Ten-membered Si-O ring with 10 methyl groups; clear colourless liquid; bp 210°C; SVHC vPvB classification.

D5 — decamethylcyclopentasiloxane, CAS 541-02-6 — is a cyclic siloxane consisting of a ten-membered Si-O ring with two methyl groups on each silicon atom. Molecular formula C₁₀H₃₀O₅Si₅, molecular weight 370.8 g/mol, density 0.957 g/cm³ at 25°C, refractive index 1.396. SEMITECH supplies D5 as a clear colourless mobile liquid at ≥99.5% purity by GC, with D4 impurity ≤0.2%, D6+ impurity ≤0.3%, water content ≤30 ppm, acidity (as HCl) ≤2 ppm, and APHA colour ≤10. Boiling point 210°C at atmospheric pressure (130°C at 50 mmHg for vacuum distillation), flash point 78°C closed cup.

D5 is produced by the same fractional distillation process used for D4, but separated as the heavier-cyclic fraction. Distillation typically gives 30–35% D5 yield from the DMC mixture, vs 50–60% D4 yield. The higher boiling point of D5 (210°C vs 175°C for D4) is the key functional differentiator in cosmetic applications: D5 evaporates more slowly from skin and hair, providing the smooth dry-feel typical of antiperspirant aerosol carriers and dry-shampoo formulations, vs D4’s faster evaporation that gives the immediate weightless feel of foundation and BB cream vehicles. Cost premium over D4 is typically 5–15% on a per-kg basis at Chinese-origin spot pricing — D5 is the slightly higher-value cyclic in the value chain due to lower yield from fractionation.

Antiperspirant aerosol, hair-care leave-on, sun-care, foundation/BB cream, dry-feel personal care, polymer feedstock.

Cosmetic and personal-care direct ingredient is the largest single application — D5 is added directly to antiperspirant aerosol formulations (5–25% of formulation), hair-care leave-on products (smoothening serum, anti-frizz spray, dry shampoo at 10–40%), foundation and BB cream (volatile-vehicle carrier at 15–30%), sun-care lotion (water-resistant SPF formulations at 5–20%), and shave gel and aftershave (emollient and dry-feel agent at 3–10%). D5 functions as a volatile carrier — it deposits the active formulation onto skin or hair, then evaporates over 5–30 minutes leaving a non-greasy dry-feel finish.

D5-derived silicone fluid manufacture uses fractionated D5 as feedstock for medium-volatility silicone fluid (5–10 cP grades) where the residual D5 monomer in the finished fluid is the desired functional component. Unlike D4-feedstock production where the goal is to minimise residual cyclics, D5-derived fluid manufacture deliberately retains a controlled fraction (10–30%) of unpolymerised D5 in the final product to provide volatile-carrier behaviour. Specialty silicone gum production for high-modulus elastomer applications uses D5 in conjunction with D4 to control chain-length distribution and polymer flexibility. Optical-clarity silicone for LED encapsulation uses D5 over D4 in some formulations because the higher boiling point reduces volatile loss during high-temperature curing of the encapsulant.

D5 listed on REACH SVHC (vPvB); wash-off cosmetic limits scheduled; leave-on limits under review.

D5 is on the ECHA REACH SVHC candidate list — listed in 2018 alongside D4 under the vPvB criterion. The regulatory timeline for D5 in personal-care products differs from D4: (1) wash-off cosmetic products (shampoo, body wash, conditioner) face a 0.1% D5 limit on a phased timeline ending 2030+; (2) leave-on cosmetic products (antiperspirant aerosol, hair-care leave-on, foundation) are under continued ECHA review with no specific limit announced yet but expected to follow the wash-off timeline plus 2–3 years; (3) industrial silicone products (sealants, lubricants, electronic encapsulation) are exempt from the cosmetic limits but still require REACH downstream-user registration and SVHC notification.

SEMITECH provides the same REACH compliance documentation packet for D5 as for D4: ECHA registrant number reference, SVHC notification template, quantitative D5 declaration (always 99.5–99.9% by GC), full SVHC SDS classification, toxicology dossier reference. Personal-care formulators using D5 as direct cosmetic ingredient should monitor ECHA timelines for their specific product category and engage REACH consultancy for product-specific reformulation pathways if their target market is the EU. Many global personal-care brands have begun reformulating D5-rich products using alternative volatile silicones (PMV — phenyl methicone, dimethicone copolyols, cyclomethicone alternatives) to derisk the EU compliance pathway.

CoA per shipment with cyclic GC breakdown; 200 kg drum / 1 t IBC; 24-month shelf life; flash point 78°C — Class II combustible.

SEMITECH issues a CoA on every batch with: D5 purity (GC, target ≥99.5%), D4 impurity (GC, target ≤0.2%), D6+ impurity (GC, target ≤0.3%), water content (Karl Fischer, target ≤30 ppm), acidity as HCl (potentiometric, target ≤2 ppm), APHA colour (target ≤10), density at 25°C, refractive index, and flash point. Standard packing 200 kg HDPE-lined steel drums; 1 t IBC totes for high-volume cosmetic manufacturers; 25 t ISO-tank for bulk silicone polymer customers. MOQ 200 kg per order. Lead time 2–4 weeks ex-Zhejiang to Asia ports, 4–6 weeks to Europe and North America after sea freight.

Storage: D5 has flash point 78°C — Class II combustible liquid (less stringent than D4’s Class IB flammable). Standard handling: store sealed below 30°C in original packaging; ground transfer equipment as standard practice; no flammable-storage cabinet required (vs D4 which does require it). Shelf life 24 months sealed; the higher boiling point makes D5 less prone to volatile loss on opened storage than D4. Cosmetic-grade certification: D5 supplied for direct cosmetic ingredient use is supplied with additional documentation — heavy metal residue (ICP-MS, target Pb/Sn/As/Hg below cosmetic limits), microbial limits (USP-NF method), and customer-specific compliance letters (China NMPA, Japan PMDA cosmetic registration support, Korea MFDS) on request with 1–2 week documentation lead time. Health and regulatory: REACH SVHC vPvB classification; FDA 21 CFR 175.300 listed for indirect food-contact in adhesive components; mild skin and eye irritant; standard PPE — nitrile gloves, splash goggles. Full REACH SVHC and cosmetic-grade compliance documentation packet on request.

D5 is the higher-boiling fractionated cyclic siloxane — direct cosmetic ingredient (antiperspirant, hair-care, foundation) + specialty silicone polymer feedstock. ≥99.5% purity. Higher boiling point than D4 gives slower-evaporation dry-feel in personal care. EU REACH SVHC vPvB classification — wash-off cosmetic limits scheduled, leave-on limits under review.

SEMITECH stocked grade; CoA per batch with cyclic GC distribution.