The glass transition temperature (Tg) of phenyl vinyl silicone is affected by the phenyl content and is not a fixed value. The following is a summary based on information from different sources:

I. Overview of glass transition temperature of phenyl vinyl silicone
The relationship between phenyl content and Tg: Generally speaking, as the phenyl content increases, the glass transition temperature of phenyl silicone rubber increases. This is because the introduction of phenyl will destroy the regularity of the molecular chain, thereby affecting its physical properties.
Experimental data: Under specific experimental conditions (such as reaction time, catalyst dosage, reaction temperature, etc.), the glass transition temperature of the prepared phenyl silicone rubber may be between -120℃ and -110℃. But please note that this is only a rough range, and the actual value will vary depending on the specific formula and process conditions.

II. Specific experimental data
According to an article on the synthesis and performance research of methyl monophenyl vinyl silicone rubber (from mobile CNKI), it was found in the experiment that the glass transition temperature of phenyl silicone rubber increases with the increase of phenyl content. Among them, the glass transition temperature of dimethyl silicone rubber (MVQ) may be lower, while PVMQ with medium phenyl content may have a higher glass transition temperature. However, the article does not give a specific Tg value.
Another article about high temperature resistant silicone sealing strips mentioned that the glass transition temperature of low phenyl silicone rubber can reach -140℃. But please note that the "low phenyl silicone rubber" and "phenyl vinyl silicone" here may differ in phenyl content, so they cannot be directly equated.

In summary, the glass transition temperature of phenyl vinyl silicone is a complex parameter affected by many factors. Its specific value will vary depending on factors such as phenyl content, preparation process, and formula. Therefore, in actual applications, it is necessary to select suitable phenyl vinyl silicone products according to specific needs, and refer to its technical specifications or related test reports to obtain accurate glass transition temperature information.