What Is Antioxidant RD (TMQ)?
Antioxidant RD, CAS 26780-96-1, also called TMQ, is the polymerised form of 2,2,4-trimethyl-1,2-dihydroquinoline – an amine-type (quinoline) antioxidant. It is one of the workhorse antioxidants of the rubber industry, giving strong protection against heat, oxygen and flex fatigue ageing. It is used mainly in tyres and heavy mechanical rubber goods.
Antioxidant RD is a staining (discolouring) antioxidant: as an amine it darkens with age and contact, so it is used in black and dark compounds rather than white or light-coloured ones. In exchange it gives a level of heat and fatigue protection that a non-staining phenolic antioxidant cannot match. PolyBlueChem supplies Antioxidant RD to a controlled specification with per-batch COA and SDS.
| CAS number | 26780-96-1 |
| Chemical name | Polymerised 2,2,4-trimethyl-1,2-dihydroquinoline |
| Synonyms | Antioxidant RD; TMQ; poly(2,2,4-trimethyl-1,2-dihydroquinoline); quinoline antioxidant |
| Molecular formula | (C12H15N)n |
| Type | Amine (quinoline) antioxidant |
| Appearance | Amber to brown granule |
| Softening point | 80 – 100 °C |
Chemistry and Structure
Antioxidant RD is an oligomeric/polymeric material: the repeating unit is derived from 2,2,4-trimethyl-1,2-dihydroquinoline, a molecule that carries a secondary amine (-NH-) and a substituted aromatic ring. Polymerisation links many of these units into a resin-like molecule of moderate molecular weight, which is why the product is supplied as amber-brown granules with a softening point rather than as a sharp-melting crystalline powder.
Two structural features drive the performance:
- The secondary amine (-NH-) is the antioxidant active site. Like a hindered phenol, it can donate hydrogen to a peroxy radical and break the oxidation chain – but the amine chemistry is more effective against heat and fatigue ageing, and it is also the reason the material is coloured.
- The oligomeric backbone gives a relatively high molecular weight and low volatility, so RD stays in the rubber during high-temperature cure and long service, and resists extraction and migration.
Because RD is a mixture/oligomer rather than a single sharp molecule, it is specified by softening point, heating loss and ash rather than by a melting point or a single-number assay.
How Antioxidant RD Works
Rubber ages by autoxidation. Heat, oxygen, dynamic stress and metal traces generate radicals (including peroxy radicals, ROO•) that attack the polymer, leading to hardening, cracking, loss of elasticity and, in tyres, premature failure. Antioxidants break this cycle. Amine antioxidants such as RD act by two routes:
- Radical scavenging – the amine donates hydrogen to peroxy radicals, converting them to stable products and interrupting the chain (like a hindered phenol).
- Stable radical formation – the resulting aminyl/nitroxide species are resonance-stabilised and can themselves trap further radicals, giving a “regenerative” style of protection that is very effective at high temperatures.
The practical consequence is that RD gives strong protection against heat ageing and flex (fatigue) ageing – the two dominant failure modes in tyres and dynamic rubber parts. That is why it is a mainstay of tyre compounds, usually combined with an antiozonant/antiflex agent such as 6PPD or 7PPD and, where colour allows, with other antioxidants.
How Antioxidant RD Is Produced
Antioxidant RD is made by the acid-catalysed condensation and polymerisation of aniline with acetone, which gives 2,2,4-trimethyl-1,2-dihydroquinoline, followed by further reaction (polymerisation) to build the oligomeric antioxidant:
- Aniline and acetone are condensed under acid catalysis to form the dihydroquinoline monomer.
- The monomer is polymerised (oligomerised) to the required degree, giving a resinous product.
- The resin is stripped of volatiles, cooled and granulated to amber-brown granules.
Process control sets the degree of polymerisation (which affects the softening point and the balance of volatility and efficiency) and minimises residual monomers, which would affect odour, colour and performance.
Specifications and Quality Control
Antioxidant RD is supplied as amber to brown granules to the following specification:
| Parameter | Specification |
|---|---|
| Appearance | Amber to brown granule |
| Softening point | 80 – 100 °C |
| Heating loss | 0.30% max |
| Ash | 0.30% max |
Each parameter controls a different aspect of quality:
| Parameter | What it controls |
|---|---|
| Softening point (80-100 °C) | Degree of polymerisation; affects handling, dispersion and volatility |
| Heating loss (0.30% max) | Volatiles and moisture; affects weighing and processing |
| Ash (0.30% max) | Inorganic residues that can affect ageing and appearance |
A specification sheet and a per-batch certificate of analysis (COA) are available on request.
