Vinyl Terminated Silicone Oil RH-Vi1305

Vinyl-terminated silicone oil RH-Vi1305 is a linear polydimethylsiloxane with vinyldimethylsilyl end groups, represented as CH₂=CH–Si(CH₃)₂O–[Si(CH₃)₂O]_n–Si(CH₃)₂–CH=CH₂. The terminal vinyl groups provide difunctional reactivity for platinum-catalyzed hydrosilylation, while the polydimethylsiloxane backbone contributes the viscoelastic and low-surface-energy behavior expected from silicone fluids. Published data for this specific configuration is limited; therefore, production specifications for RH-Vi1305 must be taken from the lot-specific certificate of analysis. Fluids in this product class are generally controlled to a nominal dynamic viscosity of 50,000–60,000 mPa·s at 25 °C, terminal vinyl content of 0.04–0.08 mmol/g, density of 0.97–0.98 g/cm³, and refractive index of 1.403–1.405. These values are class-typical and are not a substitute for lot release data.

Because the vinyl groups are located exclusively at the chain termini, network formation with a hydride-functional crosslinker proceeds through chain-end coupling rather than random side-chain grafting. This architectural difference reduces the number of dangling chain ends after cure when compared with side-chain vinyl silicones of equivalent total vinyl content. Volatile content is controlled by vacuum stripping at approximately 150 °C under pressures below 0.095 MPa. The product is typically supplied in nitrogen-padded steel drums to limit moisture ingress and oxygen exposure during storage.

How Does Terminal Vinyl Chemistry Alter Addition-Cure Kinetics Relative to Condensation-Cure Silicones?

Hydrosilylation between terminal Si–CH=CH₂ groups and Si–H crosslinker proceeds without the formation of water, methanol, or acetic acid. Condensation-cure silanol-terminated polydimethylsiloxanes release by-products during cure, which can create bond-line shrinkage or require venting in closed molds. RH-Vi1305 does not cure by moisture-driven condensation; it requires a platinum(0) complex, typically Karstedt’s catalyst, and a hydride-functional silicone crosslinker. The cure rate is controlled by platinum concentration, inhibitor concentration, SiH:Vi stoichiometry, and temperature. Typical addition-cure systems based on terminal vinyl silicones have pot life exceeding 6 h at 25 °C when an inhibitor such as 1-ethynyl-1-cyclohexanol is present at 0.05–0.20 wt%. At 150 °C, the same systems commonly cure within 30–120 s, though the exact cure window for RH-Vi1305 must be determined by curemeter testing.

The terminal vinyl architecture is functionally significant when low compression set and high elastic recovery are required. Networks produced from RH-Vi1305 have more regular chain-end linked topology than networks formed from side-chain vinyl fluids at equivalent total vinyl content. Compression set is evaluated after 22 h at 175 °C per ISO 815-1:2019 or ASTM D395-18; typical cured addition-cure compounds may show compression set below 20%, but the result depends on filler loading, post-cure completeness, and SiH:Vi ratio. Replacement of methyl-terminated silicone oil with RH-Vi1305 introduces chemical bonding rather than plasticizer behavior, so the cured part retains mechanical integrity after solvent extraction or thermal aging.

Reactive Diluent Function and High-Shear Mixing Parameters

RH-Vi1305 functions as a reactive diluent in high-viscosity silicone compounds. When a high-molecular-weight gum is difficult to mix with fumed silica, a portion of RH-Vi1305 reduces initial compound viscosity. Unlike a non-reactive methyl-terminated silicone oil, the vinyl-terminated fluid is not extractable after cure because it is incorporated into the crosslinked network. In a planetary vacuum mixer capable of achieving 15 mbar or less, the fluid, silica, and surface-treating agent are dispersed at a disperser speed of 1,000–1,500 min⁻¹ with jacket temperature held at 25–35 °C. After silica incorporation, heat treatment at 150 °C for 1–2 h under vacuum removes moisture and residual treating-agent volatiles.

On continuous compounding lines, a co-rotating twin-screw extruder with L/D ratio 48:1 can be used for filler incorporation. RH-Vi1305 is injected downstream of the silica feed to prevent torque overload. Barrel temperatures are maintained at 20–50 °C, and the vacuum vent is operated at −0.08 MPa for devolatilization. Viscosity is verified by rotational viscometry per ISO 3219-1:2021 at 25 °C after conditioning the sample for 2 h at 23 °C ± 2 °C. The terminal vinyl content is quantified by iodometric titration; this value is used to calculate the required Si–H crosslinker amount because excess Si–H can cause post-cure hardness drift.

