Polyphenylsiloxane (usually belongs to the same category of phenyl silicone oil as methylphenyl silicone oil, and here it represents a high-performance variant of phenyl silicone oil) and methylphenyl silicone oil need to be selected in combination with specific application scenarios in the temperature resistance-cost trade-off. The following is a detailed analysis:

Heat resistance
Methylphenyl silicone oil: Methylphenyl silicone oil has good stability in high temperature environments. High molar mass methylphenyl silicone oil can work stably at 250°C in air for hundreds of hours, can withstand temperatures of 250-300°C for several months in a closed system, and can withstand short-term high temperatures of 450°C. In inert gas, methylphenyl silicone oil can even be used at 400°C.
Polyphenylsiloxane: Generally speaking, polyphenylsiloxane may have a higher phenyl content, its thermal stability may be further enhanced, and it can withstand higher temperatures, but the specific temperature resistance data needs to be determined according to the product specifications. For example, some high-performance phenyl silicone oil products can operate at temperatures as low as -70℃ and as high as 320℃, and can continue to function in extreme environments.

Cost factors
Methylphenyl silicone oil: The production process of methylphenyl silicone oil is relatively mature, the cost is relatively low, and it has good price competitiveness in the market. Its price may vary depending on factors such as brand, specification, and purchase quantity, but in general, for some application scenarios that are more cost-sensitive and have certain temperature resistance requirements, methylphenyl silicone oil is a more economical choice.
Polyphenylsiloxane: Since polyphenylsiloxane may have a higher phenyl content and better performance, its production process may be more complicated and the cost of raw materials may be higher, so the product price is relatively expensive. However, its high performance may bring longer service life and better use effect, which may reduce the overall use cost in the long run.

Trade-off recommendations
Applications with extremely high temperature resistance requirements and sufficient budget: If the application scenario has extremely high requirements for temperature resistance, such as aerospace, high-end electronic equipment, etc., and the budget allows, polyphenylsiloxane may be a better choice. Although its cost is relatively high, its excellent temperature resistance and stability can ensure the reliable operation of equipment in extremely high temperature environments, reducing equipment failures and maintenance costs caused by lubrication failure.

Applications with certain requirements for temperature resistance and cost sensitivity: For some applications that have certain requirements for temperature resistance but cost is an important consideration, such as some common industrial equipment lubrication, protection of electronic components in medium and low temperature environments, methylphenyl silicone oil is a more suitable choice. It can effectively control costs while meeting basic temperature resistance requirements.