and filter to obtain the finished product.

[0053] The difference between the present comparative example and example 1 is that the synthesized catalyst and neutralizer are replaced by directly adding 30ppm of phosphazene base catalyst and 20ppm of phosphoric acid neutralizer.

[0054] Comparative example 4: The low-cyclosiloxane-content silicone oil contains the same mass fraction as example 1.

[0055] The present comparative example also provides a preparation method of a low-cyclosiloxane-content silicone oil, which specifically comprises the following steps: S1, DMC pretreatment: add analytical pure isopropyl alcohol and 18-crown-6 ether-6 to the DMC, and the mass ratio of the three is 10:5:0.05, stir and adsorb for 3h, then stand and separate and wash; add the washed DMC to the reaction kettle, stir and heat, and use a vacuum device to dehydrate at 80℃, and the dehydration amount is 10%; divinyltetramethyldisiloxane pretreatment: pass the divinyltetramethyldisiloxane through a directional molecular sieve column to remove metal impurities in the raw material; S2, synthesis of phosphazene base silanol salt catalyst: mix the methyl silicone oil with the phosphazene base and stir, react at 100℃ under N2 protection for 6h until the system is clear, and then vacuum dehydrate at 120℃ for 30min to obtain the phosphazene base silanol salt catalyst; synthesis of phosphoric acid silicate neutralizer: mix the methyl silicone oil with the phosphoric acid and stir, react at 130℃ under N2 protection for 4h until the system is clear, and then vacuum dehydrate at 120℃ for 30min to obtain the phosphoric acid silicate neutralizer; S3, polymerization and low-content removal: add the pretreated DMC to the reaction kettle, heat to 70℃, add the pretreated divinyltetramethyldisiloxane, add the phosphazene base silanol salt, stir and react for 3h, and then add the phosphoric acid silicate and neutralize for 2h. After filtration, pass nitrogen gas at 180℃ for 4h to obtain the finished product; The difference between the present comparative example and example 1 is that no Fe3O4-β-cyclodextrin is added for adsorption.

[0056] Comparative example 5: The low-cyclosiloxane-content silicone oil contains the same mass fraction as example 1.

[0057] The present comparative example also provides a preparation method of a low-cyclosiloxane-content silicone oil, which specifically comprises the following steps: S1, DMC pretreatment: add analytical pure isopropyl alcohol and 18-crown-6 ether-6 to DMC in a mass ratio of 10:5:0.05, stir and adsorb for 3 h, then stand and separate and rinse. Add the washed DMC to the reaction kettle, stir and heat, and use a vacuum device to dehydrate at 80°C, with a 10% loss; divinyltetramethyldisiloxane pretreatment: pass the divinyltetramethyldisiloxane through a directional molecular sieve column to remove metal impurities in the raw material; S2, synthesis of phosphazene base silanol salt catalyst: mix methyl silicone oil with phosphazene base and stir, react at 100°C under N2 protection for 6 h until the system is clear, and then dehydrate at 120°C under vacuum for 30 min to obtain the phosphazene base silanol salt catalyst; synthesis of phosphoric acid silicate neutralizer: mix methyl silicone oil with phosphoric acid and stir, react at 130°C under N2 protection for 4 h until the system is clear, and then dehydrate at 120°C under vacuum for 30 min to obtain the phosphoric acid silicate neutralizer; S3, polymerization and dehydrating: add pretreated DMC to the reaction kettle, heat to 70°C, add pretreated divinyltetramethyldisiloxane, add phosphazene base silanol salt, stir and react for 3 h, and then add phosphoric acid silicate and neutralize for 2 h. After filtration, pass nitrogen gas at 180°C for 4 h to dehydrate; S4, adsorption: cool to 100°C, add 1% of the product mass of β-cyclodextrin, stir and adsorb for 2 h, magnetically recover the adsorbent, and then filter to obtain the finished product.

[0058] The difference between the present comparative example and Example 1 is that β-cyclodextrin is added for adsorption.

[0059] Test Example 1: The product silicone oils of Examples 1-9 and Comparative Examples 1-5 were tested for performance, and the results are shown in Table 1.

[0060] The following tests were performed to test the performance of the product silicone oils of Examples 1-9 and Comparative Examples 1-5.

[0061] Viscosity test: pour a sufficient amount of bubble-free silicone oil sample into a beaker, place it in a 25°C constant temperature water bath, select a rotor and speed combination so that the torque reading is 80% of the scale range, start the viscometer, and record the viscosity value after the reading stabilizes, repeat the test three times and take the average value.

[0062] Volatile matter test: weigh a clean beaker with a mass of m1, add 1.5000±0.0005 g of silicone oil sample to the beaker, and weigh the total mass m2. Place the sample in an oven preheated to 180±2°C and heat for 2 h. After removing the sample, cool it to room temperature and weigh it as m3. Calculate the volatile matter (%) according to the formula: [(m2-m3) / (m2-m1)]x100%, repeat the test three times and take the average value.

