Linear PDMS with Si-H groups; clear colourless mobile liquid; releases H₂ on hydrolysis; 4–7 Si-H per chain.

Methyl hydrogen silicone oil — also called polymethylhydrosiloxane (PMHS) or methylhydrogensiloxane homopolymer, CAS 9004-73-3 — is a linear polysiloxane with the structure (CH₃)₃Si-O-[CH(H)Si-O]ₙ-Si(CH₃)₃, where each silicon atom in the chain backbone bears one methyl group AND one hydrogen instead of the two methyls of standard PDMS. Typical commercial grades have n = 30–50 silicon-oxygen repeat units, MW 2,000–4,000 g/mol, density 0.99 g/cm³, viscosity 20–40 cP at 25°C, and Si-H active hydrogen content of 1.5% by weight (corresponding to ~4–7 Si-H groups per polymer chain — the exact number depends on chain length).

SEMITECH supplies methyl hydrogen silicone at active hydrogen content 1.45–1.55% (verified by gas-volumetric measurement of H₂ released on alkaline hydrolysis), water content ≤500 ppm, viscosity at 25°C 20–40 cP, density 0.99 ± 0.01 g/cm³, and APHA colour ≤30. The compound is fully soluble in nearly all organic solvents (toluene, hexane, IPA, MEK, esters) and miscible with silicone fluids. The Si-H bond is hydrolytically stable in neutral aqueous and alcoholic media but releases H₂ gas on contact with strong acid or strong base — this controlled-release behaviour is the basis of its application chemistry. The compound is flammable (flash point 60°C), Class II combustible.

Si-H adds to vinyl (Pt-catalysed); hydrolyses to Si-OH + H₂ on basic conditions; reduces ketones and aldehydes.

Three reactivity modes drive the application chemistry of methyl hydrogen silicone: (1) hydrosilylation — Pt-catalysed addition of Si-H across C=C double bonds, used in addition-cure silicone (LSR, RTV-2) where Si-H of the crosslinker adds to the vinyl group of vinyl-PDMS to form Si-C bonds; (2) hydrolysis — Si-H + H₂O → Si-OH + H₂, occurring under acid or base catalysis or at elevated temperature; (3) reduction — Si-H acts as a hydride donor, reducing ketones, aldehydes, and certain functional groups in synthetic chemistry.

• 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

In addition-cure silicone (LSR injection moulding, RTV-2 medical and optical), methyl hydrogen silicone is metered into the B-side at 1–3% on total formulation alongside Karstedt or Speier platinum catalyst. The Si-H groups react with vinyl-PDMS A-side under Pt catalysis at 80–200°C to form covalent Si-CH₂-CH₂-Si crosslinks. Stoichiometry is typically 1.0–1.5 mol Si-H per mol vinyl on the A-side — slight excess Si-H provides a safety margin against minor catalyst poisoning. Avoid water and amine contamination — Si-H hydrolyses at higher rate than vinyl-Si reacts with Si-H, so any moisture or amine in the formulation consumes Si-H without forming productive crosslinks, leading to under-cure or post-cure tackiness.

Hydrosilylation crosslinker (largest), textile water repellent, paper release coating, stone/glass waterproofing.

Addition-cure silicone crosslinker for LSR and RTV-2 applications is the largest single use — automotive and consumer LSR injection-moulded parts, medical-device elastomers, optical encapsulation, food-contact silicone bakeware. Methyl hydrogen silicone at 1–3% on total formulation in the B-side, paired with Karstedt platinum catalyst at 5–20 ppm Pt, gives the cure profile needed for production-scale injection moulding (10–30 second cycle at 150–200°C) or RTV-2 cast moulding (5–30 min at 80–120°C).

Textile water-repellent finish uses methyl hydrogen silicone at 2–6% (as 30% emulsion) on textile fabric weight. The silicone is padded onto the fabric, then cured at 130–170°C for 1–3 minutes — during cure, the Si-H groups hydrolyse with atmospheric moisture and self-condense to form a silicone film that is permanently bonded to the textile surface, providing durable water repellency for outdoor garments, technical textiles, and rainwear. Paper release coating uses methyl hydrogen silicone at 1–3% on paper weight to produce silicone-coated release liners for pressure-sensitive adhesive label backings. Stone, brick, and concrete waterproofing uses methyl hydrogen silicone at 5–15% in solvent solution — penetrates 1–5 mm into substrate, hydrolyses with atmospheric moisture and ground moisture to form a hydrophobic silicone film that prevents water absorption while remaining vapour-permeable.

CoA per shipment with active H% verification; 200 kg drum; 12-month shelf life under N₂; flammable Class II.

SEMITECH issues a CoA on every batch with: active hydrogen content (gas-volumetric H₂ release on alkaline hydrolysis, target 1.45–1.55%), viscosity at 25°C (Brookfield, target 20–40 cP), water content (Karl Fischer, target ≤500 ppm), APHA colour (target ≤30), density at 25°C, and refractive index. Standard packing 200 kg HDPE-lined steel drums under nitrogen blanket; 25 kg HDPE jerrycans for laboratory and qualification quantities. MOQ 200 kg per order for production grade; 25 kg for trial. Lead time 2–4 weeks ex-Zhejiang to Asia ports, 4–6 weeks to Europe and North America.

Storage: methyl hydrogen silicone has flash point 60°C — Class II combustible liquid. Standard handling: store sealed below 30°C in original packaging under nitrogen blanket; avoid contact with bases (NaOH, KOH, amines, ammonia) and oxidisers — contact with concentrated bases causes rapid hydrogen evolution and pressure build-up; ground all transfer equipment for static dissipation. Shelf life 12 months sealed under N₂; opened drums should be re-blanketed and consumed within 90 days. Reactivity warnings: contact with strong base releases hydrogen gas (flammable, asphyxiant, can build up pressure in sealed containers); contact with concentrated acid (H₂SO₄, HCl) can cause exothermic decomposition; contact with primary amines can cause exothermic Si-N bond formation with H₂ release. Spill response: contain on inert media (vermiculite, dry sand), neutralise residue with cold dilute acid (vinegar, citric acid solution at 5%), dispose as Class II combustible + reactive hazardous waste. Health and regulatory: REACH-registered for industrial use; FDA 21 CFR 175.300 listed for indirect food-contact in adhesive components; mild skin and eye irritant; standard PPE — nitrile gloves, splash goggles, lab coat. SDS in EU/GHS format issued with every shipment with full reactivity classification.

Methyl hydrogen silicone (PMHS) is the Si-H functional polysiloxane — 1.5% active H content provides 4–7 Si-H crosslinking sites per chain. Largest application is hydrosilylation crosslinker in LSR/RTV-2 paired with Karstedt platinum. Avoid moisture, base, and amine contamination — Si-H hydrolyses faster than it reacts with vinyl-PDMS. Class II combustible; nitrogen-blanket storage; 12-month shelf life.

SEMITECH stocked grade; CoA per batch with active hydrogen verification.