Within the same silicone fluid family, replacing RH-Vi1305 with a lower-viscosity vinyl-terminated fluid, such as a 10,000 mPa·s product, may reduce compound viscosity and filler incorporation time but can also increase crosslink density and reduce elongation at break. Replacing it with a 100,000 mPa·s fluid may increase elongation but requires higher mixer torque and longer silica wetting time. Curemeter torque difference ΔS = M_H − M_L per ISO 6502-1:2018 is used to compare network development and to adjust crosslinker level for each vinyl fluid grade.

Addition-cure liquid silicone rubber formulations based on RH-Vi1305 are proportioned through closed-loop metering units before static mixing. A representative starting formulation uses 100 phr RH-Vi1305 as the vinyl component, 2.0–5.0 phr hydrogen-containing silicone oil with Si–H content between 4.0–8.0 mmol/g, inhibitor at 0.05–0.20 wt%, and platinum at 5–20 ppm. Published formulation data for this specific product code is limited; the SiH:Vi ratio should be adjusted using lot-specific titration data and moving-die rheometer curves. Injection molding is performed at mold temperatures of 150–200 °C, with cycle times of 30–120 s for thin-wall parts. The screw L/D ratio on liquid silicone injection machines is generally 12:1 to 15:1 with a low-compression screw, and the mixing block is cooled to 18–25 °C to prevent premature cure.

After molding, post-cure for 4 h at 200 °C is applied to complete addition reactions and remove low-molecular-weight siloxane species. For a 25 wt% fumed silica compound, typical mechanical properties measured after post-cure are tensile strength 6.0–10.0 MPa and elongation at break 300–700% per ASTM D412-16 or ISO 37:2017. Tear strength may fall between 15–35 N/mm when tested per ASTM D624-20. These ranges are representative of addition-cure liquid silicone rubber systems and are not product-specific guarantees.

When Volatile Content Exceeds 0.5 wt% During Vacuum Processing, Adhesion and Voiding Defects Appear

Volatile content in RH-Vi1305 is determined by nonvolatile content testing per ASTM D5095-22. When nonvolatile content falls below 99.0%, corresponding to volatile residuals above 1.0%, injection-molded thin-wall parts may exhibit internal voids, surface bubbles, and mold deposits at mold temperatures above 150 °C. Production vacuum stripping therefore uses a thin-film or wiped-film evaporator with pressure below 0.095 MPa. The strip temperature is held at 150–160 °C, and total residence time is limited to less than 2 h because prolonged exposure at elevated temperature can increase the risk of gel formation through radical coupling of terminal vinyl groups.

If RH-Vi1305 is used as a reactive diluent in silicone release coatings or pressure-sensitive adhesive systems, residual cyclic siloxanes above 0.5 wt% can plasticize the cured interface and reduce peel adhesion. Formulators should require volatile-content data on the certificate of analysis and should not rely on viscosity alone as a purity indicator.

Verify Regulatory Status Under 21 CFR 177.2600 and ISO 10993-1 Before Final-Article Qualification

RH-Vi1305 is an industrial raw material rather than a finished food-contact or medical article. For food-contact silicone rubber, the cured compound may be formulated and tested under 21 CFR 177.2600, which applies to rubber articles intended for repeated use in contact with food. The raw fluid does not automatically confer compliance; extraction testing on the cured article with appropriate food simulants is required. For medical device components, the cured elastomer should be evaluated under ISO 10993-1:2018 using biological risk assessment, with testing for cytotoxicity, sensitization, and irritation as required by device risk management.

RH-Vi1305 should be stored in closed nitrogen-padded vessels at 5–40 °C. Avoid combination with amine-based additives, organotin compounds, sulfur-containing additives, and strong acids because these species can poison the platinum catalyst or catalyze siloxane degradation. If containers are opened in relative humidity above 60%, the fluid should be vacuum dried at 80–100 °C under 10–20 mbar before compounding to remove surface moisture. Failure to control moisture can cause cure inhibition or surface bubbles at the molding stage.