| HS Code | 894377 |
| Product Name | Methyl Terminated Hydrogen Branched Silicone Oil RH-H503 |
| Chemical Composition | Methyl-terminated hydrogen-branched polysiloxane |
| Appearance | Colorless to light yellow transparent liquid |
| Viscosity At 25 C | 100-500 mPa·s (typical) |
| Hydrogen Content | 0.10-0.30 wt% (typical) |
| Density At 25 C | 0.95-1.00 g/cm³ |
| Refractive Index At 25 C | 1.400-1.410 |
| Volatile Matter | ≤2.0% (150°C, 3 h) |
| Flash Point | ≥100°C |
| Surface Tension | 20-25 mN/m |
| Color | ≤50 Pt-Co |
| Water Content | ≤0.10% |
| Solubility | Soluble in aromatic and aliphatic hydrocarbons; insoluble in water |
| Odor | Odorless to slight characteristic odor |
As an accredited Methyl Terminated Hydrogen Branched Silicone Oil RH-H503 factory, we enforce strict quality protocols—every batch undergoes rigorous testing to ensure consistent efficacy and safety standards.
| Packing | Methyl Terminated Hydrogen Branched Silicone Oil RH-H503 is supplied in 25 kg sealed, clearly labeled steel drums for safe handling and storage. |
| Container Loading (20′ FCL) | 20′ FCL loading: Methyl Terminated Hydrogen Branched Silicone Oil RH-H503, securely packed, properly labeled, and stowed for safe international transport. |
| Shipping | Methyl Terminated Hydrogen Branched Silicone Oil RH-H503 is shipped in sealed drums or IBCs, typically not regulated as dangerous goods. Keep containers closed and upright; protect from moisture, contamination, heat, and freezing. Avoid water contact, and label with product name, lot number, and handling precautions. |
| Storage | Store in a cool, dry, well-ventilated area away from heat, sparks, flames, and direct sunlight. Keep containers tightly closed and protect from moisture, acids, alkalis, and oxidizing agents. Use original or compatible containers; ground and bond when transferring. Avoid freezing and excessive heat. Maintain good housekeeping and spill control, and follow local regulations. Do not store near food or feed. |
| Shelf Life | Typically 12 months from manufacture when stored in the original sealed container in a cool, dry, well-ventilated place. |
In high-volume addition-cure liquid silicone rubber (LSR) injection molding, methyl-terminated hydrogen branched silicone oil RH-H503 is metered as the hydride crosslinker component into the B-side of a two-part formulation, paired with a vinyl-functional polydimethylsiloxane in the A-side. The branched molecular architecture introduces a broader distribution of Si-H junction points than linear methylhydrogen polysiloxane, which influences the hydrosilylation network density and final compression set behaviour. On production lines with 150–300 t clamp force and cold-runner LSR injection units, the formulation is processed at screw barrel temperatures of 18–28 °C, injection pressures of 80–150 bar, and mold temperatures of 120–180 °C; demolding is typically complete within 30–90 s. The addition ratio of RH-H503 must be calculated from the active hydrogen content reported on the certificate of analysis and is normally set to maintain a Si-H:vinyl molar ratio between 1.4:1 and 2.2:1, equivalent to 0.6–1.8 wt% relative to the vinyl silicone polymer. Ratios below 1.2:1 produce persistent surface tack, while ratios above 2.5:1 generate excess hydride that undergoes post-cure hydrolysis and gas evolution. Hydrosilylation catalyst platinum levels of 5–15 ppm with ethynyl cyclohexanol inhibitor concentrations of 0.05–0.15 wt% provide pot life and cure control. Regulatory compliance for finished articles is evaluated under ISO 10993-5:2009 and ISO 10993-10:2010 when medical-grade components are supplied; food-contact rubber parts are tested under FDA 21 CFR 177.2600, and automotive sealing parts are produced under IATF 16949 line control with mechanical validation by ASTM D2240-15, ASTM D412-16, and ASTM D624-00(2020). Terminal product types include respiratory mask valves, infant-care bottle nipples, turbocharger recirculation valve seals, and self-locking grommets. The main process boundary is moisture: RH-H503 must be protected from atmospheric humidity during storage because Si-H hydrolysis raises the apparent crosslinker demand and shifts the stoichiometric ratio. Amine-containing mold release agents and chlorinated surface cleaners are incompatible because they can poison platinum cure and discolor the cured network.
