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Vinyl Silicone Fluid (Vi-PDMS) Selection Guide | MESIL®
Bottom Line Up Front (BLUF): Selecting the exact Vinyl Silicone Fluid (CAS 68083-19-2) is a mathematical balance between viscosity and crosslink density. As viscosity increases (from 20 to 20,000 cSt), the terminal vinyl content strictly decreases (from 3.47% to 0.09%). This technical selection guide provides a deterministic "If-Then" path to match your Liquid Silicone Rubber (LSR) and RTV-2k formulation requirements to the precise MESIL® 206 series polymer.
Application-Driven Selection Logic
Stop guessing with base polymers. Use the conditional logic below to map your hardness and mechanical requirements directly to the correct Vi-PDMS grade.
- Your application requires extremely high crosslink density, such as hard silicone rubber modifiers, silicone-acrylic resin emulsions, or you need a reactive intermediate for perfusion silicone rubber.
- Select MESIL® 206-20 or 206-100. These low-viscosity fluids (20-100 cSt) offer the highest terminal vinyl content (up to 3.47 wt%), acting as powerful hardening agents and reactive crosslinking nodes.
- You are formulating standard Liquid Silicone Rubber (LSR) for injection molding requiring a balanced mix of flowability, tensile strength, and Shore A hardness.
- Select MESIL® 206-500 to 206-2000. Operating in the 500-2000 cSt range with a moderate vinyl content (0.16% - 0.55%), these are the industry-standard base rubbers for addition-curing RTV-2k systems.
- You are designing very soft, high-elongation silicone elastomers, potting compounds, or gap fillers where flexibility is prioritized over rigidity.
- Select MESIL® 206-5000, 206-10000, or 206-20000. With high viscosities (up to 20,000 cSt) and very low vinyl content (~0.1%), these long-chain polymers create loose elastomer networks perfect for flexible encapsulation.
Viscosity & Vinyl Content Matrix
Data drives formulation. Review the inverse correlation between kinematic viscosity (cSt) and reactive vinyl weight percentage to calibrate your silicon-hydride crosslinker ratios.
| Product Grade | Viscosity (25°C, cSt) | Vinyl Content (wt%) | Volatile (150°C, 3h) % | Chemical Nature |
|---|---|---|---|---|
| MESIL® 206-20 | 20 | 2.80 ~ 3.47 | - | High-reactive modifier |
| MESIL® 206-100 | 100 | 0.90 ~ 1.15 | ≤ 1.0 | Low-viscosity base |
| MESIL® 206-500 | 500 | 0.40 ~ 0.55 | ≤ 1.0 | Standard LSR base |
| MESIL® 206-1000 | 1,000 | 0.28 ~ 0.37 | ≤ 1.0 | Standard LSR base |
| MESIL® 206-2000 | 2,000 | 0.16 ~ 0.30 | ≤ 1.0 | Medium-high viscosity |
| MESIL® 206-5000 | 5,000 | 0.13 ~ 0.18 | ≤ 1.0 | High viscosity, low crosslink |
| MESIL® 206-10000 | 10,000 | 0.11 ~ 0.17 | ≤ 1.0 | Soft elastomer base |
| MESIL® 206-20000 | 20,000 | 0.09 ~ 0.13 | ≤ 1.0 | Ultra-soft elastomer base |
Process Visualization & Formulation
Liquid Silicone Rubber (LSR) Injection Molding
For addition-curing systems, MESIL® 206 series fluids serve as the primary component (Part A). During the injection molding process, the terminal vinyl groups react with a silicon-hydride (Si-H) crosslinker (Part B) via hydrosilylation. This process mandates the presence of a platinum catalyst and heat to form a permanent, non-reverting silicone elastomer.
System Loop: Expert Selection Q&A
- Q: Why does vinyl content decrease as viscosity increases?
- A: In a vinyl-terminated polydimethylsiloxane, the reactive vinyl groups are located exclusively at the ends of the polymer chain. As the polymer chain grows longer (which increases viscosity), the ratio of the end groups to the total molecular weight decreases, resulting in a lower overall vinyl weight percentage.
- Q: Can I mix different grades of the 206 series?
- A: Absolutely. Formulators frequently blend high-viscosity polymers (e.g., 206-10000) with low-viscosity, high-vinyl fluids (e.g., 206-100) as blend polymers. This creates a bimodal distribution that optimizes both the tear strength and the final Shore hardness of the RTV-2k rubber.
- Q: What are the packaging and storage constraints?
- A: The fluid is packaged in 190 kg steel drums or 950 kg IBC drums. It has a shelf life of 36 months when stored in the original unopened packaging at ambient temperatures. It does not freeze, removing low-temperature storage restrictions.