Preparation method of methoxy hydroxyl-terminated silicone oil

Abstract

The invention provides a preparation method of methoxy hydroxyl-terminated silicone oil, which is mainly applied to a structure control agent in the field of silicone rubber, and comprises the following steps: by taking hydrolysate (a mixture of dimethyl cyclosiloxane and hydroxyl-terminated polydimethylsiloxane linear body) as a raw material, adding a basic catalyst under the protection of inert gas, adding an end-capping reagent a: a methanol solution, and reacting at the temperature of 60-80 DEG C for 1-2 hours; the preparation method comprises the following steps: adding an end-capping reagent b, namely water or alkoxy silane, into a reaction kettle, carrying out reflux reaction at 50-80 DEG C, adding an end-capping reagent b, namely water or alkoxy silane after the viscosity of the material is stable, reacting for 0.5 hour, filtering to remove the catalyst, and removing the catalyst to obtain the hydroxyl methoxy-terminated polydimethylsiloxane. The hydroxyl-methoxyl mixed end-capped polydimethylsiloxane prepared by the method has the advantages of high flash point, good safety performance and strong tear resistance, the molecular weight of the hydroxyl-methoxyl mixed end-capped polydimethylsiloxane is several times larger than that of dimethyldimethoxysilane, but the content of active groups of the hydroxyl-methoxyl mixed end-capped polydimethylsiloxane is equivalent to that of hydroxyl silicone oil. Therefore, redundant water molecules are not generated in the anti-structuring process, so that the structural stability of the sizing material is improved.

Description

Technical Field

[0001] The invention belongs to the technical field of chemical industry, and in particular relates to a method for preparing methoxyhydroxyl-terminated silicone oil, which is mainly used in the field of structure control agents for silicone rubber. Background Art

[0002] The structure control agent mainly plays an anti-structural role, making the prepared rubber material have good stiffness and excellent process performance during re-refining and molding. At present, the commonly used structure control agents for silicone rubber products are hydroxy silicone oil and alkoxy silicone oil. The main function of the structure control agent is to inhibit the formation of hydrogen bonds between particles by interacting with the Si-OH group on the surface of silica, while also improving the storage stability of silicone rubber. Alkoxy silicone oil is usually used in combination with hydroxy silicone oil. The structure control agents on the market mainly include three categories: high-hydroxyl content hydroxy silicone oil, low-hydroxyl content hydroxy silicone oil and methoxy silicone oil. The market share of methoxy silicone oil is gradually increasing, and in 2023, it will account for nearly 40% of the structure control agents.

[0003] When preparing high temperature vulcanized silicone rubber, during the storage of the rubber, the silanol groups on the surface of the white carbon black and the siloxy groups or terminal hydroxyl groups in the raw rubber molecules will react to form hydrogen bonds or chemical bonds, causing the linear polysiloxane to be transformed into a pseudo-crosslinked semi-elastic solid structure, resulting in an increase in the gel content, which causes the silicone rubber to slowly harden during storage, reduce plasticity, and gradually lose the process performance of re-refining and molding. This phenomenon is the structuring of the rubber. After adding the structure control agent, the hydrogen bonding of the rubber can be reduced, and the degree of structuring of the rubber can be reduced.

[0004] Hydroxy silicone oil, diphenylsilanediol or dimethyldimethoxysilane can all be used as structure control agents, but diphenylsilanediol and dimethyldimethoxysilane have extremely low flash points and are not easy to transport and store. Adding too much hydroxy silicone oil to the rubber will cause the rubber to feel sticky and the vulcanization speed to be slow. During the mixing process of raw rubber and white carbon black, the methoxy-terminated silicone oil reacts with the Si-OH of white carbon black to release methanol, thereby improving the affinity between rubber ions and filler ions, reducing the formation of hydrogen bonds, improving the dispersion of fillers in the rubber, improving the mixing process and storage stability, and preventing and weakening the structuring phenomenon; at the same time, the released methanol is easily discharged to the outside of the rubber, which does not affect the transparency of the rubber, makes the rubber dry, and does not affect the electrical insulation performance, etc. However, compared with hydroxy silicone oil, the number of re-refining times is longer, and the inhibitory effect on the structuring of silicone rubber is slightly weaker than that of hydroxy silicone oil.

