Eleven epoxides in this group answer to the same question – which oxirane do I put in the formulation? – and the answer is decided by four properties that move in opposite directions: volatility, epoxide density, hydrophobicity and whether the molecule can crosslink at all. This guide puts the whole set on one page so that the choice can be made by number rather than by habit.
The Two Numbers That Define Any Epoxide
Every epoxide is described by the same pair of calculated values:
Epoxy equivalent weight (EEW) = molecular weight / number of epoxide groups
Epoxy value (eq/100 g) = 100 / EEW
EEW tells you how many grams carry one equivalent of epoxide – it is the number that drives cure stoichiometry. Epoxy value tells you how much reactivity a kilogram contains – it is the number that drives how fast and how densely a system cures. They are reciprocals of each other, so a low EEW always means a high epoxy value, and a low EEW means more hardener per 100 g of resin.
The Full Set, Side by Side
| Product | CAS | Formula / MW | Epoxide groups | EEW (calc.) | Epoxy value (calc.) | Grade |
|---|---|---|---|---|---|---|
| 1,2-Epoxyhexane (C6) | 1436-34-6 | C6H12O / 100.16 | 1 | 100.2 | 1.00 | 99.0% |
| 1,2-Epoxyoctane (C8) | 2984-50-1 | C8H16O / 128.21 | 1 | 128.2 | 0.78 | 95.0% |
| 1,2-Epoxydecane (C10) | 2404-44-6 | C10H20O / 156.26 | 1 | 156.3 | 0.64 | 95.0% |
| 1,2-Epoxydodecane (C12) | 2855-19-8 | C12H24O / 184.32 | 1 | 184.3 | 0.54 | 96.0% |
| 1,2-Epoxytetradecane (C14) | 3234-28-4 | C14H28O / 212.37 | 1 | 212.4 | 0.47 | 95.0% |
| Cyclopentene oxide | 285-67-6 | C5H8O / 84.12 | 1 | 84.1 | 1.19 | 99.0% |
| 3,4-Epoxytetrahydrofuran | 285-69-8 | C4H6O2 / 86.09 | 1 | 86.1 | 1.16 | 99.0% |
| 1,5-Hexadiene diepoxide | 1888-89-7 | C6H10O2 / 114.14 | 2 | 57.1 | 1.75 | 98.0% |
| 3,3′-Bi-7-oxabicyclo[4.1.0]heptane | 37777-16-5 | C12H18O2 / 194.27 | 2 | 97.1 | 1.03 | 95.0% |
| 1,2-Epoxy-5-hexene | 10353-53-4 | C6H10O / 98.14 | 1 | 98.1 | 1.02 | 98.0% |
| 2-(2-Bromoethyl)oxirane | 13287-42-8 | C4H7BrO / 151.00 | 1 | 151.0 | 0.66 | 98.0% |
Every EEW and epoxy value in that table is calculated from the molecular weight and the number of epoxide groups – reproduce the division yourself before accepting any certificate that quotes a different figure.
Reading the Table by Group
| Group | Members | What they are for |
|---|---|---|
| Linear alpha-olefin oxides, C6 to C14 | C6, C8, C10, C12, C14 | Reactive diluents, chain terminators, hydrophobes for surfactant and diol chemistry. Chain length sets volatility against hydrophobic character. |
| Cyclic aliphatic epoxides | Cyclopentene oxide, 3,4-epoxytetrahydrofuran | Higher epoxide density and faster ring opening than the linear grades; the fused-ring members are the reactive end of the group. |
| Difunctional epoxides | 1,5-Hexadiene diepoxide, 3,3′-bi-7-oxabicyclo[4.1.0]heptane | Crosslinkers, not diluents. Half the EEW of a comparable monoepoxide, so they pull hardener demand up steeply. |
| Epoxide plus a second handle | 1,2-Epoxy-5-hexene (vinyl), 2-(2-bromoethyl)oxirane (bromoethyl) | Materials that let you react the epoxide first and something else afterwards, or the other way round. |
Chain Length: the Trade You Are Actually Making
Across the linear series, going from C6 to C14 changes four things at once:
| As chain length increases (C6 to C14) | Direction | Consequence |
|---|---|---|
| Epoxide density (epoxy value) | Falls 1.00 to 0.47 | Less reactivity per kilogram; more mass carried per epoxide |
| Volatility and odour | Falls steeply | C6 needs workshop extraction; C12 and C14 barely register |
| Viscosity cut at equal loading | Falls | C6 dilutes hardest; C14 almost does not dilute at all |
| Hydrophobicity and water resistance | Rises | C14 gives the best barrier; C6 can make water sensitivity worse |
| Network flexibility / plasticising | Rises | Long tails lower glass transition temperature and chemical resistance |
Worked example with a liquid DGEBA at EEW 185 and 20% epoxide by mass:
| Diluent | Blend EEW | DETA phr (eq. wt 20.6) | What you gain | What you lose |
|---|---|---|---|---|
| C6 | 158.2 | 13.0 | Largest viscosity reduction | More hardener, more chain ends, odour |
| C8 | 169.9 | 12.1 | Good all-round dilution | Moderate termination |
| C10 | 178.4 | 11.6 | Mild dilution, low odour | Less viscosity gain |
| C12 | 184.9 | 11.1 | Dilution without moving the cure ratio | Plasticising; lower Tg at high loading |
| C14 | 189.9 | 10.9 | Hydrophobicity, flexibility | Little dilution; slow incorporation |
The blend EEW uses the reciprocal mixing rule: 1 / sum(mass fraction / EEW of that component). It is worth doing by hand once, because it makes the trade-off visible – the difference between C6 and C12 is not “how much it dilutes” but 1.9 phr of hardener and a different failure mode.
