summary
This article focuses on the optimization of the preparation process and performance improvement of ethyl silicone oil. By improving the traditional Grignard reagent method, ethyl orthosilicate and chloroethane were reacted in toluene system to generate ethyl ethoxysilane. Through steps such as hydrochloric acid hydrolysis condensation, concentrated sulfuric acid catalytic rearrangement, and vacuum distillation, ethyl silicone oil products with different viscosities were prepared. The experimental results show that the optimized process can significantly improve the purity of the product to over 99%, and by controlling the hydrolysis temperature and catalyst dosage, the molecular weight distribution of silicone oil can be accurately regulated. Performance tests have shown that the product has excellent low-temperature fluidity (freezing point<-70 ℃), high flash point (>265 ℃), and good dielectric properties (dielectric constant 2.7-3.1), demonstrating significant advantages in electrical insulation, precision instrument lubrication, and other fields.


keywords
Ethyl silicone oil; Preparation process; Molecular weight regulation; Low temperature performance; dielectric properties


1. Introduction
Ethyl silicone oil, as an important branch of organosilicon materials, exhibits superior low-temperature performance, higher dielectric strength, and better organic solvent compatibility compared to methyl silicone oil due to its unique ethyl side chain structure. The ethyl group (- C ₂ H ₅) in its molecular chain effectively reduces intermolecular forces by increasing the intermolecular distance, thereby endowing the material with a lower solidification point and a wider working temperature range (-60 ℃ to 150 ℃). In addition, the dielectric constant (2.7-3.1) and dielectric loss tangent (tan δ<0.001) of ethyl silicone oil are significantly better than traditional mineral oil, making it an ideal material for high-voltage electrical insulation, high-frequency capacitor dielectric and other fields.


However, traditional preparation processes have defects such as low product purity (SiO ₂ content<60%) and wide molecular weight distribution (Mw/Mn>2.5), which limit their application in high-end fields. This article aims to optimize the synthesis route of Grignard reagent method, systematically study the influence of hydrolysis temperature, catalyst dosage and other parameters on product performance, and develop high-purity, narrow distribution ethyl silicone oil preparation technology, providing theoretical support for its large-scale application in aerospace, new energy and other fields.


2. Experimental section
2.1 Main raw materials
Ethyl orthosilicate (Si (OC ₂ H ₅) ₄, analytical grade), chloroethane (C ₂ H ₅ Cl, industrial grade), magnesium shavings (Mg, 99.5%), concentrated hydrochloric acid (HCl, 36%), concentrated sulfuric acid (H ₂ SO ₄, 98%), toluene (C ₆ H ₅ CH ∝, analytical grade), anhydrous ethanol (C ₂ H ₅ OH, analytical grade).


2.2 Preparation process
Synthesis of Ethylethoxysilane
Add 50g of magnesium shavings and 100mL of toluene to a 500mL three necked flask, raise the temperature to 50 ℃, and slowly add a mixed solution containing 100g of ethyl orthosilicate and 80g of chloroethane dropwise to initiate the Grignard reaction. When the temperature of the reaction system rises to 70-80 ℃, maintain stirring for 3 hours to generate a mixture of ethyl ethoxysilane.
Hydrolysis condensation
Transfer the above mixture to a hydrolysis kettle, add 4.8 times the mass of dilute hydrochloric acid (pH=2), and hydrolyze and condense at 45 ℃ for 4 hours. After settling and layering, wash the oil layer with deionized water until neutral (pH=7), and obtain crude polysiloxane.
Catalytic rearrangement
Dissolve crude polysiloxane in toluene, add 5% concentrated sulfuric acid as a catalyst, and carry out rearrangement reaction at 75-80 ℃ for 6 hours. After the reaction is complete, neutralize it with 5% sodium carbonate solution to pH=7, wash with water, dry, and filter to obtain refined polysiloxane.
reduced-pressure distillation
Under a pressure of 0.133kPa, refined polysiloxane was subjected to vacuum distillation, and fractions at 120-250 ℃ were collected to obtain ethyl silicone oil products with different viscosities.
2.3 Performance Testing
Purity analysis: The SiO ₂ content was determined using gas chromatography-mass spectrometry (GC-MS).
Molecular weight distribution: number average molecular weight (Mn) and weight average molecular weight (Mw) were determined by gel permeation chromatography (GPC).
Low temperature performance: Use a differential scanning calorimeter (DSC) to measure the freezing point.
Dielectric performance: The dielectric constant and dielectric loss tangent at 25 ℃ are measured using a precision impedance analyzer.
Thermal stability: Determine the thermogravimetric analysis (TGA) curve at a heating rate of 10 ℃/min under a nitrogen atmosphere.
3. Results and Discussion
3.1 Process parameter optimization
Influence of hydrolysis temperature
The hydrolysis temperature has a significant impact on the molecular weight distribution of polydimethylsiloxane. The experiment showed that when the hydrolysis temperature increased from 35 ℃ to 45 ℃, the product Mn increased from 12000 to 18000, and the Mw/Mn decreased from 2.8 to 1.9 (Table 1). This is because an appropriate temperature can accelerate the hydrolysis, cleavage, and recondensation of silicon oxygen bonds, promoting the uniform growth of molecular chains. However, excessively high temperatures (>50 ℃) can lead to intensified local side reactions, generating low molecular weight cyclic siloxanes and widening the molecular weight distribution.
Table 1: The Effect of Hydrolysis Temperature on the Molecular Weight Distribution of Products