[0005] Therefore, it is necessary to develop a low-cost, low-viscosity methoxyhydroxy-terminated polydimethylsiloxane to help solve the structuring problem in the preparation process of silicone rubber. Summary of the invention

[0006] In view of the above technical problems, the present invention provides a method for preparing methoxyhydroxyl-terminated silicone oil, which has the advantages of low viscosity, low cost, environmental protection and high flash point. The methoxyhydroxyl-terminated silicone oil is mainly used in the field of silicone rubber structure control agent. Based on the above problems, the present invention provides a methoxyhydroxyl-terminated silicone oil, the total content of methoxyl and hydroxyl is 8-15%, wherein the content ratio of methoxyl and hydroxyl is 1:0.1-10, and the viscosity is 5-30 mPa·s The content ratio of the methoxy group to the hydroxyl group is 1:0.5-2, and the viscosity is 10-30 mPa·s.

[0007] In some preferred embodiments, the methoxy hydroxy mixed oil is a mixture of compounds of the following structural formula: The total content of methoxy and hydroxyl groups is 8-15%, wherein the content ratio of methoxy and hydroxyl groups is 1:0.1-10, and the viscosity is 5-30 mPa·s.

[0008] The preparation method of the structure control agent comprises the following steps: (1) Mix the hydrolyzate and the end-capping agent methanol under the protection of an inert gas and stir them evenly; (2) adding an alkaline catalyst to step (1), heating and refluxing the mixture until the viscosity is stable, and then removing the unreacted methanol (no obvious methanol reflux on the inner wall), to obtain polysiloxane; (3) adding a capping agent b to the polysiloxane product of step (2), and adding a neutralizing agent to neutralize the reaction mixture after the viscosity of the reaction mixture stabilizes; (4) The neutralized material is deionized to obtain methoxyhydroxyl-terminated silicone oil.

[0009] The hydrolyzate is a mixture of dimethylcyclosiloxane and hydroxyl-terminated polydimethylsiloxane, wherein the content of dimethylcyclosiloxane is ≥60%, and the viscosity of the hydrolyzate is within the range of 20-30 mPa·s.

[0010] Preferably, the added mass of the end-capping agent methanol in step (1) is less than 10-35wt% of the mass fraction of the hydrolyzate, and the blending speed is 100-300rpm.

[0011] Further preferably, the alkaline catalyst is any one of KOH alcohol solution, KOH alkaline gel, NaOH alcohol solution, NaOH alkaline gel or tetramethylammonium hydroxide alkaline gel; the alcohol is methanol or ethanol; and the amount of the catalyst is 0.1% to 0.5 wt % of the hydrolyzate.

[0012] The reflux reaction temperature is 50-80°C, and the reaction is terminated when the viscosity is stable.

[0013] Further preferably, the dehumidification conditions are 60°C, -0.1 to -0.5 MPa, until there are no obvious droplets on the bottle wall.

[0014] Preferably, in step (3), the end-capping agent b is water or dimethyldimethoxysilane, and the amount of the end-capping agent b is 0-20wt% of the polysiloxane; the reaction is completed at a temperature of 50-80°C until the viscosity becomes stable and unchanged; and the blending speed is 100-300rpm.

[0015] The neutralizing agent is any one of linear silicon-based phosphate and alcohol solution of phosphoric acid, and the alcohol is methanol or ethanol.

[0016] Preferably, the degassing in step (5) includes negative pressure degassing and temperature degassing, wherein the negative pressure condition is to carry out the degassing at -0.1 to -0.5 MPa, and the temperature degassing is to carry out the degassing at 80-90°C.

[0017] Preferably, the total content of methoxyl group and hydroxyl group is 8-15%, wherein the content ratio of methoxyl group to hydroxyl group is 1:0.1-10, and the viscosity is 5-30 mPa·s.

[0018] The beneficial effects of the present invention are: 1. The methanol and low molecular weight products removed by the present invention do not need to be treated as waste and can be reused. No wastewater and pollutants are generated during the reaction, which is low-cost and environmentally friendly.

[0019] 2. The raw material used is hydrolyzate (a mixture of dimethylcyclosiloxane and hydroxyl-terminated polydimethylsiloxane linear body), which has a wide source and lower cost.

