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Three aminosilane designations appear repeatedly in technical documents and procurement correspondence: KH-550, A-1100, and KBM-903. They are frequently treated as three different products. They are not. This reference explains what actually differs, and where the differences matter enough to affect your formulation.
Table of contents
- What KH-550, A-1100, and KBM-903 are
- Cross-reference table
- Where the real differences lie
- Silane A-1120: the fourth name to recognise
- Practical implications for procurement
- FAQ
- Further reading
- N-(2-aminoethyl)-3-aminopropyltrimethoxysilane, CAS 11109-97-8. This is a diamine, with a primary and a secondary amine on the same molecule.
- 3-aminopropyltrimethoxysilane, CAS 1119-00-2. This is a monoamine, with one amine group only.
1. What these three names refer to
All three describe aminofunctional silanes based on the aminopropyl scaffold. The two structural families in commercial use are:
KH-550 and A-1100 both refer to the first, the diamine. KBM-903 refers to the second, the monoamine. The distinction matters because a diamine silane is considerably more reactive and gives a different film and colour behaviour.
2. Cross-reference table
| Property | KH-550 | A-1100 | KBM-903 | Silane A-1120 |
|---|---|---|---|---|
| Chemical name | N-(2-aminoethyl)-3-aminopropyltrimethoxysilane | same as KH-550 | 3-aminopropyltrimethoxysilane | 3-aminopropyltriethoxysilane |
| CAS | 11109-97-8 | 11109-97-8 | 1119-00-2 | 2555-35-5 |
| Amine type | Diamine (primary + secondary) | Diamine | Monoamine | Monoamine |
| Alkoxy group | Methoxy | Methoxy | Methoxy | Ethoxy |
| Molecular weight | 221.37 | 221.37 | 149.26 | 163.32 |
| SiO2 content (theoretical) | 20.9% | 20.9% | 22.6% | 17.3% |
| Cure acceleration in epoxy | Strong | Strong | Moderate | Mild |
| Colour effect in clear systems | Noticeable amber shift | Noticeable amber shift | Minimal | Minimal |
3. Where the real differences lie
Since KH-550 and A-1100 are the same CAS number with the same assay, the difference between them is commercial, not technical: packaging sizes, regional availability, and price. Specifying one over the other is a sourcing decision.
The technical split is between the diamines and the monoamine, and between methoxy and ethoxy hydrolysis chemistry.
The diamine advantage is faster cure acceleration. Its cost is reactivity: the second amine group promotes autocatalytic condensation, which shortens working time and can produce a gel-like precipitate if the material is stored warm or at high pH.
The monoamine is more forgiving. It hydrolyses more slowly and gives better colour stability, at the cost of less cure acceleration.
Ethoxy chemistry, as in A-1120, hydrolyses more slowly than methoxy but releases ethanol rather than methanol and does not require the same pH control. In coatings where pH adjustment is inconvenient, that is a real practical advantage.
4. Silane A-1120: the fourth name to recognise
A-1120, 3-aminopropyltriethoxysilane, CAS 2555-35-5, is the ethoxy counterpart to KBM-903. It appears frequently in European specifications. If you receive a specification written in Shin-Etsu or Evonik nomenclature, this is usually the entry you need.
5. Practical implications for procurement
Write the CAS number into the purchase specification, not the trade name. Trade names are ambiguous, and the same name can be supplied at different assay levels by different producers.
When you change suppliers, request the COA and compare SiO2 content by GC. Two batches both labelled KH-550 can differ by more than 2% in active content, and that difference is enough to move the hydrolysis window.
If you need consistent results across multiple production sites, specify the CAS number plus a minimum assay, and require a COA with each lot.
6. FAQ
Are KH-550 and A-1100 chemically identical?
Yes. Both are N-(2-aminoethyl)-3-aminopropyltrimethoxysilane, CAS 11109-97-8, with the same molecular weight. The difference is supplier and packaging.
Is KBM-903 a weaker version of KH-550?
It is a different molecule, not a weaker one. It has one amine instead of two, so it gives less cure acceleration and better colour stability. Whether that is better depends on whether you are optimising for cure speed or for optical clarity.
Why does my clear epoxy turn amber with KH-550?
The diamine can oxidise to coloured species over time, and this shows in thin transparent coatings. Switching to a monoamine such as KBM-903 or A-1120 usually resolves it. If you need the cure acceleration, keep the KH-550 at the low end of the dosage range.
Can I mix KH-550 and KBM-903?
Yes, and this is a common way to tune the balance between cure acceleration and colour. Roughly 3:1 diamine to monoamine gives most of the acceleration with less colour shift. Verify with a control sample rather than assuming linearity.
Which one should I specify for a 2K epoxy primer?
KH-550 or A-1100 if cure speed is the priority and the film is not optically critical. KBM-903 or A-1120 if the coating must stay clear or if pot life matters more than cure speed.
Does the ethoxy form need pH adjustment?
Not to the same degree. Methoxysilanes hydrolyse faster and need more careful pH control, typically 4.5 to 5.5. Ethoxysilanes are slower and more tolerant, which is why they suit continuous or high-throughput processes.
