Methylphenyl silicone oil, also known as phenyl silicone oil, is synthesized by replacing some of the methyl groups in the methyl silicone oil molecule with phenyl groups. Its chemical structure mainly has the following two types: R1 and R2 are methyl or phenyl groups.
Synthesis of methylphenyl silicone oil
There are two main synthetic routes in industry:
Method I: Synthesize by catalytic equilibrium polymerization of methyl D4 and MDnM using the hydrolysis products of methylphenyl cyclosiloxane or methylphenyl dialkoxysilane.
Method II: First, co-hydrolyze diphenyldichlorosilane and dimethyldialkylsilane, and then catalytic equilibrium polymerization of the obtained hydrolysis products with methyl D4 and MDnM.
Characteristics of phenyl silicone oil
Viscosity-temperature coefficient: Higher, which means that its viscosity is less sensitive to temperature changes.
Freezing point and flash point: Lower, which enhances its performance in low temperature environments.
Compression resistance: Lower than methyl silicone oil, but the viscosity changes faster under pressure.
Oxidation stability and radiation resistance: Higher than methyl silicone oil, suitable for use in harsh environments.
Effect of phenyl content:
With the increase of phenyl content, the specific gravity and refractive index of silicone oil increase.
Silicone oil with low phenyl content (such as silicone oil containing 5% mole fraction of phenyl) has lower crystallization performance and freezing point, which can reach about -70℃, and is suitable for ultra-low temperature applications.
Thermal stability and radiation resistance:
The physical properties of silicone oil with medium and high phenyl content remain basically unchanged after heating at 250℃ for thousands of hours, showing excellent thermal stability.
These silicone oils can still be used after receiving radiation doses up to 2×108R at room temperature, showing good radiation resistance.
Lubricating properties:
Methyl phenyl silicone oil has better lubricating properties than methyl silicone oil and is suitable as a lubricant at high temperatures (such as 200℃), but the demolding effect is relatively poor.
Organic compatibility:
Methyl phenyl silicone oil has better organic compatibility than methyl silicone oil and can be mixed with vegetable oil, animal oil and mineral oil.
Ultra-high vacuum diffusion pump oil:
Low-viscosity methyl phenyl silicone oil is suitable for ultra-high vacuum diffusion pump oil, which requires high thermal stability and oxidation stability, as well as low vapor pressure at cooling temperature.
Compared with other types of high vacuum diffusion pump oils such as silicone oil, polyphenylene ether, and perfluoropolyether, methylphenyl silicone oil has a steeper vapor pressure/temperature curve, lower vapor pressure and freezing point, and excellent heat resistance and oxidation resistance.
Even at low temperatures, the viscosity of methylphenyl silicone oil changes little, and it is non-toxic, non-corrosive, and chemically stable. It is an ideal high vacuum diffusion pump oil.
Methylphenyl silicone oil has a long service life and can be used for a long time (more than 103 hours) at 250°C. It can be used at higher temperatures in a vacuum environment.
There are many brands of methylphenyl silicone oil circulating on the market, including 250, 255, 275, etc.
