Phenyl content has a significant effect on the low temperature performance of silicone (especially silicone rubber). This effect mainly stems from the destruction of the regularity of the dimethylsiloxane structure after the introduction of phenyl into the polysiloxane side group, which in turn affects the crystallization temperature and low temperature application range of the polymer. The following is a detailed analysis of the effect of phenyl content on the low temperature performance of silicone:

1. Classification of phenyl content and low temperature performance
Low phenyl silicone rubber:
When the phenyl content is 5%~10%, it is called low phenyl silicone rubber.
It has unique cold resistance and can still maintain the elasticity of rubber at low temperatures of -70℃~-100℃. It is the best low temperature performance among all rubbers. This type of silicone rubber is particularly suitable for occasions that require low temperature resistance, such as cold-resistant rubber in aerospace industry, cutting-edge technology, and aviation industry, as well as seals in the fields of construction, electronic appliances, automobiles, and industrial deep refrigeration.

Medium phenyl silicone rubber:
When the phenyl content is 20%~40%, it is called medium phenyl silicone rubber.
Compared with low-phenyl silicone rubber, its low-temperature resistance has decreased, but it has better flame retardancy and can self-extinguish once it catches fire. This type of silicone rubber is suitable for occasions that require flame retardancy, and also retains low-temperature resistance to a certain extent.

High-phenyl silicone rubber:
When the phenyl content is 40%~50%, it is called high-phenyl silicone rubber. The low-temperature resistance is further reduced, but it has excellent radiation resistance and significant gamma ray resistance. This type of silicone rubber is mainly used in occasions that require radiation resistance, such as nuclear industry, aerospace and other fields.

2. The mechanism of the influence of phenyl content on low-temperature performance
Changes in crystallization temperature:
The introduction of phenyl destroys the regularity of the dimethylsiloxane structure and greatly reduces the crystallization temperature of the polymer, thereby expanding the low-temperature application range of silicone. With the increase of phenyl content, the crystallization temperature of the polymer is further reduced, but the elastic modulus at low temperature will also increase accordingly, resulting in a gradual decrease in low-temperature resistance.

Changes in molecular chain rigidity:
The increase in phenyl content will cause the rigidity of the silicone rubber molecular chain to gradually increase. Molecular chains with increased rigidity are more difficult to move at low temperatures, thereby affecting the low-temperature elasticity and cold resistance of silicone.

In summary, the phenyl content has a significant effect on the low-temperature performance of silicone. Low-phenyl silicone rubber has the best low-temperature resistance and is suitable for extremely cold environments; while medium-phenyl and high-phenyl silicone rubbers perform well in flame resistance and radiation resistance, but their low-temperature resistance is relatively weak. Therefore, when selecting silicone materials, it is necessary to reasonably select the phenyl content according to the specific application environment and performance requirements.