Key Properties
| Property | Behaviour | Practical value |
|---|---|---|
| Function | Amine (chain-breaking) antioxidant | Strong heat and fatigue protection |
| Form | Amber to brown granules | Easy to weigh; low dust; good dispersion on mixing |
| Volatility | Low (oligomeric) | Survives high-temperature cure and long service |
| Colour | Staining / discolouring | For dark and non-appearance-critical compounds |
| Solubility | Compatible with rubber; disperses on mixing | Effective at typical phr loadings |
Applications
Antioxidant RD is used wherever strong heat and fatigue protection is needed and the colour requirement allows an amine.
| Industry / product | Function |
|---|---|
| Tyres | Protection of tread, carcass and sidewall compounds against heat and fatigue ageing |
| Mechanical rubber goods | Belting, hoses, anti-vibration mounts, conveyor belting |
| Dynamic rubber parts | Parts subjected to repeated flexing and heat build-up |
| General black rubber | Long-term heat/oxygen resistance |
| Adhesives and industrial rubber | Stabilisation against ageing |
- Tyres – a core antioxidant for tyre compounds, protecting the polymer against the heat generated in service and the fatigue of constant flexing.
- Conveyor and transmission belting – where repeated flexing and heat build-up demand strong fatigue protection.
- Hoses, seals and anti-vibration parts – protection of dynamic rubber goods.
Antioxidant RD vs Other Antioxidants
RD sits at the “strong protection, but staining” end of the antioxidant spectrum, opposite the non-staining phenolics.
| Antioxidant | CAS | Type | Staining | Strength | Typical role |
|---|---|---|---|---|---|
| Antioxidant RD (TMQ) | 26780-96-1 | Amine (quinoline) | Staining | Strong heat/fatigue | Tyres, dark mechanical goods |
| 6PPD / 7PPD | 793-24-8 / 3081-01-4 | Amine (PPD) | Staining | Strong ozone/flex | Anti-ozonant / antiflex for tyres |
| Antioxidant 2246 | 119-47-1 | Hindered phenolic (bis) | Non-staining | Moderate heat/oxygen | Light-coloured rubber and plastics |
| BHT (264) | 128-37-0 | Hindered phenolic (mono) | Non-staining | Fast, moderate | Plastics, oils, food |
- Dark rubber, tyres, dynamic service? An amine antioxidant (RD, 6PPD, 7PPD) gives the strongest heat/fatigue/ozone protection.
- Light-coloured goods? A non-staining phenolic (2246, BHT) – accepting weaker dynamic protection.
- Combined packages – it is common to use RD plus a PPD (6PPD/7PPD) for full heat, fatigue and ozone protection in tyres.
Dosage and Use
Antioxidant levels are set by the compound, the service conditions and the required life, and confirmed by ageing tests. The figures below are orientation only.
| Application | Starting-point guidance |
|---|---|
| Tyre compounds | A few phr, set with the antiozonant and cure system |
| Mechanical goods | A few phr, adjusted for service temperature and dynamic load |
| Combined with PPDs | Split the total antioxidant loading between RD and the PPD |
RD is supplied as granules that disperse well on mixing. Because it is an amine, it works alongside PPD antiozonants and cure systems without the colour penalty mattering in black compounds.
Staining, Discolouration and Appearance
Amine antioxidants such as RD are staining. This is not a defect – it is inherent to the amine chemistry that gives the strong heat/fatigue protection – but it restricts where RD can be used:
| Use | Suitability |
|---|---|
| Black tyres and dark rubber goods | Suitable – colour is not an issue and protection is strong |
| Light-coloured or white goods | Not suitable – use a non-staining phenolic instead |
| Goods in contact with light surfaces | Not suitable – contact staining can occur |
Where colour matters, the non-staining phenolics (2246, BHT) are used, accepting a lower level of dynamic protection.
Safety, Handling and Storage
- Low hazard – Antioxidant RD is of low acute toxicity and is widely used in the rubber industry.
- Dust/low-dust form – the granule form is low-dusting, which is cleaner to handle than a powder.
- Hygiene – good industrial hygiene; wash after contact.
- Storage – keep sealed, cool and dry; store away from strong oxidisers. The granules may soften in hot storage (softening point 80-100 °C).
Regulatory Status
| Use | Status (as commonly cited) |
|---|---|
| Rubber (industrial) | Governed by the buyer’s specification and article requirements |
| Light-coloured / food-contact | Generally not used because it stains; confirm any specific rule for your market |
Packaging, Logistics and Supply
| Item | Standard options |
|---|---|
| Packaging | 25 kg PP/PE bags or fibre drums |
| Documentation | Per-batch COA and SDS |
| Incoterms | FOB and CIF |
| Storage | Sealed, cool and dry |
As a specialty rubber antioxidant, price tracks the aniline/acetone feedstock and the degree of polymerisation. Buying on committed tonnage gives the best terms.
