Polyetheramines on a COA: a lot outside its amine value is a rejection, not a dose change

A drum lot of RS-D230, a polyetheramine diamine, arrives with its certificate of analysis (COA). The amine value on it sits just below 454 mg KOH/g, the floor of the grade’s 454 to 488 mg KOH/g range. The QC manager wants the lot sent back. The formulator would rather keep it and raise the curing-agent charge to make up the missing amine. A week later, a lot of a different grade arrives with its amine value printed in meq/g, and nobody on the line can say at a glance whether it passed.

Both cases end the same way. A lot gets released against a number the plant has not read correctly.

Which lines on a COA for polyetheramines decide whether a lot is accepted?

A polyetheramine lot is released against every line of its sales specification: amine value, moisture, color, appearance and, where the grade specifies them, primary amine, viscosity or acetylatables. RS-D230 (polyetheramine D-230) specifies amine value at 454 to 488 mg KOH/g, moisture at 0.30 max wt% and color at 30 max APHA. Specific gravity and AHEW are typical values and do not release a lot.

Each grade keeps two kinds of numbers apart, and the COA inherits that split. RS-D230’s sales specification also sets viscosity at 15 max mPa·s at 25 °C and requires a colorless to light yellow liquid. Its specific gravity of 0.95 g/cm³ at 25 °C and its AHEW of 60 g/eq are typical values. The polyetheramine D-230 grade page shows the same split.

Accept or reject on the specification lines only. When a typical value moves between lots, read the specification lines on that lot more closely before you sign off on it.

The polyetheramine grade overview sets the grades side by side. The table below pulls out the release lines that a COA will report against.

– not specified; ask the desk.

Three units for one titration

Amine value counts the basic nitrogen in a gram of sample by titration with acid. The grades specify that one measurement on three scales. RS-D230 uses mg KOH/g. RS-D400, RS-D2000, RS-T403 and RS-T5000 use meq/g. RS-D4000, RS-ED900, RS-SD2001 and the two monoamines use mmol/g.

The conversion is a single factor. Potassium hydroxide supplies 56.1 mg KOH per meq, according to the PubChem compound record for potassium hydroxide, so a value in mg KOH/g equals the meq/g value multiplied by 56.1. For an amine titration, one millimole of basic nitrogen is one milliequivalent, so meq/g and mmol/g are the same number.

Before you compare a COA reading with any range, put the reading on the grade’s own unit. A mg KOH/g result checked against a meq/g range will fail or pass for the wrong reason.

The CAS line on the COA cannot do the grade identification for you. RS-D230, RS-D400, RS-D2000 and RS-D4000 all carry CAS 9046-10-0, which the EPA Substance Registry Services record names “Polypropylene glycol bis(aminopropyl) ether”. SRS lists that substance on the TSCA Inventory (EPA Substance Registry Services, retrieved October 2026), the list EPA compiles and keeps current under TSCA section 8(b), 15 U.S.C. 2607(b). That listing settles an inventory question. It says nothing about which chain length is in the drum.

The monoamines show how far this goes. RS-M2005 and RS-M2070 share CAS 83713-01-3. Their amine value ranges, 0.44 to 0.52 mmol/g and 0.45 to 0.51 mmol/g, overlap almost completely. A lot of either grade can pass the other grade’s amine value line. On the COA, only the grade code tells them apart. The difference is in the backbone: RS-M2005 has a PO/EO mol ratio of 29/6, and the polyether chain of RS-M2070 gives it water solubility. No release line measures either property. Refuse a COA that identifies the material by CAS alone.

What does the primary amine line tell you that amine value cannot?

Amine value counts every basic nitrogen. The primary amine line reports how much of that nitrogen sits as primary amine. The distinction matters for stoichiometry, because a primary nitrogen carries two reactive hydrogens and a secondary nitrogen carries one. RS-D230 and RS-D400 specify 95.0 min wt%, RS-D2000 specifies 97 min wt%, and the triamine RS-T403 specifies 90.0 min wt%.

The same stoichiometry turns this into a lot check. For a diamine whose amine groups are all primary, AHEW in g/eq is 1,000 divided by twice the amine value in meq/g. For an all-secondary diamine, it is 1,000 divided by the amine value. Because primary amine is specified as a minimum below 100%, the arithmetic is approximate and should only cross-check the grade AHEW. Run it on every lot, and set the tolerance band your inspection plan will accept before the first COA arrives.

On RS-SD2001, the line reverses. This grade is a difunctional secondary amine, and its specification caps primary amine at 5 max %. Its lower reactivity suits work that needs a slower cure, with longer working time and a lower reaction exotherm. Residual primary amine works against that purpose: a lot over the cap is the one most likely to gel early. Read that line before the amine value.

