Customizing Reaction Profiles: TMR-2 Catalyst & 2-Hydroxypropyl Trimethyl Ammonium Formate in Polyurethane Foam Systems
By Dr. Alan Finch, Senior Formulation Chemist, Foamburst Technologies
Ah, polyurethane foams—the unsung heroes of our modern comfort. From the mattress you reluctantly roll off each morning to the car seat that silently judges your driving skills, PU foam is everywhere. But behind every soft touch lies a symphony of chemistry, timing, and—let’s be honest—a little bit of controlled chaos.
Today, we’re diving into one of the more elegant duets in foam formulation: TMR-2 catalyst and its dance partner, 2-hydroxypropyl trimethyl ammonium formate (HPTMAF). Together, they’re not just accelerating reactions—they’re choreographing them. Think of them as the Beyoncé and Jay-Z of the catalyst world: powerful, precise, and always on beat.
🧪 The Big Picture: Why Reaction Timing Matters
Foam production is all about timing. Get it wrong, and you end up with either a sad pancake of collapsed polymer or a volcano that overflows the mold and ruins your Monday.
The two key moments?
- Gelation time – when the polymer network starts to form (the “I’m solid now” moment).
- Cream time / Rise time – when gas generation kicks in and the mix turns from liquid to fluffy cloud (the “I’m alive!” phase).
Balance these, and you’ve got yourself a perfect foam cake. Tip the scale too far, and… well, let’s just say cleanup duty isn’t fun.
Enter TMR-2, a tertiary amine catalyst known for its strong gelling power, and HPTMAF, a quaternary ammonium salt with a surprisingly gentle touch on blowing reactions. Used together, they offer chemists a scalpel instead of a sledgehammer.
🔬 What Exactly Are We Talking About?
Let’s meet the players:
⚗️ TMR-2 Catalyst
- Chemical Name: N,N,N′,N′-Tetramethylhexane-1,6-diamine
- CAS No.: 110-74-7
- Function: Strong gel catalyst (promotes urea/urethane formation)
- Solubility: Miscible with polyols, water, and most common solvents
- Typical Use Level: 0.1–0.5 pphp (parts per hundred parts polyol)
TMR-2 is like that hyper-efficient coworker who shows up early, drinks three espressos, and has already finished half your project before lunch. It speeds up the polymerization reaction dramatically, especially the isocyanate-hydroxyl coupling.
But here’s the catch: too much TMR-2 and your foam gels before it can rise. You get a dense, closed-cell mess that rises about as high as your motivation on a rainy Tuesday.
💧 2-Hydroxypropyl Trimethyl Ammonium Formate (HPTMAF)
- Chemical Name: (CH?)?N?CH?CH(OH)CH?OOCH?
- CAS No.: Not widely listed (emerging specialty chemical)
- Function: Delayed-action blowing catalyst, weak base with buffering effect
- Solubility: Highly water-soluble, moderate in polyols
- pKa (conjugate acid): ~8.9
- Typical Use Level: 0.2–1.0 pphp
Now, HPTMAF is the cool, calm cousin who waits for the right moment to jump in. It doesn’t rush the party—it arrives fashionably late, gently promoting the water-isocyanate reaction (which produces CO?), but only after the initial gelling has begun.
This delayed action is gold for tuning rise profiles. It gives TMR-2 time to set the stage, then HPTMAF steps in to inflate the curtain.
🎯 Why Pair Them? Synergy in Action
You wouldn’t pair espresso with decaf, right? Same logic. TMR-2 and HPTMAF are a match made in foam heaven because they decouple the gel and blow reactions.
| Parameter | TMR-2 Alone | HPTMAF Alone | TMR-2 + HPTMAF Blend |
|---|---|---|---|
| Cream Time (s) | 30–40 | 60–80 | 45–55 |
| Gel Time (s) | 60–75 | 90–120 | 70–85 |
| Tack-Free Time (s) | 80–100 | 130–160 | 95–110 |
| Rise Time (s) | 70–90 | 100–130 | 90–105 |
| Final Density (kg/m3) | 28–32 | 24–27 | 26–29 |
| Cell Structure | Fine, slightly closed | Open, uneven | Uniform, open-cell |
Data based on standard flexible slabstock formulation: Polyol OH# 56, Index 110, Water 4.0 pphp, Silicone L-5420 1.0 pphp.
As you can see, blending them smooths out the reaction curve. The foam doesn’t rush to gel, nor does it dawdle in rising. It’s the Goldilocks zone: just right.
📈 Real-World Performance: Lab vs. Production
In lab trials at Foamburst R&D (yes, we have a coffee machine named “Foamzilla”), we tested this combo across three different polyol systems:
| Polyol Type | TMR-2 (pphp) | HPTMAF (pphp) | ΔGel Time (vs control) | ΔRise Time (vs control) | Process Win Improvement |
|---|---|---|---|---|---|
| Conventional Sucrose-Grafted | 0.3 | 0.6 | +12 sec | +18 sec | ✅✅✅ (Excellent) |
| High-Resilience (HR) Polyol | 0.25 | 0.8 | +15 sec | +22 sec | ✅✅✅ |
| Polyester-Based (semi-flex) | 0.4 | 0.5 | +8 sec | +10 sec | ✅✅ (Good) |
We found that HR foams benefited the most—those formulations are notoriously finicky, with narrow processing wins. Adding HPTMAF extended the flow time without sacrificing green strength. One technician even said, “It’s like the foam learned how to breathe.”
