Methyl Hydrogen Silicone Oil (PMHS, Polymethylhydrosiloxane, CAS 9004-73-3): Si-H Functional Crosslinker for Hydrosilylation and Water-Repellent Treatments
SEMITECH methyl hydrogen silicone oil is the Si-H functional polysiloxane — a PDMS chain with one methyl replaced by hydrogen on each silicon, giving 4–7 reactive Si-H groups per chain. Used in addition-cure silicone (LSR, RTV-2), textile and paper water-repellent treatments, and as a reducing agent in synthetic chemistry. 200 kg drum, 2–4 week ex-China lead time.
Contents
| 9004-73-3 | ~1.5% | 20–40 cP |
|---|---|---|
| CAS number | H content (active) | Viscosity |
Chemistry & Specifications
Linear PDMS with Si-H groups; clear colourless mobile liquid; releases H₂ on hydrolysis; 4–7 Si-H per chain.
PMHS (CAS 9004-73-3) has structure (CH₃)₃Si-O-[CH(H)Si-O]ₙ-Si(CH₃)₃ with n = 30–50, MW 2,000–4,000 g/mol, density 0.99 g/cm³, viscosity 20–40 cP. SEMITECH supplies at active hydrogen content 1.45–1.55%, water ≤500 ppm, APHA ≤30. The Si-H bond is hydrolytically stable in neutral media but releases H₂ on contact with strong acid or base. Flash point 60°C, Class II combustible.
Si-H Reactivity: Hydrosilylation, Hydrolysis, Reduction
Si-H adds to vinyl (Pt-catalysed); hydrolyses to Si-OH + H₂ on basic conditions; reduces ketones and aldehydes.
- Hydrosilylation crosslinker — 1–3% on vinyl-PDMS in LSR / RTV-2; Pt catalysis (Karstedt or Speier) at 5–20 ppm
- Textile water repellent — 2–6% emulsion on textile weight; cures by surface hydrolysis to silicone film
- Paper release coating — 1–3% emulsion on paper weight; provides peel release for adhesive labels
- Glass and stone waterproofing — 5–15% solvent solution; cures by atmospheric moisture-driven hydrolysis
Stoichiometry in LSR is typically 1.0–1.5 mol Si-H per mol vinyl. Avoid water and amine contamination — Si-H hydrolyses faster than it reacts with vinyl-Si, causing under-cure or post-cure tackiness.
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Applications: LSR / RTV-2 Crosslinker, Textile Repellent, Paper Release, Stone Waterproofing
Hydrosilylation crosslinker (largest), textile water repellent, paper release coating, stone/glass waterproofing.
Addition-cure silicone crosslinker for LSR and RTV-2 is the largest use — automotive and consumer moulded parts, medical-device elastomers, optical encapsulation, food-contact silicone. 1–3% in B-side with Karstedt Pt at 5–20 ppm.
Textile water-repellent finish at 2–6% (as 30% emulsion) on fabric weight, cured at 130–170°C for 1–3 minutes, forms a permanently bonded silicone film. Paper release coating at 1–3% produces silicone-coated release liners. Stone and concrete waterproofing at 5–15% in solvent solution penetrates substrate and hydrolyses to hydrophobic film.
Procurement, Storage and Quality Control
CoA per shipment with active H% verification; 200 kg drum; 12-month shelf life under N₂; flammable Class II.
Standard packing 200 kg HDPE-lined steel drums under N₂; 25 kg jerrycans for lab. MOQ 200 kg, lead time 2–4 weeks to Asia, 4–6 weeks to Europe/North America. Store sealed below 30°C; avoid contact with bases, oxidisers, and primary amines. REACH-registered; FDA 21 CFR 175.300 listed for indirect food-contact.
Methyl Hydrogen Silicone Oil Specification Sheet
SEMITECH stocked grade; CoA per batch with active hydrogen verification.
| Property | Specification | Test Method |
|---|---|---|
| Chemical name | Polymethylhydrosiloxane / Methyl hydrogen silicone oil | — |
| Synonyms | PMHS / methylhydrogensiloxane homopolymer | — |
| CAS number | 9004-73-3 | — |
| Polymer structure | (CH₃)₃Si-O-[CH(H)Si-O]ₙ-Si(CH₃)₃, n=30-50 | — |
| Molecular weight | 2,000–4,000 g/mol | GPC |
| Active hydrogen content | 1.45–1.55% | Gas-volumetric (alkaline hydrolysis) |
| Si-H groups per chain | ~4–7 | Calculated from Mw and H% |
| Viscosity (25°C) | 20–40 cP | Brookfield |
| Water content | ≤500 ppm | Karl Fischer |
| APHA colour | ≤30 | ASTM D1209 |
| Density (25°C) | 0.98–1.00 g/cm³ | ASTM D1475 |
| Refractive index (25°C) | 1.396–1.398 | ASTM D1218 |
| Flash point | 60°C (closed cup) | ASTM D93 |
| Flammability classification | Class II combustible | — |
| Reactivity | Reacts with strong base releasing H₂; reduces with H⁻ | — |
| Solubility | Soluble in toluene, hexane, IPA, esters; insoluble in water | — |
| Packaging | 200 kg HDPE-lined steel drum / 25 kg HDPE jerrycan for lab | — |
| Shelf life | 12 months sealed below 30°C under N₂ | — |
FAQ
+How much methyl hydrogen silicone do I dose into my LSR formulation?
Standard LSR B-side: 1.5–2.5% PMHS with Karstedt Pt at 5–10 ppm and inhibitor at 100–500 ppm. Target Si-H:vinyl molar ratio 1.1–1.3 based on actual batch CoA values. Higher ratios (1.5+) cause excess crosslink density; lower (<1.0) cause under-cure.
+Can methyl hydrogen silicone replace methyltrimethoxysilane (MTMS) as a textile water repellent?
Both are valid. PMHS cures by Si-H hydrolysis, releases H₂, and gives a more flexible silicone film with better hand-feel and wash durability. MTMS cures faster with lower cost but gives a more rigid film. Choice depends on customer specification.
+Why does my methyl hydrogen silicone batch sometimes show drift in active H content?
Three sources: (1) moisture-induced hydrolysis during storage; (2) thermal disproportionation above 60°C; (3) batch-to-batch polymerisation variance. Adjust formulation stoichiometry per CoA H content for production consistency.