Vinyl Terminated Silicone Oil RH-Vi1325

In fully automated LSR injection cells, the RH-Vi1325 fluid is volumetrically proportioned to a methylhydrogen crosslinker and a platinum(0)-divinyltetramethyldisiloxane complex inside a static mixer of length 300 mm to 500 mm, with downstream pressure held at 0.2 MPa to 1.0 MPa. The molar ratio of silicon hydride to terminal vinyl is maintained between 1.2:1 and 2.5:1; ratios below 1.1:1 produce under-cured tensile slabs with surface tack, while ratios above 3.0:1 cause excessive post-cure embrittlement and a drop in elongation at break measured per ISO 37:2017. Platinum catalyst concentration in the mixed compound is typically 5 ppm to 15 ppm as platinum metal, and 0.05 wt% to 0.30 wt% of 1-ethynylcyclohexanol is used to suppress premature gelation in the barrel, which is held at 25°C to 35°C. Shot-to-shot variation in a production cell with a cold runner and closed-loop hydraulic injection frequently originates from shear heating in the check ring, and barrel temperatures above 40°C are observed to initiate partial vulcanization within 3 min to 5 min of dwell time. Mold temperatures are set from 150°C to 190°C, with cure times of 15 s to 120 s depending on wall thickness; demolding at Shore A hardness 20 to 25 reduces tear-induced gate breakage. The cured parts are typically characterized by hardness 20 to 70 Shore A per ASTM D2240-15e1, tensile strength 6 MPa to 11 MPa, elongation at break 300% to 800%, tear strength 20 kN/m to 45 kN/m per ISO 34-1:2022, and compression set 10% to 30% after 22 h at 175°C per ISO 815-1:2019. For medical teats and respiratory valve seals processed from RH-Vi1325-based LSR, compliance testing is formulation-dependent and normally includes ISO 10993-5:2009 for cytotoxicity and 21 CFR 177.2600 for repeat-use rubber articles, provided no peroxide by-products are present.

Addition-cure injection molding cells that use direct feed from a 55 US gallon drum should specify a gear pump with a tungsten carbide rotor and dynamic seals compatible with dimethylpolysiloxane; nitrile O-rings swell and leak, causing air entrapment and hydraulic pressure fluctuations. The inhibitor 1-ethynylcyclohexanol undergoes oxidative evaporation from the mixed compound during prolonged barrel residence above 35°C, which shifts the scorch time from 8 min to less than 2 min without a corresponding increase in crosslinker concentration. When a cold mold is used below 140°C, cure advances through a diffusion-limited mechanism, and the part develops a hard skin with a soft core because the low thermal diffusivity of silicone, approximately 1 × 10⁻⁷ m²/s, delays internal temperature rise. Production molds therefore incorporate vented runners of 0.5 mm to 1.0 mm diameter and vacuum levels of -0.08 MPa to -0.09 MPa to prevent gas entrapment and backrinding at gate points. Post-molding shrinkage of addition-cured LSR is typically 0.8% to 1.5% linear, and the part should not be subjected to post-cure above 200°C unless the hydride excess is below 1.5:1, otherwise surface hardening causes a permanent Shore A increase of 5 to 10 points.

Liquid Silicone Rubber Shot-to-Shot Cure Uniformity With Telechelic Vinyl Polymers

Because high-molecular-weight silicone gum reaches Mooney viscosity above 80 MU without plasticization, a 50 mm twin-screw compounding line with L/D 44 is used to add RH-Vi1325 at the first feed port before fumed silica incorporation at a loading of 30 phr to 50 phr. The oil level is typically 5 phr to 15 phr; replacement of gum with a telechelic vinyl fluid above 20 phr leads to a measurable loss in green strength on a two-roll mill and increases the migration of low-molecular-weight siloxanes to the surface of calendered sheet. Filler wetting is completed with in-situ treatment using hexamethyldisilazane or vinyltrimethoxysilane at 90°C to 140°C, while the melt temperature is kept below 120°C to avoid platinum poisoning from ammonia released during silazane treatment if an addition-cure package is subsequently added. The process bottleneck at production scale is the formation of compacted silica agglomerates in the screw kneading blocks; when agglomerates reach the strainer, pressure rises to 8 MPa to 12 MPa and unreacted vinyl oil is pressed out as a visible film on the strand, which reduces final crosslink density. The compounded batch is discharged through a 150 µm to 200 µm screen pack and then catalyzed on a two-roll mill with roll gaps of 0.5 mm to 2.0 mm at 40°C to 70°C. For high-consistency rubber used in automotive O-rings and wire insulation, post-cure is required at 200°C for 4 h to drive off peroxide decomposition residues when a peroxide initiator is used instead of platinum. Physical properties are measured on pressed slabs per ASTM D412-16, ASTM D395-18, and ISO 289-1:2015; typical values are tensile strength 6 MPa to 10 MPa, elongation 200% to 600%, and compression set 15% to 35% after 22 h at 150°C.

