PACM epoxy curing agent is a colourless alicyclic diamine, 4,4'-diaminodicyclohexyl methane (CAS 1761-71-3), sold at 50-80 mPa·s and APHA 30 or below. Four amine hydrogens on a 210.36 g/mol molecule give a calculated AHEW of 52.6 g/eq, which puts YLE-128 at 28.1 phr. Specification and dosage follow. Figure 1. Calculated demand for PACM (52.6 g/eq), MACM (60 g/eq) and DACH (28.5 g/eq) across 120-220 g/eq; marked points are the grades in Table 4. 1. Introduction: Why the Unsubstituted Ring Matters Alicyclic diamine hardeners suit coatings that must stay hard and stay light in colour but cannot take the short pot life of diethylenetriamine. PACM is the unsubstituted member of that family: two cyclohexane rings joined by a methylene bridge, each carrying one primary amine. Its published specification is five lines and one CAS number, with viscosity at 50-80 mPa·s at 25 °C. Melting point, flash point and density are not on the page, so they are left out here rather than filled from memory. Three sources feed the numbers: the PACM product page, three comparable alicyclic diamines from the same catalogue, and stoichiometry. 2. Materials and Methods: PACM Epoxy Curing Agent Specification One CAS number and four lines pin the identity down. 2.1 Product Identification and Published Limits Table 1 lists the identifiers that belong on a purchase order and on the COA review sheet. Table 1. Product identification of PACM; values marked calculated come from molecular structure, not from the product page. Item Information Trade designation PACM Chemical name 4,4'-Diaminodicyclohexyl methane CAS No. 1761-71-3 Molecular formula (calculated) C13H26N2 Molecular weight (calculated) 210.36 g/mol Amine hydrogen equivalent weight (calculated) 52.6 g/eq from four active hydrogens Appearance Colourless or slightly yellow transparent liquid, packed in drums Table 2 repeats the five published limits beside the test basis a laboratory would normally apply to each. Table 2. Published specification of PACM with the corresponding test method. Item Published limit Test basis Appearance Colourless liquid, no suspended matter visual, per current TDS Colour APHA 30 maximum ASTM D1544 Viscosity at 25 °C 50-80 mPa·s ASTM D445 Purity 99.0% minimum supplier method Water 0.20% maximum ASTM E203 2.2 Test Methods and Data Sources Resin epoxy equivalent weight is determined by titration according to ASTM D1652, with ISO 3001 as the alternative route. Colour is read according to ASTM D1544 against the Gardner scale, viscosity according to ASTM D445 at 25 °C. Water moves first after a drum is opened, so it is measured by Karl Fischer titration according to ASTM E203 on duplicate portions, reported as the mean of n = 3. Amine hydrogen equivalent weight is not printed on the product page. It follows from molecular weight divided by active hydrogens: 210.36 ÷ 4 = 52.59 g/eq. That arithmetic reproduces two published values on the same catalogue, 60 g/eq for MACM and 28.5 g/eq for DACH, to within 1%, which is why 52.6 g/eq is used in every dosage table here. 3. Results and Discussion: Ring Geometry and Cure Response Ring geometry, not molecular weight, separates PACM from the linear aliphatic amines. 3.1 Why the Cyclohexane Ring Changes Hardness and Colour Both amines sit on a cyclohexane ring, making them primary amines on secondary carbons. Steric hindrance there slows the addition to an epoxide, so a PACM mix stays workable longer than a DETA mix of the same equivalent weight. Crosslink density moves the other way. At 52.6 g/eq with four hydrogens, PACM creates more network junctions per 100 g of resin than a 60 g/eq hardener, and the rigid ring lifts hardness and heat deflection without aromatic structure. Colour holds because no aromatic chromophore is present to yellow under UV, although the surface stays a primary amine that reacts with carbon dioxide. 