Vinyl Terminated Silicone Oil RH-Vi303

In liquid silicone rubber injection molding, RH-Vi303 is metered into the vinyl-functional A-component of a two-part platinum-catalyzed addition-cure system prior to static mixing. The A-component and the hydride-functional B-component are combined at a volumetric ratio of 1:1 in a meter-mix dispenser with a static mixer length of 12–24 elements; the mixed compound is then injected into a cooled runner and heated mould. Because RH-Vi303 carries terminal vinyl groups on low-molecular-weight polydimethylsiloxane chains, it participates in hydrosilylation as a chain extender and reactive diluent rather than as an unreactive plasticiser. The practical consequence is a reduction in compound viscosity at mould-filling shear rates without a proportional loss of cure state, provided the Si-H:Si-vinyl molar ratio is maintained inside the range of 1.2:1 to 1.8:1. Below 1.2:1, the cure may remain tacky under moving-die rheometer torque criteria; above 1.8:1, residual hydride can continue crosslinking during post-cure and produce embrittlement. The relevant rheological target is usually a complex viscosity at 10 s⁻¹ and 25 °C between 80,000 mPa·s and 450,000 mPa·s, although published data for RH-Vi303 in this specific injection configuration are limited. Mould temperature is typically held between 120 °C and 170 °C, with demoulding hardness measured by ASTM D2240-15 on Type A or Type D scales after 4 h post-cure at 200 °C. Tensile and elongation values are extracted from die-cut plaques according to ASTM D412-16, and tear resistance according to ASTM D624-00. On production-scale 120–180-metric-ton clamp-force injection machines, the key processing conflict is that hot-runner residence time and injection shear must remain low enough to prevent premature gelation, yet high enough to fill thin-wall cavities. Residence time above 60 s at 60–80 °C can produce viscosity drift and gate drool. Sulfur-containing additives, amino-functional silanes, and organotin condensation-cure catalysts must be excluded from the compounding area because they poison the platinum catalyst at parts-per-million levels. Volatile content after moulding is monitored by ISO 3251 or equivalent, and final articles destined for food-contact use require extraction data under FDA 21 CFR 177.2600 before commercial compliance is determined.

Shear-thinning behaviour determines shot-weight consistency. At injection shear rates above 1,000 s⁻¹, the dynamic viscosity of vinyl-terminated silicone oil compounds falls sufficiently to fill microchannels, but at low shear the compound must retain enough yield stress to prevent slumping before cure. Capillary rheometry at 120 °C is used to measure apparent viscosity; the flow index derived from a two-point power-law fit is typically less than 0.5. Mould fouling is evaluated by gravimetric deposit accumulation after 500–1,000 shots. Demoulding tack is minimized by post-cure at 200 °C for 4 h, and volatile matter is checked by ISO 3251. If volatile content exceeds 0.5 wt%, extraction or post-cure must be extended. Part shrinkage after post-cure is measured by ASTM D955-21 or optical comparator; addition-cure LSR parts typically shrink 2–3% depending on filler content and crosslink density. The use of RH-Vi303 at high levels may increase linear shrinkage because it lowers filler content and increases the number of short-chain crosslinks.

How Does RH-Vi303 Modify the Fumed Silica Network in Peroxide-Cured High-Consistency Rubber?