RS-T5000 adds a second titration. It specifies acetylatables at 0.58 to 0.63 meq/g alongside an amine value of 0.50 to 0.57 meq/g. Acetylation counts hydroxyl and amine ends together, so the gap between the two lines reflects chain ends that were never converted to amine. Both lines are release lines. Check them as a pair.

Water and color: small numbers that still reject a lot

Moisture limits sit in a narrow band across the family, from 0.20 max % on RS-SD2001 to 0.35 max % on RS-ED900. In epoxy cure, water does not enter the amine-hydrogen count. In polyurea and polyurethane work, it does: water competes with the amine for isocyanate and releases carbon dioxide into the part. The same discipline applies on the other side of the reaction, which is why polyurethane polyol systems carry their own water limits.

RS-D2000, RS-D4000 and RS-SD2001 are packed in nitrogen-blanketed drums. If you take one of those grades into isocyanate work, a drum that arrives without its blanket intact needs a water test before use, whatever the COA says.

Color is the release line where a genuine trade-off exists. APHA and Pt-Co are the same platinum-cobalt scale under two names, so a 25 max Pt-Co line on RS-T5000 and a 25 max APHA line on RS-D2000 set the same ceiling.

In a clear coat or a clear cast part, color carries straight through into the finished resin. In a pigmented primer, a lot slightly over its color maximum may cure the same as a compliant lot. Accepting that lot under a written deviation is a reasonable commercial call. The amine value line never offers that kind of choice, and the next section explains why.

Why an off-spec amine value is a rejection, not a dose change

Every epoxy charge built on these grades runs through the grade AHEW. For RS-D230 at 60 g/eq, the dose numerator is 6,000, so parts per hundred resin equals 6,000 divided by the resin’s epoxy equivalent weight. For RS-T403 at 81 g/eq, the numerator is 8,100. The charge weight follows the AHEW directly. Against the same resin, RS-D4000 at 1000 g/eq takes 16.7 times the weight of RS-D230 at 60 g/eq. Any error in the basis passes straight into the charge.

That 60 g/eq is a typical value. It holds because amine value and primary amine sit inside their ranges. A lot below the amine value floor has lost amine for a reason the COA does not state. Possible causes include unconverted hydroxyl ends, extra water or a shifted chain-length distribution. Each cause changes the cure in a different way. Re-dosing from one titration assumes you know which cause applies.

The epoxy curing agent selection guide covers how far a cured network tolerates an off-ratio charge. Unless your own cure trials have mapped dose against amine value, re-dosing a lot is not a calibrated step.

Blends make the arithmetic less forgiving. The AHEW of a blend of polyetheramine diamines is a harmonic mean. Divide each component’s mass fraction by its AHEW, add those terms, and take the reciprocal. A linear weight-average overstates the blend AHEW, so dosing on it over-charges amine hydrogens. An off-spec component lot carries its error into a calculation that is already easy to get wrong.

This position could be wrong for one kind of plant. A site that runs its own validated amine value and primary amine methods, and whose change control allows a documented re-dose, may rescue an off-spec ISO tank at a lower cost than returning it. That plant has replaced the grade specification with its own measurement. If your plant has not done that work, the COA is the only evidence you hold.

What to write into your incoming inspection plan

The inspection plan should treat the COA as a contract document. The guide to reading a chemical technical data sheet covers where these specification values come from. The supplier audit checklist covers how to verify that a COA reports the lot it claims to report.

1. Require the RS grade code and lot number on every COA, and reject a COA that identifies the material by CAS alone.
2. Put the amine value reading on the grade’s unit (divide mg KOH/g by 56.1 to reach meq/g), and accept the lot only inside the specified range.
3. Run the AHEW cross-check on each lot against the grade AHEW, for example 60 g/eq on RS-D230, and hold any lot outside the tolerance band you set.
4. Reject a lot whose primary amine falls below its minimum. On RS-SD2001, reject a result above 5 max %.
5. Reject a lot over its moisture limit, for example 0.30 max wt% on RS-D230, and retest opened drums before isocyanate work.
6. Reject a lot over its color maximum unless the end use is pigmented and a written deviation is on file.

Whether an off-spec drum goes back comes down to one question. Can your plant show, by titration and primary amine testing on that lot, which cause moved the amine value? If it cannot, the grade AHEW no longer describes the material in the drum.

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. The 56.1 factor is from the PubChem compound record for potassium hydroxide; CAS identity and TSCA Inventory status are from EPA Substance Registry Services (retrieved October 2026) and TSCA section 8(b), 15 U.S.C. 2607(b).