Dimethyl Silicone Oil: PDMS Production and Viscosity Grades
title: "Dimethyl Silicone Oil: PDMS Production and Viscosity Grades" description: "How polydimethylsiloxane (PDMS) silicone oil is produced, the range of viscosity grades available, and how buyers select the right grade for their application." section: "midstream"
Production Route
Polydimethylsiloxane (PDMS) silicone oil is manufactured by equilibrating DMC or D4 with a chain-stopping agent—typically hexamethyldisiloxane (MM) for methyl-terminated oil—under acid or base catalysis at 100–160 °C. The ratio of MM to cyclic monomer determines chain length and therefore viscosity. After equilibration, residual cyclics are stripped under vacuum to reduce D4/D5 content below regulatory thresholds (the EU limits D4 in rinse-off cosmetics to <0.1%).
The reaction is straightforward chemistry, but precise viscosity control requires tight temperature management and accurate MM dosing. Low-viscosity grades (1–100 cSt) are produced at higher MM-to-DMC ratios and shorter equilibration times; high-viscosity grades (100,000–1,000,000 cSt) require longer equilibration and minimal chain stopper.
Viscosity Grade Map
| Grade (cSt) | Typical Appearance | Primary Applications |
|---|---|---|
| 1–10 | Water-clear, mobile liquid | Cosmetic carrier, antifoam active |
| 20–100 | Low viscosity oil | Hydraulic fluid, textile softener, mold release |
| 200–1,000 | Medium oil | Transformer fluid, damping fluid, personal care |
| 5,000–60,000 | Thick oil | Sealant extender, thermal interface base |
| 100,000–1,000,000 | Gel-like | Pressure-sensitive adhesive base, vibration damping |
Viscosity is measured at 25 °C by Ubbelohde capillary viscometry (cSt) or by Brookfield rotational viscometry (mPa·s ≈ cP). For Newtonian PDMS grades below ~10,000 cSt, the two values are numerically equivalent.
Grade Selection and Procurement Notes
Buyers should specify: (1) target viscosity ± tolerance (typically ±10% for standard grades), (2) refractive index as a purity check (pure PDMS: ~1.403 at 25 °C), (3) volatility specification for food-contact or cosmetic applications (typically <0.3% weight loss at 150 °C / 3 h), and (4) D4 content if required for regulatory compliance.
Chinese producers offer commodity PDMS at competitive prices in 200 L drums or IBC totes, but lot-to-lot viscosity consistency can vary. For applications requiring tight batch-to-batch uniformity—cosmetic formulations, medical devices, precision damping—qualifying against a COA-verified reference lot and specifying certificate of analysis requirements upfront reduces re-qualification costs.