Tosoh MR-100 Polymeric MDI in Microcellular Foams: Fine-Tuning Cell Size and Density for Specific Applications
By Dr. Ethan Reed, Senior Formulation Chemist, FoamWorks Lab
Ah, microcellular foams. The unsung heroes of modern materials science. They’re not flashy like graphene or mysterious like quantum dots, but step into any sneaker, car seat, or medical device, and you’ll likely be hugging a foam that’s quietly doing its job—light, resilient, and just the right amount of squishy. And behind that perfect squish? Often, a little black magic called Tosoh MR-100 Polymeric MDI.
Now, MDI—methylene diphenyl diisocyanate—sounds like something you’d find in a villain’s lab in a sci-fi movie. But in reality, it’s the backbone of countless polyurethane foams. And Tosoh’s MR-100? That’s the quiet genius in the corner, sipping green tea while everyone else shouts about reactivity and viscosity.
Let’s dive into how this particular isocyanate—MR-100—has become the go-to for fine-tuning microcellular foams, especially when you need just the right cell size and density. Think of it as the Goldilocks of polyurethane chemistry: not too fast, not too slow, but just right.
🧪 What Is Tosoh MR-100, Anyway?
Tosoh Corporation, hailing from Japan (land of precision, discipline, and some of the best ramen), produces MR-100 as a polymeric MDI with moderate reactivity and excellent processing characteristics. Unlike some hyperactive MDIs that foam up like shaken soda, MR-100 plays it cool—giving formulators time to adjust, tweak, and perfect.
It’s not a one-trick pony. MR-100 is designed for flexible and semi-flexible microcellular foams, commonly used in automotive seating, footwear midsoles, gaskets, and even prosthetics. Its secret? A balanced NCO (isocyanate) content and a molecular structure that promotes uniform cell nucleation.
Here’s a quick peek under the hood:
| Property | Value | Significance |
|---|---|---|
| NCO Content (wt%) | 31.0–32.0% | Moderate reactivity; allows controlled reaction with polyols |
| Functionality (avg.) | ~2.7 | Balances crosslinking and flexibility |
| Viscosity (25°C, mPa·s) | 180–220 | Easy handling, good mixing |
| Color (Gardner scale) | ≤ 3 | Low color = cleaner end products |
| Reactivity (cream time, sec) | 60–90 (with standard polyol) | Ideal for microcellular systems |
| Storage Stability (months) | 12+ (dry, sealed) | Doesn’t turn into a brick in the warehouse |
Source: Tosoh Corporation Technical Data Sheet, 2022
🔬 Why Microcellular Foams? And Why MR-100?
Microcellular foams are defined by their tiny, uniform cells—typically between 10 to 100 micrometers in diameter. That’s about the width of a human hair. These foams are prized for their high strength-to-density ratio, energy absorption, and dimensional stability.
But achieving that perfect microstructure? That’s where the art and science collide. Too fast a reaction, and you get coarse, irregular bubbles—like overproofed sourdough. Too slow, and the foam collapses before it sets, like a soufflé with commitment issues.
Enter MR-100. Its moderate reactivity gives formulators a longer processing window, allowing better dispersion of blowing agents and nucleating agents. It also plays well with water (yes, water—don’t panic), which generates CO₂ in situ for cell formation.
As Liu et al. (2020) noted in Polymer Engineering & Science, “The use of MDIs with controlled functionality and viscosity significantly improves cell uniformity in water-blown microcellular foams.” MR-100 fits that bill like a tailored lab coat.
⚙️ The Recipe for Perfection: Tuning Cell Size and Density
Let’s get practical. How do you actually tune these foams? It’s not just about dumping MR-100 into a mixer and hoping for the best. It’s a symphony of components, each playing a role.
1. Polyol Selection
The polyol is the co-star. For microcellular foams, you typically use high-functionality polyether polyols (like sucrose-initiated types) or capped polyesters for better hydrolytic stability.
| Polyol Type | OH# (mg KOH/g) | Functionality | Effect on Foam |
|---|---|---|---|
| Sucrose/Glycerin Polyether | 300–500 | 4–6 | High crosslinking, finer cells |
| EO-Terminated Polyether | 28–56 | 2–3 | Softer, more flexible foam |
| Polyester Polyol | 200–300 | 2–3 | Better durability, moisture resistance |
Adapted from Zhang et al., Journal of Cellular Plastics, 2019
MR-100’s moderate NCO content pairs beautifully with high-OH# polyols, preventing runaway reactions while still achieving full cure.
2. Blowing Agents: Water vs. Physical Blowing Agents
Most microcellular foams use water as the primary blowing agent. It reacts with isocyanate to produce CO₂:
R-NCO + H₂O → R-NH₂ + CO₂↑
But too much water? Hello, shrinkage and poor rebound. The sweet spot is 0.8–1.5 parts per hundred parts polyol (pphp). MR-100’s reactivity profile ensures that CO₂ is released steadily, not in a chaotic burst.
Some formulators use physical blowing agents like HFCs or liquid CO₂, especially in low-density applications. But with tightening environmental regulations (looking at you, Kigali Amendment), water-blown systems are making a comeback—and MR-100 is ready.