3.2 Comparison with Alternative Diamine Hardeners Table 3 sets the PACM epoxy curing agent beside three alicyclic diamines from the same catalogue, on the lines that decide a formulation. Table 3. Published properties of four alicyclic diamine hardeners; calculated AHEW values follow the method in section 2.2. Property PACM MACM DACH 1,3-BAC CAS No. 1761-71-3 6864-37-5 694-83-7 2579-20-6 Ring substitution none two methyl none aminomethyl arms Colour, APHA 30 max 30 max 30 max not published Viscosity, 25 °C 50-80 mPa·s 80-120 mPa·s not published not published Water 0.20% max not published 0.3% max 0.3% max AHEW 52.6 g/eq 60 g/eq 28.5 g/eq 35.6 g/eq Dosage tracks the equivalent weight almost linearly. On a 187 g/eq bisphenol A resin, DACH needs 15.2 phr, 1,3-BAC 19.0 phr, PACM 28.1 phr and MACM 32.1 phr at the same stoichiometry. Viscosity is where the grade earns its place: 50-80 mPa·s carries more filler and less solvent than MACM at 80-120 mPa·s, which decides whether a high-solids primer stays under a VOC ceiling. Speed is the trade-off: DACH reacts fast at 28.5 g/eq and suits thin films in a cold shop, but rules itself out of a 3 mm casting. 4. Formulation and Dosage Calculation Dosage comes from one equation: phr = 100 × AHEW ÷ EEW, with 52.6 g/eq for PACM and the EEW of the resin actually in the pot. Table 4 applies it to four resins at full and 0.90 stoichiometry. Table 4. Calculated PACM demand in phr for four Yolatech resins, at 1.00 and 0.90 stoichiometric index. Resin EEW, g/eq Dosage at 1.00 index, phr Dosage at 0.90 index, phr YLCE-2021 125-135 39.0-42.1 35.1-37.9 YLE-170 160-180 29.2-32.9 26.3-29.6 YLE-127 176-184 28.6-29.9 25.7-26.9 YLE-128 184-190 27.7-28.6 24.9-25.7 A 0.90 index leaves about a tenth of the epoxide unreacted. In practice most ambient-cure coatings run there, because a slight amine excess tolerates surface moisture and carbon dioxide better than an exact ratio. Below 0.85 the film stays soft and chemical resistance drops; above 1.05 the surplus amine plasticises the network and pushes colour up. Neither end recovers with longer curing, so verify the index before scaling up. The same equivalent weight serves polyurethane work: against an isocyanate equivalent of 42.02 g/eq, 100 g of NCO groups consume 125.2 g of PACM. 5. Processing Notes and Operating Window Four settings decide whether a PACM system behaves in the plant the way it did in the laboratory. Mix by weight, never by volume. Density differences between a filled resin and an amine shift volume ratios by several percent. Keep the shop between 18 and 30 °C. Below 10 °C the addition reaction slows sharply and a 24-hour cure stretches to three days; if the plant runs colder, extend induction and accept overnight tack. Hold relative humidity under 70%. Beyond that, carbamate forms faster than the film cures and the haze is permanent. Post-cure at 80 °C for 2 hours where heat deflection matters; no Tg is published, so confirm on your own laminate. Figure 2. Temperature bands for a PACM-cured ambient system; the 18-30 °C band holds both the published viscosity and a 24-hour cure. Batch size is the practical control on exotherm. Five kilograms in a thin tray is safe at 25 °C; the same five kilograms in a 20 cm drum will gel in the pot. 6. Applications Five roles appear on the product page. Typically coatings is trialled first. Table 5. Application roles of PACM and the property that carries each one. Segment Function of PACM Typical level What decides success Protective coatings curing agent 27-29 phr blush resistance, hardness Adhesives curing agent 28-31 phr colour, bond-line rigidity Composites curing agent 28-41 phr wet-out viscosity, pot life Saturated polyurethane chain extender 125 g per 100 g NCO urea segment regularity Polyamide hardeners amine intermediate set by the adduct amine value of the adduct Figure 3. The five roles listed on the product page, with the property that governs each. Filament winding is the composite case worth checking first, because 50-80 mPa·s wets out roving without solvent yet stays in the bath. For polyamide intermediates the grade is a building block, not a hardener, so the amine value of the finished adduct sets the dosage. 7. Limitations and Material Verification Three limits appear in the first month of use, and none is solved by adding more hardener. 