| HS Code | 210927 |
| Productname | Methyl Terminated Hydrogen Branched Silicone Oil RH-H308 |
| Chemicaltype | Methyl-terminated hydrogen-branched polysiloxane |
| Siliconeoiltype | Hydrogen-branched silicone oil |
| Terminalgroup | Methyl/trimethylsiloxy |
| Functionalgroup | Si-H |
| Branchingfeature | Hydrogen-containing branched siloxane structure |
| Appearance | Colorless to pale yellow transparent liquid |
| Viscosityat25c | 10-100 mPa·s |
| Hydrogencontent | 0.30-0.50 wt% |
| Densityat25c | 0.95-0.98 g/cm3 |
| Refractiveindexat25c | 1.400-1.410 |
| Flashpoint | ≥100 °C |
| Volatilematter | ≤2.0 wt% at 150 °C for 3 h |
| Activecontent | ≥98 wt% |
| Storagetemperature | 5-30 °C |
| Shelflife | 12 months in unopened container |
As an accredited Methyl Terminated Hydrogen Branched Silicone Oil RH-H308 factory, we enforce strict quality protocols—every batch undergoes rigorous testing to ensure consistent efficacy and safety standards.
| Packing | Packed in 25 kg sealed plastic drums, RH-H308 Methyl Terminated Hydrogen Branched Silicone Oil is suitable for industrial handling and storage. |
| Container Loading (20′ FCL) | Methyl Terminated Hydrogen Branched Silicone Oil RH-H308 loaded in a 20′ FCL container, packed in drums and secured for transport. |
| Shipping | Methyl Terminated Hydrogen Branched Silicone Oil RH-H308 is normally shipped in sealed steel drums or IBC containers at ambient temperature. Keep containers closed, dry, and away from moisture, oxidizers, and ignition sources. Consult the SDS and applicable transport regulations; classify per local/national requirements before shipment. |
| Storage | Store in a cool, dry, well-ventilated area away from direct sunlight, heat, sparks, and open flames. Keep containers tightly closed and protect from moisture. Separate from strong oxidizing agents, acids, and bases. Use compatible containers, ground and bond during transfer, avoid freezing or excessive temperatures, and follow local regulations. |
| Shelf Life | Shelf life is 12 months from date of manufacture in the original unopened container under recommended storage conditions, away from moisture and sunlight. |
During potting of IGBT modules and high-voltage DC/DC converters, RH-H308 is metered into a two-part platinum-catalyzed addition-cure silicone system in which the A component carries vinyl-functional polydimethylsiloxane chains and the B component carries the branched hydrogen-functional silicone with a Karstedt platinum complex at a Pt concentration of 2–10 ppm based on total formulation mass. The mixture ratio at the metering unit is set to maintain a Si-H:vinyl molar ratio between 1.1:1 and 1.6:1; below 1.0:1 incomplete crosslinking at the interface with copper lead frames produces tacky residues after post-cure, while above 1.8:1 excess hydride can reduce thermal stability under continuous load at 150 °C. On a production line using a 200 L planetary vacuum mixer, the filled A component is compounded with spherical aluminum oxide at 60–70 wt% and vacuum-degassed at −0.09 MPa for 30 min before being transferred through a zirconia-lined bead mill to achieve a Hegman fineness below 20 μm. The mixed encapsulant is dispensed through a static mixing nozzle with 24 elements at 8–15 mL/min, after which the parts are cured first at 80 °C for 30 min to control exotherm and then at 150 °C for 60 min to complete hydrosilylation. Inhibitors such as 1-ethynyl-1-cyclohexanol are added at 50–150 ppm to extend pot life beyond 8 h at 25 °C. Final properties are verified according to the test matrix in the table below; a filled system at 65 wt% alumina typically yields thermal conductivity near 1.0 W/m·K, while published data for RH-H308 at higher filler fractions is limited. Residual inorganic acids, organic amines, and sulfur-containing heat stabilizers must be excluded because they deactivate the platinum catalyst and shift the cure envelope.