What Governs Thermal Shock Resistance in Silicone Potting Gels for Power Modules?

When RH-Vi1325 is crosslinked with a low-hydrogen silicone fluid at a SiH:SiVi molar ratio below 2.0:1, the resulting network displays a low storage modulus and remains optically clear after 1,000 h at 150°C, which is required for potting of IGBT and silicon carbide power modules. The mixed two-part formulation is vacuum degassed at -0.09 MPa for 30 min before dispensing to remove air bubbles that would otherwise create partial discharge sites under 1,500 V insulation testing. Cure is performed at 80°C to 120°C for 30 min to 120 min; deep-section cure at 10 mm thickness is retarded by the low thermal conductivity of the gel, and a stepped profile of 60°C for 30 min followed by 120°C for 60 min is used to avoid bubble growth from volatile low-molecular-weight siloxanes. The cured gel has a penetration reading of 3 mm to 10 mm per ASTM D217-21 or Shore 00 hardness of 20 to 70 per ASTM D2240-15e1, dielectric strength 15 kV/mm to 25 kV/mm per IEC 60243-1:2013, and volume resistivity greater than 1 × 10¹⁵ Ω·cm per ASTM D257-14. Catalyst poisoning is the dominant production failure: adhesion promoters containing primary amines, solder flux residues containing rosin acid, and sulfur-containing phenolic curing agents reduce gelation to a tacky surface and require a platinum concentration increase to 20 ppm to 50 ppm. Adhesion to copper leadframes and ceramic substrates is established with 0.5 wt% to 2.0 wt% of 3-glycidoxypropyltrimethoxysilane; without the silane, the gel exhibits cohesive failure at the metal interface after thermal cycling from -40°C to 125°C for 200 cycles.

Table 1 records representative values from a formulation containing 30 wt% quartz filler; these are not product specifications for RH-Vi1325.

Replacing 10 wt% of the base gel with spherical alumina raises thermal conductivity to 0.8 W/m·K to 1.2 W/m·K per ASTM E1530-19, but the addition of alumina above 40 wt% causes thixotropic settling and a reduction in needle penetration from 8 mm to 2 mm before cure, which complicates automated dispensing through 25 gauge needles.

Removing solvent from a release coating line forces the wet film thickness to fall to 1 g/m² to 3 g/m², at which point crosslinker miscibility and platinum catalyst deactivation become the controlling variables. A vinyl-terminated silicone oil such as RH-Vi1325 is blended with a methylhydrogen siloxane crosslinker at a SiH:SiVi ratio of 1.8:1 to 3.0:1, and the mixture is applied directly to glassine or biaxially oriented polypropylene with a five-roll coating head at 100 m/min to 300 m/min. Cure is triggered in a forced-air oven at 140°C to 180°C for 5 s to 15 s; residual solvent is absent, but unreacted hydride remains on the release surface and can cause secondary adhesion loss in subsequently applied pressure-sensitive adhesives. Paper substrates with moisture content above 6% require pre-drying at 80°C to 100°C before coating, because water hydrolyzes the siloxane crosslinker and generates hydrogen gas that creates pinholes in the cured film. Nitrogen-containing retention agents and amine-based antistatic coatings poison the platinum catalyst, producing zones of uncured silicone that transfer to the adhesive during unwind. Release force is measured at 180° peel and 300 mm/min per FINAT FTM 3, with target values from 5 cN/25 mm to 50 cN/25 mm depending on the label adhesive and die-cut configuration. The cured coating thickness is 0.8 µm to 1.5 µm per ISO 4593:2019; extractable siloxanes are kept below 0.5 wt% when the coating is used for food-contact labels tested under 21 CFR 177.2600. The working bath at 25°C has a pot life of 6 h to 12 h; after 12 h, viscosity increases by 50% to 80% due to slow platinum-mediated addition, and coat weight control becomes unstable above 2 g/m² on a five-roll coater. Adding 0.2 wt% of a low-volatile maleate inhibitor extends the bath life beyond 24 h but increases minimum cure temperature to 160°C.