7.1 Known Limitations and Unsuitable Cases No ring methyl groups means the unmethylated alicyclic diamines are the ones that thicken or crystallise in an unheated store. The page publishes no melting point, so the pour point has to come from the COA of the lot before a winter shipment. Cold curing is not its strength. At 10 °C a film still cures, but the surface stays tacky far longer than a DACH or DETA film, and dust becomes the limiting factor. Sections above roughly 50 mm need a slower hardener or a staged ramp; this one alone will crack from exotherm. Food contact, potable water and medical use fall outside the published data, with no migration testing listed. 7.2 Incoming Inspection, Packaging, Storage and Safety A receiving check needs four numbers: APHA colour, viscosity at 25 °C, water by Karl Fischer and purity by the supplier method. Anything outside Table 2 goes back before the drum reaches production. Purity at 99.0% leaves up to 1% of other amines and water, enough to shift colour and pot life between lots. Material ships in drums and keeps at least 12 months from manufacture in the original packing at ambient. Keep the cap closed, away from flame and sunlight, and blanket part-used drums with dry nitrogen. Check with the supplier before blending lots of different dates. The liquid is alkaline and attacks copper alloys, so gloves, goggles and local exhaust are the minimum; the MSDS governs. RoHS and REACH declarations are issued per shipment on request, and nothing here certifies the grade. 8. Frequently Asked Questions What is the amine hydrogen equivalent weight of PACM? It is 52.6 g/eq: 210.36 g/mol divided by four active hydrogens. The page does not print it; the result matches the published 60 g/eq of MACM and 28.5 g/eq of DACH. How much PACM does YLE-128 resin need? YLE-128 at 184-190 g/eq takes 27.7-28.6 phr at full stoichiometry, or 24.9-25.7 phr at a 0.90 index. The exact figure depends on the lot EEW, so the COA value belongs in the formula. Is PACM the same as MACM? No. PACM is unsubstituted at CAS 1761-71-3, AHEW 52.6 g/eq and 50-80 mPa·s; MACM carries two ring methyl groups at CAS 6864-37-5, AHEW 60 g/eq and 80-120 mPa·s. They are not interchangeable by weight. Why does a PACM film blush in humid weather? Primary amines react with carbon dioxide and water to form carbamates at the surface. The reaction runs fastest below 15 °C and above 70% relative humidity, and the haze cannot be washed off with solvent. Can PACM serve as a polyurethane chain extender? Yes. It reacts with isocyanate to build a urea segment, and 100 g of NCO groups take 125.2 g of PACM. Reactivity is high, so prepolymer processes suit it better than one-shot systems. What pot life should be expected at 25 °C? No gel time is published, and none can be calculated from AHEW. Run a 100 g cup test at shop temperature; treat any quoted figure, ours included, as a starting point. 9. Conclusions Light colour, 50-80 mPa·s and a calculated AHEW of 52.6 g/eq put dosage at 27.7-28.6 phr on YLE-128. The value sits in hardness and colour retention at high solids, not cure speed, so DACH stays faster and MACM more storage-tolerant. Two numbers decide most formulations: resin EEW and the index between 0.90 and 1.00. Both can be measured before the drum is opened. 10. References 1. Yolatech product page, PACM (CAS 1761-71-3), https://www.yolatech.com/44-diaminodicyclohexyl-methane-pacm-cas-1761-71-3 (accessed 2026-10-23). 2. Yolatech technical data sheet for PACM, specification and pack size (available on request). 3. Yolatech material safety data sheet for PACM, CAS 1761-71-3 (available on request). 4. ASTM D1652, epoxy content of epoxy resins (EEW). 5. ISO 3001, determination of epoxy equivalent. 6. ISO 9702, amine group nitrogen content of amine epoxide hardeners. 7. ASTM D445, kinematic viscosity. 8. ASTM D1544, Gardner color of transparent liquids. 9. ASTM E203, water content by Karl Fischer titration.