Selection Table
| Requirement | Choose | Because |
|---|---|---|
| Cut viscosity hard, no concern about Tg | 1,2-Epoxyhexane (C6) | Lowest EEW of the linear set, strongest solvent-like action |
| Cut viscosity without disturbing the cure ratio | 1,2-Epoxydodecane (C12) | EEW 184.3 sits on top of a DGEBA at 185 |
| Hydrophobicity and flexibility, low odour | 1,2-Epoxytetradecane (C14) | Longest tail; acts as a plasticiser rather than a diluent |
| Increase crosslink density | 1,5-Hexadiene diepoxide | Two epoxides per molecule, EEW 57.1 |
| Fast cationic UV cure | 3,3′-Bi-7-oxabicyclo[4.1.0]heptane or cyclopentene oxide | Cyclic structures open faster under photoacid |
| Acid scavenging / HCl absorption | C12 or C14 | Hydrophobic epoxide that stays in the organic phase |
| Epoxide plus a polymerisable handle | 1,2-Epoxy-5-hexene | Vinyl group available for radical chemistry |
| Epoxide plus a leaving group | 2-(2-Bromoethyl)oxirane | Bromide allows a second substitution step |
| Water-soluble-ish, high epoxide density | 3,4-Epoxytetrahydrofuran | Small oxygenated ring, EEW 86.1 |
Specification Pitfalls Common to the Whole Group
- Assay is not epoxy value. A GC purity of 96% tells you how much of the peak is the epoxide; only titration tells you how much reactive epoxide the drum contains. Buy on epoxy value for stoichiometric work.
- Water and acid are the two enemies. Both open the ring to the diol, and acid does it catalytically. A drum stored for a year in a warm warehouse will show a lower epoxy value than the certificate said at shipment.
- Colour is a free assay. These are colourless liquids; a yellow cast means ring opening, metal contamination or an old batch.
- Grade differences of 1% are real. 95%, 96% and 99% in this table reflect how much the manufacturer paid to remove diol and isomers – not marketing.
Storage and Handling Across the Group
All members share the same storage rules, and they matter more than the assay on the certificate: sealed containers, cool and out of sunlight, away from acids, bases, amines and oxidising agents, and never returned to the drum after use. Iron and rust catalyse ring opening, so stainless steel or HDPE is the correct material of construction. The difunctional grades can gel in the container if contaminated, and the low-EEW cyclic grades are the most reactive of the set – treat them as the materials most likely to run away in a warm drum.
Frequently Asked Questions
Which epoxide is the best reactive diluent?
There is no single best – C6 dilutes hardest, C12 dilutes without changing the hardener ratio, C14 plasticises. Pick by what you can afford to lose: viscosity, stoichiometry or glass transition temperature.
Can I swap one chain length for another weight-for-weight?
No. EEW ranges from 100.2 to 212.4 g/eq across the linear series, so an equal-mass swap changes both the hardener demand and the crosslink density. Recalculate the blend EEW.
Are the difunctional grades just stronger diluents?
They are the opposite. A diepoxide adds crosslinks and raises hardener demand; a monoepoxide terminates chains and lowers it. 1,5-Hexadiene diepoxide at EEW 57.1 will stiffen a system, not thin it.
Why do the cyclic grades have higher epoxy values?
Because the molecules are small (C5 and C4 rings, MW 84 to 86) with one epoxide each, so a kilogram contains far more epoxide equivalents than a C12 linear chain does.
References and Disclaimer
- Molecular formula and molecular weight for each CAS as recorded in PubChem; epoxide functionality from the structure.
- EEW and epoxy values are calculated (MW / functionality, and 100 / EEW). Blend EEW uses the reciprocal mixing rule; phr values assume diethylenetriamine at 20.6 g/eq and a base resin at EEW 185.
- Assay figures are the current commercial specifications for these grades.
Disclaimer: technical and commercial information for industrial buyers, not a specification or SDS. Confirm cure ratios against your own resin and hardener, and handle according to the current SDS.
PolyBlueChem supplies the C6 to C14 linear epoxyalkanes plus the cyclic, difunctional and functionalised members of this group, each with a per-batch COA reporting assay and epoxy value. Tell us the viscosity target, the cure system and the property you cannot compromise, and we will confirm which grade fits. Read the technical guide to 1,2-epoxydodecane (C12) for the worked formulation arithmetic.