If Vinyl-Terminated Silicone Oil Is Added to Silicone PSA as a Reactive Diluent

Silicone pressure-sensitive adhesives are conventionally produced by condensing MQ resin with silanol-functional polysiloxane, but a second addition-cure pathway uses RH-Vi1325 as a high-viscosity reactive diluent to increase crosslink density without adding solvent. The MQ resin-to-polymer ratio is held between 0.8:1 and 1.5:1; above 1.7:1 the adhesive loses tack and becomes a laminating adhesive, while below 0.6:1 the cohesive strength is insufficient to survive 24 h of constant load at 1 kg. The addition-cure PSA is coated from a solvent blend onto polyimide or PTFE carrier at dry coat weights of 20 g/m² to 60 g/m², then cured at 150°C for 3 min. Platinum catalyst at 30 ppm to 100 ppm is required because the silicone PSA contains residual silanol groups that compete with vinyl-hydride addition and can deactivate the catalyst at elevated temperature. Adhesion to stainless steel is measured per ASTM D3330/D3330M-04 and typically falls between 10 N/25 mm and 30 N/25 mm for a 60 g/m² coat weight; loop tack values are 8 N/25 mm to 25 N/25 mm; holding power on steel at 70°C exceeds 24 h at 1 kg when the SiH:SiVi ratio is above 1.2:1. The crosslink density of the cured PSA is affected by the degree of terminal vinyl conversion, which can be monitored by transmission FTIR by following the 1600 cm⁻¹ vinyl band; incomplete conversion below 70% produces adhesive transfer and a loss of shear adhesion failure temperature above 250°C. Migrating free siloxanes from the adhesive are reduced by selecting a high-viscosity vinyl oil, but published data for the specific migration rate of RH-Vi1325 in a production PSA matrix is limited and should be verified by GC-MS after Soxhlet extraction if the tape is destined for electronics bonding. The addition-cure PSA is used for masking tapes in plasma spraying, high-temperature electrical tape, and silicone foam gasketing; in those applications, it is incompatible with sulfur-containing acrylic liners that can poison the platinum during cure and cause adhesive delamination at the silicone-liner interface.

When a closed-cell silicone sponge is blown with azodicarbonamide at decomposition temperatures of 195°C to 215°C, cell coalescence is limited by selecting a vinyl polymer with a narrow molecular weight distribution, which RH-Vi1325 supplies as a telechelic vinyl-terminated dimethylpolysiloxane. The sponge formulation combines 100 phr silicone gum, 10 phr to 20 phr RH-Vi1325, 1 phr to 3 phr azodicarbonamide, and 0.5 phr to 1.0 phr of a platinum or dicumyl peroxide cure system; the blowing agent is predispersed in a portion of the oil to prevent dusting and to control gas evolution during 170°C to 200°C compression molding. Material processed below 170°C releases gas before the silicone network has developed sufficient modulus, producing large open-celled voids and a density below 0.30 g/cm³; processing above 220°C causes thermal depolymerization of unreacted vinyl oil and a visible surface oil bloom. The cured foam density is controlled between 0.40 g/cm³ and 0.70 g/cm³ per ISO 845:2006, with compression set under 15% after 22 h at 70°C per ISO 1856:2018. Closed-cell structure is evaluated by SEM at 100× to 500× magnification; cell size should remain below 200 µm for compression recovery below 15% after 1,000 cycles. Production-scale failure in conveyorized ovens is overblow at thick sections above 20 mm, where the core temperature lags the surface by 20°C to 30°C and the outer skin crosslinks before the center expands, leaving a dense core. The resulting cellular silicone is used for automotive HVAC gaskets, vibration isolators, and battery pack cushioning pads; compliance for automotive underhood parts is verified per ASTM D1056-20 or by OEM specifications requiring heat aging at 150°C for 1,000 h. Published data on RH-Vi1325 in azodicarbonamide-blown silicone sponge is limited; the processing limits stated here derive from general vinyl-terminated polydimethylsiloxane behaviour and require pilot-trial confirmation before full-scale production.