Compounding of high-consistency silicone rubber begins with the addition of RH-Vi303 to a two-roll mill or internal mixer before the incorporation of fumed silica and process aids. The vinyl-terminated oil wets the silica surface and lowers the yield stress of the masterbatch, which reduces the energy input required to reach the desired dispersion. On a 51 cm two-roll mill operating at a friction ratio of 1.2:1 and roll temperature 40–60 °C, the incorporation time for 30–35 phr of hydrophobic fumed silica can be shortened by the reactive diluent, but the oil addition must be offset against the mechanical strength of the peroxide-cured compound. The base polymer remains a high-molecular-weight vinyl-capped gum, while RH-Vi303 acts as a low-viscosity vinyl source that increases the free chain-end population and reduces the average molecular weight between crosslinks after peroxide cure. Mooney viscosity ML(1+4) at 100 °C is measured by ASTM D1646-19; values for cable and gasket compounds are often specified in the range 25–70 MU depending on filler loading. Tensile strength according to ASTM D412-16 or DIN 53504 and die C tear strength according to ASTM D624-00 typically decline when the low-molecular-weight vinyl oil is overdosed, because the resulting network contains a larger fraction of short-chain segments and less chain entanglement. The practical upper limit is usually determined by the minimum tensile strength required for the part, not by cure state. A peroxide cure system based on 0.8–1.5 phr of dicumyl peroxide or 2,5-dimethyl-2,5-di(tert-butylperoxy)hexane is added after the silica has been dispersed. Cure rate is checked by moving-die rheometry at 170 °C using ASTM D5289-19; the addition of RH-Vi303 can reduce the maximum torque relative to the same formulation without it, depending on oil vinyl content and dosage. Post-cure at 200 °C for 4 h is standard for volatile removal. Acetone extraction by procedures derived from ASTM D297 can be used to identify unreacted low-molecular-weight species. In gasket production, compression set is tested after 22 h at 175 °C under ASTM D395-18 Method B; soft formulations containing high diluent levels can show compression set above 30%, which is unacceptable for certain flange sealing specifications. The same incompatibility rule applies as in liquid silicone rubber: the compound must not be contaminated with amines, sulfur vulcanization chemicals, or organotin catalysts.

On a production internal mixer with tangential rotors and a chamber volume of 50–200 L, the addition of RH-Vi303 before fumed silica reduces ram pressure and motor current by wetting the mix. Dispersion is judged by refracted-light microscopy or by measuring the number of undispersed silica agglomerates per unit area. The critical threshold is reached when the oil dosage exceeds the amount that can be chemically bound into the peroxide network; beyond that point, acetone-extractable content rises and compression set deteriorates. Therefore the dosage is normally limited to 5–15 phr in finished compounds, although the exact ceiling depends on the vinyl content of the oil and the specific silica surface area. For silica grades with BET surface areas of 200–300 m²/g, the wetting requirement is higher than for 130–160 m²/g semi-reinforcing grades. Hardness is measured by ASTM D2240-15 or DIN 53505.

After degassing of a two-part addition-cure gel formulation containing RH-Vi303, the filled aliquot is transferred under vacuum to the dispensing head and injected into the housing cavity at a pressure below 0.05 MPa to avoid entrained air. In this application the silicone oil functions as a low-viscosity vinyl carrier that reduces the initial mixed viscosity to a level compatible with needle dispensing and self-leveling. Formulators usually target a mixed viscosity below 1,500 mPa·s at 25 °C before addition of thermal fillers; after the addition of alumina or boron nitride, the viscosity rises by orders of magnitude and the dispense strategy changes from needle flow to positive-displacement metering. Gel hardness is measured with a Shore 00 durometer or cone penetration method, with ASTM D2240-15 Shore 00 values below 50 commonly specified for stress-sensitive chips. The cured gel must maintain adhesion to aluminium, FR-4, and ceramic substrates, and it must not exude free oil under thermal cycling. Dielectric breakdown strength is determined by IEC 60243-1; unfilled silicone gels of this class typically fall in the range 15–25 kV/mm, while filled versions may be lower. Volume resistivity is measured by ASTM D257-14, with values commonly above 10¹³ Ω·cm for unfilled platinum-cured silicone gels. Cure temperature is usually 80–100 °C for 1–2 h, but thick sections require a step-cure profile to prevent exotherm and void formation; the thermal conductivity of unfilled silicone is approximately 0.15–0.20 W/(m·K) as measured by ASTM D5470. Pot life at 25 °C is controlled by the inhibitor system, typically 1-ethynyl-1-cyclohexanol at 100–300 ppm; this provides working time of 8–24 h in a clean two-part batch but can be shortened by contact with contaminated metal surfaces. Platinum poisoning by amine-based solder flux residues, sulfur, or unsaturated plasticizer additives is a known field failure mode. For medical or skin-contact devices, final articles require cytotoxicity data under ISO 10993-5 and extraction data under ISO 10993-12; the formulation itself must be validated on the specific cure schedule and post-cure process. Published data for RH-Vi303 in thick-section potting configurations are limited, so production qualification must include thermal cycling per the end-use class, such as IEC 60068-2-14. For electronic applications, the final module must satisfy RoHS Directive 2011/65/EU; raw silicone oil is outside the direct substance restrictions, but filled compounds can contain regulated flame retardants or pigments.