HMDA epoxy curing agent 1,6-hexanediamine (CAS 124-09-4) is an aliphatic diamine hardener sold at 99.90% minimum purity with water below 0.05%. Its calculated amine hydrogen equivalent weight is 29.1 g/eq, and so the stoichiometric demand lands at 15.5 phr in a bisphenol A epoxy resin of 187.0 g/eq. Figure 1. Calculated stoichiometric demand against resin epoxy equivalent weight for HMDA (29.1 g/eq), MXDA (34.0 g/eq) and DETA (20.6 g/eq); curves follow phr = 100 x AHEW / EEW as derived in section 4. 1. Introduction: Where a Short-Chain Diamine Fits Straight-chain aliphatic diamines sit at the fast, high-crosslink-density end of the amine hardener range. 1,6-Hexanediamine is the shortest member that still keeps a flexible C6 spacer between its two primary amine groups, and four active hydrogens per molecule build a tight network at low loading, which is what high-solids coatings and rigid adhesive formulations ask for. The same shortness creates the two practical problems quantified below. A literature melting point of about 41-42 °C, absent from the product page, means drums can wax in a cool warehouse. The strong ammonia odour, stated openly on the product page, rules out indoor work without forced ventilation. Selection depends on whether the formulation accepts those constraints in exchange for reactivity. 2. Materials and Methods: Published Specification of 1,6-Hexanediamine 2.1 Product Identification and Published Specification The grade is sold under the trade name HMDA, chemical name 1,6-hexanediamine, CAS 124-09-4. Four specification items are published on the product page: appearance, purity, water content and the PRI value. Everything else in this report is calculated from structure or marked as literature data, never presented as a published figure. Table 1. Product identification of HMDA, with calculated and literature descriptors marked as such. Item Information Trade name HMDA Chemical name 1,6-Hexanediamine (hexamethylenediamine) CAS No. 124-09-4 Molecular formula C6H16N2 (literature) Active hydrogens per molecule 4, from two primary amine groups (calculated) Amine hydrogen equivalent weight 29.1 g/eq (calculated, 116.2 / 4) Product page yolatech.com/16-hexanediamine-hmda-cas-124-09-4 Table 2. Published specification items on the product page. Property Published value Appearance Colorless to pale yellow liquid Purity, % Min. 99.90 Water, % Max. 0.05 PRI value, mmol/t Max. 100 The liquid appearance on the specification sheet deserves one comment. A diamine that solidifies at about 41-42 °C stays liquid only in warm storage, so check the drum temperature before assuming the contents are pourable. 2.2 Test Methods and Data Sources Three data classes are kept apart. Published values come from the product page and its certificate documents. Calculated values, such as the 29.1 g/eq equivalent weight, follow from the molecular weight of 116.2 g/mol and four active hydrogens, and any reader can recompute them. Literature values, such as the melting point, are labelled as such and should be confirmed against the TDS and MSDS supplied with each lot. Where a formulation example is needed, the resin baseline is the bisphenol A liquid grade YLE-128 with an epoxy equivalent weight of 184-190 g/eq; all arithmetic is performed at the mid-point of 187 g/eq, and every demand figure in section 4 follows the same division. Purity enters as shipped, since the 99.90% floor leaves at most 0.1% for correction, less than normal plant weighing error. 3. Results and Discussion: HMDA Epoxy Curing Agent Against Alternative Polyamines 3.1 Structure-Reactivity Behaviour Two primary amines on a straight C6 chain give four hydrogens of nearly equal reactivity, so gelation arrives early and the exotherm is front-loaded. No steric shielding and no ether oxygen slow the addition, so this diamine reaches handle strength faster than ether-extended adducts at equal loading. The C6 spacer moderates the brittleness short diamines usually cause. Six carbons between the nitrogen nodes let the network deform before it cracks, a small but real gain over ethylene diamine type structures. The gain is relative: against polyetheramines or adducts the film stays harder and less forgiving. Humidity sensitivity is the weak point. The product page states that the material absorbs water and carbon dioxide from air. Carbamate on exposed amine surfaces shows up as blushing and poor intercoat adhesion, so open time in the mixer matters. 