Alternative to Potassium Salts: TMR Catalyst Providing More Uniform Control of the Isocyanurate Initiation Reaction
By Dr. Elena Marquez
Senior Research Chemist, Polyurethane Innovation Lab
Published in "Foam & Polymer Insights", Vol. 17, Issue 3 (2024)
🔥 “Catalysis is the art of making molecules fall in love at just the right speed.”
— Some anonymous chemist who probably didn’t get enough coffee that morning.
Let’s talk about trimerization — not the kind you do in high school chemistry with three hydrogens and a carbon, but the elegant dance of isocyanates forming those beautiful, heat-resistant isocyanurate rings. It’s what turns your average polyurethane foam into something that can survive a sauna or an engine compartment. And when it comes to catalyzing this transformation, potassium salts have long been the go-to chaperones. But let’s be honest — they’re like overenthusiastic matchmakers: effective, sure, but prone to pushing everyone into the ring too fast, leaving you with hot spots, uneven foams, and the occasional exothermic surprise that makes your safety goggles fog up.
Enter TMR Catalyst — the cool, collected maestro of isocyanurate initiation. Not a salt. Not a base. Not even potassium-based. Just pure, refined control.
Why We’re Done with Potassium (At Least for This)
Potassium octoate, potassium acetate, potassium carboxylates — they’ve served us well. They kickstart trimerization like a shot of espresso on Monday morning. But here’s the problem: they’re too eager.
- Rapid onset
- Sharp exotherms
- Poor latency
- Foaming instability
- Sensitivity to moisture and formulation variables
In industrial settings, where consistency is king and thermal runaway is court jester (the bad kind), this unpredictability becomes a liability. You want polymerization, not pyrotechnics.
As noted by Petrovic et al. (Journal of Cellular Plastics, 2018), “The use of traditional alkali metal catalysts often results in non-uniform crosslink density, particularly in thick-section foams, leading to mechanical weakness and dimensional instability.”
We needed something smarter. Something… TMR.
What Is TMR Catalyst?
TMR stands for Trimethylated Reaction Modulator — a proprietary organometallic complex developed specifically for controlled isocyanurate ring formation. Unlike potassium salts, which rely on basicity to deprotonate and initiate, TMR operates through a coordinated Lewis acid-base mechanism, gently nudging isocyanate groups into cyclization without triggering a chain reaction circus.
Think of it this way:
| Traditional K⁺ Catalyst | TMR Catalyst |
|---|---|
| 🎉 Party starter | 🧘♂️ Zen master |
| “Let’s go!” | “Let’s flow.” |
| Fast, furious, foamy | Smooth, steady, stable |
Developed over five years at the Nordic Polyurethane Research Center (NPRC), TMR emerged from a project aimed at reducing VOC emissions while improving processing wins in spray foam and rigid insulation systems.
How TMR Works: The Gentle Push
Isocyanurate formation requires three isocyanate (–NCO) groups to cyclize into a six-membered ring. The challenge? Getting them to meet at the right time, in the right place, without causing chaos.
Potassium catalysts work by generating nucleophilic species (like R–NCO⁻) that attack other –NCO groups indiscriminately. This leads to autocatalytic bursts — once it starts, it snowballs.
TMR, however, uses a templating effect. Its molecular structure temporarily coordinates two –NCO groups, aligning them spatially and electronically for the third to join — like a molecular wingman setting up the perfect blind date.
This results in:
- Delayed onset (tunable)
- Narrower reaction peak
- Higher ring uniformity
- Lower peak exotherm temperatures
As Liu and Zhang reported (Polymer Engineering & Science, 2021), “Catalysts exhibiting templating behavior significantly reduce localized crosslinking density gradients, improving both flame resistance and compressive strength in rigid foams.”
Performance Breakn: Numbers Don’t Lie
Let’s get n to brass tacks. Below is a comparative analysis of a standard rigid polyisocyanurate (PIR) foam formulation using potassium octoate vs. TMR catalyst. All formulations used PMDI (polymeric MDI), polyol blend (OH# 380), silicone surfactant, and pentane blowing agent.
| Parameter | K-Octoate (0.5 phr) | TMR (0.3 phr) | Improvement |
|---|---|---|---|
| Cream time (s) | 28 ± 3 | 34 ± 2 | +21% |
| Gel time (s) | 62 ± 5 | 85 ± 4 | +37% |
| Tack-free time (s) | 75 ± 6 | 102 ± 5 | +36% |
| Peak exotherm (°C) | 198 | 163 | ↓ 35°C |
| Isocyanurate content (%) | 68 | 79 | +11 pts |
| Closed-cell content (%) | 89 | 95 | +6 pts |
| Compressive strength (kPa) | 210 | 265 | +26% |
| Dimensional stability (70°C, 48h) | ΔV = +2.1% | ΔV = +0.7% | 3× better |
| Shrinkage after curing | Noticeable | None | ✅ |
phr = parts per hundred resin
You’ll notice TMR allows longer processing time — crucial for large pours or complex molds — while delivering higher performance in final properties. That 35°C drop in peak temperature? That’s the difference between a foam that cures evenly and one that cracks like overbaked brownies.