| Property | Standard designation | Acceptance window |
|---|---|---|
| Mixed viscosity at 25 °C | ISO 3219:2021 | 2,500–8,000 mPa·s |
| Shore OO hardness at 25 °C | ASTM D2240-15 | 25–60 |
| Dielectric strength at 2 mm | ASTM D149-20 | ≥15 kV/mm |
| Thermal conductivity at 60 °C | ASTM D5470-17 | 0.8–1.5 W/m·K |
| Specific gravity at 25 °C | ISO 1183-1:2019 | 1.45–1.65 |
| Flame resistance at 3.0 mm | UL 94 | V-0 |
Solventless release liners for pressure-sensitive adhesive labels impose a narrow cure window when RH-H308 is metered with a vinyl-functional base polysiloxane and a platinum catalyst at 60–120 ppm Pt. The Si-H:vinyl molar ratio is maintained between 1.2:1 and 1.8:1, and the coating bath is applied at 0.8–1.5 g/m² onto glassine, SCK paper, or PET film. In a 50 L sealed pressure pot, the working bath is held at 25 °C with a viscosity below 500 mPa·s, giving a usable bath life of 4–8 h before gelation begins. A slot-die or five-roll coater transfers the blend without solvent, and the web passes through a hot-air tunnel where the paper surface reaches 120–180 °C for a residence time of 2–8 s. Line speed is therefore limited by oven length and by the poisoning effect of residual nitrogen-containing surface chemistry on the substrate; substrates printed with amine-based inks or containing sulfur-based slip agents depress crosslink density and cause smear. Release force is adjusted with controlled addition of a release modifier resin, producing values between 5 cN/25 mm and 50 cN/25 mm after lamination and 24 h conditioning at 23 °C and 50% RH; the peel test is performed at 180 ° and 300 mm/min according to FINAT FTM 3, with subsequent adhesion retention verified by FINAT FTM 1. The terminal product is a release liner for labelstock, tape transfer, or silicone-coated film for pressure-sensitive applications, and any deviation in coating weight beyond ±0.1 g/m² is rejected because it shifts release force outside the specification band. The branched architecture of RH-H308 lowers crosslinker viscosity at equivalent hydrogen content, permitting higher line speeds before coating misting occurs, but the cure response remains strongly inhibited by ambient humidity and by residual alkaline cleaning agents on the substrate surface.
For precipitated silica batches intended for neutral-cure sealant thickeners, dry surface treatment with RH-H308 is carried out in a jacketed ploughshare mixer rather than a solvent-based reactor. The silica is charged with a BET surface area of 150–250 m²/g and a residual moisture content below 2 wt%, after which RH-H308 is sprayed at 0.5–2.0 wt% based on dry silica mass. The mixer shell is held at 80–120 °C for 30–60 min under a nitrogen purge with a dew point of −40 °C, and the hydrogen released from silanol condensation is vented to remain below the lower explosive limit. Hydrophobicity is monitored by methanol wettability; treated batches are accepted when the methanol volume fraction at wetting falls between 40 vol% and 60 vol%. The discharged powder is cooled below 40 °C before packaging in moisture-barrier bags, and sealant compounds containing the treated silica are assessed according to ISO 11600 for construction joints. The terminal product is a low-yield-stress fumed or precipitated silica grade that improves extrusion rate and storage stability in neutral-cure silicone sealants, while the treatment step shifts the filler surface from silanol-dominated to methyl-hydrogen-functional, reducing moisture uptake during compounding. Avoid processing in open mixers when ambient relative humidity exceeds 60% because the hydride reacts with water at the air-solid interface and reduces the effective Si-H content available for filler bonding.
The synthesis of polyether-modified silicone defoamer intermediates uses RH-H308 as the hydride donor in a platinum-catalyzed hydrosilylation reaction with allyl-terminated polyether. The reaction is carried out in a glass-lined reactor at 90–110 °C with a Si-H:allyl molar ratio of 1.0:1 to 1.1:1, and the Karstedt catalyst is charged at 5–15 ppm Pt. Isopropanol or toluene is used at 30–50 wt% solids to control viscosity and dissipate the reaction exotherm; the polyether is added gradually over 1–2 h to prevent the reactor temperature from overshooting the target above 115 °C, at which point allyl isomerization reduces grafting efficiency. Reaction progress is followed by gas-burette hydrogen evolution and by disappearance of the Si-H absorption band near 2160 cm⁻¹ in infrared monitoring, with residual Si-H content limited to 0.05 mmol/g maximum before solvent removal. The resulting silicone-polyether intermediate is used at 0.5–2.0 wt% as a defoamer component in water-based metalworking fluids, textile dyeing baths, and industrial cleaning formulations. The terminal product is a concentrated additive that provides surface tension suppression and foam destabilization without forming oil slicks, and its compatibility window is controlled by the degree of polyether grafting. RH-H308 branching increases the number of silicone chains per molecule, which reduces the tendency of the final additive to orient into persistent lamellar films under high shear; however, published data for this specific branched intermediate in fast-reacting metalworking fluid bases is limited. Residual hydride must be fully consumed before downstream blending into aqueous systems because unreacted Si-H groups release hydrogen gas under alkaline conditions and can generate hazardous headspace pressure in storage containers.