3.2 Selection Comparison Table 3 compares the diamine with the polyamine alternatives stocked on the same site, all AHEW values determined by the same molecular-weight division for a fair basis. The choice depends on which constraint binds first: loading accuracy, odour, blush, or flexibility. Table 3. Selection comparison of HMDA with alternative amine hardeners; equivalent weights and phr values are calculated against YLE-128 at 187 g/eq. Attribute HMDA (this grade) Alternative polyamines AHEW, g/eq (calculated) 29.1 DETA 20.6; MXDA 34.0; DMAPA 44.1; MACM 52.6 Stoichiometric phr in YLE-128 15.5 DETA 11.0; MXDA 18.2; DMAPA 23.6; MACM 28.1 Purity floor, % 99.90 (published) DETA high-purity grade; others per their pages Form at 25 °C Solid below about 41-42 °C (literature); liquid when warm MXDA liquid; MACM low-melt solid Odour Very strong ammonia odour (published) Lower for MACM; MXDA sharper but less volatile Blush tendency High in humid air; absorbs CO2 and water (published) MACM lower; DETA also blush-prone Network character Dense and rigid, C6 spacer adds slight flex MXDA aromatic ring raises Tg; DMAPA tertiary N slows cure Read the table by constraint, not by column. If loading accuracy at high purity binds, the 99.90% floor and the 15.5 phr figure make the diamine easy to dose and audit. If blushing or odour binds, pick a cycloaliphatic hardener and accept the higher phr. 4. Formulation and Dosage Calculation The stoichiometric rule is one line: phr = 100 x AHEW / EEW. With AHEW at 29.1 g/eq and the YLE-128 mid-point of 187 g/eq, demand is 100 x 29.1 / 187 = 15.5 phr. Every figure below follows from that division, with no hidden constant. Table 4. Calculated stoichiometric demand of HMDA across three resin grades, with DETA shown for cross-checking. Resin grade EEW, g/eq HMDA phr (calculated) HMDA kg per 100 kg resin DETA phr (calculated) YLE-127 180 16.1 16.1 11.4 YLE-128 187 15.5 15.5 11.0 YLE-170 (BPF) 170 17.1 17.1 12.1 Two corrections sit on top. First, if the lot certificate reports an EEW of 191 g/eq, demand drops to 15.2 phr, so dose from the certificate rather than the datasheet mid-point. Second, under-dosing shows as a tacky surface at room temperature; half a phr of deviation is already visible, which makes this hardener less tolerant of sloppy weighing than higher-AHEW alternatives. 5. Processing Notes and Operating Window Mixing behaviour is unforgiving but predictable. The material wets epoxy resin quickly, the exotherm peaks early in a mass batch, and pot life at bench scale is short once the amine is in. Plan the pour before mixing, not after. Workable practice, distilled from the published properties and the literature melting point: - Warm waxed or solidified drums to 45-50 °C until fully liquid, then homogenise before weighing; unmelted lumps dose badly. - Weigh the amine into the resin within minutes of opening the container. Air exposure builds carbamate skin that later reads as fish eyes in the film. - Keep mixed mass thin during induction when the batch exceeds a few litres; the four-hydrogen structure releases heat fast and a thick pile can discolour. - Ventilate the metering area. The published odour description is not a formality; operators judge leaks by smell long before instruments do. - If a batch must wait, seal the part container with a nitrogen blanket or desiccant, because the water ceiling of 0.05% is easy to exceed through uptake from humid air. Figure 2. Storage temperature scenarios against the literature melting point of about 41-42 °C; bars below the green line mark conditions where drum contents wax or solidify. 6. Applications Fit is best where reactivity and network density pay for themselves and appearance demands are modest. The four segments below all appear as application pages on this site; the table records why the diamine fits or does not. Table 5. Application fit of HMDA by segment. Segment Fit Reasoning Heavy-duty coatings Good with management Dense network resists chemicals; blush control needed in humid shops Structural adhesives Good Fast strength build at 15.5 phr in YLE-128; C6 spacer keeps some flex Composites Conditional Short pot life suits casting and lamination, not long layup schedules Clear decorative coats Poor Odour and carbamate blushing disqualify it where appearance leads Figure 3. Calculated stoichiometric demand of HMDA versus DETA across the three standard resin grades, at the mid-point EEW of each published range. 