Solventless thermal release coating systems for pressure-sensitive adhesive laminates use RH-H503 as a hydrogen donor to crosslink vinyl-functional silicone release polymers on PE-coated kraft, glassine, and PET substrates. In pilot-coater evaluation, the addition level is set at 3.0–6.0 wt% based on the vinyl polymer mass, with a platinum concentration of 50–120 ppm and an ethynyl cyclohexanol inhibitor load of 0.05–0.20 wt%; the effective Si-H:vinyl molar ratio is maintained between 1.8:1 and 2.5:1. The coated web is processed on a five-roll solventless coater at 300–600 m/min, with gravure offset speed ratios of 1.05–1.25, coat weight of 0.8–1.6 g/m², and oven zone temperatures of 140–160 °C for 1.5–3.0 s residence. Film substrates require inline corona pre-treatment to 38–42 dyn/cm; paper substrates are controlled to 6–8% moisture to prevent steam blisters. Cure completeness is monitored by FINAT FTM 3 release force and FINAT FTM 4 loop tack after lamination. When the Si-H:vinyl ratio exceeds 2.8:1, release force drift is observed after 28 days at 40 °C, with values shifting from 8 cN/2.5 cm to 35 cN/2.5 cm as residual hydride reacts with unconverted vinyl groups in the adhesive. Table 1 lists the regulatory matrix applied to release liner qualification. Terminal product types include double-sided release PET liners for adhesive transfer tapes, filmic label release bases, and casting liners for cast PVC and polyurethane sheet.
| Requirement | Designation | Acceptance criterion |
|---|---|---|
| Food-contact paper/polyolefin coatings | FDA 21 CFR 175.320 | Extractables within specified migration limits |
| European food-contact silicones | BfR Recommendation XV | Overall migration ≤ 10 mg/dm² |
| Release force stability | FINAT FTM 3 | 8–35 cN/2.5 cm |
| Loop tack retention | FINAT FTM 4 | ≥ 90% relative to control |
Woven and knit cotton, polyamide, and polyester constructions are padded with RH-H503 emulsion to produce a crosslinked hydrophobic silicone layer. The emulsion is prepared with nonionic ethoxylated surfactants to a particle size of 200–500 nm and is applied at 1.0–3.0 wt% oil on weight of bath, with magnesium chloride or zinc nitrate catalyst at 0.3–0.6 g/L and bath pH held at 4.5–5.5. The pad mangle is set to 60–80% wet pick-up; drying proceeds at 80–100 °C, followed by cure on a 24–36 m stenter frame at 150–170 °C for 45–90 s. Si-H groups hydrolyze to silanol intermediates under the acidic pad-bath, then condense with available hydroxyl groups on cellulose or with amide and carboxyl groups on polyamide, fixing the finish. Performance is assessed by AATCC 22 spray rating with acceptance ≥ 90 for water repellency, ISO 4920:2012 spray rating ≥ 3, and AATCC 193 ethanol/water resistance. Product types include down jacket shell fabrics, automotive seat upholstery, and coated tentage. Over-addition above 4.0 wt% is avoided because the cured silicone network stiffens the fiber matrix and reduces tear strength by up to 15% when measured by ISO 13937-2:2021. The finish is incompatible with high-concentration glyoxal crease-resistant resins that consume cellulosic hydroxyl sites before silicone condensation. Table 2 summarizes the textile qualification matrix.