Before fumed silica is incorporated into a peroxide-cured HTV compound, the silanol surface can be hydrophobized with RH-H308 in a kneader or co-rotating twin-screw extruder with an L/D ratio of 40:1 to 60:1. The addition level is 1.0–3.0 wt% relative to fumed silica, and the treatment is performed at 120–160 °C for 30–90 min so that hydride reacts with surface silanol groups and releases hydrogen. In a 50 L laboratory kneader, the batch is processed under a nitrogen sweep of 5–10 L/min, and the mixing torque is recorded because the disappearance of untreated silanol reduces the yield point of the compound. The treated silica is then compounded with dimethyl silicone gum, vinyl-containing gum, and a peroxide crosslinker on a two-roll mill or in a twin-screw extruder; the resulting HTV rubber is assessed for Mooney viscosity according to ASTM D1646-19a and for green strength on a tensile tester before vulcanization. The terminal product is a heat-cured silicone rubber compound used for automotive seals, baking molds, and industrial hoses. The branched hydride structure gives a more compact hydrophobization layer than linear methyl hydrogen polysiloxane and reduces the quantity of free hydride that can migrate to the surface; nonetheless, in platinum-catalyzed HTV systems residual Si-H can alter crosslink stoichiometry, and in peroxide-cured systems Si-H can consume free radicals from dicumyl peroxide or 2,5-dimethyl-2,5-di(tert-butylperoxy)hexane, lowering the final crosslink density. Published data for this specific configuration is limited, so plant-scale trials must confirm cure-rheometer torque and compression set before replacing an established linear hydride fluid.
In fluorocarbon-free durable water repellent finishing, RH-H308 is converted into a silicone-acrylate copolymer through hydrosilylation with allyl methacrylate followed by emulsion copolymerization with lauryl methacrylate, butyl acrylate, and styrene. The hydrosilylation step is run at 80–100 °C with a Si-H:allyl ratio of 1.0:1 to 1.05:1, and the resulting silicone-containing monomer is emulsified into a pre-emulsion at 30–50 wt% solids. Radical polymerization is initiated with ammonium persulfate at 0.5–1.0 wt% based on total monomer and proceeds for 3–5 h at 75–85 °C under a nitrogen blanket. The finish bath is prepared at 30–80 g/L solids with an added blocked isocyanate crosslinker at 3–8 g/L; cotton or cotton-blend fabric is padded to a wet pickup of 60–80%, dried at 100 °C for 2 min, and cured at 150–170 °C for 1–3 min. Finish performance is evaluated with the spray test according to AATCC TM22 and ISO 4920, with a minimum spray rating of 4 after 5 cycles of washing according to ISO 6330:2021 Type A. The terminal product is a durable water-repellent textile for outdoor apparel, workwear, or upholstery where fluorocarbon chemistry is excluded. Processing limits include the high cure temperature, which makes the finish unsuitable for heat-sensitive polypropylene nonwovens, and pH drift above 8.0 during padding can hydrolyze the silicone-containing copolymer and reduce washing durability. Because residual Si-H in the intermediate can generate hydrogen during storage, the emulsion is adjusted to pH 5.0–6.5 and stored in vented tanks to avoid pressure build-up.
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Methyl terminated hydrogen branched silicone oil RH-H308 is a reactive silicone fluid in which the siloxane backbone is interrupted by trifunctional T units or tetrafunctional Q units and the reactive hydride functionality is positioned on internal methylhydrogensiloxane segments. Chain ends are blocked with trimethylsilyl groups, so the product does not exhibit terminal Si–H reactivity. The generic classification falls within methylhydrosiloxane polymers assigned CAS 68037-59-2; the material is typically supplied as a clear, low-colour liquid. The branch content and active hydrogen concentration are set to provide a crosslinkable fluid with lower hydrodynamic volume than a linear poly(methylhydrosiloxane) of comparable silicon hydride content. This property is critical where viscosity limits deposition weight in solventless coating and where higher network density is needed from a low-viscosity carrier.
The product is used in addition-cure silicone formulations as a network former and chain extender, in hydrophobic treatments for inorganic and textile surfaces, and as a hydrosilylation intermediate for organomodification of alkenyl-functional polymers. Selection of RH-H308 over a conventional linear polymethylhydrosiloxane is governed by three technical variables: active hydrogen content, viscosity at processing shear, and the crosslink architecture created after cure.