[0063] Ring content test: 1.0000 ± 0.0005 g of silicone oil sample was diluted with toluene and injected into the gas chromatograph, and the specific content of the ring was obtained according to the peak area, and the average value was obtained by repeating the test three times. Example Product viscosity (mPa-s) Product volatile (%) Product ring and ball content (ppm) Example 1 426 0.16 173 Example 2 395 0.19 190 Example 3 427 0.16 180 Example 4 212 0.14 176 Example 5 10320 0.13 168 Example 6 433 0.08 94 Example 7 437 0.11 109 Example 8 425 0.17 195 Example 9 426 0.10 113 Comparative Example 1 410 0.25 303 Comparative Example 2 386 0.77 936 Comparative Example 3 421 0.24 266 Comparative Example 4 417 0.29 330 Comparative Example 5 422 0.22 254

[0064] Comprehensive comparison, the formula of example 1 prepares the silicone oil viscosity 426 mPa·s, volatile 0.16%, ring content 173 ppm, is the best balanced proportion; DMC content provides the main raw material for polymerization reaction; The proportion of catalyst and neutralizer is well matched, which can ensure sufficient reaction and completely terminate the reaction; The amount of capping agent is appropriate, and the target viscosity product silicone oil is obtained; 1% of the magnetic adsorbent can effectively capture and remove most of the ring, and control the volatile component to remove small molecules.

[0065] Example 2 (catalyst 0.5%, neutralizer 0.4%) viscosity 395 mPa·s, volatile 0.19%, ring content 190 ppm; The amount of catalyst is insufficient, the reaction time needs to be extended, which leads to too few initiation active sites, incomplete polymerization reaction, resulting in low molecular weight of the product and increased unreacted ring content; The amount of neutralizer is reduced accordingly, which directly affects the product performance.

[0066] Example 3 (catalyst 2%, neutralizer 2%) viscosity 427 mPa·s, volatile 0.16%, ring content 180 ppm; The amount of neutralizer is greatly increased, and the excess silicon phosphate becomes a new source of impurities, which interferes with the adsorption process and increases the ring content.

[0067] Example 4 (DMC 92%, crown ether 0.2%, capping agent 3.5%) viscosity 212 mPa·s, volatile 0.14%, ring content 176 ppm; The content of DMC is significantly reduced, which leads to insufficient monomer concentration in the reaction system, and the molecular weight distribution is widened; The relative proportion of non-reactive components increases, which will remain as impurities or small molecules; The concentration of capping agent is increased, the average molecular chain is reduced, and the viscosity is reduced; It shows that this process is suitable for low viscosity products.

[0068] Example 5 (DMC 97%, crown ether 0.8%, capping agent 0.35%) viscosity 10320 mPa·s, volatile 0.13%, ring content 168 ppm; High DMC content, the relative proportion of non-reactive components is reduced, the actual molar concentration in the reaction system is reduced, which leads to slow initiation and polymerization rate, incomplete reaction, and thus the ring content cannot be further reduced; High proportion of DMC dilutes functional additives, affecting reaction efficiency; The concentration of capping agent is reduced, the average molecular chain is increased, and the viscosity is increased; It shows that this process is suitable for high viscosity products.

[0069] Example 6 (low-temperature removal 200°C) viscosity 433 mPa-s, volatile 0.08%, ring content 94 ppm; increasing the low-temperature removal temperature, more low-molecular substances are removed, the product viscosity increases, and the ring content decreases.

[0070] Example 7 (low-temperature removal time 6h) viscosity 437 mPa-s, volatile 0.11%, ring content 109 ppm; extending the low-temperature removal time, more low-molecular substances are removed, the product viscosity increases, and the ring content decreases.

[0071] Example 8 (adsorbent 0.5%) viscosity 425 mPa-s, volatile 0.17%, ring content 195 ppm; the adsorbent dosage is insufficient, and it fails to provide sufficient surface area and inclusion sites to completely remove the rings in the system, resulting in a high ring content.

[0072] Example 9 (adsorbent 2%) viscosity 426 mPa-s, volatile 0.10%, ring content 113 ppm; increasing the adsorbent dosage increases the ring removal rate, but the cost increases.

[0073] Comparative Example 1 (step S1 without additional treatment of DMC) viscosity 410 mPa-s, volatile 0.25%, ring content 303 ppm; without treatment of DMC, impurities in DMC are not removed, affecting the degree of polymerization reaction, and the end-capping group causes molecular chain degradation and recombination at high temperatures, resulting in an increased ring content.

[0074] Comparative Example 2 (low-temperature removal temperature in step S3 is 150°C) viscosity 386 mPa-s, volatile 0.77%, ring content 936 ppm; the low-temperature removal temperature is too low, and small-molecule rings are difficult to be completely removed, making it difficult to reduce the volatile content.

