What Is Hydrogen-Containing Fluorosilicone Oil?
Hydrogen-Containing Fluorosilicone Oil is a fluorinated polysiloxane liquid with silicon-hydrogen bonds (Si-H) on side chains or terminal groups, with the general chemical formula:
[CF₃CH₂CH₂Si(CH₃)O]ₘ[HSi(CH₃)O]ₙ
Here, trifluoropropyl groups provide oil and solvent resistance, while silicon-hydrogen bonds serve as active reaction sites, undergoing hydrosilylation with vinyl groups under platinum catalyst action to form a three-dimensional crosslinked network.
Hydrogen-containing fluorosilicone oil is not a final product itself, but a key component—the crosslinker—in addition-cure fluorosilicone rubber systems. Its dosage and structure directly determine the crosslink density, hardness, tensile strength, and media resistance of the vulcanized fluorosilicone rubber.
Core Technical Parameters
Active Hydrogen Content
Active hydrogen content is the most critical indicator of hydrogen-containing fluorosilicone oil, typically expressed as a weight percentage (wt%), ranging from 0.1% to 1.6%. Higher active hydrogen content means more crosslinking points per unit mass of oil, resulting in higher crosslink density and hardness of the vulcanized compound, but correspondingly lower elongation.
Typical specifications:
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Low active hydrogen type: 0.1%-0.3%, for soft fluorosilicone rubber (Shore A 20-40)
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Medium active hydrogen type: 0.4%-0.8%, for medium-hardness fluorosilicone rubber (Shore A 40-60)
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High active hydrogen type: 0.9%-1.6%, for hard fluorosilicone rubber (Shore A 60-80)
Viscosity
The viscosity of hydrogen-containing fluorosilicone oil typically ranges from 10-500 cSt (25°C). Low-viscosity products have good flowability, mix easily with vinyl fluorosilicone raw rubber, and are suitable for liquid injection molding processes; high-viscosity products have low volatile content and are suitable for high-temperature compression molding processes.
Functionality
Based on the position of silicon-hydrogen bonds in the molecular structure, hydrogen-containing fluorosilicone oil can be classified as:
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Side-chain hydrogen-containing type: Si-H bonds located on side groups of the molecular chain, with evenly distributed crosslinking points and excellent mechanical properties of vulcanized rubber—this is the mainstream choice
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Terminal hydrogen-containing type: Si-H bonds located at both ends of the molecular chain, mainly used as chain extenders or surface treatment agents
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Side-chain + terminal hydrogen-containing type: Combines both structures, enabling more complex network topologies
Volatile Content
High-quality hydrogen-containing fluorosilicone oil should have volatile content controlled below 1% (150°C × 2h). Excessive volatiles generate bubbles during vulcanization, affecting product appearance and performance consistency.
Role Mechanism in Addition-Cure Fluorosilicone Rubber
The vulcanization reaction of addition-cure fluorosilicone rubber is essentially a hydrosilylation reaction:
≡Si-H + CH₂=CH-Si≡ → ≡Si-CH₂-CH₂-Si≡
This reaction proceeds under the action of a platinum catalyst (such as Karstedt catalyst) and has the following characteristics:
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No By-Products: Unlike peroxide vulcanization, hydrosilylation produces no small-molecule by-products, resulting in no shrinkage or bubbles in the product—suitable for potting and precision molding
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Room Temperature or Heat-Curable: Reaction rate can be adjusted via temperature and catalyst dosage; long pot life at room temperature, rapid curing when heated
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Deep Vulcanization Capability: Reaction is not inhibited by oxygen, allowing thick products to vulcanize uniformly
The molar ratio of hydrogen-containing fluorosilicone oil to vinyl fluorosilicone raw rubber (Si-H/Vi) is typically controlled between 1.0-1.5. When the ratio is less than 1, crosslinking is incomplete and the compound becomes sticky; when greater than 1.5, excess Si-H bonds may cause post-curing or affect heat resistance.
Typical Application Scenarios
Liquid Injection Molded Fluorosilicone Rubber
In LSR processes, hydrogen-containing fluorosilicone oil serves as the core component of Component B (crosslinker component), mixed with Component A (vinyl fluorosilicone raw rubber + platinum catalyst) and injected into molds, vulcanizing rapidly at 100-150°C. This process is widely used in mass production of precision products such as automotive turbocharger hose seals and fuel system O-rings.
Fluorosilicone Potting Compounds
In electronic potting applications, hydrogen-containing fluorosilicone oil is formulated with vinyl fluorosilicone resin, reinforcing fillers, and platinum catalyst into a two-component potting compound. After vulcanization, it forms a transparent or translucent elastomer that protects sensitive electronic components from erosion by fuel, lubricating oil, and solvents. Typical applications include potting protection for aircraft engine sensors and fuel pump control modules.
Fluorosilicone Coatings
Hydrogen-containing fluorosilicone oil can serve as a crosslinker in coating systems, combined with vinyl fluorosilicone resin to form oil-resistant and waterproof coatings on fabric or metal surfaces. This coating maintains the media resistance of fluorosilicone rubber while offering thinner thickness and better flexibility, suitable for protective clothing, fuel tank liners, and other scenarios.
Foamed Fluorosilicone Rubber
In foamed fluorosilicone rubber formulations, hydrogen-containing fluorosilicone oil not only acts as a crosslinker but can also be combined with vinyl-containing blowing agents to achieve a uniform and fine cell structure by balancing crosslinking rate and foaming rate. Foamed fluorosilicone rubber is used in aerospace seals, combining lightweight properties with sealing performance.
Selection and Ratio Recommendations
When selecting hydrogen-containing fluorosilicone oil, the following factors should be comprehensively considered:
Compatibility with Raw Rubber
The fluorine content of hydrogen-containing fluorosilicone oil should match that of vinyl fluorosilicone raw rubber to ensure uniform mixing without phase separation. Typically, the trifluoropropyl content of both should be similar.
Molar Ratio of Active Hydrogen to Vinyl
A Si-H/Vi molar ratio of 1.0-1.2 is recommended, with specific optimization through experimentation. For thick products or low-temperature vulcanization systems, the ratio can be appropriately increased to 1.3-1.5 to ensure complete crosslinking.
Catalyst Compatibility
Impurities in hydrogen-containing fluorosilicone oil (such as alkynes, amines) may poison platinum catalysts, leading to incomplete vulcanization. It is recommended to select high-purity products and add appropriate inhibitors (such as ethynylcyclohexanol) to the formulation to extend pot life.
Storage Stability
Hydrogen-containing fluorosilicone oil is sensitive to moisture; Si-H bonds may react with water to release hydrogen gas, causing package swelling or activity loss. It should be stored sealed in a cool, dry place and used promptly after opening.
Methyl hydrogen Fluorosilicone Oil IOTA-25H