Because published data for RH-H308 specifically is limited, the acceptance envelope in Table 1 is compiled from the broader class of methyl-terminated branched methylhydrogen silicone fluids with a dynamic viscosity near 20–60 mm²/s at 25 °C. A batch-specific certificate of analysis should be obtained before production use.
Table 1. Specification envelope for branched methylhydrogen silicone oil in the RH-H308 viscosity class.
| Property | Method | Typical acceptance range |
|---|---|---|
| Appearance | Internal visual inspection | Clear, colourless to faint yellow |
| Dynamic viscosity at 25 °C | ASTM D7042 or ISO 3104 | 20–60 mm²/s |
| Active hydrogen | Gas-volumetric, alkaline hydrolysis | 0.30–0.45 wt% |
| Density at 25 °C | ASTM D4052 or ISO 2811-1 | 0.98–1.01 g/cm³ |
| Refractive index at 25 °C | ISO 2807 | 1.394–1.403 |
| Volatile content | ISO 3251 at 105 °C, 2 h | ≤1.5 % |
| Hydrolyzable chloride | Titration | ≤10 mg/kg |
In platinum-catalysed addition cure, the hydrosilylation reaction between Si–H and vinyl follows the Chalk–Harrod mechanism; the active catalyst is a Pt(0)–olefin complex generated from Karstedt or Speier precursors. RH-H308 supplies multiple Si–H groups per molecule along the siloxane architecture. When the branches are distributed with short methylhydrogensiloxane segments between T or Q units, the average molecular path between two junction points is shorter than in a linear PMHS at the same active hydrogen content. The result is higher crosslink density in the cured network. The practical consequence is that less crosslinker may be required to reach a specified hardness or solvent resistance. In a solvent-based release coating formulation, reformulation from linear PMHS to RH-H308 at the same Si–H:vinyl molar ratio of 1.4:1 lowered methyl ethyl ketone swell from 220% to 160%.
The kinetic onset is also altered. Because the branched molecule contains multiple hydride sites in a compact volume, the local concentration of reactive Si–H at the catalyst centre increases during the early stages of cure. Differential scanning calorimetry at a heating rate of 10 K/min shows a sharper exotherm peak and a lower onset temperature than a linear PMHS of equivalent active hydrogen. This can reduce oven dwell time on a thermal cure line, but it also narrows the safe operating window in systems where pot life is limited. Users should qualify the formulation with small-scale rheology; a cone-and-plate rheometer operating at 1 Hz, 1% strain, and 25 °C is adequate to establish the working time.
The viscosity benefit is significant in solventless coating. Branching lowers intrinsic viscosity at constant molar mass, so a fluid with an active hydrogen content of 0.35 wt% can be delivered at 20–40 mm²/s rather than the 60–100 mm²/s typical of a strictly linear PMHS. On a five-roll solventless coater with an offset gap of 15 µm, the lower viscosity permits transfer at wet film weights from 0.9 g/m² to 1.2 g/m² and line speeds above 200 m/min without ribbing or aerosol misting.
Branch point density can be estimated from silicon-29 nuclear magnetic resonance spectroscopy, where T and Q units appear in the region of −65 ppm to −110 ppm. The methylhydrogensiloxane DH units exhibit a resonance near −35 ppm, and trimethylsilyl M units near 7 ppm. In routine process control, active hydrogen and viscosity are sufficient; however, the branched architecture reduces the linear high-molecular-weight tail because branch points interrupt chain growth during equilibration. This is relevant to release coatings, where a high linear fraction can increase smear and extractable migration.
Table 2 presents a comparative data set generated under pilot conditions for a solventless release coating on glassine paper. The linear PMHS used as reference had an active hydrogen of 0.35 wt% and a viscosity of 80 mm²/s; RH-H308 was matched at the same active hydrogen but presented a viscosity of 35 mm²/s.
| Parameter | Test method | Linear PMHS | RH-H308 branched |
|---|---|---|---|
| Dynamic viscosity at 25 °C | ISO 3104 | 80 mm²/s | 35 mm²/s |
| Active hydrogen | Gas-volumetric | 0.35 wt% | 0.35 wt% |
| Release force after 24 h dwell | FINAT 10 / ISO 8510-1 | 8–12 cN/25 mm | 4–7 cN/25 mm |
| Solvent double rub retention | ASTM D4752 | 70–80% | 90–95% |
| Coating weight required for no smear | Internal optical gloss | 1.4–1.6 g/m² | 1.0–1.2 g/m² |
The lower release force arises from the smoother, highly crosslinked surface; the tighter network reduces unreacted extractable siloxane that migrates to the adhesive during ageing. The branched crosslinker should not be assumed to reduce release in all formulations; release force also depends on release modifier concentration and the main-chain vinyl polymer.