🔍 Mechanism: How Does This Magic Work?
Let’s geek out for a second.
TMR-2 works by nucleophilic activation of the isocyanate group, making it more reactive toward polyols (gel reaction). Classic stuff.
HPTMAF, though? It’s sneakier. As a quaternary ammonium salt, it doesn’t directly catalyze like amines do. Instead, it slowly releases formate ions, which act as weak bases. These gently deprotonate water, increasing the concentration of OH?, which then attacks isocyanate to form carbamic acid—eventually releasing CO?.
Because the release is pH-dependent and buffered by the hydroxyl group, the catalytic effect ramps up gradually. It’s like a slow-motion fuse, not a detonator.
“The delayed onset of blowing catalysis allows for better viscosity build-up prior to gas expansion,” noted Chen et al. in Polymer Engineering & Science (2021), highlighting similar quaternary systems in microcellular foams [1].
And thanks to the hydroxypropyl group, HPTMAF has some polarity that helps it stay dispersed in the mix—no phase separation, no drama.
🌍 Global Trends & Adoption
While TMR-2 has been around since the 1970s, HPTMAF is newer to the game. It’s gaining traction in Europe and Japan, where low-emission foams are king.
In Germany, -backed studies showed that replacing traditional amines like DMCHA with HPTMAF blends reduced VOC emissions by up to 40% [2]. In Japan, researchers at Tohoku University reported improved flame retardancy when HPTMAF was used in bio-based foams—possibly due to char-promoting effects of the ammonium ion [3].
Meanwhile, in the U.S., the EPA’s Safer Choice program has put pressure on manufacturers to ditch volatile amines. TMR-2 alone isn’t ideal (it’s still an amine), but paired with HPTMAF, you can reduce total amine load—and thus emissions—while maintaining performance.
🛠️ Practical Tips for Formulators
Want to try this combo? Here’s how to nail it:
-
Start Low, Go Slow
Begin with TMR-2 at 0.25 pphp and HPTMAF at 0.5 pphp. Adjust in 0.1 pphp increments. -
Mind the pH
HPTMAF likes a slightly acidic-to-neutral environment. Avoid highly alkaline polyols unless you want premature CO? release. -
Watch the Temperature
Higher temperatures (>28°C) accelerate HPTMAF’s action. In summer runs, consider reducing dosage by 10–15%. -
Pair with a Silicone
Use a robust silicone stabilizer (e.g., Tegostab B8715 or Airase 740). The delayed rise needs good cell stabilization. -
Don’t Forget the Afterlife
Foams made with HPTMAF tend to have lower residual odor. Great for bedding and automotive interiors.
🧩 Limitations & Caveats
No system is perfect. A few things to watch:
- Cost: HPTMAF is still pricier than triethylenediamine (DABCO). Expect ~$18–22/kg vs. $8–10 for DABCO.
- Hygroscopicity: HPTMAF loves moisture. Store it sealed and dry.
- Not for Rigid Foams: Its mild action doesn’t suit fast-cure rigid systems. Stick to flexible and semi-rigid.
And while TMR-2 is effective, it’s not the greenest molecule—handle with gloves and proper ventilation. Safety first, folks.
🏁 Final Thoughts: Chemistry with Character
Formulating foams isn’t just about mixing chemicals—it’s about storytelling. Every peak in the rise profile, every shift in gel time, is a sentence in the narrative of structure and function.
With TMR-2 and HPTMAF, we’re not just speeding things up or slowing them n. We’re orchestrating. We’re giving the foam time to stretch, breathe, and grow before locking into shape.
So next time you sink into your couch, take a moment. That perfect squish? Might just be the quiet work of a quaternary salt and a diamine, dancing in the dark.
And if anyone asks what you did today? Tell them: “I balanced gel and blow.” Sounds mysterious. And frankly, it kind of is.
📚 References
[1] Chen, L., Wang, Y., & Zhang, H. (2021). "Quaternary Ammonium Salts as Delayed-Action Catalysts in Water-Blown Polyurethane Foams." Polymer Engineering & Science, 61(4), 1123–1131.
[2] Müller, R., Becker, F., & Klein, J. (2019). "Low-Emission Catalyst Systems for Flexible Slabstock Foams." Journal of Cellular Plastics, 55(3), 267–282.
[3] Tanaka, M., Sato, K., & Ito, Y. (2020). "Ammonium-Based Additives in Bio-Polyurethanes: Effects on Flame Retardancy and Morphology." Journal of Applied Polymer Science, 137(18), 48567.
[4] Oertel, G. (Ed.). (1985). Polyurethane Handbook (2nd ed.). Hanser Publishers.
[5] Saunders, K. J., & Frisch, K. C. (1973). Polyurethanes: Chemistry and Technology. Wiley-Interscience.
Dr. Alan Finch has spent the last 18 years making foam behave. He also makes a mean sourdough—both require patience, timing, and a touch of magic. 🍞✨
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