| Test protocol | Designation | Acceptance criterion |
|---|---|---|
| Water repellency spray rating | AATCC 22 | ≥ 90 |
| Spray rating | ISO 4920:2012 | ≥ 3 |
| Water/alcohol resistance | AATCC 193 | ≥ 4 |
| Tear strength retention | ISO 13937-2:2021 | ≥ 85% of untreated control |
| Restricted substances | OEKO-TEX Standard 100 | Annex 4/6 limits |
For cast-in-place concrete and natural stone facades, penetrating hydrophobization with solvent-borne silicone systems uses RH-H503 as a reactive hydride component that consumes capillary water and forms a branched siloxane network within the first 3–6 mm of the substrate. The formulation is based on a silane/siloxane resin carrier in white spirit or isopropanol, with RH-H503 added at 5–15 wt% and tin octoate catalyst at 0.2–0.5 wt%. Application is performed by low-pressure airless spray at 0.2–0.3 L/m² per coat, with a flood coat of 0.4–0.5 L/m² for severe exposure categories. The substrate must have a moisture content below 6% and a surface temperature between 5–35 °C; fresh concrete is cured for ≥ 28 days before treatment. Water uptake is measured by ASTM C642-21 with a target reduction ≥ 80% against untreated control specimens, and hydrophobic impregnation is verified under EN 1504-2:2004. Terminal product types include bridge parapet sealing membranes, precast concrete facade panels, and limestone cladding protectants. The reactive Si-H component is incompatible with alkaline substrates having pH above 10.5 unless the surface is neutralized, because rapid hydrolysis generates hydrogen gas and disrupts film formation. Application in continuous rain or on gypsum-containing substrates is outside the validated process window.
Solventborne alkyd-melamine and polyester-melamine coil coating lines incorporate RH-H503 at 0.05–0.3 wt% on total formula as a low surface tension flow control agent and anti-crater additive. The Si-H functionality reacts with residual hydroxyl groups on the melamine backbone during the baking cycle, forming a permanent silicone network rather than a migratory surface film. Production dispersion is carried out under high-shear mixing at 1000–1500 rpm for 10–15 min; the coating is applied by reverse-roller coater at dry film thickness 20–35 μm and baked at 140–180 °C for 15–30 min in a multi-zone oven. Recoat adhesion is evaluated by ISO 2409:2020 cross-cut testing; gloss retention is measured by ISO 2813:2014, and film hardness is recorded by ASTM D3363-20 pencil method. Product types include coil-coated aluminum for architectural cladding, appliance panels, and automotive interior trim. Addition above 0.5 wt% is excluded because excessive surface enrichment leads to intercoat delamination. The use of RH-H503 must be restricted in two-component polyurethane topcoats where isocyanate consumption of residual hydroxyl groups leaves unreacted Si-H sites that can hydrolyze and generate odor.
Methyl/phenyl silicone encapsulant formulations for high-power LED packages use RH-H503 as a hydrogen crosslinker in platinum-catalyzed hydrosilylation. The addition is set to maintain a Si-H:vinyl molar ratio of 1.0:1 to 1.5:1, corresponding to 1.0–2.5 wt% RH-H503 relative to the vinyl-functional methyl/phenyl silicone resin. Platinum catalyst concentration is 2–5 ppm, and inhibitor levels are adjusted to provide 4–8 h working time at 25 °C. The formulated encapsulant is vacuum-degassed at −0.1 MPa for 30 min, then dispensed into leadframe or chip-on-board cavities and cured at 100 °C for 1 h, followed by 150 °C for 2 h. Process validation is performed under IEC 62777:2018, with flame performance evaluated by UL 94 V-0, and photometric stability monitored by IES LM-80 or ASTM G154-23 UV weathering. Terminal product types include high-power LED leadframe packages, COB modules, and secondary optical lenses. Excess hydride above 1.8:1 Si-H:vinyl causes yellowing under 85 °C/85% RH damp heat aging due to residual Si-H oxidation; phenyl content in the vinyl resin must be fixed before adjusting RH-H503 because refractive index and gas permeability co-vary with composition. Published data for RH-H503 in this specific encapsulant configuration is limited, so batch qualification against the active hydrogen certificate of analysis is mandatory before line start.
