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Silane USi-6221 – Dimethyldimethoxysilane
Non-Reactive Chain Control Agent for Silicone Rubber & Oil Modification
CAS No.: 1112-39-6
EINECS No.: 214-189-4
Molecular Weight: 120.22 g/mol
Chemical Name:
DimethyldimethoxysilaneSilane USi-6221 is a high-purity non-organoreactive alkoxysilane featuring two methyl groups and two methoxy groups bonded to silicon. Unlike functional silanes, it contains no hydrolyzable Si–H or organofunctional (e.g., amino, epoxy, vinyl) groups, making it ideal as a chain terminator, structural control agent, and hydroxyl scavenger in silicone formulations. It enhances processing stability, extends shelf life, and improves mechanical consistency in high-consistency rubber (HCR) and silicone fluids.
🧪 Product Description
Chemical Formula: (CH₃)₂Si(OCH₃)₂
Chemical Structure:
![Structure: (CH₃)₂–Si–(OCH₃)₂]USi-6221 plays a critical but invisible role in silicone manufacturing:
- Acts as a chain stopper during polymerization of polydimethylsiloxane (PDMS), controlling molecular weight and viscosity
- Scavenges residual silanol (Si–OH) groups in compounded silicone rubber—preventing post-cure hardening and viscosity drift
- Improves machinability (extrusion, molding) by stabilizing polymer structure
- Extends storage stability of masterbatches and compounded rubber by suppressing condensation reactions
- Also used to cap silicone oils, replacing terminal hydroxyls with stable dimethylmethoxy end groups—enhancing thermal and hydrolytic stability
⚠️ Note: USi-6221 is not a coupling agent—it does not bond organic polymers to inorganic fillers. Its value lies in internal silicone matrix control.
📊 Typical Technical Data
The following values are typical and not intended for specification. Please confirm with our technical team before finalizing product requirements.
Parameter Specification Appearance Colorless transparent liquid Specific Gravity (20°C) 0.850 – 0.890 g/cm³ Refractive Index (nD25) 1.3700 – 1.3800 Purity (GC, %) ≥ 99.0%
🏭 Key Applications
🔹 Structural Control Agent in High-Consistency Silicone Rubber (HCR)
- Added during compounding to stabilize polymer chain ends
- Prevents uncontrolled crosslinking during storage → extends pot life
- Reduces batch-to-batch variability in hardness, tensile strength, and elongation
🔹 Chain Extender / Terminator in Silicone Fluid Synthesis
- Controls molecular weight distribution in linear PDMS fluids
- Produces fluids with defined viscosity and low volatility
🔹 Hydroxyl Scavenger in Fumed Silica-Filled Systems
- Reacts with surface silanols on reinforcing silica and residual Si–OH in polymer
- Minimizes thixotropy drift and viscosity increase during storage
- Improves transparency and surface finish in cured parts
🔹 End-Capping Agent for Silicone Oils
- Converts reactive –OH terminated oils into inert –OCH₃ capped oils
- Enhances thermal stability, oxidative resistance, and hydrophobicity
- Used in lubricants, defoamers, and personal care formulations requiring long-term stability
📦 Packaging
Available in industrial-grade containers:
- 20 kg pail
- 170 kg drum
- 1000 L IBC tote
All packaging is sealed to prevent moisture ingress, which could cause premature reaction.
⚠️ Safety & Storage
- Store in original unopened containers at or below 35°C
- Keep away from heat and open flame (product is flammable)
- Shelf Life: 12 months from production date under recommended conditions
- Use in well-ventilated areas; avoid prolonged skin/eye contact
- Consult the latest Safety Data Sheet (SDS) at www.usi-chemical.com or upon request
📞 Contact Us
Nanjing Union Silicon Chemical Co., Ltd.
Specialist in Non-Reactive Alkoxysilanes for Precision Silicone Manufacturing- Headquarters:
Room 2002, Overseas Chinese Plaza, No.1 Daqiao North Road, Nanjing 210031, Jiangsu, P.R. China - Factory Address:
Dongcheng Guanli District, Gaizhou 115200, Liaoning, P.R. China - Tel: +86-25-5889 5266 / 5889 5699
- Fax: +86-25-5830 5349
- Website: www.usi-chemical.com
- Email: bella@usichemical.com
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