4-Hydroxy-TEMPO (H-TEMPO)
A stable nitroxide radical used to stop unwanted free-radical polymerization. CAS 2226-96-2, 99.0% minimum assay, for styrene, acrylic and diene monomers, peroxide crosslinking, and radiation-curable inks and coatings.
A stable nitroxide radical used to stop unwanted free-radical polymerization. CAS 2226-96-2, 99.0% minimum assay, for styrene, acrylic and diene monomers, peroxide crosslinking, and radiation-curable inks and coatings.
4-Hydroxy-TEMPO is 4-hydroxy-2,2,6,6-tetramethylpiperidin-1-oxyl, a nitroxide radical stable enough to store and ship as a solid. Added to a reactive material, it captures the carbon-centred free radicals that would otherwise start or continue a polymerization. Phenolic inhibitors such as MEHQ need dissolved oxygen to work; a nitroxide does not, which is why it is used in distillation sections and other low-oxygen parts of a monomer plant.
H-TEMPO is our trade name for it. The same molecule is sold as TEMPOL, 4-OH-TEMPO, 4-HT and polymerization inhibitor 701, all under CAS 2226-96-2. It is a different substance from TEMPO (CAS 2564-83-2) and from BHT.
In-process inhibitor for styrene, acrylic acid and its esters, butadiene and vinyl acetate, usually paired with a slower-acting retarder for shutdown protection.
Scorch retarder in peroxide-cured EPDM, LDPE and wire and cable compounds. It holds back premature cure during mixing and extrusion, and the peroxide outlasts it at cure temperature.
In-can stabilizer for UV-curable inks, coatings and acrylate oligomers, which are built to polymerize on demand and must not start early in the drum.
Gel-time control, including resins for cured-in-place pipe lining: gel time lengthens as the 4-hydroxy-TEMPO level rises, which gives the installer a longer working window.
For radiation-curable coatings the other side of the chemistry is the initiator. Deuteron UV 1240, a cationic photoinitiator, and the rest of the line are on coatings additives.
Search for TEMPOL and most of what comes back is research material sold by the gram. We supply 4-hydroxy-TEMPO by the drum for industrial use. Its Safety Data Sheet lists food, drug, cosmetic, pesticide and biocide use as uses advised against.
Specification values are from the PAT H-TEMPO technical data sheet. Properties are from the PAT Safety Data Sheet and the substance's REACH registration.
| Property | Value | Basis |
|---|---|---|
| Appearance | Tangerine needle-like flakes | Specification |
| Assay | 99.0% minimum | Specification, GC |
| Melting point | 64 to 72 °C | Specification |
| Melting point, literature | 69 to 73 °C | Property |
| Water | 0.50% maximum | Specification |
| Ash | 0.10% maximum | Specification |
| Molecular formula | C9H18NO2 | Property |
| Molecular weight | 172.24 g/mol | Property |
| Water solubility | 629 g/L | At 20 °C |
| Relative density | 1.127 | At 20 °C |
| CAS | 2226-96-2 | 4-Hydroxy-TEMPO |
| EC number | 218-760-9 | EINECS |
PAT H-TEMPO is packed in 25 kg fiber drums and supplied to order.
Keep drums tightly closed in a cool, dry, well-ventilated place, protected from light and moisture and away from strong oxidizers and peroxides. Storage below 25 °C maintains quality. The certificate of analysis gives the retest date of each lot.
Read the current Safety Data Sheet for hazard information before handling. It calls for tight-sealing chemical safety goggles. The material is not regulated for transport under US DOT, IMDG, IATA or Canadian TDG.
Our Safety Data Sheet is written to the 2024 OSHA Hazard Communication Standard. A Technical Data Sheet is available, and a certificate of analysis ships with every lot. 4-Hydroxy-TEMPO is active on the TSCA Inventory and listed on Canada's DSL and EU EINECS.
Yes. H-TEMPO is PAT's trade name for 4-hydroxy-TEMPO, CAS 2226-96-2, the same molecule sold as TEMPOL and 4-OH-TEMPO. PAT supplies it as an industrial chemical. Its Safety Data Sheet lists food, drug, cosmetic, pesticide and biocide use as uses advised against.
TEMPO is 2,2,6,6-tetramethylpiperidin-1-oxyl, CAS 2564-83-2, formula C9H18NO. 4-Hydroxy-TEMPO carries a hydroxyl group at the 4-position of the same piperidine ring, giving CAS 2226-96-2 and formula C9H18NO2. Both are stable nitroxide radicals. 4-Hydroxy-TEMPO is freely soluble in water, 629 g/L at 20 °C.
4-Hydroxy-TEMPO dissolves in water at 629 g/L at 20 °C and is soluble in ethanol, acetone and other polar organic solvents, so it can be dosed as a solution into aqueous or organic process streams.
It depends on the system. Published patent examples dose nitroxide inhibitors of this type at about 15 to 60 ppm in styrene alongside a quinone methide retarder, and use 4-hydroxy-TEMPO at 0.25 to 0.40 percent of the polymer as a scorch retarder in peroxide-cured EPDM and LDPE. These are published examples, not recommendations; the right level is set by trial in the customer's own process.
Yes. Inhibitor 701 is the name Chinese producers use for 4-hydroxy-TEMPO, CAS 2226-96-2. It is a different substance from BHT, which some listings wrongly attach to the same name.
PAT supplies 4-hydroxy-TEMPO as flakes in 25 kg fiber drums. Keep drums tightly closed in a cool, dry, well-ventilated place, protected from light and moisture and away from strong oxidizers and peroxides. Storage below 25 °C maintains quality, and the certificate of analysis gives the retest date of each lot.
No. PAT's Safety Data Sheet lists it as not regulated under US DOT, IMDG, IATA or Canadian TDG, and not a marine pollutant. Read the current Safety Data Sheet for handling and hazard information before use.
A Safety Data Sheet written to the 2024 OSHA Hazard Communication Standard, a Technical Data Sheet, and a certificate of analysis with every lot. The substance is listed active on the TSCA Inventory and appears on Canada's DSL and the EU EINECS list as 218-760-9.