What is Octamethylcyclotetrasiloxane CAS 556-67-2?

Octamethylcyclotetrasiloxane, commonly called D4, CAS 556-67-2, is a cyclic dimethylsiloxane tetramer with the molecular formula C8H24O4Si4. It is a colorless, low-viscosity liquid used mainly as a silicone monomer and feedstock.

What is the main industrial use of D4?

D4 is primarily used as a precursor in silicone manufacturing. Through ring-opening polymerization, it is converted into polysiloxane backbones used to make silicone oils, silicone rubbers and silicone resins.

How does D4 differ from D5 and other cyclic siloxanes?

D4 contains four silicon atoms in its ring, while D5 contains five and D6 contains six. This changes molecular weight, boiling point, vapor pressure and end-use behavior, even though all are cyclic dimethylsiloxanes used in silicone chemistry.

What are typical physical properties of D4?

D4 is normally a colorless clear liquid with a boiling point of about 175-176 C, freezing point around 17-18 C, density around 0.95-0.96 g/mL, and a closed-cup flash point in the region of 51-60 C. It has very low water solubility and is moderately volatile.

Are there regulatory considerations for D4?

D4 is regulated in some consumer and cosmetic applications, especially in the EU, because cyclic volatile methyl siloxanes may be persistent or bioaccumulative. Industrial polymer synthesis remains a key use, but buyers should confirm end-use compliance and any D4/D5/D6 residue requirements for their region.

Octamethylcyclotetrasiloxane CAS 556-67-2

Octamethylcyclotetrasiloxane CAS 556-67-2 is a low molecular weight cyclic volatile methyl siloxane (cVMS) chemically defined as a cyclic dimethylsiloxane tetramer, functioning primarily as a fundamental monomer in the ring-opening polymerization of silicone rubber and oil manufacturing. Often designated as D4 or OMCTS within the organosilicon industry, this substance serves as a critical intermediate for synthesizing polydimethylsiloxane (PDMS) chains and is utilized to adjust the degree of polymerization in downstream silicone production processes. We provide professional access to this material with competitive factory pricing and the ability to meet customized specifications for various manufacturing requirements. Our commitment to technical transparency ensures that every shipment is accompanied by comprehensive MSDS, TDS, COA documentation to support your quality assurance protocols, and we maintain capacity for consistent bulk supply to facilitate large-scale industrial operations.

CAS: 556-67-2
Synonyms: D4, OMCTS, Cyclic dimethylsiloxane tetramer, 2,2,4,4,6,6,8,8-Octamethylcyclotetrasiloxane, Cyclotetrasiloxane octamethyl
Einecs: 209-136-7
Molecular Formula: C₈H₂₄O₄Si₄
Grade: Industrial Grade
Package: 200 kg drum / 1000 kg IBC (customizable)

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Product Description

D4 is a colorless, low-viscosity liquid with moderate volatility and excellent silicone compatibility. In industrial production, it is widely used as a key feedstock for manufacturing silicone oils, silicone rubbers, and silicone resins through controlled polymerization routes. Its stable structure and low surface tension can be beneficial in certain industrial formulations where silicone-type slip, spreading, or processing performance is required.

1 Physicochemical Properties

2 Applications

3 Storage Conditions

4 Safety Precautions

Physicochemical Properties

Typical values for reference; final specifications follow batch COA.

Item	Typical Value / Specification
Appearance	Colorless, clear liquid
CAS	556-67-2
EC (EINECS)	209-136-7
Molecular formula	C₈H₂₄O₄Si₄
Molecular weight	296.62 g/mol
Melting / freezing point	~17 °C
Boiling point	~175–176 °C
Density (20–25 °C)	~0.95–0.96 g/mL
Flash point (closed cup)	~51–55 °C
Water solubility	Very low / practically insoluble
Vapor pressure (25 °C)	~124 Pa (typical reference)

Applications

Silicone polymer manufacturing: feedstock/intermediate for silicone oils, rubbers, resins (ring-opening polymerization)
Industrial process fluid / carrier for selected formulations where silicone compatibility is required (user evaluation recommended)
Laboratory / specialty chemical use where cyclic siloxane properties are needed (subject to compliance)

For downstream silicone fluid options, see Polydimethylsiloxane (PDMS) and Dimethicone.

Storage Conditions

Store in tightly sealed containers in a cool, dry, well-ventilated area.
Keep away from heat, sparks, open flames, and strong oxidizers.
Recommended storage temperature: below 30°C (typical guidance).
Prevent moisture/impurity contamination; keep container closed when not in use.

Safety Precautions

Handle as a flammable liquid: keep away from ignition sources; use grounded equipment when transferring.
Avoid inhalation of vapors; ensure good ventilation. Wear chemical goggles and protective gloves.
Spills: contain with inert absorbent; prevent discharge to drains/waterways.
Regulatory note (EU): D4 is addressed under EU REACH restrictions for certain uses (notably wash-off cosmetic products and broader cyclosiloxane emission controls). Confirm compliance for your target market and application.

FAQ - Technical & Supply Chain

Q:
What is Octamethylcyclotetrasiloxane CAS 556-67-2?

A: Octamethylcyclotetrasiloxane, commonly called D4, CAS 556-67-2, is a cyclic dimethylsiloxane tetramer with the molecular formula C8H24O4Si4. It is a colorless, low-viscosity liquid used mainly as a silicone monomer and feedstock.
Q:
What is the main industrial use of D4?

A: D4 is primarily used as a precursor in silicone manufacturing. Through ring-opening polymerization, it is converted into polysiloxane backbones used to make silicone oils, silicone rubbers and silicone resins.
Q:
How does D4 differ from D5 and other cyclic siloxanes?

A: D4 contains four silicon atoms in its ring, while D5 contains five and D6 contains six. This changes molecular weight, boiling point, vapor pressure and end-use behavior, even though all are cyclic dimethylsiloxanes used in silicone chemistry.
Q:
What are typical physical properties of D4?

A: D4 is normally a colorless clear liquid with a boiling point of about 175-176 C, freezing point around 17-18 C, density around 0.95-0.96 g/mL, and a closed-cup flash point in the region of 51-60 C. It has very low water solubility and is moderately volatile.
Q:
Are there regulatory considerations for D4?

A: D4 is regulated in some consumer and cosmetic applications, especially in the EU, because cyclic volatile methyl siloxanes may be persistent or bioaccumulative. Industrial polymer synthesis remains a key use, but buyers should confirm end-use compliance and any D4/D5/D6 residue requirements for their region.

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COA, TDS, SDS/MSDS and packing details are available on request.

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