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Karstedt Platinum Catalyst (Platinum-Divinyltetramethyldisiloxane Complex): The Industry-Standard Hydrosilylation Catalyst for LSR and RTV-2
SEMITECH supplies Karstedt platinum complex at 2%, 3% and 5% Pt loadings in vinyl-functional siloxane solvent — the modern industry standard for hydrosilylation cure of LSR injection moulding, RTV-2 medical and optical encapsulation, and food-contact silicones. Far more selective than chloroplatinic acid (Speier), no chloride residue, no part discolouration. 1 kg / 500 g packing under nitrogen blanket.
Contents
| 2 / 3 / 5% | 5–20 ppm | 1 kg |
|---|---|---|
| Pt loadings stocked | Typical use level | MOQ |
Chemistry & Specifications
Pt(0) complex with 1,1,3,3-tetramethyl-1,3-divinyldisiloxane ligand — soluble in vinyl-PDMS, no chloride.
Karstedt's catalyst is a Pt(0)-DVTMDS complex, supplied at 2, 3, and 5 wt% Pt in vinyl-functional siloxane solvent (5,000–10,000 cP). Clear pale-yellow to amber liquid; Pt content verified by ICP-MS to ±0.05%. The vinyl-siloxane solvent is reactive and incorporates into the cure network, leaving no extractable solvent.
Cure Mechanism: Pt(0)-Catalysed Hydrosilylation of Vinyl-PDMS + Si-H
Vinyl-PDMS coordinates to Pt centre, oxidative addition of Si-H, β-vinyl insertion, reductive elimination — Chalk-Harrod cycle.
The net result is Markovnikov-selective addition of Si-H across vinyl-PDMS, forming a Si-CH₂-CH₂-Si crosslink with no byproduct.
- Loading 5–10 ppm Pt — fast-cure LSR injection moulding (10–30 sec at 150–200°C)
- Loading 10–20 ppm Pt — RTV-2 cast moulding (5–30 min at 80–120°C); medical and optical
- Loading 20–50 ppm Pt — partial-poisoning override; high-clarity optical encapsulant
Karstedt produces no chloride residue and is fully consumed in cure. Inhibition is the dominant operational issue — reversibly inhibited by alkynes (cure-rate moderators), irreversibly poisoned by sulphur, tertiary amines, organotin, phosphines, and heavy-metal salts (Pb, Hg, Bi).
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Applications & Formulation Guidance
LSR injection moulding (largest), RTV-2 medical/optical, food-contact silicone, electronic encapsulation, skin adhesives.
LSR injection moulding — Karstedt at 5–10 ppm Pt, 10–30 second cycles at 150–200°C for automotive, baby-care, medical, and kitchenware parts. RTV-2 mould rubber — 10–20 ppm Pt, 30 min at 80°C or 4 hr at 23°C; chosen over tin systems for faster cure, lower shrinkage, and food-contact compliance. Optical/electronic encapsulation — 10–15 ppm Pt with high-clarity vinyl-PDMS; chloride-free chemistry required for reliability under DC bias. Skin-adhesive silicone — 15–25 ppm Pt for wound dressings and transdermal patches. Food-contact silicone — Karstedt is the only catalyst meeting most national food-contact regulations.
Procurement, Storage and Quality Control
1 kg / 500 g tinted glass under N₂; ICP-MS Pt assay; light-sensitive; 12-month shelf life.
CoA per batch: Pt content (ICP-MS, ±0.05%), APHA colour, viscosity, active species verification. MOQ 500 g (5% grade), 1 kg (2/3% grades). Lead time 2–3 weeks to Asia, 3–4 weeks to Europe/North America. Store in tinted glass, sealed under nitrogen, below 25°C, away from sunlight. Replace rubber gaskets with PTFE or Kalrez. Shelf life 12 months sealed. Pt content drives ~85% of cost; SEMITECH passes through monthly LBMA fixings on bulk orders.
Karstedt Platinum Catalyst Specification Sheet
SEMITECH stocked grades; CoA per batch with ICP-MS Pt assay.
| Property | Karstedt 2% | Karstedt 3% | Karstedt 5% |
|---|---|---|---|
| Pt content (ICP-MS) | 2.00 ± 0.05% | 3.00 ± 0.05% | 5.00 ± 0.05% |
| Solvent | Vinyl-PDMS, 5,000 cP | Vinyl-PDMS, 5,000 cP | Vinyl-PDMS, 8,000 cP |
| Appearance | Pale yellow liquid | Yellow liquid | Amber liquid |
| APHA colour | ≤200 | ≤300 | ≤500 |
| Viscosity (25°C) | 5,000–6,000 cP | 5,000–6,000 cP | 8,000–10,000 cP |
| Density (20°C) | 0.97 g/cm³ | 0.97 g/cm³ | 0.98 g/cm³ |
| Active complex | Pt(0)-DVTMDS dimer | Pt(0)-DVTMDS dimer | Pt(0)-DVTMDS dimer |
| Typical use level | 5–20 ppm Pt | 5–20 ppm Pt | 5–20 ppm Pt |
| Packaging | 1 kg amber glass | 1 kg amber glass | 500 g amber glass |
| Storage | Tinted glass, N₂ blanket, <25°C | Tinted glass, N₂ blanket, <25°C | Tinted glass, N₂ blanket, <25°C |
| Shelf life | 12 months sealed | 12 months sealed | 12 months sealed |
FAQ
+Why does my LSR fail to cure on a sulphur-vulcanised rubber tool insert?
Sulphur is the most aggressive Pt poison — even ppm-level migration produces tacky uncured layers. Solutions: replace with sulphur-free elastomer, bake at 200°C for 4 hr, apply barrier primer, or raise Pt to 30–50 ppm.
+Which Pt loading should I order — 2%, 3% or 5%?
Order 5% for production-scale LSR (lower shipping cost per Pt unit). Order 2/3% for lab-scale development where dosing accuracy at small volumes is critical.
+How do I confirm a Karstedt batch is still active?
Gel test: 50 g vinyl-PDMS + 10 ppm Pt + 1.5 wt% Si-H crosslinker at 23°C. Fresh batch gels in 15–30 min; deactivated batch shows 45–90+ min or fails to cure tack-free.