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D4 (Octamethylcyclotetrasiloxane, CAS 556-67-2): Fractionated Cyclic Siloxane for Cosmetic-Grade, Pharmaceutical-Grade, and Optical-Clarity Silicone
SEMITECH D4 is the fractionated cyclic siloxane — distillation-purified octamethylcyclotetrasiloxane at ≥99.5% — for applications where the unfractionated DMC mixture cannot meet purity requirements: cosmetic-grade silicone fluid, pharmaceutical USP-NF dimethicone, optical-clarity LED encapsulation, and laboratory hydrosilylation chemistry. EU REACH SVHC documentation packet on every shipment. 200 kg HDPE drum, 2–4 week ex-China lead time.
Contents
| 556-67-2 | ≥99.5% | 296.6 |
|---|---|---|
| CAS number | Purity | MW (g/mol) |
Chemistry & Specifications
Eight-membered Si-O ring with 8 methyl groups; clear colourless liquid; bp 175°C; SVHC vPvB classification.
D4 (CAS 556-67-2) — MW 296.6, density 0.956 g/cm³, RI 1.396, bp 175.7°C, flash point 57°C (Class IB flammable). SEMITECH supplies at ≥99.5% by GC, D3 ≤0.2%, D5+ ≤0.3%, water ≤30 ppm, acidity ≤2 ppm, APHA ≤10. Produced by fractional distillation of DMC at ~25–35% cost premium reflecting fractionation energy.
Applications: Cosmetic, Pharmaceutical, Optical, R&D
Cosmetic silicone fluid, USP-NF dimethicone, LED optical encapsulation, hydrosilylation chemistry research.
Cosmetic-grade silicone fluid (largest) — EU REACH 2027 restricts D4 residual to ≤0.1% in leave-on products, requiring controlled-purity D4 feedstock. Pharmaceutical USP-NF dimethicone — documented cyclic-content control per monograph. Optical-clarity silicone — 99.9%+ specification for LED encapsulation where trace impurities cause photonic defects. Lab hydrosilylation — single-cyclic model substrate for kinetic studies.
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EU REACH SVHC Designation and Compliance Documentation
D4 listed on REACH SVHC candidate list (vPvB); industrial-feedstock use permitted with documented compliance pathway.
D4 is listed as SVHC under vPvB criterion (2018). Industrial silicone feedstock use is permitted under REACH registrations. Downstream products with >0.1% D4 require SVHC notification. Personal-care leave-on products face ≤0.1% limit from 2027. SEMITECH provides full compliance documentation on every shipment.
Procurement, Storage and Quality Control
CoA per shipment with cyclic GC breakdown; 200 kg drum; 24-month shelf life; flash point 57°C requires Class IB storage.
CoA per batch: D4 purity (≥99.5%), D3 (≤0.2%), D5+ (≤0.3%), water (≤30 ppm), acidity (≤2 ppm), APHA (≤10). MOQ 200 kg. Lead time 2–4 weeks Asia, 4–6 weeks Europe/North America. Flash point 57°C — Class IB flammable, dedicated storage required. Shelf life 24 months sealed.
D4 Specification Sheet
SEMITECH stocked grade; CoA per batch with cyclic GC distribution.
| Property | Specification | Test Method |
|---|---|---|
| Chemical name | Octamethylcyclotetrasiloxane | — |
| CAS number | 556-67-2 | — |
| Molecular formula | C₈H₂₄O₄Si₄ | — |
| Molecular weight | 296.6 g/mol | — |
| Purity (D4) | ≥99.5% | Gas chromatography |
| D3 impurity | ≤0.2% | GC |
| D5+ impurity | ≤0.3% | GC |
| Water content | ≤30 ppm | Karl Fischer |
| Acidity (as HCl) | ≤2 ppm | Potentiometric titration |
| APHA colour | ≤10 | ASTM D1209 |
| Density (25°C) | 0.956 g/cm³ | ASTM D1475 |
| Refractive index (25°C) | 1.396 | ASTM D1218 |
| Boiling point | 175.7°C (atmospheric) | — |
| Flash point | 57°C (closed cup) | ASTM D93 |
| Flammability classification | Class IB / EU CLP Flammable Liquid Cat. 3 | — |
| EU REACH | SVHC candidate list (vPvB) — industrial feedstock use permitted | — |
| Packaging | 200 kg HDPE-lined steel drum / 1 t IBC | — |
| Shelf life | 24 months sealed below 30°C | — |
FAQ
+When is fractionated D4 worth the cost premium over DMC?
Worth it when documented residual-cyclic control is required: cosmetic leave-on products (EU REACH 2027 D4 ≤0.1%), pharmaceutical USP-NF dimethicone, optical-clarity LED encapsulation, and regulatory submissions requiring controlled feedstock. Not worth it for commodity silicone fluid, HCR rubber, RTV base polymer, or defoamer base.
+Will the EU REACH D4 SVHC designation block silicone sales in Europe?
No. Industrial silicone products remain marketable with REACH registration and SVHC notification. Personal-care leave-on products with >0.1% residual D4 face the 2027 limit and need reformulation or post-polymerisation stripping.
+What is the typical impurity profile from Chinese D4 fractionation?
Standard (50-plate column): D4 99.5–99.7%, D3 0.1–0.2%, D5 0.1–0.3%. Premium (80-plate): 99.9% at 30–40% additional cost. SEMITECH stock grade is 99.5%; 99.9% premium available make-to-order (4-week lead, 1 t MOQ).