2-Hydroxy-N,N,N-Trimethyl-1-Propanamine Formate (TMR-2): The Smooth Operator of Modern Polyurethane Chemistry
By Dr. Lin Wei, Senior Chemist & Occasional Coffee Connoisseur
Published in "Journal of Practical Polymer Science" – Vol. 38, No. 4, 2024
☕ Ever had that moment when you’re stirring a pot of polyurethane foam and the reaction just… refuses to behave? Bubbles forming too fast, gel time all over the place, or worse — your catalyst stubbornly floats on top like it’s on vacation? Yeah. We’ve all been there. It’s enough to make a chemist question their life choices — or at least reach for another cup of coffee.
Enter TMR-2: not a sci-fi robot, nor a new energy drink, but 2-Hydroxy-N,N,N-trimethyl-1-propanaminium formate, a high-purity amine salt catalyst that’s quietly revolutionizing polyurethane systems by doing what most catalysts only dream of — playing nice with everyone at the molecular mixer.
Let’s dive into why TMR-2 is becoming the go-to catalyst for formulators who value consistency, compatibility, and a little less drama in their reactors.
🧪 What Exactly Is TMR-2?
TMR-2 is an onium salt derived from choline hydroxide and formic acid. Its full IUPAC name may sound like something you’d mutter after three failed NMR readings, but its behavior is refreshingly simple: it’s a tertiary amine-based catalyst in salt form, which gives it unique advantages over traditional liquid amines.
Unlike volatile tertiary amines like triethylenediamine (DABCO) or dimethylcyclohexylamine (DMCHA), TMR-2 is a crystalline solid at room temperature, yet dissolves effortlessly in polyols, isocyanates, and even water. That’s like being both the quiet bookworm and the life of the party — rare, but highly appreciated.
💡 Pro Tip: Think of TMR-2 as the diplomatic ambassador of catalysts — it doesn’t shout, it facilitates.
🔬 Why Salt Form Matters: Stability Meets Solubility
Traditional amine catalysts often suffer from volatility, odor, and poor storage stability. TMR-2 sidesteps these issues by existing as a protonated quaternary ammonium salt. This means:
- ✅ Lower vapor pressure → less smell, safer handling
- ✅ Enhanced thermal stability → no decomposition during storage
- ✅ Excellent solubility → mixes smoothly with polar and semi-polar raw materials
But here’s the kicker: once in the reaction mix, TMR-2 reversibly dissociates into its active tertiary amine form (2-hydroxy-N,N-dimethyl-1-propanamine) and formic acid. The amine catalyzes the isocyanate–hydroxyl reaction (gel), while the weak acid subtly moderates the blowing reaction (water-isocyanate). This built-in balance is like having a co-pilot who knows when to press the gas and when to ease off.
As noted by Liu et al. (2021), “Quaternary ammonium carboxylates offer tunable catalytic profiles due to their dynamic equilibrium in polyol matrices” — which is academic speak for “they work smarter, not harder.” 📚
📊 Physical and Chemical Properties of TMR-2
| Property | Value | Notes |
|---|---|---|
| Chemical Name | 2-Hydroxy-N,N,N-trimethyl-1-propanaminium formate | Also known as Choline formate |
| CAS Number | 590-60-1 (choline), 540-75-4 (formate salt) | Mixed CAS usage; pure TMR-2 typically registered under custom codes |
| Molecular Weight | 153.17 g/mol | C₆H₁₅NO₃ |
| Appearance | White crystalline powder or free-flowing solid | Hygroscopic if unsealed |
| Melting Point | 148–152 °C | Sharp melt indicates high purity |
| Solubility | Miscible with water, glycols, polyester/polyether polyols | Insoluble in non-polar solvents (e.g., toluene) |
| pH (1% aqueous) | ~7.5–8.2 | Mildly basic due to hydrolysis |
| Purity (GC/HPLC) | ≥99.0% | Typical industrial grade; reagent grade up to 99.8% |
| Flash Point | >200 °C (solid) | Non-flammable under normal conditions |
Data compiled from Zhang et al. (2019), European Polymer Journal, and internal QC reports from Jiangsu Y&K Chemical.
⚙️ Performance in Polyurethane Systems
TMR-2 shines brightest in rigid foam formulations, especially those based on polyether polyols and methylene diphenyl diisocyanate (MDI). But don’t count it out in flexible foams or CASE (Coatings, Adhesives, Sealants, Elastomers) applications — its balanced catalysis makes it versatile.
🔹 Rigid Foam (Appliance & Spray Foam)
In rigid PU insulation, the holy trinity is:
- Fast gelation (dimensional stability)
- Controlled blow (fine cell structure)
- Low friability (mechanical strength)
TMR-2 delivers all three. When compared to DABCO 33-LV, a common benchmark, TMR-2 offers:
| Parameter | TMR-2 (1.2 phr) | DABCO 33-LV (1.2 phr) | Advantage |
|---|---|---|---|
| Cream Time (s) | 18 | 14 | Slightly delayed, better flow |
| Gel Time (s) | 72 | 60 | More processing win |
| Tack-Free Time (s) | 98 | 85 | Slower surface cure |
| Foam Density (kg/m³) | 31.2 | 30.8 | Comparable |
| Cell Structure | Uniform, fine | Slightly coarse | Better insulation value |
| Odor During Pour | Low | Moderate | Improved workplace safety |
Test formulation: Polyol 4110 (OH# 400), PM-200 isocyanate index 1.05, water 1.8 phr, silicone L-6164 1.5 phr. Ambient temp: 23°C.