Thermal cycling performance is evaluated by JEDEC JESD22-A104 or IEC 60068-2-14; the gel must not crack, delaminate, or lose adhesion after 500 cycles between -40 °C and 125 °C. The low glass-transition temperature of polydimethylsiloxane is below -120 °C, but filled systems may stiffen. Viscosity creep under constant shear is monitored with a cone-and-plate rheometer at 25 °C; a stable material should show less than 10% viscosity drift over 4 h after mixing. In module assemblies, the housing materials should be checked for catalyst inhibitors such as sulfur-cured elastomer gaskets, tin-catalyzed silicone residues, and amine-cured epoxy outgassing. The final encapsulated module is subjected to partial discharge testing under IEC 60664-1 if the gel is used as solid insulation in high-voltage circuits.

When a Solventless Addition-Cure Release Coating Is Applied at Line Speeds Above 150 m/min

When the release coating is applied to a corona-treated polyethylene terephthalate film at coat weights below 1.5 g/m², RH-Vi303 is used to depress the mixed viscosity of the platinum-cured formulation and to adjust the crosslink density of the cured release surface. On a five-roll solventless coater running at 150–300 m/min, the combined A and B components are mixed in the nip of the coating rolls; the working viscosity must be low enough to form a continuous film without misting. A typical hydrosilylation-catalyzed release coating cure window is 130–160 °C oven temperature for 5–20 s residence time. Release force is determined on a 25 mm wide laminate strip by FINAT FTM 3 at 300 mm/min peel speed and 180° peel angle. Easy-release grades fall between 3–10 cN/25 mm, medium-release grades between 10–30 cN/25 mm, and tight-release grades above 30 cN/25 mm. Subsequent adhesion of the release liner is tested by FINAT FTM 11; acceptable retained adhesion is usually above 85% of a control laminate. The main formulation conflict is between cure speed and platinum poisoning: raising oven temperature accelerates hydrosilylation but also increases the rate of volatile formation and migration of low-molecular-weight species into the adhesive. The Si-H:Si-vinyl ratio is usually held between 1.5:1 and 2.0:1 for release coatings to ensure complete surface cure without excessive extractable hydride. Residual hydride content can be checked by attenuated total reflectance infrared spectroscopy or extraction followed by GC-MS. Crosslink density must be low enough to prevent brittle transfer but high enough to prevent silicone rub-off; this is evaluated on the substrate by FINAT FTM 6 or equivalent rub-off testing. The low viscosity of RH-Vi303 also shifts the viscoelastic response of the coating at high shear, which can reduce ribbing and air entrainment defects on direct gravure and five-roll coaters. Incompatible additives include amino-functional wetting agents, sulfur-containing surfactants, and tin-based polycondensation catalysts, all of which suppress platinum activity. Release liners destined for food packaging require migration testing under EU Regulation 10/2011 or FDA 21 CFR 175.300 for the finished laminate, not merely the coating alone.

High line speed intensifies mist generation at the coater nip. Mist is quantified by gravimetric collection on a reference foil positioned 30–50 cm from the nip for a fixed run time. Low-viscosity vinyl oils can increase misting if applied at too low a shear; this is controlled by adjusting roll differential speed and by selecting the correct molecular weight of RH-Vi303. The coating head temperature is held between 20 °C and 30 °C. If the bath viscosity drops below 200 mPa·s at 25 °C, misting and ribbing defects become more frequent. The reverse is that too high a viscosity above 1,000 mPa·s at 25 °C can impair levelling and produce visible streaks.