[0075] Comparative Example 3 (directly adding 30 ppm of phosphazene base catalyst and 20 ppm of phosphoric acid for neutralization in step S3) viscosity 421 mPa-s, volatile 0.24%, ring content 266 ppm; when the catalyst and neutralizer are not used to form a copolymer with siloxane, they are difficult to completely dissolve with DMC at once, and the reaction speed is slow. The phosphoric acid silicate is more efficient than directly using phosphoric acid for neutralization.

[0076] Comparative Example 4 (without adding Fe3O4-β-cyclodextrin for adsorption in step S4) viscosity 417 mPa-s, volatile 0.29%, ring content 330 ppm; lacking an adsorbent, a large amount of rings and small-molecule oligomers remain in the product, resulting in a reduced viscosity. The low-temperature removal in S3 can only remove most of the volatile and rings with low boiling points, and cannot reduce the ring content to a very low level. Lacking the adsorption step, the remaining rings and small-molecule substances remain in the final product.

[0077] Comparative Example 5 (adsorption with 1% β-cyclodextrin added alone in step S4) viscosity 422 mPa-s, volatile matter 0.22%, ring content 254 ppm; when only cyclodextrin adsorption treatment is used, it is difficult to separate the silicone oil system efficiently due to solubility limitations. Cyclodextrin does not have a hydrophobic cavity of composite material, and the adsorption amount of ring is reduced, and the recycling efficiency is reduced.

Claims

1. A silicone oil with low cyclic content, characterized in that, The silicone oil contains the following components by mass fraction: DMC 92-97%, crown ether 0.2-0.8%, phosphazene alkaline silanol catalyst 0.5-2%, phosphate silicone ester neutralizer 0.4-2%, and divinyltetramethyldisiloxane 0.35-3.5%.

2. The low-cyclic silicone oil according to claim 1, characterized in that, The silicone oil contains the following components by mass fraction: DMC 95-96.5%, crown ether 0.4-0.6%, phosphazene alkaline silanol catalyst 0.8-1.5%, phosphate silicone ester neutralizer 0.5-1%, and divinyltetramethyldisiloxane 1-3%.

3. The low-cyclic silicone oil according to claim 1 or 2, characterized in that, The volatile content of the silicone oil is <0.2% (150℃ for 3h), and the cyclic content (D3-D10) is <200ppm.

4. The low-cyclic silicone oil according to claim 1 or 2, characterized in that, The mass ratio of phosphazene base to methyl silicone oil in the phosphazene base silanol catalyst is (0.5-2):

100.

5. The low-cyclic silicone oil according to claim 1 or 2, characterized in that, The mass ratio of phosphoric acid to methyl silicone oil in the phosphate silicate neutralizer is (0.2-1):

100.

6. The low-cyclic silicone oil according to claim 1 or 2, characterized in that, The crown ether is one or both of 15-crown ether-5 and 18-crown ether-6.

7. A method for preparing a low-cyclic-content silicone oil according to any one of claims 1-6, characterized in that, Includes the following steps: S1, Divinyltetramethyldisiloxane is purified by passing it through a directional molecular sieve column; crown ether and isopropanol are added to DMC for separation and washing, followed by vacuum dehydration; S2, respectively synthesized phosphazene alkaline silanol catalyst and phosphate silicon ester neutralizer; S3, add pretreated divinyltetramethyldisiloxane and phosphazene alkaline silanol catalyst to dehydrated DMC, introduce N2 and equilibrate the reaction at 60~100℃ for 2~6h, add phosphate silicon ester neutralizer, stir and filter, introduce N2 and heat to 170~220℃, pressure -0.099~ -0.1MPa for dehydration for 3-8h; S4, cool down and add Fe3O4-β-cyclodextrin, stir to adsorb the cyclic compounds for 2-6 hours, and filter to obtain a silicone oil product with low cyclic compound content.

8. The method for preparing low-cyclic silicone oil according to claim 7, characterized in that, The preparation method of the phosphazene alkali silanolate catalyst in step S2 is as follows: methyl silicone oil and phosphazene alkali are mixed and stirred, and reacted at 80~120℃ under N2 protection for 4~8h until the system is clear. The catalyst is then degraded under vacuum at 100~120℃ for 10~60min to obtain the phosphazene alkali silanolate catalyst.

9. The method for preparing low-cyclic silicone oil according to claim 7, characterized in that, The preparation method of the phosphate silicon ester neutralizer in step S2 is as follows: methyl silicone oil and phosphoric acid are mixed and stirred, and reacted at 100~140℃ under N2 protection for 2~6 hours until the system is clear. The mixture is then degraded under vacuum at 100~140℃ for 10~60 minutes to obtain the phosphate silicon ester neutralizer.

10. The method for preparing low-cyclic silicone oil according to claim 7, characterized in that, In step S4, the amount of Fe3O4-β-cyclodextrin added is 0.5-2% of the product.