Antioxidant RD in Tires and Dynamic Rubber
Tyres are the largest single use of Antioxidant RD, and they illustrate why an amine antioxidant is chosen. A tyre heats up as it rolls, flexes constantly, and is expected to survive years of service; its rubber must resist heat ageing and fatigue ageing at the same time.
| Tyre/part | Why RD helps |
|---|---|
| Tread | Heat build-up and fatigue at the running surface |
| Carcass and body | Long-term retention of strength under heat and flex |
| Sidewall | Heat/oxygen protection (with an antiozonant for ozone) |
| Innerliner and bead | Durability under temperature cycling |
In tyres, RD is typically used with an antiozonant/antiflex agent such as 6PPD or 7PPD: the PPD protects against ozone cracking and dynamic fatigue at the surface, while RD provides bulk heat-ageing protection. Together they cover the main ageing mechanisms a tyre faces.
Combining RD with Antiozonants and Cure Systems
RD is rarely used alone in demanding compounds. Its strength is best realised as part of a protective package.
| Additive | Role alongside RD |
|---|---|
| 6PPD / 7PPD (PPD antiozonants) | Ozone cracking and dynamic fatigue protection at the surface |
| Hindered phenolic (2246, BHT) | Additional heat/oxygen protection (usually in lighter-coloured parts) |
| Secondary antioxidant (thioester) | Hydroperoxide decomposition for longer heat-ageing life |
| Sulfenamide / thiazole accelerators | Cure system; confirm cure rate by test |
Because amides and amines can interact with cure chemistry and with some accelerators, the total antioxidant/antiozonant package is balanced against the cure system and confirmed by rheometer and ageing tests. The aim is to cover heat, fatigue and ozone ageing together, without over-loading (which risks bloom and cost) or under-loading (which risks premature failure).
Quality: Reading an RD Certificate of Analysis
Antioxidant RD is an oligomeric material, so its certificate looks different from a crystalline antioxidant’s. The softening point and the heating loss/ash are the numbers that matter.
| Parameter | What it tells you |
|---|---|
| Softening point (80-100 °C) | The degree of polymerisation; a consistent softening point means consistent performance and handling |
| Heating loss (0.30% max) | Volatiles/moisture; too much means variable weighing and processing |
| Ash (0.30% max) | Inorganic residues that could affect ageing or appearance |
| Appearance (amber to brown granule) | Consistency of the resinous product |
Because RD is a mixture, buyers should specify the softening-point band and check it on each batch rather than expecting a single-number assay. A batch that is out of the softening-point band will behave differently in the mixer and in service.
Handling, Dispersion and Mixing
Antioxidant RD is supplied as amber-brown granules, which is a practical advantage over the powdered antioxidants: granules are low-dusting, flow and weigh well, and disperse into the rubber during mixing without caking.
| Practical point | Note |
|---|---|
| Form | Granules – low dust, good flow, easy to weigh |
| Mixing | Added to the compound during mixing like other rubber chemicals; disperses as the stock is worked |
| Softening point | 80-100 °C – avoid hot storage that could soften or cake the granules |
| Weighing | Consistent softening point and heating loss keep batch weights consistent |
Because RD is an oligomeric resin rather than a sharp-melting crystalline solid, its handling is closer to that of a low-softening rubber chemical. Keeping it cool and dry preserves its granule form and its free-flowing behaviour in the weighing room.
Frequently Asked Questions about Antioxidant RD (TMQ)
What is Antioxidant RD?
Antioxidant RD (TMQ, CAS 26780-96-1) is polymerised 2,2,4-trimethyl-1,2-dihydroquinoline, an amine antioxidant used mainly in tyres and dark rubber goods.
What is the CAS number of TMQ?
26780-96-1.
Does Antioxidant RD stain?
Yes – it is a staining/discolouring antioxidant, so it is used in black and dark compounds, not white or light-coloured ones.
What is RD used for?
Heat, oxygen and fatigue protection in tyres, belting, hoses and other dynamic rubber goods.
How does it differ from 6PPD?
Both are amine antioxidants. RD is mainly a heat/fatigue antioxidant; 6PPD is used mainly as an antiozonant/antiflex agent. They are often combined in tyres.
Can it be used with a phenolic antioxidant?
Yes – in dark compounds it can be combined with, or chosen over, a phenolic antioxidant depending on the ageing mechanism to be covered.
How is it stored?
Sealed, cool and dry; it is a granule with a softening point of 80-100 °C, so avoid hot storage.
Related reading
- Antioxidant RD (TMQ) in tires and rubber
- Rubber antioxidants and accelerators: selection guide
- Antioxidant 2246: properties and applications
- Butylated hydroxytoluene (BHT): properties and applications
- Antioxidant RD (TMQ, CAS 26780-96-1) – product page
PolyBlueChem supplies Antioxidant RD (TMQ, CAS 26780-96-1) to a controlled specification, with per-batch COA and SDS, competitive pricing on bulk volumes and FOB/CIF delivery. Contact us with your application, tonnage and delivery port.