[0020] 3. The structure control agent obtained by the present invention is a mixed end-capped structure control agent, the main component of which is methoxyhydroxy mixed end-capped polydimethylsiloxane, which has the advantages of hydroxy silicone oil and methoxy silicone oil, and the ratio of hydroxyl and methoxy can be adjusted according to needs, thereby improving the processing performance and storage period of silicone rubber.

[0021] 4. The operation process of the present invention is not complicated, the reaction does not require high temperature and high pressure procedures, and the safety is high. DETAILED DESCRIPTION

[0022] The technical solution of the present invention is further explained below in conjunction with specific embodiments. It is worth noting that the following embodiments are only preferred embodiments of the present invention and should not be construed as limiting the present invention. The protection scope of the present invention shall be subject to the contents recorded in the claims. Any modification or replacement made by a person skilled in the art to the technical solution of the present invention without creative work shall fall within the protection scope of the present invention.

[0023] Example 1 Under the protection of inert gas, 200g of hydrolyzate (a mixture of dimethylcyclosiloxane and hydroxyl-terminated polydimethylsiloxane) and 40g of methanol are placed in a three-necked flask with a stirring and reflux device, and stirred evenly; 2g of 20% (m / m) KOH methanol solution is added, and the mixture is heated to 70°C, refluxed at this temperature, and after reacting for 5h, 2.8g of a methanol solution of a neutralizing agent H3PO4 is added, and the concentration is 20% (m / m). After neutralization for 0.5h, the material is placed at 85°C and -0.09MPa for degassing, and finally alkoxy hydroxyl-terminated silicone oil is obtained by filtration. The methoxy hydroxyl mixed silicone oil is a mixture formed by compounds of the following structural formula: .

[0024] The product viscosity is 20mPa·s, methoxy content: 5.0%; hydroxyl content: 3.2%.

[0025] Example 2 Under the protection of inert gas, 200g of hydrolyzate (a mixture of dimethylcyclosiloxane and hydroxyl-terminated polydimethylsiloxane) and 15g of methanol are placed in a three-necked flask with a stirring and reflux device, and stirred evenly; 1.5g of 20% (m / m) KOH methanol solution is added, and the mixture is heated to 70°C, refluxed at this temperature, and unreacted methanol is removed after 5h of reaction. The degassing conditions are 60°C, -0.8MPa, and the degassing time is 15min; the reaction is stopped and heated, and 60g of water is added and the reaction is continued for 0.5h. 2.1g of methanol solution of neutralizer H3PO4 is added, and the concentration is 20% (m / m). After neutralization for 0.5h, the material is placed at 85°C, -0.09MPa for degassing, and finally alkoxyhydroxy-terminated silicone oil is obtained by filtration. The methoxyhydroxy mixed silicone oil is a mixture formed by compounds of the following structural formula: .

[0026] The product viscosity is 28 mPa·s, hydroxyl content is 6.2% and methoxy content is 3.0%.

[0027] Example 3 Under the protection of inert gas, 200g of hydrolyzate (a mixture of dimethylcyclosiloxane and hydroxyl-terminated polydimethylsiloxane) and 30g of methanol are placed in a three-necked flask with a stirring and reflux device, and stirred evenly; 2g of 20% (m / m) KOH methanol solution is added, and the mixture is heated to 75°C, refluxed at this temperature, and the unreacted methanol is removed after 5 hours of reaction. The degassing conditions are 60°C, -0.8MPa, and the degassing time is 15min; after the system stops heating, 30g of water is added to continue the reaction for 0.5h. 2.8g of methanol solution of neutralizer H3PO4 is added, with a concentration of 20% (m / m). After neutralization for 0.5h, the material is placed at 85°C, -0.09MPa for degassing, and finally alkoxyhydroxy-terminated silicone oil is obtained by filtration. The methoxyhydroxy mixed silicone oil is a mixture formed by compounds of the following structural formula: .

[0028] The product viscosity is 25 mPa·s, hydroxyl content is 4.8% and methoxy content is 3.7%.