7. Limitations and Material Verification 7.1 Known Limitations and Unsuitable Uses Say it plainly: this hardener is the wrong choice for water-clear, low-blush finishes, for unventilated indoor work, and for formulations that must sit in an open container for hours. Odour and carbon dioxide uptake rule those uses out regardless of price. Viscosity, epoxy equivalent weight of the amine adduct, and cure kinetics are not published on the product page, so any pot-life or film-property claim beyond the stoichiometry above would be speculation. When those properties matter to a design, request the current TDS and confirm by trial batch; the calculation method in section 4 transfers, but the measured numbers must come from the lot. 7.2 Incoming Inspection, Packaging and Storage A duplicate titration on arrival is cheap insurance. Check purity and water against the certificate; the PRI ceiling of 100 mmol/t flags oxidised amine and is worth a spot check on every new lot. Store drums sealed, off cold floors, above the waxing window in Figure 2. If a drum has solidified, melt once at 45-50 °C and use it soon; repeated melt-solidify cycles waste colour stability and can raise the PRI reading. Packaging and shelf life follow the product page documents. 8. Frequently Asked Questions How much HMDA is needed per 100 parts of bisphenol A epoxy resin? 15.5 phr at a resin EEW of 187 g/eq, calculated as 100 x 29.1 / 187. Dose from the lot certificate EEW when one exists, because a 191 g/eq lot needs 15.2 phr instead. Why has my drum of 1,6-hexanediamine turned solid? The literature melting point is about 41-42 °C, so any storage below that lets the contents crystallise. Warm the sealed drum to 45-50 °C, homogenise, and weigh soon after. Does HMDA cure epoxy faster than DETA? Not faster per equivalent; DETA has the lower AHEW of 20.6 g/eq and gels quickly too. The difference is network density and loading, with HMDA at 15.5 phr against 11.0 phr in the same resin. Can 1,6-hexanediamine be used for clear coatings? Rarely a good idea. Carbon dioxide uptake blushes the film and the ammonia odour needs extraction. Cycloaliphatic hardeners such as MACM serve clear work better. What does the PRI value of 100 mmol/t mean? It is the published ceiling for an oxidation-related index on the specification sheet. A rising PRI reading across lots signals amine oxidation, so track it during incoming inspection. Is the 29.1 g/eq equivalent weight measured or calculated? Calculated, from the molecular weight of 116.2 g/mol and four active hydrogens. It is not a published specification item, and any measured amine value from the certificate takes precedence for dosing. 9. Conclusions As an HMDA epoxy curing agent, 1,6-hexanediamine earns its place where a dense, fast-building network at a modest 15.5 phr matters more than cosmetics. The 99.90% purity floor and 0.05% water ceiling make dosing auditable, and the arithmetic behind every figure in this report is one division a formulator can repeat. Melting behaviour and odour are the two constraints; both are manageable with warmed drums and ventilation, and both argue for cycloaliphatic or adduct hardeners when appearance leads the specification. 10. References 1. Yolatech product page: HMDA, 1,6-Hexanediamine, CAS 124-09-4, https://www.yolatech.com/16-hexanediamine-hmda-cas-124-09-4 2. HMDA technical data sheet, material safety data sheet and certificate of analysis, supplied with each commercial lot. 3. ASTM D1652, standard test practice for epoxy content of epoxy resins, used as the reference basis for resin EEW values. 4. ISO 3001, plastics, epoxy compounds, determination of epoxy equivalent weight. 5. ASTM E203, standard test method for water using volumetric Karl Fischer titration, referenced for the water ceiling.