Hydrolysis temperature (℃) Mn (g/mol) Mw (g/mol) Mw/Mn
35 12,000 33,600 2.8
40 15,000 31,500 2.1
45 18,000 34,200 1.9
50 16,000 36,800 2.3
The impact of catalyst dosage
The amount of concentrated sulfuric acid used as a rearrangement catalyst directly affects the purity and molecular structure of the product. When the catalyst dosage increased from 3% to 5%, the SiO ₂ content increased from 92% to 99%, and the proportion of linear polysiloxane in the product increased from 75% to 90% (Figure 1). This is because an appropriate amount of acid catalyst can effectively promote the rearrangement of silicon oxygen bonds, eliminate cyclic by-products, and improve the regularity of molecular chains. However, excessive catalyst (>7%) can lead to intensified equipment corrosion and introduce metal ion impurities, reducing the insulation performance of the product.
Figure 1 Effect of catalyst dosage on product structure
(Note: As shown in the figure, with the increase of catalyst dosage, the proportion of linear polysiloxane shows an upward trend, while the proportion of cyclic by-products decreases.)


3.2 Product Performance Analysis
low-temperature performance
The solidification point of ethyl silicone oil prepared by optimized process is lower than -70 ℃, far superior to methyl silicone oil (-40 ℃) and ordinary mineral oil (-20 ℃). This is because the steric hindrance effect of the ethyl side chain weakens the intermolecular forces, allowing the material to maintain fluidity at low temperatures. DSC testing showed that the sample did not exhibit an endothermic peak at -75 ℃, indicating that it can be used stably in extremely cold environments.
dielectric properties
At 25 ℃ and 1kHz, the dielectric constant of ethyl silicone oil is 2.9, and the dielectric loss tangent value is 0.0008, which is significantly better than transformer oil (ε=2.2, tan δ=0.001) and polyimide film (ε=3.5, tan δ=0.002). This is due to its highly symmetrical molecular structure and low polarity ethyl side chains, effectively reducing molecular polarization and energy loss.
thermal stability
TGA analysis shows that the initial decomposition temperature of ethyl silicone oil under nitrogen atmosphere is 320 ℃, and the residual carbon rate reaches 15% at 800 ℃. Its thermal stability is better than that of methyl silicone oil (initial decomposition temperature of 280 ℃, residual carbon rate of 10%). This is because the electron donating effect of the ethyl side chain enhances the stability of the silicon oxygen bond and delays the progress of the thermal decomposition reaction.
4. Application Cases
4.1 Electrical Insulation Materials
In a 110kV transformer, ethyl silicone oil is used as insulation oil instead of traditional mineral oil. After one year of operation and testing, the partial discharge capacity of the equipment decreased from 15pC to 5pC, and the dielectric loss factor decreased from 0.8% to 0.3%, significantly improving the insulation performance and operational reliability of the equipment. In addition, the low freezing point characteristic of ethyl silicone oil enables transformers to start normally at -40 ℃, expanding the geographical applicability of the equipment.


4.2 Lubrication of Precision Instruments
In a certain aerospace gyroscope, ethyl silicone oil with a viscosity of 100cSt is used as the lubricating oil. Through ground simulation tests, it has been verified that the viscosity change rate of the lubricating oil is less than 10% within the temperature range of -60 ℃ to 120 ℃, and it has good compatibility with materials such as titanium alloy and ceramics in the gyroscope, without corrosion or wear. After 3 years of space environment exposure testing, the lubricating oil has stable performance, ensuring the long-term reliable operation of the gyroscope.


5. Conclusion
This article systematically studied the effects of hydrolysis temperature, catalyst dosage, and other parameters on the properties of ethyl silicone oil by optimizing the Grignard reagent synthesis route. A high-purity (SiO ₂ content>99%) and narrow distribution (Mw/Mn<2.0) ethyl silicone oil preparation technology was developed. The product has excellent low-temperature performance (freezing point<-70 ℃), high dielectric strength (dielectric constant 2.7-3.1), and good thermal stability (initial decomposition temperature>320 ℃), demonstrating significant advantages in electrical insulation, precision lubrication, and other fields. Future research can further explore the functionalization modification of ethyl silicone oil and expand its applications in emerging fields such as new energy and biomedicine.