It is currently difficult to directly provide a temperature resistance-viscosity index relationship graph of silicone oils with different phenyl mole fractions, but the relationship can be analyzed in combination with relevant information. Generally speaking, as the phenyl mole fraction increases, the temperature resistance of silicone oil increases, and the viscosity index may decrease first and then remain stable. The following is a specific analysis:

Relationship between phenyl mole fraction and temperature resistance
The phenyl mole fraction reflects the degree of phenyl substitution for methyl in silicone oil molecules. The introduction of phenyl will destroy the symmetry of polysiloxane molecules, thereby changing the physical and chemical properties of silicone oil. Generally speaking, with the increase of phenyl mole fraction, the high temperature resistance of silicone oil is significantly improved. For example, high molar mass methylphenyl silicone oil can work stably at 250℃ in air for hundreds of hours, can withstand temperatures of 250~300℃ for several months in a closed system, and can withstand short-term high temperatures of 450℃. In inert gas, methylphenyl silicone oil can even be used at 400℃.

Relationship between phenyl mole fraction and viscosity index
The viscosity index is an indicator to measure the sensitivity of lubricating oil viscosity to temperature changes. The higher the viscosity index, the smaller the viscosity change with temperature, that is, the better the viscosity-temperature performance. However, although the introduction of phenyl improves the temperature resistance of silicone oil, it may also have a certain impact on the viscosity index. Studies have shown that the viscosity index of phenyl-modified silicone oil decreases with the increase of phenyl content. This is because the rigid benzene ring has a stronger shielding effect than the methyl group, thereby reducing the intermolecular force and causing the product's viscosity-temperature performance to deteriorate. But even so, the minimum viscosity index of phenyl-modified silicone oil is much greater than the viscosity index of super-high viscosity index lubricating oil (viscosity index greater than 110), indicating that the silicone oil grafted with phenyl still has excellent viscosity-temperature performance, and the viscosity is less affected by temperature changes.

Prediction of the temperature resistance-viscosity index relationship graph
Based on the above analysis, it can be inferred that the temperature resistance-viscosity index relationship graph of silicone oils with different phenyl mole fractions may show the following trend: as the phenyl mole fraction increases, the temperature resistance of the silicone oil gradually increases, while the viscosity index may first decrease slightly and then stabilize. This is because the introduction of phenyl groups may have a certain effect on the intermolecular force while improving the temperature resistance, thereby reducing the viscosity index. However, as the phenyl mole fraction further increases, this effect may gradually weaken, and the viscosity index tends to stabilize.