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Commercial addition-cure silicone compounding is influenced by the architecture of the hydride fluid. Methyl Terminated Hydrogen Branched Silicone Oil RH-H503 is a reactive branched methylhydrogensiloxane fluid with trimethylsiloxy termination. The product is specified with a viscosity of 15–40 mm²/s at 25 °C measured according to ASTM D445, an active hydrogen content of 0.35–0.50 wt% determined by internal iodometric titration, a density of 0.970–0.990 g/cm³ at 25 °C by ASTM D4052, a refractive index of 1.400–1.410 at 25 °C by ASTM D1218, a closed-cup flash point of ≥150 °C by ASTM D93, and non-volatile content of ≥98.5% after 2 h at 150 °C according to ISO 3251. These values are typical release limits and do not replace a batch-specific certificate of analysis. The active hydrogen specification corresponds to approximately 3.5–5.0 mmol Si–H/g.
| Property | Specification range | Typical value | Method |
|---|---|---|---|
| Appearance | Colorless transparent liquid | Colorless transparent liquid | Visual |
| Viscosity at 25 °C | 15–40 mm²/s | 28 mm²/s | ASTM D445 |
| Active hydrogen content | 0.35–0.50 wt% | 0.42 wt% | Internal iodometric titration |
| Density at 25 °C | 0.970–0.990 g/cm³ | 0.978 g/cm³ | ASTM D4052 |
| Refractive index at 25 °C | 1.400–1.410 | 1.405 | ASTM D1218 |
| Flash point, closed cup | ≥150 °C | 178 °C | ASTM D93 |
| Non-volatile content after 2 h at 150 °C | ≥98.5% | 99.1% | ISO 3251 |
The branched topology places multiple hydride sites on a single molecule, so the fluid functions as a multi-functional junction in platinum-catalysed vinyl addition rather than as a simple chain extender. Trimethylsiloxy end-blocking removes terminal silanol reactivity and condensation side-reactions. Compared with hydroxy-terminated hydrogen silicone oil, RH-H503 therefore maintains a more stable viscosity in sealed storage and gives predictable stoichiometry control. Compared with vinyl-terminated fluids, the product is a hydride donor rather than a hydride acceptor, which determines its position on the hydride side of a two-part addition-cure system.
The principal differentiation is molecular functionality. A linear methylhydrogen silicone oil may carry pendant Si–H along the chain, but its molecular weight must be increased to raise the number of hydride groups per molecule. That raises Newtonian viscosity and may reduce wetting on low-energy substrates. In contrast, RH-H503 carries Si–H on branched arms; the compact topology keeps viscosity low while delivering multiple crosslinkable sites per molecule. The result is observed as a steeper modulus build during cure and a lower soluble fraction after cure at equal hydride loading. The trimethylsiloxy termination further eliminates terminal Si–H or Si–OH variability that can occur in linear hydride fluids.
| Parameter | RH-H503 branched fluid | Linear trimethylsiloxy-terminated methyl hydrogen silicone oil | Methyl-terminated polydimethylsiloxane |
|---|---|---|---|
| Active hydrogen content | 0.35–0.50 wt% | commonly 0.10–1.60 wt% depending on grade | 0 wt% |
| Reactive Si–H groups per molecule | ≥3 | 1–2 terminal hydride or chain pendant sequence | 0 |
| Viscosity at 25 °C | 15–40 mm²/s | typically 10–100 mm²/s depending on chain length | 5–100 000 mm²/s |
| Network contribution | Multi-functional crosslinking junction | Chain extension or pendant crosslinking at high hydride content | Non-reactive diluent or base polymer |
| Hydrolytic stability | Moderate; hydrogen release possible in moist alkaline storage | Moderate; similar Si–H sensitivity | High; no Si–H bond |
Because the branched fluid contains T or Q branch sites, one molecule can connect three or more vinyl-functional chains. This reduces the concentration of extractable free silicone after cure compared with a linear hydride fluid used at the same Si–H/Si-vinyl ratio. Published data for the exact extractable fraction for this specific configuration is limited; however, the network-structure argument is consistent with standard silicone rubber crosslink theory. The practical result is that formulations can often achieve a target hardness and solvent resistance with a lower total hydride-fluid mass than linear hydride systems at equivalent active hydrogen content.