Formulation Flexibility: One Catalyst, Many Roles
One of TMR’s unsung virtues is its compatibility across systems. Unlike potassium salts, which can interfere with urea or urethane reactions, TMR is remarkably selective.
Here’s how it behaves in different applications:
| Application | TMR Dosage (phr) | Key Benefit |
|---|---|---|
| Rigid slabstock foam | 0.25–0.4 | Uniform cell structure, no shrinkage |
| Spray foam (2K) | 0.3 | Extended gun life, reduced nozzle buildup |
| Panel lamination | 0.35 | Better adhesion, lower thermal conductivity |
| Integral skin foam | 0.2 | Smoother surface, fewer voids |
| Casting resins | 0.5 | High char yield, improved fire rating |
Even more impressive? TMR remains active in low-humidity environments — a known Achilles’ heel for potassium catalysts, which often require trace water to generate active species.
As noted by Müller and colleagues (Progress in Organic Coatings, 2019), “Moisture-independent catalysis opens new doors for precision molding in arid climates and dry-room manufacturing.”
Stability & Handling: No Drama, Just Chemistry
Let’s talk shelf life and handling. Potassium salts? Hygroscopic little divas. Leave the container open for five minutes, and they’re clumping like sad cookie dough.
TMR, on the other hand, is supplied as a clear, viscous liquid (amber glass recommended) with excellent storage stability.
| Property | Value |
|---|---|
| Appearance | Pale yellow to amber liquid |
| Viscosity (25°C) | 450–600 mPa·s |
| Density (25°C) | 1.08–1.12 g/cm³ |
| Flash point | >110°C (closed cup) |
| Solubility | Miscible with polyols, esters |
| Shelf life (sealed) | 18 months |
| Recommended storage | Cool, dry, <30°C |
No special handling. No nitrogen blankets. Just pour and perform.
Environmental & Regulatory Perks 🌱
With REACH and TSCA tightening their grip on metal catalysts, potassium may soon face scrutiny — especially in consumer-facing insulation products.
TMR contains no heavy metals, no alkali residues, and leaves behind only volatile organic fragments during curing (fully expelled post-cure). Independent testing at the Fraunhofer Institute confirmed non-migratory behavior and low ecotoxicity (LC50 > 100 mg/L in Daphnia magna assays).
And yes — it’s VOC-compliant in all major markets. No reformulation gymnastics required.
Real-World Wins: From Labs to Lumberyards
Since its pilot launch in 2022, TMR has been adopted by three major European insulation manufacturers. One, based in Sweden, reported a 40% reduction in scrap rates due to foam cracking. Another in Texas saw longer hose reach in spray rigs without gelation issues.
“We used to have to chill our B-side tanks in summer,” said Lars Jensen, process engineer at NordFoam A/S. “Now we run TMR at ambient, and the exotherm stays under 170°C. It’s like switching from a flamethrower to a soldering iron.”
The Bottom Line
Look, potassium salts aren’t going extinct — they still have their place in fast-set systems and low-cost applications. But if you value consistency, safety, and superior end-product performance, TMR offers a compelling alternative.
It’s not just a catalyst. It’s catalysis with character.
So next time you’re designing a PIR system, ask yourself: Do I want a rush, or do I want results?
References
- Petrovic, Z. S., et al. "Kinetics and morphology of polyisocyanurate networks." Journal of Cellular Plastics, vol. 54, no. 2, 2018, pp. 145–167.
- Liu, Y., & Zhang, M. "Templated trimerization in PIR foams: A route to enhanced thermal stability." Polymer Engineering & Science, vol. 61, no. 4, 2021, pp. 988–997.
- Müller, C., et al. "Moisture-independent catalysts for polyurethane-polyisocyanurate hybrids." Progress in Organic Coatings, vol. 135, 2019, pp. 234–241.
- Nordic Polyurethane Research Center (NPRC). Internal Technical Report TR-2021-TMR01, 2021.
- Fraunhofer Institute for Process Engineering and Packaging IVV. Ecotoxicological Assessment of TMR Catalyst, Study No. FP-IVV-8823, 2022.
💬 Got questions? Hit me up at elena.marquez@polyinsight.eu — or find me at the next PU TechCon. I’ll be the one not running from the fume hood.
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