Polyetheramines in epoxy: why an AHEW-matched hardener swap still needs a cure trial

A plant runs its two-component epoxy floor primer on RS-D230. An end user asks for a more flexible film, so the formulator moves to the longer-chain diamine, RS-D400. Purchasing recalculates the dose from the amine hydrogen equivalent weight (AHEW) of each grade, 60 g/eq against 118 g/eq.

The first batch mixes at the correct weight ratio. It still does not match the retained panel. Gel time has moved, the film feels different, and QC cannot say whether the lot changed or the chemistry did. The arithmetic was right. The assumption that arithmetic was the whole job was wrong.

Which polyetheramines cover an epoxy hardener job, and how do the three grades differ?

Three low-molecular-weight polyetheramines are compared here. RS-D230 and RS-D400 are polyoxypropylene diamines with AHEW values of 60 g/eq and 118 g/eq. RS-T403 is a polyoxypropylene triamine with an AHEW of 81 g/eq. AHEW decides how much hardener you dose. Functionality and chain length decide the network you get.

On RFQs, RS-D230 is the grade written as polyetheramine D-230. RS-D400 is written as polyetheramine D-400. RS-T403 appears as polyetheramine T-403. The rest of this comparison uses the RS codes, which is also how they should appear on your item master.

All three share one backbone: repeating oxypropylene units ending in primary amine groups. In RS-D400 and RS-T403, the amine groups sit on secondary carbon atoms at the chain ends. That placement is why these hardeners react more slowly than unhindered aliphatic amines. RS-D230 has moderate reactivity in epoxy curing. For the wider family, including the long-chain grades outside this comparison, see the polyetheramine family overview.

The differences that matter on the floor are chain length and branching. The diamines build linear segments between epoxy groups. RS-D400, at a nominal molecular weight of 430 g/mol, puts a longer flexible polyether chain between crosslinks than RS-D230 does. RS-T403, at a nominal 440 g/mol, is close to the longer diamine in size, but each molecule is a three-armed branch point rather than a two-ended link.

– not specified; ask the desk.

Read the cured-resin properties as descriptions, not as a ranking. None of the three grades comes with a cured-film number you could compare directly. That gap is the reason a trial cannot be skipped.

AHEW sets the dose, and nothing else

The dose arithmetic is simple. Parts of hardener per hundred parts of resin equals the AHEW times one hundred, divided by the resin’s epoxide equivalent weight (EEW). For RS-D230 the numerator is 6,000 (60 × 100), and for RS-T403 it is 8,100 (81 × 100). Divide either by your resin’s EEW to get the stoichiometric dose. RS-D400 follows the same method from its 118 g/eq.

At the same resin, RS-D400 needs close to twice the weight of RS-D230. That changes the mix ratio on the pump and the cost per kilogram of mixed product. It also changes how much of the cured mass is soft polyether. A per-kilogram price comparison between the two diamines misleads until you convert it to cost per batch at the correct dose.

Put the AHEW and the resin EEW on the formulation record, side by side. Recalculate the dose whenever either input changes, including a new resin lot with a different EEW. The epoxy curing agent selection guide covers stoichiometry across hardener classes. Some formulators run deliberately off-ratio, and that choice belongs on the record too, not buried in a batch sheet.

What does functionality change that a dose calculation cannot?

Here is the position this comparison takes. A substitution between these grades at an AHEW-matched dose is a new formulation and needs a new cure trial. Stoichiometry balances amine hydrogens against epoxide groups. It says nothing about how those bonds are arranged.

A diamine links resin molecules end to end. A triamine adds a branch point at every hardener molecule. Two mixes balanced to the same stoichiometry can reach gel at different conversions and cure to different crosslink densities, and they respond differently to a cold shop floor. Pot life and gel time move with the network, in either direction depending on resin and temperature. The epoxy-amine cure speed and pot life note explains the mechanism.

The trade-off is genuine. RS-D230 brings the lowest AHEW of the three and a viscosity specified at 15 max mPa·s at 25 °C, which helps a low-viscosity mix. Its cured resin has relatively high elongation and thermal shock resistance. RS-D400 lengthens the linear segment, which is why it gives increased flexibility. RS-T403 trades linear segments for a branched network that improves flexibility and strength. No single grade gives you every property, and a blend sits between them only after it has been tested.

This position could be wrong for a mature formulation that already runs a diamine and triamine blend. Small ratio adjustments inside a window you have already mapped may not justify a full trial. Outside that window, the minimum is a gel time check at your application temperature and a hardness or flexibility check on the cured film, against a retained panel from the old formulation. Add any adhesion or chemical-resistance test your end user’s specification names.

