n-Octyltrimethoxysilane (CAS No. 3069-40-7) is a long-chain alkyl-functional silane used primarily as a hydrophobic surface treatment and water-repellent agent. The n-octyl group provides strong hydrophobicity and oleophobicity, while the trimethoxysilane moiety chemically bonds to inorganic substrates such as silica, glass, concrete, and metal oxides, improving water resistance, durability, and surface protection in coatings, construction materials, fillers, and pigments.
| Chemical Name | n-Octyltrimethoxysilane |
|---|---|
| CAS No. | 3069-40-7 |
| EINECS No. | 221-336-6 |
| Empirical Formula | C₁₁H₂₆O₃Si |
| Molecular Weight | 234.41 g/mol |
Synonyms : n-Octyltrimethoxysilane / Octyltrimethoxysilane / Trimethoxy(octyl)silane / Octyl-functional silane / Alkylsilane (C8) / OTMS / C8-TMS / KH-171 / A-137 / Z-6070
Category : Organosilicon Chemicals / Silanes / Functional Silanes / Polysulfide Silanes ; Alkyl Functional Silane / Hydrophobic Surface Treatment Silane / Water-Repellent Silane / Trialkoxy Organosilane / Long-Chain Alkyl Silane (C8) / Functional Organosilicon Intermediate
n-Octyltrimethoxysilane (CAS No. 3069-40-7) is a long-chain alkyl-functional silane designed to impart durable hydrophobicity to inorganic substrates. The C8 n-octyl group provides strong water repellency and improved resistance to moisture penetration, while the trimethoxysilane moiety hydrolyzes and covalently bonds to hydroxylated surfaces—such as silica, glass, concrete, stone, metal oxides, pigments, and mineral fillers—forming stable Si–O–Si / Si–O–M linkages.
Compared with short-chain alkyl silanes, n-Octyltrimethoxysilane offers enhanced hydrophobic performance, lower surface energy, and longer-lasting water resistance, without significantly altering vapor permeability or substrate appearance when properly applied. It is widely used as a surface treatment and water-repellent additive in construction materials, coatings, sealants, fillers, and pigments, where it improves durability, reduces water uptake, and enhances resistance to weathering, staining, and freeze–thaw cycles.
| Item | Specification |
|---|---|
| Appearance | Colorless to pale yellow clear liquid |
| Purity | ≥ 95% (typical commercial grade ≥97%) |
| Density (25 °C) | ~0.88–0.92 g/cm³ |
| Viscosity (25 °C) | Low |
| Boiling Point | ~255–265 °C |
| Flash Point | > 95 °C |
| Refractive Index (25 °C) | ~1.420–1.425 |
| Solubility | Soluble in alcohols and most organic solvents; reacts with water |
| Hydrolyzable Methoxy Content | ~36–38 wt% |
| Functional Group | n-Octyl (C8) alkyl chain |
| Hydrophobic Performance | High; long-chain alkyl provides durable water repellency |
| Moisture Sensitivity | Moisture-sensitive (trialkoxy silane) |
| Storage Stability | 12 months in unopened, tightly sealed original container |
| Recommended Storage | Cool, dry, well-ventilated area; protect from moisture, heat, and direct sunlight |
Note: The above values are typical reference data. Actual specifications may vary slightly depending on batch and test methods.
| Item | Description |
|---|---|
| Chemical Name | n-Octyltrimethoxysilane |
| CAS No. | 3069-40-7 |
| Molecular Formula | C₁₁H₂₆O₃Si |
| Molecular Weight | 234.41 g/mol |
| Chemical Type | Alkyl-functional trialkoxy silane |
| Physical State | Liquid |
| Appearance | Colorless to pale yellow transparent liquid |
| Odor | Mild |
| Density (25 °C) | ~0.88–0.92 g/cm³ |
| Viscosity (25 °C) | Low |
| Boiling Point | ~255–265 °C |
| Flash Point | >95 °C |
| Solubility | Soluble in alcohols and most organic solvents; reacts with water |
| Hydrolysis | Methoxy groups hydrolyze in presence of moisture |
| Condensation | Forms durable siloxane network on inorganic surfaces |
| Stability | Moisture-sensitive; stable when dry and sealed |
| Item | Information |
|---|---|
| GHS Classification | Skin Irritation; Eye Irritation |
| Signal Word | Warning |
| Hazard Statements | H315: Causes skin irritation; H319: Causes serious eye irritation |
| GHS Pictogram | Exclamation Mark |
| PPE | Protective gloves, goggles, protective clothing |
| Handling Notes | Avoid skin and eye contact; ensure adequate ventilation |
| Storage Conditions | Cool, dry, well-ventilated; tightly sealed containers |
| Incompatibilities | Strong acids/bases, oxidizing agents, moisture |
| UN Number | Not classified as dangerous goods (typical) |
| Transport | ADR / IMDG / IATA: Generally not regulated |
| Packaging | HDPE drums or lined steel drums |
| Regulatory Status | REACH / TSCA compliant (supplier-dependent) |
| Documentation | SDS available upon request |
Q1: What is the main function of n-Octyltrimethoxysilane?
It provides durable hydrophobic surface modification for inorganic materials.
Q2: How does it differ from short-chain alkyl silanes?
The C8 alkyl chain offers stronger and longer-lasting water repellency.
Q3: Does it affect vapor permeability of concrete?
When properly applied, it maintains vapor permeability while reducing liquid water uptake.
Q4: Can it be used in filler surface treatment?
Yes. It improves moisture resistance and dispersion of mineral fillers in polymers.
Q5: How should it be stored?
Store sealed, dry, and protected from moisture, heat, and direct sunlight.
Packaging: 500 g / 1 kg / 5 kg / 25 kg / 200 kg drums / 1000L IBC container (Customized packaging is available).
Storage: Store in tightly sealed original containers in a cool, dry, and well-ventilated place. Protect from moisture, humidity, and direct sunlight, and keep away from acids, alcohols, amines, and oxidizing agents. Recommended storage temperature: ambient conditions.
Shelf Life: 12 months from date of manufacture when stored under recommended conditions.
“The information provided herein is based on general industry experience and is intended for reference purposes only. Actual performance and optimal usage conditions may vary depending on formulation, processing methods, substrate characteristics, and end-use requirements. Users are responsible for conducting their own tests and evaluations to determine suitability for their specific applications. No warranty, express or implied, is made regarding the completeness, accuracy, or applicability of this information.”
Grace Gao / Sales Manager
Email : Inquiry@SiliconChemicals.com
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