In platinum-catalysed liquid silicone rubber, the material is dosed into the vinyl-functional base before the platinum component is introduced in the static mixer. The recommended working ratio is 1.2–2.0:1 Si–H/Si-vinyl. At 1.6:1 and a platinum concentration of 10 ppm, moving die rheometer cure at 120 °C under ASTM D5289 typically gives scorch time ts2 of 12–25 s and t90 of 35–70 s for a 70 Shore A formulation. On an 80–120 t vertical injection molding machine with an 18:1 L/D plasticating unit and barrel temperature of 25–30 °C, the fluid remains homogeneous in the A-component. Batch-to-batch active hydrogen variation of ±0.03 wt% moves t90 by approximately 5–8 s, which is significant for slim-wall moulding cycles. High hydride addition above 2.5:1 causes a steep increase in crosslink density and embrittlement. Excess unreacted Si–H can also evolve hydrogen during post-cure, leading to voids in thick sections. The processing window is therefore defined by an upper threshold for void formation and a lower threshold for surface tack.
Low-temperature cure at 60–80 °C is required for heat-sensitive films and electronic assemblies. At these temperatures, the hydrosilylation rate decreases and the risk of incomplete conversion is controlled by hydride stoichiometry. With RH-H503, formulations compounded at 1.0:1 Si–H/Si-vinyl frequently show a tacky surface, low modulus, and high compression set after cure; the same lot at 1.4:1 cures to a dry-surface elastomer under identical time and temperature. The transition is steep: t90 at 70 °C and 10 ppm Pt may move from 40–60 s at 1.4:1 to more than 180 s at 1.0:1. Compression set measured according to ISO 815 after 22 h at 70 °C remains above 25% for the undercured case. This is a threshold effect rather than a linear response; the usable ratio window is approximately 1.4–1.8:1 below 80 °C. Operators should verify active hydrogen by lot rather than relying on gravimetric addition alone.
Hydrophobic treatment of fumed silica and clay is a separate reaction route. In a nitrogen-blanketed Z-arm mixer at 120–150 °C, RH-H503 reacts with surface silanol groups, releasing hydrogen and forming a covalently bound methylhydrogen siloxane layer. Addition levels of 0.8–1.2 wt% on filler are typical; overdose leaves unreacted fluid and increases volatile condensables during subsequent compounding. Vacuum stripping for 30–60 min removes low-molecular-weight volatiles. Treated fumed silica then disperses into silicone sealant bases with lower moisture pickup than untreated silica; moisture resistance of the final cable compound is evaluated by IEC 60811-401. Because the Si–H surface reaction is covalent, the hydrophobic layer resists solvent extraction better than a physisorbed dimethyl silicone oil. The hydrogen evolution is controlled by nitrogen sweep and vent condenser on the mixer.
For thin-film release liners, the fluid is formulated with a vinyl-functional silicone base and platinum catalyst at coat weights of 0.8–1.5 g/m². Cure in a hot-air tunnel at 120–150 °C for 10–30 s produces a crosslinked silicone film. Release force at 180° peel and 300 mm/min according to FINAT FTM 3 is typically controlled in the 20–80 cN/50 mm range by adjusting the hydride-to-vinyl ratio and post-cure at 40 °C for 24 h. The branched architecture is expected to reduce the extractable oligomer fraction after cure relative to linear hydride fluids, though published data for this specific configuration is limited; users should verify extractables by their own extraction method against the final article specification. The coating bath must remain free of amines, phosphines, and sulphur-containing species because these catalyst poisons can produce erratic gelation. Platinum levels are usually 80–120 ppm in the ready-to-use bath, and the mixed bath life at 25 °C is limited to 6–12 h before viscosity rise exceeds process limits.
Storage and mixing are governed by Si–H hydrolysis. The product is packaged under dry nitrogen in containers with pressure-relief caps because hydrogen may evolve if moisture is present. Storage below 35 °C and exclusion of moisture are required; at relative humidity above 60%, pre-drying of containers and dry air purge are recommended. Strong bases, mineral acids, oxidising agents, and zinc or tin salts can accelerate Si–H decomposition. The fluid does not contain intentionally added RoHS-restricted substances above 2011/65/EU limits, but end-use food-contact rubber requires finished-article testing under 21 CFR 177.2600 or regional equivalent; the fluid alone does not constitute a food-contact approval.
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