Vinyl Terminated Silicone Oil RH-Vi1305

Vinyl Terminated Silicone Oil RH-Vi1305 is a linear α,ω-bis(dimethylvinylsiloxy)polydimethylsiloxane supplied as a reactive base fluid for platinum-catalyzed addition-cure elastomers, gels, and encapsulants. The terminal dimethylvinylsilyl groups permit hydrosilylation with polymethylhydrosiloxane crosslinkers at Si-H/Si-Vinyl molar ratios commonly set between 1.2:1 and 1.8:1 in injection-molded liquid silicone rubber compounds. In a typical two-component LSR system, the A-component contains the vinyl oil, fumed silica, platinum catalyst at 5–15 ppm Pt, and a low-molecular-weight inhibitor such as 1-ethynyl-1-cyclohexanol; the B-component contains a second portion of the same vinyl oil, the hydrogen crosslinker, and additional silica. Mixing through a static mixer with 24–32 elements at a volume ratio of 1:1 produces a thixotropic compound with a room-temperature pot life commonly exceeding 8 h before a 10% rise in dynamic viscosity. The product designation RH-Vi1305 indicates a vinyl-functional polydimethylsiloxane; published data for this specific configuration is limited in some application-specific tests, but the fluid conforms to the batch-release ranges listed below.

What Specification Ranges and Batch Consistency Markers Apply to RH-Vi1305?

The batch-release specification is based on control of end-capping conversion and stripping efficiency during manufacture. Equilibrium polymerization is followed by neutralization of the alkaline catalyst, filtration, and devolatilization under reduced pressure; residual cyclic siloxanes are controlled by thin-film stripping. The following values apply to unopened, unfilled material stored at 5–30 °C.

In filling operations, the viscosity plateau determines transfer pump selection. Drum pumps with progressing-cavity stators and 6:1 air motors are adequate at room temperature; gear pumps with hardened steel internals are preferred for continuous metering at 0.5–3.0 kg/min. Batch-to-batch variation is monitored by Fourier-transform infrared spectroscopy of the terminal vinyl Si-C=C stretch near 1595 cm⁻¹ and by gel-permeation chromatography against narrow polystyrene standards; a polydispersity index above 1.6 indicates broadening from uncontrolled chain transfer. For platinum-catalyzed cure, the objective is a narrow molecular-weight distribution because low-molecular-weight cyclic species do not participate in the network and can migrate to the mould surface. Producers using 25 kg vacuum planetary mixers observe that base fluid viscosity below 900 mm²/s reduces filler wetting time but increases creeping; viscosity above 1,600 mm²/s increases static mixer pressure drop and can require barrel temperatures above 35 °C. The specification range therefore balances silica incorporation and dispense accuracy.

Batch release also uses ¹H NMR to confirm terminal capping. The Si-CH=CH₂ protons appear between 5.7 ppm and 6.0 ppm, while the absence of terminal Si-H signals near 4.5–4.7 ppm confirms complete end-capping. Cure-check gel time is recorded against a reference hydrogen silicone fluid at a Si-H/Si-Vinyl ratio of 1.5:1 and 10 ppm Pt at 120 °C; a typical gel time for 1 g in a heated aluminum cup is 10–30 s. Deviation from that window triggers headspace gas chromatography of low-boiling contaminants and Karl Fischer titration before release.

Differences from Alkyl-Terminated and Silanol-Terminated Silicone Oils

The terminal functionality separates RH-Vi1305 from non-reactive polydimethylsiloxane release agents and from condensation-cure silanol fluids. In methyl-terminated polydimethylsiloxane, the trimethylsilyl end groups are inert; such fluids do not enter the crosslinked network and remain extractable. In silanol-terminated polydimethylsiloxane, cure occurs through moisture-driven condensation with alkoxysilane or oxime crosslinkers, releasing low-molecular-weight by-products such as ethanol, oxime, or acetic acid. RH-Vi1305 cures by platinum-catalyzed hydrosilylation and releases no volatile condensation by-product, which is critical for electronics encapsulation where acetic acid attack on copper traces is unacceptable. Unlike peroxide-cured methyl vinyl gums, the vinyl oil does not require high temperatures for peroxide decomposition; addition cure can be initiated at 110 °C and completed above 150 °C, depending on the inhibitor content and part wall thickness.