[0029] Example 4 Under the protection of inert gas, 200g of hydrolyzate (a mixture of dimethylcyclosiloxane and hydroxyl-terminated polydimethylsiloxane) and 30g of methanol are placed in a three-necked flask with a stirring and reflux device, and stirred evenly; 2g of 20% (m / m) KOH methanol solution is added, and the mixture is heated to 75°C, refluxed at this temperature, and the unreacted methanol is removed after 5 hours of reaction. The degassing conditions are 60°C, -0.8MPa, and the degassing time is 15min; after the system stops heating, 30g of water is added to continue the reaction for 0.5h. 5.6g of neutralizing agent silicon-based phosphate is added, and the concentration is 10% (m / m). After neutralization for 0.5h, the material is placed at 85°C, -0.09MPa for degassing, and finally methoxyhydroxy-terminated silicone oil is obtained by filtration. The methoxyhydroxy mixed silicone oil is a mixture formed by compounds of the following structural formula: .

[0030] The product viscosity is 22mPa·s, hydroxyl content: 4.5%; methoxy content: 4.0%.

[0031] Example 5 Under the protection of inert gas, 200g of hydrolyzate (a mixture of dimethylcyclosiloxane and hydroxyl-terminated polydimethylsiloxane) and 30g of methanol are placed in a three-necked flask with a stirring and reflux device, and stirred evenly; 2.5g of 20% (m / m) KOH methanol solution is added, and the mixture is heated to 65°C, refluxed at this temperature, and the unreacted methanol is removed after 4 hours of reaction. The degassing conditions are 60°C, -0.8MPa, and the degassing time is 15min; after the system stops heating, 30g of dimethyldimethoxysilane is added to continue the reaction for 0.5h. 3.5g of methanol solution of neutralizer H3PO4 is added, with a concentration of 20% (m / m). After neutralization for 0.5h, the material is placed at 85°C, -0.09MPa for degassing, and finally alkoxyhydroxy-terminated silicone oil is obtained by filtration. The methoxyhydroxy mixed silicone oil is a mixture formed by compounds of the following structural formula: .

[0032] The product viscosity is 7.5 mPa·s, hydroxyl content: 0.5%; methoxy content: 7.5%.

[0033] Comparative Example 1 Preparation of hydroxy silicone oil: 200g D3 (hexamethylcyclotrisiloxane), 150g acetone and 20g water are added to a 500 mL three-necked flask and mixed until a transparent homogeneous phase is obtained. 0.014g KOH is added and a ring-opening polymerization reaction is carried out at 45°C. Phosphoric acid is added and stirred for 30 minutes to make the pH value of the system reach 6 to 7. The temperature is raised to 80°C, and part of the acetone solvent is evaporated under normal pressure. After there is no fraction, the system temperature is lowered to 50°C and the vacuum pump is started to remove the remaining solvent. After dehydration by a high-speed centrifuge, low-viscosity hydroxy silicone oil is obtained. The structural formula of the hydroxy silicone oil is as follows: .

[0034] The product viscosity is 28cs and the hydroxyl content is 7.1%.

[0035] Comparative Example 2: Preparation of methoxy silicone oil: 400g of dehydrated DMC (dimethylsiloxane mixed ring body) and 100g of dimethyldimethoxysilane are placed in a three-necked flask with a stirring and reflux device, and stirred evenly; 1.2g of 10% (m / m) KOH methanol solution is added and reacted at 100°C. After reacting for 4h, degassing at the reaction temperature for 1h finally obtains low-viscosity methoxy silicone oil, the structural formula of which is as follows:

[0036] The product viscosity is 5.2cs and the methoxy content is about 10.5%.

[0037] Taking hydroxy silicone oil and methoxy silicone oil as comparative examples, the mixed rubber was prepared and evaluated together with Example 2. The evaluation indicators were mainly the number of re-refining, hardness, ML, MH, and tc90. The configuration ratios of the base rubber were: 140g of methyl vinyl silicone rubber; 70g of precipitated white carbon black; and 5g of structure control agent. The evaluation results are as follows:

[0038] The results show that (1) after adding methoxy silicone oil, the rubber has good stiffness and is not sticky; (2) the higher the hydroxyl content, the shorter the number of re-refining times of the sample, while the number of re-refining times of the methoxy silicone oil without hydroxyl is relatively long. In Example 3-4, methoxy and hydroxyl groups exist at the same time, and the hydroxyl content is not much different from the methoxy content, and the re-refining time is moderate. (3) ML: represents the fluidity of the rubber. The lower the ML, the better the fluidity; MH: characterizes the shear modulus, hardness, tensile strength and cross-linking density of the rubber. Generally, the higher the MH, the better the degree of cross-linking. The methoxy-hydroxyl-terminated silicone oil maintains good fluidity and hardness, and the vulcanization time is moderate.

