What Is Hydroxyl-Terminated Fluorosilicone Oil?

Hydroxyl-terminated fluorosilicone oil, also known as hydroxyl fluorosilicone fluid or hydroxyl-terminated fluorosiloxane oligomer, is a low-molecular-weight fluorosilicone polymer with hydroxyl functional groups at the molecular chain ends. Common CAS numbers include 63148-56-1 and 68607-77-2. The introduction of trifluoropropyl groups provides wide-temperature stability, oil resistance, solvent resistance and low surface tension, while the terminal hydroxyl groups enable further condensation, crosslinking or grafting reactions.Therefore, it can serve as a structural control agent in fluorosilicone rubber processing, a base fluid or diluent for room-temperature-vulcanizing fluorosilicone rubber, and a raw material for oil-resistant defoamers, lubricants, water/oil repellents and surface-modifying systems. The product typically appears as a colorless or light yellow transparent liquid, with a high flash point, low volatility and good chemical stability. It should be stored in sealed containers, protected from moisture, light and acidic or alkaline substances.

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Key Technical Indicators

Appearance and State Hydroxyl-terminated fluorosilicone oil is usually a colorless or light yellow transparent liquid without visible mechanical impurities.Low-viscosity grades flow easily, while higher-viscosity grades may appear paste-like or highly viscous, depending on molecular weight and specification. Viscosity Range Viscosity can vary widely. Common specifications include 80-130 mPa·s, 130-180 mPa·s and 1,000-10,000 mPa·s, with some products covering 50-50,000 mPa·s or higher.Low-viscosity grades are suitable as structural control agents, diluents or surface modifiers; medium- to high-viscosity grades can be used as base fluids, sealant components or lubricating materials. Hydroxyl Content Hydroxyl content determines reactivity and crosslinking density. Different grades may have hydroxyl contents ranging from about 0.5% to 7%.Higher hydroxyl content provides stronger reactivity in condensation, grafting or crosslinking systems, but may also affect storage stability. The optimal level depends on the downstream formulation. Flash Point and Volatility The flash point is typically no less than 240°C, with some grades exceeding 260°C. Volatility at 200°C for 4 hours is generally no more than 5%.High flash point and low volatility support safe high-temperature processing and stable storage. Service Temperature Range Hydroxyl-terminated fluorosilicone oil can remain stable across a wide temperature range, commonly from about -50°C to +200°C or +250°C, depending on molecular weight, hydroxyl content and application system.Compared with ordinary silicone oil, it offers better stability in fuels, oils and non-polar solvents. Surface Tension and Refractive Index Due to the trifluoropropyl structure, it has low surface tension and a lower refractive index than many conventional silicone oils, typically around 1.37-1.39.Low surface tension improves wetting, release and defoaming performance; low refractive index can be useful in optical clarity adjustment or low-gloss coating systems. Storage Stability The product should be stored in sealed containers, away from acids, alkalis, moisture and oxidizing agents.Hydroxyl end groups are reactive; exposure to moisture or catalysts may cause condensation or viscosity changes. Typical shelf life is 6-12 months, subject to the supplier's technical data.

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Main Performance Features

• Hydroxyl reactivity: terminal hydroxyl groups enable condensation, crosslinking and grafting.
• Oil and solvent resistance: trifluoropropyl groups improve resistance to fuels, oils and non-polar solvents.
• Low surface tension: supports defoaming, release, leveling and surface modification.
• Wide-temperature stability: maintains fluidity at low temperature and shows low volatility at high temperature.
• Structural control: treats silica surface hydroxyls and suppresses fluorosilicone rubber structuring.
• Base fluid or diluent: suitable for RTV fluorosilicone rubber and reactive elastomer systems.
• Non-hazardous transport: many grades can be shipped as non-dangerous goods, supporting international sampling and bulk delivery.

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Typical Application Scenarios

Structural Control Agent for Fluorosilicone Rubber During fluorosilicone rubber compounding, surface hydroxyls on silica can cause structuring, leading to increased hardness and reduced processability. Hydroxyl-terminated fluorosilicone oil interacts with filler surface hydroxyls, improves dispersion and enhances storage stability, extrusion and molding performance. Base Fluid for RTV Fluorosilicone Rubber The hydroxyl end groups allow it to function as a base fluid or diluent in condensation-cured RTV fluorosilicone systems, enabling oil-resistant sealants, solvent-resistant coatings and elastomeric potting materials. Automotive and Aerospace Sealant Modification Used in fuel system seals, engine-area oil-resistant elastomers and aerospace fluorosilicone components to improve resistance to fuels, lubricants and temperature cycling. Oil-Resistant Defoamer Effective in oil-containing systems, lubricants, chemical media and fluorosilicone processing, providing defoaming and anti-foam performance while maintaining thermal and chemical stability. Lubricant and Surface Treatment Agent Suitable for micro-mechanical lubrication, mold lubrication, metal surface protection and hydrophobic/oleophobic treatment, reducing friction and improving solvent resistance. Coating and Sealant Modifier Can be incorporated into oil-resistant sealants, fluorosilicone coatings, protective coatings and elastomer composites to improve wetting, surface slip and chemical-media resistance.

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Selection and Usage Recommendations

• Select viscosity by application: choose low viscosity for structural control and defoaming; choose medium to high viscosity for base fluids, sealants and lubrication.
• Match hydroxyl content to curing system: confirm hydroxyl level when used in crosslinking, grafting or condensation-cure formulations.
• Control storage conditions: keep sealed, dry and away from acids, alkalis and moisture to prevent premature condensation.
• Distinguish from methyl fluorosilicone oil: hydroxyl-terminated grades are reactive and suitable for structural control and crosslinking; methyl fluorosilicone oils are generally more inert and suited for lubrication and release.
• Verify compatibility with fillers: different silica types, fillers and vulcanization systems may require different dosage levels; small-scale trials are recommended.
• Key points for overseas customers: highlight hydroxyl reactivity, oil/solvent resistance, low surface tension, wide-temperature stability, structural control function and customizable viscosity to support sampling, formulation trials and bulk orders.

Hydroxyl Fluorosilicone Oil IOTA-25O