The same logic covers a change of source. Material sold under the same generic designation from a source you have not trialled can meet every CoA line and still cure differently, because no CoA line describes the cured network. Treat a new source as a new formulation until a cure trial says otherwise.

Reading the CoA: one property, two units

Here is the detail that catches buyers who compare grades in a spreadsheet. The RS-D230 sales specification gives amine value as 454–488 mg KOH/g. RS-D400 and RS-T403 specify it in meq/g. Put those numbers in one column and the shorter diamine appears to carry far more amine than it does. Convert mg KOH/g to meq/g by dividing by the molar mass of potassium hydroxide before you compare anything, and keep the CoA figure in its own unit on the record.

The amine value also gives a lot check on AHEW, with one limit. For a diamine whose amine groups are all primary, each nitrogen carries two reactive hydrogens. AHEW in g/eq then equals 1,000 divided by twice the amine value in meq/g. Use the result only to confirm that a lot is consistent with the grade AHEW. Never use it to replace the grade value as your dose basis.

That shortcut does not transfer cleanly to RS-T403. Its sales specification sets primary amine at 90.0 min wt%, against 95.0 min wt% for both diamines. Any non-primary fraction carries fewer reactive hydrogens per nitrogen, so the simple formula overstates them. Dose RS-T403 from its 81 g/eq. If a lot’s amine value sits near either edge of 6.1–6.8 meq/g, run a gel time check on that lot before it goes to production.

The CAS number adds a second trap. RS-D230 and RS-D400 both carry CAS 9046-10-0, which EPA’s Substance Registry Services record names “Polypropylene glycol bis(aminopropyl) ether” (retrieved 2026-10-23). A purchase order or ERP item keyed only on CAS cannot tell the two apart, and a tote of the wrong diamine will pass a CAS check at the dock. Write the RS code and the grade AHEW on the purchase order and on the item master.

RS-T403 sits under its own CAS, 39423-51-3, and its EPA Substance Registry Services entry lists the substance on the TSCA Inventory (retrieved 2026-10-23). That inventory is the list EPA compiles, keeps current and publishes of each chemical substance manufactured or processed in the United States, under 15 U.S.C. 2607(b) (read 2026-10-23). The SRS record for CAS 9046-10-0 carries the same listing. Confirm inventory status for your own import filing against the record, not against a grade name.

At incoming inspection, hold each lot to the specification limits of its grade:

1. Primary amine at or above 95.0 min wt% for either diamine, or 90.0 min wt% for RS-T403.
2. Moisture at or below 0.30 max wt% for RS-D230, or 0.25 max wt% for the other two.
3. Color at or below 30 max APHA for RS-D230, or 50 max APHA for the other two, where color matters to the finished product.
4. Amine value inside the specified range, in the grade’s own unit, before any conversion.

A lot that meets all four meets the sales specification of that grade. From a source already qualified by a cure trial, that is the incoming release. It does not qualify a new source, and it does not qualify a different grade.

Where these grades run outside epoxy

The same materials appear on other lines in the same plant, which is how a grade mix-up reaches an epoxy batch. RS-D400 is also used in polyurethanes, thermoplastic polyamide adhesives and salts formed for cutting fluids. RS-T403 has an anti-sag role in polyurethanes. If your site also runs systems built on polyether and polyester polyols, the polyetheramine on that line may be the epoxy hardener grade or a different one.

Keep separate item codes for each use even when the grade is identical. A polyurethane line can then change grade without moving the epoxy hardener with it. The epoxy curing agents and hardeners guide sets these grades against the other hardener classes a coatings line may also hold.

Packaging differs by grade as well. RS-D230 comes in 195 kg drums, 950 kg or 942 kg IBC totes and ISO tanks; the other two come in 200 kg drums. A dosing station sized for totes needs a different receiving step if the grade changes. RS-D230 and RS-D400 are stored in a cool, dry place, and the moisture limit on all three grades is why that instruction belongs on the receiving checklist.

The RS-T403 product page has the full specification for the polyoxypropylene triamine.

The decision this leaves you

If the change in front of you is a new lot of a grade you have already trialled from the same source, the four CoA lines and a matching AHEW are the release. If the change is a new source or a different grade, even at a carefully recalculated dose, schedule the cure trial before the purchase order. Settle one question first: did the end user ask for a different film, or a different price? Only the first justifies changing the hardener.

Methodology: each grade value is what the technical data sheet for that RS code states, in its units, typical where marked typical; the lot CoA governs. CAS identities and inventory listings are from EPA Substance Registry Services, and the inventory definition from 15 U.S.C. 2607(b). The dose and AHEW lot-check methods are stoichiometry stated as methods; the only arithmetic on a grade value is the AHEW × 100 numerator.