[0039] The rubber compound with added hydroxy silicone oil has a shorter re-refining time, while the methoxy and hydroxyl mixed end-capping retains the advantages of both, with a better re-refining time and the rubber compound is not sticky.

Claims

1. A methoxyhydroxyl-terminated silicone oil, characterized in that: The total content of methoxyl group and hydroxyl group is 8-15%, wherein the content ratio of methoxyl group to hydroxyl group is 1:0.1-10, and the viscosity is 5-30 mPa·s.

2. The methoxyhydroxyl-terminated silicone oil according to claim 1, characterized in that The content ratio of methoxy group to hydroxyl group is 1:0.5-2, and the viscosity is 10-30 mPa·s.

3. The methoxyhydroxyl-terminated silicone oil according to claim 1, characterized in that The methoxy hydroxyl-terminated silicone oil is a mixture formed by the following structural formula: 、 。 4. The method for preparing the methoxyhydroxyl-terminated silicone oil according to any one of claims 1 to 3, characterized in that: The steps include: (1) Under the protection of inert gas, place the hydrolyzate and the end-capping agent methanol in a stirring and reflux device, mix and stir evenly; (2) adding an alkaline catalyst to step (1), heating and refluxing the mixture until the viscosity is stable, and then removing excess methanol (no obvious methanol reflux on the inner wall), to obtain polysiloxane; (3) adding a capping agent b to the polysiloxane product of step (2), and adding a neutralizing agent to neutralize the reaction mixture after the viscosity of the reaction mixture stabilizes; (4) The neutralized material is deionized to obtain methoxyhydroxyl-terminated silicone oil.

5. The method for preparing the methoxyhydroxyl-terminated silicone oil according to claim 4, characterized in that: The hydrolyzate is a mixture of dimethylcyclosiloxane and hydroxyl-terminated polydimethylsiloxane, wherein the content of dimethylcyclosiloxane is ≥60%, and the viscosity of the hydrolyzate is within the range of 20-30 mPa·s.

6. The method for preparing the methoxyhydroxyl-terminated silicone oil according to claim 4, characterized in that: The end-capping agent methanol described in step (1) is used in an amount of 10-35wt% of the amount of the hydrolyzate.

7. The method for preparing the methoxyhydroxyl-terminated silicone oil according to claim 4, characterized in that: The alkaline catalyst in step (2) is selected from any one of KOH alcohol solution, KOH alkaline gel, NaOH alcohol solution, NaOH alkaline gel or tetramethylammonium hydroxide alkaline gel; the alcohol is methanol; the amount of the catalyst is 0.1% to 0.5wt% of the hydrolyzate; The reflux reaction temperature is 50-80°C, and the reflux reaction is carried out until the viscosity becomes stable.

8. The method for preparing the methoxyhydroxyl-terminated silicone oil according to claim 4, characterized in that: In step (3), the end-capping agent b is water or dimethyldimethoxysilane, and the amount of the end-capping agent b is 0-20wt% of the polysiloxane; the reaction is carried out at a temperature of 50-80°C until the viscosity is stable; The neutralizing agent is any one of an alcohol solution of linear silicon-based phosphate and an alcohol solution of phosphoric acid, and the alcohol is methanol or ethanol.

9. The method for preparing a methoxyhydroxyl-terminated silicone oil according to claim 4, wherein: The dehydration includes negative pressure dehydration and temperature dehydration, wherein the negative pressure condition is to carry out dehydration at -0.1~-0.5MPa, and the temperature dehydration is to carry out dehydration at 80-90℃.

10. The method for preparing the methoxyhydroxyl-terminated silicone oil according to any one of claims 1 to 9, characterized in that: The total content of methoxyl group and hydroxyl group is 8-15%, wherein the content ratio of methoxyl group to hydroxyl group is 1:0.1-10, and the viscosity is 5-30 mPa·s.

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