In the field of modern silicone materials, hydroxy-terminated methylvinyl silicone oil is a key additive that combines the functions of structural control and crosslinking enhancement. Through its unique molecular design, it plays a vital role in applications such as silicone rubber, sealants, and coatings. This article provides a detailed introduction to its properties, chemical structure, mechanism of action, and typical applications.

1. Basic Properties and Chemical Structure

Hydroxy-terminated methylvinyl silicone oil is a modified polysiloxane with hydroxyl groups (–OH) at both ends of its molecular chain and vinyl groups (CH=CH₂) on its side chains. Its typical parameters include:

• Viscosity (25°C): ≤35 mm²/s (low viscosity, easy to disperse)

• Vinyl content: 6.5–7.5 mol% (providing reactive sites for crosslinking)

• Hydroxyl content: ≥6.0% (enhances interaction with fillers)

• Flash point: ≥60°C (high safety, suitable for industrial processing)

Its chemical structure can be represented as:
HO—[Si(CH₃)(CH=CH₂)O]ₙ—[Si(CH₃)₂O]ₘ—OH
Here, the vinyl groups are located on the side chains, while the hydroxyl groups are at the termini. This design gives it dual functionality.

2. Dual Mechanism of Action

1. Structural Control Agent: Interaction Between Hydroxyl Groups and Silica

In silicone rubber (e.g., high-temperature vulcanized silicone rubber, HTV), fumed silica (nanoscale silicon dioxide) is a commonly used reinforcing filler. However, the surface silanol groups (Si–OH) of silica tend to agglomerate, leading to a sharp increase in viscosity (structuralization effect). The terminal –OH groups of hydroxy-terminated methylvinyl silicone oil can form hydrogen bonds or undergo condensation reactions with the –OH groups of silica, coating the filler particles and significantly improving dispersion while suppressing structuralization. This enhances the processability of the rubber compound.

2. Crosslinking Enhancer: Vinyl Groups Participate in Vulcanization

Traditional hydroxy silicone oil only acts as a structural control agent, whereas the introduction of vinyl groups allows it to participate in peroxide-cured systems, co-crosslinking with the vinyl groups in the raw rubber. This "chemical bonding" is more efficient than physically blended vinyl silicone oil, ultimately improving the mechanical strength, heat resistance, and resilience of the vulcanized rubber.

3. Applications

1. High-Temperature Vulcanized Silicone Rubber (HTV)

Used in molded products, cable insulation layers, etc., it optimizes both processing and performance through its dual functions:

• Processing stage: Prevents silica agglomeration, reduces Mooney viscosity.

• Vulcanization stage: Vinyl crosslinking increases tear strength (up to 15 kN/m or higher).

2. Liquid Silicone Rubber (LSR)

In injection-molded LSR, its low viscosity facilitates rapid mold filling, while the hydroxyl groups improve compatibility with fillers, and the vinyl groups ensure deep vulcanization.

3. Sealants and Coatings

As an additive, it enhances adhesion to substrates (hydroxyl effect) and improves the weather resistance of coatings (vinyl crosslinking network).

4. Advantages Compared to Other Silicone Oils

5. Future Development Trends

With the growing demand for high-performance silicone rubber, innovations in such multifunctional additives include:

• Precise molecular weight control: Balancing viscosity and reactive group density.

• Eco-friendly formulations: Developing solvent-free variants.

• Composite applications: Compatibility with platinum catalyst systems for medical-grade materials.

Conclusion

Hydroxy-terminated methylvinyl silicone oil solves the challenge of simultaneously optimizing silicone rubber processing and performance through its "dual-function" design, showcasing the sophistication of silicone molecular engineering. In the future, its modified derivatives are expected to push performance boundaries further in fields such as new energy and aerospace.