Compared with vinyl-terminated oils of lower viscosity, RH-Vi1305 provides a higher initial molecular weight and therefore a lower crosslink density contribution from the same molar amount of crosslinker. This shifts failure properties toward higher elongation and softer Shore A hardness, but can reduce tear resistance if the total network strand density is not corrected with vinyl MQ resin. In tensile testing under ISO 37, a 40 Shore A LSR formulation based on RH-Vi1305 commonly exhibits tensile strength of 6–9 MPa and elongation at break of 300–600%; published data for this specific configuration is limited, and values depend on filler surface treatment, silica loading, and Si-H/Si-Vinyl ratio. Vinyl MQ resin addition at 10–25 wt% raises hardness and modulus but increases the compound viscosity and may require adjustment of static mixer pressure. Tear strength under ISO 34-1 Method B for a 40 Shore A compound remains below 25 kN/m unless reinforcing silica with surface area 200–300 m²/g is used and well dispersed.

Within the broader family of vinyl silicone oils, RH-Vi1305 is differentiated by the combination of a 1,000–1,500 mm²/s kinematic viscosity and terminal vinyl placement. Lower-viscosity grades such as 100–500 mm²/s are used when a lower compound viscosity is needed for coating or micro-moulding; higher-viscosity grades such as 10,000 mm²/s are used for high-extrusion compounds. The terminal vinyl structure means each chain carries two reactive sites, whereas vinyl gum may contain both terminal and pendant vinyl groups. Pendant vinyl groups can consume hydrogen crosslinker without forming linear chain extension, producing a more brittle network with higher Shore A hardness but lower elongation at break. This distinction is measured through the swelling ratio and Flory-Rehner crosslink density; for the same Si-H/Si-Vinyl ratio, a terminal vinyl network typically has a lower sol fraction than a pendant-randomized network. Published data for this specific configuration is limited, but the structural distinction is documented in addition-cure silicone literature.

The storage and use boundaries for RH-Vi1305 are determined by oligomeric volatility and catalyst-poisoning risk. Sealed HDPE drums and stainless steel intermediate bulk containers are used; polyethylene liners should be free of slip additives because migrating erucamide can alter surface cure. The product is non-corrosive to carbon steel on short contact, but static storage over 12 months is preferably in stainless steel or HDPE. At temperatures below 0 °C, the fluid may become cloudy or crystallize; warming to 25 °C restores clarity without loss of reactivity. Long-term storage above 45 °C accelerates cyclic regeneration and can degrade the vinyl group by oxidation; nitrogen blanketing or sealed headspace with less than 5% oxygen is recommended. For metering, positive-displacement pumps calibrated at 25 °C with mass-flow verification against batch weight provide repeatability within ±0.5 g per shot in multi-component dispensing. The product cannot be steam-sterilized in open systems because residual hydrogen crosslinker in mixed materials can off-gas; closed mold curing is required.

When Vinyl-Terminated Oil Replaces Methyl-Terminated Oil in Heat-Cured Rubber

When a formulator replaces a methyl-terminated silicone oil with RH-Vi1305 in a heat-cured rubber formulation, the fluid changes from a plasticizer to a reactive polymer. The replacement is not a drop-in substitution because the vinyl end groups consume Si-H crosslinker and alter the network. If the crosslinker amount is not increased to compensate for the new reactive sites, the formulation loses cure efficiency and may show surface tack. In a typical LSR comprising 100 parts by weight of vinyl oil, 20–30 parts fumed silica, 3–7 parts hydrogen silicone fluid, and 0.1–0.5 parts inhibitor, the reactive oil contributes both network chain extension and crosslink density. The practical mixing sequence on a production-scale kneader with 45 L capacity is: base fluid and silica are combined at 25–35 °C under 50–80 mbar vacuum for 20–40 minutes; the batch is then cooled below 30 °C before catalyst addition. Premature addition of platinum catalyst to a silica-filled base at 60 °C can generate gel particles within 2–3 minutes. Therefore, thermal history is controlled by jacketed mixing equipment and by limiting shear energy input.