Low-Density Silicone Foam Compounding and Cell-Stabilization Thresholds

To produce low-density silicone foam, RH-Vi303 is blended with a vinyl-functional high-viscosity base, a platinum catalyst, and a chemical blowing agent such as azodicarbonamide at 0.5–2.0 phr or water-generating hydride side reactions. The low-viscosity vinyl oil improves the dispersion of the blowing agent in a planetary mixer at 20–60 rpm and lowers the pre-cure compound viscosity, which permits gas bubbles to nucleate without premature escape. The cure profile is normally started at 100–120 °C to trigger gas formation, then ramped to 150–170 °C to complete hydrosilylation. Foam density is tested under ASTM D1056; closed-cell silicone foams used in gaskets and thermal barriers are commonly specified from 0.25 g/cm³ to 0.60 g/cm³. Compression set is measured by ASTM D395-18 Method B after 22 h at 100 °C. The main process conflict is that overdosing the vinyl oil reduces the elastic modulus of the cell walls and can cause cell collapse before the network sets; concentrations that produce good mixing and low density may still fail compression set and tear resistance requirements. Tear strength of foams is measured by ASTM D624-00, but values are generally lower than solid rubbers of comparable formulation. Cell size distribution is assessed by optical microscopy or scanning electron microscopy on microtomed sections. In production, batch-to-batch variation in ambient humidity above 60% RH can alter the decomposition behaviour of moisture-sensitive blowing agents and change the final density, which requires pre-drying of fillers or controlled storage of the blowing agent. The compound must be free of sulfur, amines, and organotin species for the same platinum catalyst compatibility reasons described above. Flame-retardant filler additions for building and transportation seals require end-use flammability testing under UL 94 or FMVSS 302, depending on the application, and the final article must be validated on the specific foam density and thickness.

Cell collapse in low-density foam is observed as density-gradient bands across the part thickness. The lower surface may densify while the core remains open-celled. This is evaluated by sectioning the cured foam and measuring density according to ASTM D1056 on discrete slices. The vinyl oil level, blowing agent decomposition range, and crosslinker ratio must be co-optimized so that the gel point occurs after gas generation but before drainage. A moving-die rheometer cure trace according to ASTM D5289-19 can be compared with the blowing agent decomposition profile from differential scanning calorimetry at a heating rate of 10 °C/min under ISO 11357. If the gel point occurs too early, the foam becomes closed-cell with high density; if too late, the cell walls rupture and the foam collapses. Production batches are therefore qualified on density and compression set after each adjustment of oil dosage.

Cure Inhibition Is Not the Only Failure Mode in High-Surface-Area Textile Coating

A textile coating line running a solventless or low-solvent addition-cure silicone formulation uses RH-Vi303 as a reactive diluent to achieve the penetration and leveling required by knife-over-roll or dip-coating equipment. Woven glass cloth, aramid fabric, and polyester scrim each present a high surface area that can adsorb platinum inhibitor and deplete the catalyst, but the more immediate failure mode in production is viscosity drift during the working bath. Mixed viscosity at 25 °C is monitored by rotational viscometer and is typically held below 10,000 mPa·s for knife-over-roll application; the low viscosity supplied by RH-Vi303 lowers the bath viscosity without the high volatile organic content of solvent-borne systems. Coated fabric tensile properties are measured by ASTM D751-19, and the coating adhesion is tested by ISO 4624-2016 pull-off or the appropriate fabric-specific method. Hydrostatic resistance of coated fabrics is assessed by ISO 811:2018 or ASTM D3393-91. Cure is performed in a tenter frame oven at 140–180 °C for 30–120 s depending on fabric weight and add-on. A key limitation is that RH-Vi303 is not a substitute for high-molecular-weight gum in applications requiring tear resistance; it is added up to the level that still permits the cured film to pass the specified tear and abrasion tests. Abrasion resistance is evaluated by ASTM D4060-19 Taber abrasion or ISO 5470-1:2016. The formulation must avoid amino-functional adhesion promoters, which can poison the platinum catalyst, and sulfur-containing dyes or sizing agents on the fabric should be removed by scouring before coating. Final articles for protective clothing or industrial barrier applications require end-use standards such as EN ISO 11611 for welding protective garments or EN 14116 for heat and flame protective clothing; those standards apply to the finished textile assembly and not to the silicone component alone.

Knife-over-roll coating of high-surface-area textiles demands that the mixed formulation remain homogeneous and free of skin formation at the doctor blade. Skin formation is caused by solvent evaporation or by premature hydrosilylation at the bath surface; the addition of RH-Vi303 lowers initial viscosity but does not eliminate the need for continuous circulation and nitrogen blanketing when storage life is critical. Viscosity is measured from the coating bath every 30–60 min during a production run using a spindle viscometer at 25 °C; an increase of more than 20% from the initial value indicates partial gelation or filler settling. The coated fabric is cured to a consistent add-on weight, often 20–80 g/m² depending on the textile and end use, and then conditioned at 23 ± 2 °C and 50 ± 5% RH before testing. The final physical properties are influenced as much by the substrate construction as by the silicone network; therefore, coatings are tested on the actual production fabric rather than on free films. This is a critical distinction for compliance testing under ASTM D751-19 and ISO 811:2018.