Amino Silane Coupling Agents Compared: Monoamine, Diamine and Bis-Silane (A-1100, A-1120, A-1130, A-1170, A-2120)

Why “amino silane” is not a specification

Six grades account for almost all industrial amino silane demand, and a purchase order that says only “amino silane” or “3-aminopropylsilane” does not identify one of them. Two variables decide the product: how many amine nitrogens sit on the molecule, and whether the three hydrolysable groups are methoxy or ethoxy. Neither variable appears in the generic name. The consequences do appear – in dosage, in cure speed, in colour, in the solvent released at the oven, and in whether a plant can use the product at all.

This is a comparison of the six grades as they are actually traded, with the arithmetic that makes the choice checkable rather than intuitive. Every figure below is calculable from the molecular formula on the certificate, so a buyer can verify a quotation instead of trusting it.

The two axes that define the family

Every amino silane in commercial supply is a propyl spacer with an amine at one end and a silicon at the other. What changes is how the amine end is built and what leaving groups sit on the silicon:

Monoamine (one nitrogen): A-1100 and A-1110. The reference grades.
Diamine (two nitrogens, one primary and one secondary): A-1120, A-1130, A-2120. Roughly double the amine per unit weight.
Bis-silane (one secondary nitrogen, two silicons): A-1170. Inverts the ratio – double the silicon, half the amine.
Trifunctional vs difunctional silicon: every grade above carries three hydrolysable groups except A-2120, which carries two plus a methyl.

Those four bullets contain the entire selection problem. Everything else is arithmetic.

The six grades side by side

Property	A-1100 / KH-550	A-1110 / KH-540	A-1120 / KH-792	A-1130	A-1170	A-2120 / KH-602
CAS	919-30-2	13822-56-5	1760-24-3	5089-72-5	82985-35-1	3069-29-2
Nitrogens	1 primary	1 primary	1 primary + 1 secondary	1 primary + 1 secondary	1 secondary	1 primary + 1 secondary
Silicons	1	1	1	1	2	1
Hydrolysable groups	3 ethoxy	3 methoxy	3 methoxy	3 ethoxy	6 methoxy	2 methoxy + methyl
Molecular weight	221.37	179.29	222.36	264.44	341.55	206.36
Amine equivalent (g/mol N)	221.37	179.29	111.18	132.22	341.55	103.18
Silicon equivalent (g/mol Si)	221.37	179.29	222.36	264.44	170.78	206.36
Silicon content	12.69%	15.66%	12.63%	10.62%	8.22%	13.61%
Alcohol per kg on full hydrolysis	624 g ethanol	536 g methanol	432 g methanol	523 g ethanol	563 g methanol	311 g methanol
Density (20-25 degC)	0.945	1.016	1.020	0.965	1.048	0.970
Colour stability	Good	Good	Yellows	Yellows	Best of the family	Yellows

Amine equivalent: the most expensive mistake in the family

Two grades in that table have almost the same molecular weight and completely different amine content. A-1100 is 221.37 g/mol with one nitrogen; A-1120 is 222.36 g/mol with two. A formulator who substitutes one for the other at equal weight doubles the amine loading in the system without noticing, because nothing in the drum – not viscosity, not density, not refractive index – signals the change.

The arithmetic to apply before any trial:

If the recipe specifies	And you substitute with	The dose must change by
A-1100 (221.37 g/mol N)	A-1120 (111.18 g/mol N)	Halve the weight for the same amine
A-1120 (111.18 g/mol N)	A-1100 (221.37 g/mol N)	Double the weight for the same amine
A-1120 (222.36 g/mol Si)	A-1170 (170.78 g/mol Si)	Reduce silicon-basis dose by about 23%
A-1120 (222.36 g/mol Si)	A-2120 (206.36 g/mol Si)	Reduce by about 7% on silicon, but expect a softer interface

The symptoms of getting this wrong are consistent: a batch that cures far too fast, a clear coating that yellows, or adhesion failure at the interface rather than in the bulk. All three look like a resin problem and are usually a silane-equivalent problem.

Methoxy or ethoxy: a plant decision

The alkoxy group governs how fast the silane hydrolyses and which alcohol leaves the oven. It is the variable most often treated as a commercial detail and most often responsible for a failed qualification.

Methoxy hydrolyses faster. It reaches the condensed state at a lower temperature or in a shorter time, and per kilogram it delivers more silicon because the leaving group is lighter: A-1110 gives 5.58 mol Si per kg against 4.52 for A-1100, roughly 23% more coupling sites for the same drum weight.

The price is methanol. Every methoxy group releases one molecule of methanol when it condenses, and the numbers per kilogram of silane are large enough to be a process constraint rather than a footnote:

Grade	Alkoxy	Alcohol released per tonne	Regulatory position of the alcohol
A-1100 (919-30-2)	3 ethoxy	624 kg ethanol	Not a methanol-restricted substance
A-1130 (5089-72-5)	3 ethoxy	523 kg ethanol	Not a methanol-restricted substance
A-1110 (13822-56-5)	3 methoxy	536 kg methanol	Regulated toxicant, occupational limits apply
A-1120 (1760-24-3)	3 methoxy	432 kg methanol	Regulated toxicant, occupational limits apply
A-1170 (82985-35-1)	6 methoxy	563 kg methanol	Regulated toxicant, occupational limits apply
A-2120 (3069-29-2)	2 methoxy	311 kg methanol	Lowest methanol of the family

A tonne of A-1110 generates over half a tonne of methanol on full cure. In a plant without the ventilation and monitoring for that, the compliant route is the ethoxy grade even though it is the less efficient one per kilogram. In a plant with an oven and an exhaust designed for solvent, the methoxy grade is the better buy.

