I. Molecular Structure Characteristics
Main Chain Structure
Phenyl silicone consists of a polysiloxane backbone (-Si-O-Si-), with phenyl groups (-C₆H₅) introduced into the side chains to replace some methyl groups (-CH₃). The introduction of phenyl groups significantly improves the thermal stability and radiation resistance of the material through steric hindrance and π-electron conjugation.

Phenyl Content Classification
Low-phenyl silicone (phenyl content <10%): Retains the flexibility of methyl silicone and offers excellent low-temperature resistance (-120°C).
Medium-phenyl silicone (phenyl content 10%-30%): Balances temperature resistance (-100°C to 200°C) with mechanical strength.
High-phenyl silicone (phenyl content >30%): Offers outstanding high-temperature resistance (up to 250°C), but suffers from reduced low-temperature performance.

Cross-linked Structure
Through hydrosilylation or peroxide curing, a three-dimensional network is formed. The hydrophobicity of the phenyl group (contact angle >100°) imparts water and chemical resistance to the material.

II. Mechanism of Impact on Sealing Performance
Heat Resistance
The rigid structure of the phenyl group inhibits thermal motion of the main chain, resulting in a compression set of <15% at high temperatures (compared to >30% for conventional silicone), making it suitable for sealing in aerospace hydraulic systems.

Chemical Resistance
The high electron cloud density of the phenyl group improves resistance to acids, alkalis, and fuel oils, extending its service life in automotive oil seals by 3-5 times that of methyl silicone.

Low-Temperature Elasticity
Low-phenyl silicone maintains elasticity at -120°C (glass transition temperature <-150°C), making it suitable for liquefied natural gas (LNG) pipeline seals.

Radiation Resistance
The conjugated structure of the phenyl group absorbs gamma rays, resulting in a performance degradation of <10% for seals used in nuclear power plants at a radiation dose of 10⁶Gy.

III. Typical Application Comparison
Performance:                                               Low-Phenyl Silicone              Medium-Phenyl Silicone           High-Phenyl Silicone
Applicable Temperature Range:                          -120°C–150°C                        -100°C–200°C                     -50°C–250°C
Oil Resistance (ASTM #1 Oil, 70°C x 24h):      Volume Change <5%               Volume Change <3%         Volume Change <1%
Tensile Strength:                                                   4-6 MPa                                5-8 MPa                            6-10 MPa
Main Applications: Medical Device Seals, Automotive Engine Seals, Spacecraft Ablation-Resistant Seals
Note: Data based on GB/T 16585-2016 test standard.