I. Chemical Structural Characteristics
‌Basic Molecular Structure‌
The backbone of phenyl silicone consists of silicon-oxygen bonds (Si-O-Si), with phenyl groups (C₆H₅-) attached to the side chains. Its structural unit can be represented as PhSiO₃/₂ (phenyl T-type unit), with the general molecular formula being (C₆H₅SiO₃/₂)ₙ, where n represents the degree of polymerization.

‌Low-phenyl silicone rubber‌: Phenyl content is 5%-10% (phenyl to silicon atom ratio), partially disrupting structural regularity and significantly lowering crystallization temperature.
‌Medium-phenyl silicone rubber‌: Phenyl content is 10%-20%, enhancing molecular chain rigidity.
‌High-phenyl silicone rubber‌: Phenyl content is 30% or more, and the backbone contains phenylsiloxane or methylphenylsiloxane segments.
‌Influence of Structural Differences‌: The introduction of phenyl groups disrupts the regularity of the silicone molecules, resulting in reduced crystallinity and imparting unique cold resistance to the material. A higher phenyl content increases molecular rigidity and radiation resistance, but also reduces cold resistance.

II. Performance Characteristics
Physical Properties
Mechanical Properties: Density 1.1-1.3 g/cm³, Hardness 30-80 Shore A, Tensile Strength 5-12 MPa, Elongation at Break 150%-500%.
Temperature Resistance: -110°C to 300°C. Low-phenyl silicone rubber maintains elasticity at -115°C, offering the best low-temperature performance among all rubbers.
Other Properties: Less hydrophobic than methylated silicone rubber, but with higher thermal stability.
Chemical Properties
Environmental Resistance: It exhibits aging resistance, moisture resistance, and electrical insulation, with radiation resistance 5-15 times that of ordinary silicone rubber.
Special Features:
Medium-phenyl silicone rubber is self-extinguishing (it extinguishes itself if caught).
High-phenyl silicone rubber exhibits excellent radiation resistance and is suitable for use as a spacecraft sealing material.

III. Mechanisms of the Correlation Between Molecular Composition and Performance
‌The Role of Phenyl Groups‌
‌Reducing Crystallinity‌: The steric hindrance of phenyl groups disrupts the regular arrangement of the molecular chain, inhibiting crystallization and thus improving cold resistance (for example, the glass transition temperature of low-phenyl silicone rubber is as low as -115°C).
‌Enhancing Rigidity‌: Increasing the phenyl content increases molecular chain rigidity, improving radiation resistance and flame resistance, but excessive increases can compromise low-temperature elasticity.
‌Application-Driven Design‌
‌Low-Temperature-Resistant Applications‌: Low-phenyl silicone rubber is preferred (e.g., seals for polar equipment).
‌Radiation-Resistant Applications‌: High-phenyl silicone rubber is selected (e.g., nuclear industry or aerospace components).

IV. Summary
The performance of phenyl silicone is highly dependent on its phenyl content and molecular structure design. By manipulating the phenyl content, the material's cold resistance, radiation resistance, or flame retardancy can be optimized to meet the extreme environmental requirements of aerospace, electronics, and other fields. However, a high phenyl content can lead to processing difficulties and reduced mechanical properties, requiring a trade-off in practical applications.