What Is Low-Phenyl Silicone Raw Gum?

Low-phenyl silicone raw gum is an elastomeric base polymer obtained by introducing diphenylsiloxane or methylphenylsiloxane units into methyl vinyl siloxane chains, typically appearing as a colorless or semi-transparent high-viscosity solid rubber.Its phenyl content generally ranges from 5% to 15%, making it the lowest-temperature-resistant grade within phenyl silicone rubbers. The bulky phenyl groups disrupt the regular arrangement of dimethylsiloxane segments, suppress low-temperature crystallization, and significantly reduce the glass transition temperature and brittle point.When the phenyl-to-silicon molar ratio is around 5%–10%, the hardening temperature can drop to approximately -115°C, and the rubber remains flexible and elastic even at -100°C, ranking among the best low-temperature silicone elastomers available. Compared with general-purpose methyl vinyl silicone rubber, low-phenyl silicone raw gum maintains higher elasticity under extreme cold and shows better low-temperature compression resilience. Compared with medium-phenyl and high-phenyl grades, it offers superior low-temperature elasticity along with better processability and mechanical performance.Therefore, it is commonly used as a base gum for low-temperature phenyl compounds, and for producing cryogenic seals, damping materials, aerospace elastomers, extruded profiles and compression-molded parts.

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Key Technical Indicators

Phenyl Content Low-phenyl silicone raw gum typically contains 5%–15% phenyl groups, with the 5%–10% range delivering the best low-temperature performance.Insufficient phenyl content may not adequately suppress low-temperature crystallization, while excessive phenyl content increases chain rigidity and raises the glass transition temperature, reducing low-temperature elasticity. Vinyl Content Vinyl content affects crosslink density, cure speed, hardness and compression set. A moderate vinyl level helps achieve balanced elasticity, tensile properties and compression recovery; excessive vinyl may increase hardness and reduce elongation, so selection should match hardness targets, molding processes and sealing requirements. Vinyl Position Terminal vinyl gums generally form more uniform networks during curing, leading to better mechanical performance and elastic recovery; uniformly distributed side-chain vinyl groups can also improve crosslink density and cure stability. Molecular Weight and Mooney Viscosity Molecular weight is typically in the hundreds of thousands to around one million. Higher molecular weight improves green strength and compound stability but may increase mixing difficulty. Mooney viscosity should match internal mixing, open mill mixing, extrusion or compression molding processes. Volatiles Low volatiles help reduce bubbles, pinholes and weight loss during curing, which is especially important for aerospace, electronic sealing and transparent applications. Low-Temperature Performance Indicators Common indicators include glass transition temperature, brittle point, low-temperature compression resilience factor, low-temperature rebound retention and low-temperature modulus change. Low-phenyl silicone raw gum can reach glass transition temperatures around -105°C to -115°C and retain flexibility near -100°C.

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Main Performance Features

• Excellent low-temperature resistance: phenyl groups suppress crystallization; brittle temperature can reach approximately -115°C, with elasticity retained at -100°C.
• Stable wide-temperature elasticity: relatively stable shear modulus and elastic retention from cryogenic to moderate-high temperatures.
• Good damping characteristics: retains energy-absorbing capability at low temperatures, suitable for vibration isolation, shock absorption and flexible joints.
• Good heat-aging resistance: inherits siloxane backbone heat, oxidation and weather resistance.
• Excellent electrical insulation: suitable for cryogenic electronic insulation, cable jackets and sensor encapsulation.
• Good physiological inertness: certain grades can be used in medical low-temperature seals, blood refrigeration seals and similar applications.
• Customizable formulation: phenyl content, vinyl content, molecular weight and vinyl position can be adjusted per application.

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Typical Application Scenarios

Low-Temperature Seals and Gaskets Used for O-rings, gaskets, sealing strips, flexible joints and cryogenic equipment in aerospace, refrigeration, low-temperature piping, vacuum systems and polar applications, addressing brittleness, hardening or elasticity loss of standard silicone rubber below -60°C. Aerospace Elastomer Components Suitable for satellites, aircraft, space docking mechanisms, cryogenic door seals and aviation instrument damping materials, meeting requirements for low temperature, vacuum, radiation resistance and long-term reliability. Base Gum for Phenyl Compounds Serves as the base raw gum for phenyl silicone compounds, combined with fumed silica, structure control agents, curing agents and functional additives to produce low-temperature compression molding compounds, extrusion compounds, transparent compounds and high-damping compounds. Cryogenic Damping and Vibration Isolation Used for precision instrument bases, cryogenic vibration pads, flexible connectors and energy-absorbing sealing structures, leveraging relatively stable shear modulus and damping behavior across wide temperature ranges. Low-Temperature Extruded Tubing and Profiles Applicable to silicone tubing, sealing profiles, special shapes and cable jackets for low-temperature service, produced via extrusion followed by hot-air vulcanization. Wide-Temperature-Range Absorber and Stealth Sealing Materials Can serve as a matrix for absorber rubbers requiring combined low-temperature elasticity, dielectric performance and sealing reliability.

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Selection and Usage Recommendations

• Confirm minimum service temperature first: if continuous service is below -60°C, or elasticity at -80°C to -100°C is required, low-phenyl silicone raw gum is more suitable than general-purpose methyl vinyl silicone rubber.
• Select by phenyl content: 5%–10% phenyl offers optimal low-temperature elasticity; 10%–15% can balance low-temperature performance with processability.
• Check vinyl content and position: terminal vinyl and uniform vinyl distribution help achieve lower compression set and stable curing.
• Match curing system: peroxide or platinum curing systems can be selected depending on transparency, odor, compression set and process temperature requirements.
• Note media resistance limits: phenyl silicone rubber excels in low-temperature elasticity but is less resistant to fuels, lubricants and non-polar solvents than fluorosilicone rubber; volume swelling should be evaluated for oil-contact applications.
• Key points for overseas customers: emphasize phenyl content range, vinyl content and position, molecular weight range, glass transition temperature, low-temperature compression resilience, volatiles level, compatible curing systems, compatibility with silica/additives, low-temperature elasticity retention and customization options to support low-temperature seal development, phenyl compound formulation, aerospace elastomer qualification and cryogenic damping material evaluation.

Methyl phenyl vinyl silicone rubber IOTA 3120