T-9 Stannous Octoate

Overview

T-9 — stannous octoate, also written as tin(II) 2-ethylhexanoate, CAS 301-10-0 — is the divalent tin counterpart to the Sn(IV) catalysts (DBTDL, DOTL) in the organotin family. The Sn(II) divalent state is what differentiates T-9: divalent tin is more reactive and air-sensitive — T-9 oxidises to Sn(IV) on prolonged air exposure, forming a brown-black tin oxide precipitate that signals catalyst death — but the toxicology profile is meaningfully different. Sn(II) species are not subject to the REACH Annex XVII organotin restrictions that apply to dialkyltin(IV) compounds, making T-9 the preferred catalyst for skin-contact and food-contact silicone applications.

Molecular formula Sn(C₈H₁₅O₂)₂, molecular weight 405.1 g/mol, density 1.25 g/cm³ at 20°C, viscosity 250–400 cP at 25°C — supplied as a clear yellow viscous liquid at ≥95% active content with tin assay 27.5–28.5% by ICP-OES. Storage under nitrogen blanket is mandatory beyond initial sealed shelf life; opened drums should be re-blanketed and consumed within 30 days for consistent activity. The 9-month sealed shelf life is shorter than the 12-month for Sn(IV) DBTDL and DOTL grades because of the greater air-sensitivity of divalent tin.

In flexible polyurethane foam — the dominant application accounting for ~80% of global T-9 demand — T-9 selectively catalyses the urethane (isocyanate + polyol) gel reaction over the urea (isocyanate + water) blowing reaction, the inverse of amine catalysts. A typical flexible slab-stock formulation pairs T-9 at 0.10–0.30 phr with an amine blowing catalyst at 0.05–0.15 phr; the amine kicks off CO₂ generation while T-9 builds polymer network strength, the timing balance between the two determines cell structure and density.

In condensation-cure RTV silicone, T-9 catalyses silanol-alkoxysilane condensation at substantially lower activity than DBTDL — typical tack-free times are 90–180 minutes at 23°C and 50% RH at 0.30% loading. The slow cure profile is acceptable for dental impression (where the operator wants 90+ seconds working time), prosthetic mould-making, and skin-contact medical silicones where lower toxicity is mandated.

Technical Specifications

Applications

Flexible Polyurethane Foam

Slab-stock continuous foam lines for mattress and furniture cushion use T-9 at 0.15–0.25 phr; moulded automotive seating and headliner foam at 0.20–0.40 phr; integral-skin foam for steering wheels and shoe soles at 0.10–0.20 phr. Typically metered as a 30–50% solution in dioctyl phthalate to improve dispensing accuracy on PU foam machines.

Microcellular PU Elastomer

Footwear midsoles, vibration mounts, microcellular industrial rollers use T-9 at 0.05–0.15% on polyol weight as the gel catalyst.

Dental Impression Silicone

Condensation-cure putty and light-body dental impression material uses T-9 at 0.30–0.50% — the lower toxicity profile compared to DBTDL is required for any product entering the oral cavity. EU MDR Class IIa device classification accepts T-9 in compliant formulations.

Prosthetic and Skin-Contact Silicone

Skin-contact body-forming RTV, scar treatment sheets, prosthetic-orthotic silicone use T-9 at 0.20–0.40% for biocompatibility under ISO 10993-5 cytotoxicity testing.

Industrial RTV-1 Medical Device Assembly

T-9 at 0.10–0.30% paired with alkoxysilane crosslinker — the longer cure time relative to DBTDL is acceptable in batch assembly where parts cure overnight.

Selection Guide vs Other Catalysts

T-9 sits between the high-activity Sn(IV) catalysts (DBTDL, DOTL) and the platinum addition-cure systems (Karstedt, Speier) on the activity spectrum. Choose T-9 when: skin-contact regulatory pathway requires elimination of Sn(IV) organotin (dental, prosthetic, cosmetic); flexible PU foam application needs a gel catalyst with selective urethane vs urea kinetics. Choose DBTDL/DOTL when: industrial RTV cure speed and shelf life matter more than skin-contact compliance. Choose Karstedt platinum when: organotin must be completely eliminated from the finished part (medical implant, food-contact, optical encapsulation).

Equivalent Grades

• Air Products Dabco T-9 — primary North American equivalent (the namesake grade)
• Galata Catalyst T-9 — alternative North American grade
• Goldschmidt Kosmos 29 — European equivalent
• Generic Stannous Octoate — Chinese commodity grade ≥95%