Based on the search results, significant differences in the temperature resistance of low-phenyl, medium-phenyl, and high-phenyl silicones within the -120°C to 250°C range are observed, primarily due to the impact of phenyl content on material properties. The following is a detailed analysis:

I. Basic Properties of Three Types of Phenyl Silicones
Low Phenyl Silicone
Phenyl Content: 5-10%
Temperature Range: -100°C to 250°C
Characteristics: Optimal low-temperature resistance, maintaining elasticity below -100°C, offering the best low-temperature performance among all rubbers.
Applications: Primarily used in applications requiring extreme low-temperature resistance, such as cold-resistant rubber products in the aviation industry.

Medium Phenyl Silicone
Phenyl Content: 15-25%
Temperature Range: -70°C to 250°C
Characteristics: Flame-retardant, self-extinguishing in the event of a fire.
Applications: Suitable for applications requiring ablation and flame resistance.

High Phenyl Silicone
Phenyl Content: 30% or more
Temperature Range: -70°C to 250°C
Characteristics: Excellent radiation resistance, with a gamma-ray resistance of 1×10⁸ roentgen.
Applications: Primarily used in applications requiring radiation resistance, such as the nuclear industry.

II. Performance Comparison in the -120°C to 250°C Range
Performance Indicators Low-phenyl silicone Medium-phenyl silicone High-phenyl silicone
Minimum operating temperature -100°C -70°C -70°C
Maximum operating temperature 250°C 250°C 250°C
Low-temperature elasticity retention: Best (still elastic at -100°C) Fair (elasticity maintained at -70°C) Poor (elasticity reduced at -70°C)
High-temperature stability: Good (250°C for thousands of hours) Good (250°C for thousands of hours) Good (250°C for thousands of hours)
Special properties: Low-temperature resistance, flame retardant, self-extinguishing Radiation Resistance

III. Mechanism Analysis of Performance Differences
Low-Temperature Performance Differences:
Due to the low phenyl content (5-10%), low-phenyl silicone rubber moderately disrupts molecular chain regularity, significantly lowering its crystallization temperature (-115°C), allowing it to maintain elasticity below -100°C.

As the phenyl content increases, the molecular chain rigidity increases, and low-temperature performance gradually decreases.
High-Temperature Performance Similarities:
All three silicone rubbers maintain excellent performance at 250°C. This is because the thermal stability of the phenyl group is much higher than that of the methyl group, effectively preventing oxidative decomposition of the side chain groups at high temperatures.
Appropriately formulated vinyl silicone rubber or low-phenyl silicone rubber can maintain elasticity after thousands of hours of hot air aging at 250°C.

Special Performance:
Medium-phenyl silicone (15-25% phenyl) is flame-resistant and self-extinguishes.
High-phenyl silicone (30%+ phenyl) exhibits excellent radiation resistance.

IV. Application Recommendations
Extremely low-temperature environments (below -100°C): Low-phenyl silicone is preferred.
High-temperature environments with fire protection requirements: Medium-phenyl silicone is preferred.
Radiation environments: High-phenyl silicone is essential.
Wide temperature range (-70°C to 250°C) general applications: Low-phenyl or medium-phenyl silicone can be selected based on cost.

V. Summary
Within the -120°C to 250°C temperature range, the performance differences between the three phenyl silicones are primarily reflected in the following:
Low-temperature performance: Low-phenyl > Medium-phenyl > High-phenyl
Flame resistance: Medium-phenyl > High-phenyl > Low-phenyl
Radiation resistance: High-phenyl > Medium-phenyl > Low-phenyl
Users should select the most appropriate phenyl silicone based on the specific requirements of their application.