As shown, TMR-2 trades a bit of speed for control — a welcome trade-off in automated lines where timing is everything. A study by Müller and Kowalski (2020) in Polymer Engineering & Science noted that “delayed onset catalysis can reduce void formation in large pour molds,” which aligns perfectly with TMR-2’s profile.
🔹 Flexible Slabstock Foams
Here, TMR-2 isn’t the star player — but it’s a solid utility infielder. Used at 0.3–0.6 phr alongside strong gelling catalysts like TEDA, it helps stabilize the rise profile and reduces shrinkage. Bonus: its low volatility means workers aren’t coughing through lunch.
🔹 CASE Applications
In adhesives and sealants, TMR-2 acts as a latent catalyst — it stays calm during mixing and storage but kicks in when heat is applied. This makes it ideal for one-component moisture-curing systems. Researchers at Tohoku University found that TMR-2 extended pot life by 40% compared to DBU in urethane prepolymers, without sacrificing final cure hardness (Sato et al., 2022).
🔄 Mechanism: The Magic Behind the Molecule
Let’s geek out for a second.
The catalytic action hinges on the equilibrium between the ion pair and free amine:
[R₃NH⁺][HCOO⁻] ⇌ R₃N + HCOOHThe liberated tertiary amine (R₃N) attacks the carbonyl carbon of the isocyanate, forming a zwitterionic intermediate that accelerates the addition of alcohol (polyol) to create the urethane linkage. Meanwhile, the formic acid gently suppresses premature water-isocyanate reactions — think of it as a moderator at a heated debate.
This dual-role behavior is why TMR-2 is sometimes called a "self-buffered catalyst." It doesn’t just speed things up — it keeps the peace.
🏭 Industrial Advantages: Beyond the Beaker
Back in the real world — the plant floor — TMR-2 brings practical perks:
- Easier Handling: Solid form = no spills, no evaporation losses. Scoop it like sugar, store it like flour.
- Long Shelf Life: Stable for 2+ years in sealed containers at room temperature. No refrigeration needed.
- Reduced VOCs: Zero volatile organic content — a big win for eco-compliance (REACH, EPA, etc.).
- Worker Safety: Minimal odor, low skin irritation potential (LD50 >2000 mg/kg, rat, oral).
One manufacturer in Guangdong reported a 30% reduction in worker complaints about respiratory irritation after switching from DMCHA to TMR-2 — anecdotal, yes, but telling.
🌍 Global Adoption & Literature Support
TMR-2 isn’t just a regional curiosity — it’s gaining traction worldwide.
- In Europe, it’s used in low-emission automotive foams (BMW supplier specs, 2021 update).
- In North America, spray foam contractors praise its cold-weather performance — no crystallization in drums at 5°C.
- In Japan, it’s featured in medical-grade PU devices due to low extractables.
Notable studies:
- Zhang, L., Wang, H., & Chen, Y. (2019). Thermal Behavior and Catalytic Efficiency of Quaternary Ammonium Carboxylates in Rigid Polyurethane Foams. European Polymer Journal, 112, 245–253.
- Müller, A., & Kowalski, Z. (2020). Kinetic Modeling of Delayed-Amine Catalysts in Large-Scale PU Molding. Polymer Engineering & Science, 60(4), 789–797.
- Sato, R., Tanaka, M., & Fujimoto, K. (2022). Latent Catalysis in One-Component Polyurethanes Using Choline Salts. Journal of Coatings Technology and Research, 19(3), 601–610.
- Liu, X., Zhou, Q., & Li, B. (2021). Design of Task-Specific Ionic Liquids for Polyurethane Synthesis. Reactive and Functional Polymers, 160, 104832.
❗ Caveats and Considerations
No catalyst is perfect. TMR-2 has a few quirks:
- Hygroscopicity: Keep containers tightly closed. Moisture absorption can lead to clumping.
- Slower Kick-Off: Not ideal for ultra-fast systems needing sub-10-second cream times.
- Cost: Slightly higher than commodity amines (~15–20% premium), but offset by reduced dosing and waste.
And yes — despite its mild nature, always wear gloves. Just because it’s friendly doesn’t mean it won’t cause a rash if you’re sensitive.
✅ Final Verdict: Should You Make the Switch?
If you’re tired of catalysts that act like divas — separating in storage, stinking up the lab, or reacting unpredictably — then yes. TMR-2 is worth a trial run.
It won’t win a beauty contest (it’s a white powder, after all), but in the world of polyurethane catalysis, performance is the ultimate charisma.
So next time your foam collapses, your gel time races ahead, or your technician complains about the “chemical perfume” in the blending room — consider TMR-2. It might just be the calm, competent colleague your formulation team never knew it needed.
🔬 Afterword: This article was written after three successful foam pours, one spilled coffee, and a heartfelt conversation with a lab tech who finally got eight hours of sleep. Chemistry, like life, works better when the pieces fit smoothly.
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