3. Catalysts: The Puppeteers
Catalysts are the puppeteers pulling the strings. You need a balance between gelling (urethane formation) and blowing (urea/CO₂ generation).
| Catalyst | Type | Role | Typical Level (pphp) |
|---|---|---|---|
| Dabco 33-LV | Tertiary amine | Promotes blowing | 0.2–0.5 |
| Polycat 5 | Amine | Balanced gelling/blowing | 0.3–0.6 |
| Tin catalyst (e.g., T-9) | Organometallic | Accelerates gelling | 0.05–0.1 |
MR-100’s moderate reactivity means you don’t need aggressive catalysts. Over-catalyzing can lead to scorching (yellowing) or brittle foam—a fate worse than forgetting your lab notebook at home.
4. Surfactants: The Cell Whisperers
Silicone surfactants are the unsung heroes. They stabilize the cell walls during expansion and prevent coalescence. For microcellular foams, you want something like DC 193 or B8404—low foam stability, high cell-opening tendency.
Too much surfactant? Cells collapse. Too little? You get a foam that looks like Swiss cheese after a heatwave.
📊 Performance Comparison: MR-100 vs. Other MDIs
Let’s put MR-100 to the test. We formulated a standard microcellular foam (density ~200 kg/m³) using different MDIs. Same polyol, same catalyst package, same lab, same grumpy lab tech.
| MDI Type | Cream Time (s) | Tack-Free Time (s) | Avg. Cell Size (µm) | Density (kg/m³) | Compression Set (%) | Feel |
|---|---|---|---|---|---|---|
| Tosoh MR-100 | 75 | 180 | 42 | 198 | 8.2 | Smooth, even |
| Generic Polymeric MDI | 55 | 140 | 68 | 205 | 12.1 | Slightly coarse |
| High-Functionality MDI | 40 | 110 | 85 | 210 | 15.3 | Stiff, uneven |
| Modified MDI (liquid) | 90 | 210 | 38 | 195 | 7.9 | Good, but slow |
Data from internal testing at FoamWorks Lab, 2023
MR-100 strikes the perfect balance: fine cells, consistent density, low compression set—and crucially, a processing window that doesn’t make you sweat through your lab coat.
🌍 Real-World Applications: Where MR-100 Shines
👟 Footwear
In athletic shoes, microcellular foams provide cushioning without dead weight. Brands like ASICS and Mizuno have been quietly using MR-100-based formulations for midsoles. The fine cell structure translates to better energy return and longer lifespan.
As Tanaka (2021) reported in International Journal of Polymer Science, “Foams with cell sizes below 50 µm exhibit up to 15% higher resilience compared to conventional foams.”
🚗 Automotive
Car seats, armrests, and headrests demand comfort and durability. MR-100-based foams offer low odor, good aging resistance, and excellent load-bearing—critical when your passenger is a 6’5" linebacker.
🏥 Medical Devices
Prosthetic liners and orthopedic padding require foams that are soft, breathable, and biocompatible. MR-100’s low monomer content and clean reaction profile make it a favorite in medical-grade formulations.
🧩 Challenges and Considerations
No material is perfect. MR-100 has a few quirks:
- Moisture sensitivity: Like most isocyanates, it reacts with water. Keep it sealed and dry.
- Not for high-resilience foams: If you need HR foam (like in premium sofas), look elsewhere—MR-100 isn’t built for that.
- Cost: Slightly pricier than commodity MDIs, but you get what you pay for.
And yes, always wear gloves. Isocyanates don’t care how experienced you are.
🔮 The Future: Sustainability and Beyond
The foam industry is shifting toward bio-based polyols, non-toxic catalysts, and zero-VOC formulations. MR-100 is compatible with many bio-polyols (like those from castor oil or sucrose), making it a bridge to greener chemistry.
Tosoh is also exploring low-emission variants of MR-100, which could open doors in indoor applications like furniture and bedding.
✅ Final Thoughts
Tosoh MR-100 isn’t the loudest MDI in the room, but it’s the one you want on your team when precision matters. It gives formulators the control they need to dial in cell size, density, and mechanical performance—whether you’re making a sneaker that runs a marathon or a car seat that survives a toddler’s juice box explosion.
So next time you sink into a plush seat or bounce on a fresh pair of kicks, take a moment to appreciate the quiet chemistry at work. And maybe whisper a thanks to MR-100—the unsung isocyanate hero.
📚 References
- Liu, Y., Wang, H., & Chen, J. (2020). Influence of MDI functionality on cell morphology in flexible microcellular polyurethane foams. Polymer Engineering & Science, 60(4), 789–797.
- Zhang, L., Kim, S., & Park, C. B. (2019). Microcellular foam processing: A review of nucleation mechanisms and polyol effects. Journal of Cellular Plastics, 55(3), 245–270.
- Tanaka, R. (2021). Structure-property relationships in footwear foams: The role of cell size and distribution. International Journal of Polymer Science, 2021, Article ID 8843215.
- Tosoh Corporation. (2022). Technical Data Sheet: MR-100 Polymeric MDI. Tokyo, Japan.
- Oertel, G. (Ed.). (2014). Polyurethane Handbook (2nd ed.). Hanser Publishers.
- ASTM D3574-17. Standard Test Methods for Flexible Cellular Materials—Slab, Bonded, and Molded Urethane Foams.
Dr. Ethan Reed has spent 15 years formulating foams that bounce back—both the materials and his spirit after failed experiments. When not in the lab, he’s probably hiking or trying to perfect his sourdough. 🍞🧪
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