Silane Coupling Agent Si 69

Chemical Name:

Bis-[3-(triethoxysilyl)-propyl]-tetrasulfide

Structural Formula:

(C2H5O)3SiCH2CH2CH2-S4-CH2CH2CH2Si(OC2H5)3

CAS Number: 40372-72-3

Equivalent Product Name:

SI-69 (Degussa),Z-6940 (Dowcorning),A-1289 (Crompton),KBE-846 (Shin-Etsu),KH-845-4 (China)

Physical Properties:

It is a pale yellow, transparent liquid with a faint alcoholic smell. It dissolves readily in solvents such as alcohol, acetone, benzene and toluene, yet is immiscible with water. Upon exposure to water or moisture, hydrolysis will occur. Its specific gravity is 1.08 g/mL.

Bis-[3-(triethoxysilyl)-propyl]-tetrasulfide (TESPT / Si‑69) is a bifunctional polysulfide organosilane coupling agent developed for silica-filled rubber cured by sulfur. It is a pale yellow transparent liquid with a faint alcoholic odor. The product is freely soluble in alcohols, acetone, benzene, toluene and other organic solvents, but immiscible with water. Its ethoxy groups tend to hydrolyze when exposed to liquid water or ambient moisture. Its specific gravity is 1.08 g/mL at 25℃.

SI‑69 serves as a high-performance bifunctional polysulfide organosilane coupling agent widely applied within the rubber sector. It is formulated for vulcanized rubber systems reinforced with fillers including silica, glass fiber, talc, mica and clay. SI‑69 enhances the reinforcing effect of these fillers and boosts the abrasion resistance of rubber compounds.

It works as a rubber additive, vulcanizing agent and activator for polymers such as NR, IR, SBR, BR, NBR and EPDM. During vulcanization, the crosslinking rate of polysulfide alkyl groups matches the sulfur desulfurization rate. This feature delivers anti-reversion performance, optimizing dynamic flex characteristics including heat build-up and crack growth. The four sulfur atoms in its molecular structure function as a vulcanization activator.

Under both dynamic and static service conditions, SI‑69 is ideal for manufacturing rubber goods like tires, hoses, rubber rollers, conveyor belts, cables, shoe soles and mechanical rubber components. It improves abrasion resistance, cut resistance and compression resistance, lowers hysteresis loss and water absorption, enhances mechanical strength and bonding performance, and upgrades thermal aging resistance, modulus and flex fatigue life.

When this sulfur-silane coupling agent is incorporated into tire rubber formulations, it reduces the risk of tire puncture caused by excessive heat generation during high-speed or prolonged driving. It also decreases tire rolling resistance, cutting fuel consumption and CO₂ emissions to meet low-carbon environmental requirements.

Recommend dosage: 1.0 - 4.0 PHR.

1. Packaging: Available in 25 kg, 200 kg and 1000 kg plastic drums.
2. Storage: Store in a cool, dry and well-ventilated area with containers tightly sealed.
3. Shelf Life: More than 2 years under proper storage conditions.

1. What fillers can SI‑69 work with in rubber formulations?

A: SI‑69 is compatible with silica, glass fiber, talc, mica and clay. It forms stable chemical bonds between inorganic filler surfaces and rubber polymer chains, greatly improving filler-rubber interfacial adhesion.

2. What core benefits does SI‑69 bring to tire compounds?

A: In tire formulations, SI‑69 reduces rolling resistance and heat build-up during high-speed or long-time driving. It lowers fuel consumption and CO₂ emissions, while improving abrasion resistance and cutting resistance and mitigating overheating-related puncture risks.

3. What happens when SI‑69 contacts moisture or liquid water?

A: SI‑69 contains ethoxy groups which are prone to hydrolysis upon exposure to liquid water or ambient humidity. Proper sealed storage is required to avoid premature hydrolysis and performance degradation.

4. What rubber products can be manufactured using SI‑69 modified compounds?

A: SI‑69 modified rubber compounds are used for tires, hoses, rubber rollers, conveyor belts, cables, footwear and mechanical rubber parts. It improves flex fatigue life, modulus, thermal aging performance and reduces hysteresis loss and water absorption.

5. How does SI‑69 achieve anti-reversion effect during vulcanization?

A: The crosslinking rate of polysulfide alkyl groups matches the sulfur desulfurization rate. This characteristic suppresses vulcanization reversion, optimizing dynamic performance including heat build-up and crack propagation.