In injection molding of addition-cure LSR, the mold temperature is commonly held at 120–170 °C, with thin-wall parts cured in 15–60 s depending on thickness and thermal conductivity. Clamping force for a multi-cavity silicone mold ranges from 800 kN to 3,000 kN, and injection pressure is usually maintained below 20 MPa because flash caused by low melt viscosity is controlled by precision parting-line seals rather than high clamp force. The low viscosity of RH-Vi1305, compared with high-viscosity gum, supports fill of micro-features below 50 µm in optical and microfluidic parts. However, the same low viscosity can cause inter-mould leakage if mould vent lands exceed 0.01 mm. Processing at relative humidity above 60% requires pre-drying of silica and use of moisture-tight closures; water droplets at the interface between A- and B-components generate localized voids and surface cure defects. Sulfur-containing release agents, amine-based additives, and tin-based compounds should not contact mixed platinum-catalyzed material; they poison the catalyst and produce sticky, under-cured surfaces. Trace-metal contamination from brass or copper transfer fittings can also accelerate gelation; stainless steel or polypropylene fittings are used.

Mold temperature control should be maintained within ±5 °C; larger deviations cause inconsistent cure at the parting line. At the upper boundary, the mixed compound may scorch in the cold runner before cavity filling; at the lower boundary, the part may demould with low tear resistance and produce high compression set after post-cure. Compression set after 22 h at 175 °C according to ASTM D395 Method B is typically 15–25% for a 40 Shore A formulation; the value increases above 35% if the network is under-cured or if the vinyl oil contains excessive monofunctional species. A post-cure of 4 h at 200 °C in a forced-air oven removes volatile cyclic species and improves compression set to 8–15% for molded seals. Post-curing is also required where low-molecular-weight siloxane migration must be minimized for optical or medical surfaces.

In optical encapsulants, RH-Vi1305 is used as the reactive fluid component in low-hardness gels. The cured gel hardness can be controlled from 0.5–5.0 on the Shore 00 scale by adjusting the Si-H/Si-Vinyl ratio from 1.2:1 to 0.7:1; a substoichiometric Si-H ratio leaves reactive vinyl groups that can be overmolded or bonded later. The low volatile content under ISO 3251 reduces optical haze from volatile condensation on LED packages. For microfluidic chips, the fluid’s low viscosity before cure supports pressure-driven filling of channels from 200 µm to 500 µm in width, and cure shrinkage is below 0.5% by volume; published data for this specific configuration is limited. Under ISO 6721-1, a formulation based on terminal vinyl oil typically shows a tan δ at 10 Hz below 0.10 at 25 °C after complete cure; a comparable pendant-vinyl network may show higher tan δ due to network defects. Volume resistivity of cured unfilled film is commonly on the order of 1 × 10¹⁴ Ω·cm under IEC 62631-3-1 after conditioning at 23 °C and 50% RH.

Under EU REACH Regulation (EC) No 1907/2006, the product is a polymer and is not subject to registration as a monomer, but imported substances present at ≥0.1% require safety-data-sheet review. Compliance with RoHS Directive 2011/65/EU for restricted substances is confirmed by batch X-ray fluorescence screening for lead, mercury, cadmium, hexavalent chromium, polybrominated biphenyls, and polybrominated diphenyl ethers below the maximum concentration values. Food-contact use is not implied by default; verification under 21 CFR 177.2600 or EU Regulation (EU) No 10/2011 is required for specific applications. The product must not be formulated with amine-based additives, tin catalysts, or sulfur-containing release agents in platinum-cured systems; these materials create a direct incompatibility and impair cure completion.