Bis[3-(trimethoxysilyl)propyl]amine (CAS 82985-35-1), sold as A-1170, is the only grade in the amino silane family that puts two silicon atoms on a single secondary amine. It inverts the ratio every other amino silane is built on: instead of one coupling site per amine, it offers two. That is why it is specified where crosslink density and low volatility matter, and why it is not a general-purpose substitute for the A-1120 diamine. PolyBlueChem supplies it as a clear to yellow liquid with per-batch COA and SDS.
Specifications
| Property | Specification |
|---|---|
| CAS number | 82985-35-1 |
| Chemical name | Bis[3-(trimethoxysilyl)propyl]amine; 3-(trimethoxysilyl)-N-[3-(trimethoxysilyl)propyl]propan-1-amine |
| Trade designations | A-1170 |
| Formula / MW | C12H31NO6Si2 / 341.55 g/mol |
| Appearance | Colourless to yellow transparent liquid |
| Purity | 95.0% min |
| Density (20 degC) | 1.048 +/- 0.005 g/cm3 |
| Refractive index (n25D) | 1.4320 +/- 0.0050 |
| Silicon content | 8.22% total, but 5.86 mol Si per kilogram – the highest in the family |
| Amine equivalent | 341.55 g per mol N (one secondary nitrogen, two silicons) |
| Silicon equivalent | 170.78 g per mol Si |
| Alcohol by-product | Methanol, 563 g per kg on full hydrolysis |
| Storage | Sealed, dry, cool; nitrogen preferred – the secondary amine still takes up moisture |
The ratio is inverted – that is the whole product
The standard way to add more amino functionality is to move from a monoamine to a diamine, as in the A-1120 grade. This product takes the opposite route: it keeps one nitrogen and doubles the silicon. The two are not interchangeable, and the arithmetic makes the difference explicit.
| Property | This product (A-1170, 82985-35-1) | A-1120 grade (1760-24-3) |
|---|---|---|
| Silicons per molecule | 2 | 1 |
| Nitrogens per molecule | 1 (secondary) | 2 (one primary, one secondary) |
| Molecular weight | 341.55 | 222.36 |
| Amine equivalent | 341.55 g/mol N | 111.18 g/mol N |
| Silicon equivalent | 170.78 g/mol Si | 222.36 g/mol Si |
| Silicon per kilogram | 5.86 mol Si | 4.50 mol Si |
| Hydrolysable groups per molecule | 6 | 3 |
| Methanol released per kg | 563 g | 432 g |
| Volatility | Lowest in the family | Higher |
| Choose when | High crosslink density, low volatility, slower reaction, better colour | Maximum amine reactivity per unit weight |
Read the two equivalent columns together and the design intent is obvious: A-1120 delivers amine cheaply and silicon expensively; A-1170 delivers silicon cheaply and amine expensively. A formulator who replaces one with the other at equal weight changes the interface chemistry in both directions at once.
Three consequences of a secondary amine between two silicons
- Slower reaction, longer working life. A secondary amine is sterically hindered compared with a primary amine, and the two bulky silylpropyl arms make it more so. Reaction with epoxy is measurably slower, which is a disadvantage in a fast line and an advantage wherever open time is the constraint.
- Better colour retention. The yellowing of amino silanes comes largely from oxidation of primary amine structures. A hindered secondary amine oxidises less readily, which is why this grade is specified in clear and light-coloured systems where the A-1120 diamine would discolour. Note the appearance specification allows yellow: the product can be light yellow as supplied, and that is normal, not a deviation.
- Lowest volatility in the family. At 341.55 g/mol this is the heaviest amino silane on the shelf. In thin films, high-temperature cure or vacuum processes, the silane stays where it was applied instead of leaving in the exhaust.
Why the purity is 95% and not 98%
Buyers comparing certificates often flag the 95.0% minimum as a lower grade. It is not. A bis-silane is made by a route that leaves the mono-silane homologue – 3-aminopropyltrimethoxysilane – as the principal related substance, and the commercial specification sets the minimum where the product still delivers its designed silicon density. The number to ask for is not a higher headline purity but the content of the mono-silane related substance, because that is the species that shifts the silicon-to-amine ratio the product was chosen for. A certificate that reports only total purity tells you less than one that reports the homologue.
Applications
- High-crosslink adhesion promotion – systems where two coupling bonds per amine are wanted at the interface, such as demanding structural adhesives and composite sizings.
- Colour-critical coatings and clear systems – where a diamine would yellow but extra coupling density is still required.
- High-temperature and thin-film processes – low volatility keeps the coupling agent in the film.
- Mineral and glass filler treatment – silica, glass microspheres, alumina and silicate fillers in epoxy and polyurethane systems.
- Resin modification – introducing pendant trimethoxysilyl groups into a polymer backbone for moisture-cure or adhesion functionality.
Buying notes
- Dose by silicon equivalent, not amine equivalent. 170.78 g/mol Si here against 222.36 for the A-1120 diamine; the amine number alone will mislead.
- Ask for the mono-silane homologue content rather than arguing about the 95% headline figure.
- Ask for methanol and water. Six hydrolysable groups per molecule make this grade the most methanol-intensive in the family at 563 g per kg.
- Expect a yellow tint. Colourless to yellow is the specification; a light yellow drum is compliant.
- Confirm the grade by density and refractive index – 1.048 g/cm3 and 1.4320 n25D; there is no other amino silane with this density.
Packaging and supply
Supplied as a clear to light yellow liquid in steel drums, IBCs or ISO tanks, with nitrogen padding recommended for long sea freight. Every lot ships with a COA and SDS, and FOB or CIF terms are quoted against destination. Because this grade is usually qualified against a diamine, we will quote both and send the silicon and amine equivalents in writing so the substitution can be calculated rather than guessed.
PolyBlueChem supplies bis[3-(trimethoxysilyl)propyl]amine (CAS 82985-35-1, A-1170 class) as a clear to light yellow liquid with per-batch COA and SDS and FOB/CIF delivery. If you are replacing a diamine with this grade, tell us the current dose – we will return the equivalent dose on a silicon basis so the trial starts in the right place.