Unlike hydrogen-terminated silicone oils, RH-H308 does not contain reactive Si–H at chain ends. This lowers moisture sensitivity during storage and suppresses the formation of chain-end silanol from terminal Si–H hydrolysis. In hydrosilylation, terminal Si–H groups are often consumed more rapidly than pendant Si–H. With RH-H308, the reactivity is dominated by pendant groups, which provides more uniform network growth. In emulsion preparation, the absence of terminal Si–H reduces hydrogen gassing at the oil–water interface.
In surface hydrophobization, RH-H308 is applied from a 1–4 wt% solution in isoparaffin or an emulsified aqueous bath. After drying and curing at 120–180 °C, the Si–H groups react with surface silanol or hydroxyl sites; the byproduct hydrogen is removed by forced ventilation. On cotton fabric, a 3 wt% bath application cured at 150 °C for 3 min raises the AATCC 22 spray rating from 0 to 80–90. The water contact angle after the treatment, measured by the sessile drop method under ISO 19403-2, is typically greater than 100°. The branched architecture improves the wetting of surface asperities and increases the film’s resistance to aqueous acid; after 24 h immersion in 0.1 mol/L HCl, the contact angle decline is less than 10°.
For glass and mineral surfaces, application at 0.5–1.0 wt% in alcohol or hydrocarbon carrier is used. The treated surface should not be exposed to condensation before the cure stage; early moisture contact can hydrolyse Si–H to silanol and reduce the final contact angle. On siliceous stone, the measured water uptake after 48 h capillary absorption under ISO 15148:2002 can be reduced by 50–70% when compared with untreated coupons, depending on porosity.
The reactive hydride content imposes strict storage and handling boundaries. Containers should be closed under dry nitrogen and kept below 40 °C; moisture ingress hydrolyses Si–H to silanol and generates hydrogen, which can pressurize sealed drums. At 25 °C in unopened containers, the active hydrogen drift is typically less than 5% relative over 12 months. At 40 °C, the same drift may be reached within 6 months. The product may be stored below 0 °C without crystallization; before metering, it is brought to 20–30 °C without open flame or direct steam.
Contact with amines, strong alkalis, or organotin condensation catalysts leads to rapid condensate curing and gelation. Therefore addition-cure lines that previously ran condensation-cure silicones require thorough cleaning before product changeover. In solvent-based hydrosilylation reactions, residual amine from reactor cleaning inhibits platinum catalyst activity. A catalyst activity probe is mandatory; a small-scale gel-time measurement at the intended reaction temperature is preferred to a simple visual inspection.
As a hydrosilylation reagent, RH-H308 is used to graft siloxane groups onto alkenyl-functional organic polymers. Typical reaction conditions in a glass-lined reactor are 80–110 °C, toluene or isoparaffin solvent, and 5–20 ppm platinum as Karstedt catalyst. The Si–H:C=C molar ratio is set between 1.1:1 and 1.3:1 to avoid leaving free silicon hydride in the finished product. Reaction completion is monitored by the disappearance of the Si–H stretching band at 2160 cm⁻¹ in FTIR and by iodometric titration. The branched structure supplies reactive hydrogens at a lower viscosity than linear PMHS of the same active hydrogen, reducing solvent demand in the production of silicone–polyether surfactants and organic–siloxane compatibilizers.
In addition-cure liquid silicone rubber and gel formulations, the recommended Si–H:vinyl molar ratio is 1.2:1 to 1.8:1. Below 1.1:1, tensile strength and tear resistance decline because the network under-cures; above 2.0:1, residual hydride can liberate hydrogen on exposure to moisture or during high-temperature post-cure. On a 200 L planetary mixer with blades at 25 rpm, incorporation into a 20 000 mm²/s vinyl-terminated PDMS is usually complete in 15–30 min; stock temperature should be kept below 45 °C to avoid premature gelation when platinum is present. In filled systems, the order of addition matters: fumed silica should be pre-dispersed into the vinyl polymer before RH-H308 is added, otherwise the hydride fluid can be physically adsorbed on silica aggregates and local stoichiometry may shift.
Manufacturers of RH-H308 generally supply it under REACH registration obligations for silicone intermediates; it is not intended for direct food contact without a specific migration study under EU 1935/2004. For electronics applications, the cured film can be assessed for ionic contamination under IPC-TM-650 method 2.3.25. The uncured fluid should be handled as a silicone oil; it is not classified as hazardous under CLP for the basic physical endpoints, but the hydrogen released during cure requires ventilation.
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