Silicon density versus amine density: the A-1170 inversion

There are two ways to put more reactive sites at an interface, and the family offers both. The standard route is to add amine – A-1120 doubled the nitrogen. A-1170 takes the opposite route: it keeps one secondary nitrogen and doubles the silicon.

Property	A-1120 (diamine)	A-1170 (bis-silane)
Silicons per molecule	1	2
Nitrogens per molecule	2	1
Amine equivalent	111.18 g/mol N	341.55 g/mol N
Silicon equivalent	222.36 g/mol Si	170.78 g/mol Si
Silicon per kilogram	4.50 mol	5.86 mol
Volatility	Higher	Lowest in the family

Read the equivalent columns together and the design intent is unambiguous: A-1120 buys amine cheaply and silicon expensively; A-1170 buys silicon cheaply and amine expensively. The secondary amine is also sterically hindered by two bulky silylpropyl arms, so it reacts with epoxy more slowly – a disadvantage on a fast line, an advantage wherever open time is the constraint – and it oxidises less readily, which is why A-1170 is the grade specified where a clear or light-coloured system must not yellow.

Its commercial specification sets purity at 95.0% rather than 98.0%, and that is not a lower grade: the manufacturing route leaves the mono-silane homologue as the principal related substance. The number worth asking for is the homologue content, not a higher headline purity, because the homologue is what shifts the silicon-to-amine ratio the grade was chosen for.

Difunctional A-2120: softer interface, more stable bond

Three hydrolysable groups form three Si-O bonds to a mineral surface; two form two. A-2120 carries two methoxy groups and a methyl, so it builds a deliberately lower crosslink density at the interface. Three consequences follow, and all three are useful:

More flexible interface – it tolerates differential thermal expansion between a mineral filler and an organic matrix without cracking, which is why it appears in sealants and elastomeric systems rather than in structural adhesives.
Better hydrolytic stability – fewer siloxane bridges means fewer bonds available to be re-hydrolysed by water over the life of the part.
Lowest methanol release of the family – 311 g per kilogram, which in a methanol-constrained plant can decide whether an amino silane is usable at all.

The cost is mechanical: where maximum bond strength and rigidity are the requirement, the trifunctional grade wins. Difunctional is a design choice, not a cheaper version of the same thing.

Where each grade actually lands

Application	Typical first choice	Reason
Glass-fibre sizing	A-1100, A-1120	Coupling into polyester, epoxy and phenolic resins; ethanol by-product in the oven
Structural and assembly adhesives	A-1120, A-1130	Maximum amine for demanding substrates; ethoxy version where methanol is restricted
Flexible and hybrid sealants	A-2120	Lower modulus interface, better movement accommodation
Colour-critical clear systems	A-1170, A-1100	Hindered secondary amine or monoamine; both resist yellowing
Fast-cure coatings and primers	A-1110	Methoxy hydrolysis at oven temperature; highest silicon per kilogram
Mineral and pigment filler treatment	A-1100, A-1110	Cost-effective coverage; methoxy where the filler is dried
Methanol-constrained plants	A-1100, A-1130	Ethanol by-product only

Process parameters that matter more than the grade

The grade can be right and the process still fail. Four parameters account for most of it:

The amine self-catalyses hydrolysis. No acetic acid addition is needed, and equally, a dilute working solution has a limited life. A 5% aqueous solution is normally consumed the same shift; left overnight it still wets out but the oligomer distribution has moved and bonding performance drops.
Dose on the filler, not on the batch. Typical treatment levels are 0.5 to 1.5% of filler weight for a trifunctional grade, and the correct number depends on the filler’s surface area. A silica at 200 m2/g needs more silane per kilogram than a coarse talc.
pH window for solution work. Amino silanes sit naturally alkaline; where an acid is added to bring a working solution to the 3.5 to 5.5 range used for other silane families, the amine is partly neutralised and the coupling behaviour changes. Decide deliberately rather than by habit.
Water in the drum is a shelf-life clock. Because hydrolysis needs no added catalyst, a drum opened warm or resealed in humid weather degrades from the headspace down. Ask for moisture on the certificate and track it batch to batch.

Buying checklist for the family

Name the CAS, not the generic name. Six products share the “amino silane” description and three pairs are routinely confused: 919-30-2 against 13822-56-5, 1760-24-3 against 5089-72-5, and 3069-29-2 against 1760-24-3.
State the basis of the dose – amine equivalent or silicon equivalent – in the purchase specification itself, so a supplier substitution cannot silently change the loading.
Require assay plus free amine value, not total nitrogen: partially hydrolysed or carbamate-contaminated material still contains nitrogen.
Require chloride, water and the alcohol content on the same certificate. Chloride is the hydrosilylation residue that attacks glass on ageing; water is the hydrolysis clock; methanol or ethanol is the process constraint.
Use density, not refractive index, to separate methoxy from ethoxy in the monoamine pair: 0.945 against 1.016 g/cm3, while the refractive indices differ by 0.0010 and are indistinguishable in practice.
Plan packaging against consumption. All six grades are hygroscopic and self-hydrolysing; a drum opened repeatedly over a year is a declining material, and nitrogen padding on the headspace is worth arranging for slow-moving lines.

What PolyBlueChem supplies

All six grades are held as clear liquids in steel drums, IBCs or ISO tanks, with per-batch COA and SDS and FOB or CIF terms quoted against destination. Because the family is defined by two variables rather than one, we quote the monoamine and diamine grades together – and the ethoxy alternate alongside the methoxy one – so a plant can qualify its compliant second source before it needs it.

Send us the resin system, the substrate and the dose basis (amine or silicon), and we will return the equivalent dose and the correct grade rather than a catalogue reference.