Technical Specifications
| Property | Unit | Typical Value | Test Method |
|---|---|---|---|
| Appearance | Colorless or light yellow liquid | Visual | |
| Density at 20 °C | kg/m³ | 960 | ASTM D4052 |
| Viscosity at 40 °C | mm²/s | 125 | ASTM D445 |
| Flash Point | °C | 150 | ASTM D93 |
| Purity | % | 100 | GC |
| RBOT | min | 330 | ASTM D2272 |
* Typical values from batch production. Batch-specific COA available on request.
Technical content reviewed by the CheMost additives team · Specifications last reviewed
Molecular Structure
Molecular structure · hindered phenolic ester
Isooctyl 3-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate (C₂₅H₄₂O₃) · CAS 125643-61-0
A high-molecular-weight hindered-phenol ester — the di-tert-butyl phenol donates a hydrogen to trap radicals; the bulky branched-alkyl ester gives very low volatility so it stays in the oil at high temperature.
What Is a High Molecular Weight Phenolic Antioxidant (AO135)?
CheMost-AO135 is a liquid, 100%-active high-molecular-weight phenolic antioxidant — chemically the C7–9 branched-alkyl ester of 3-(3,5-di-tert-butyl-4-hydroxyphenyl)propionic acid (β-(3,5-di-tert-butyl-4-hydroxyphenyl) isooctanol propionate). It is a hindered-phenolic primary antioxidant that controls deposit formation, supports piston cleanliness and protects long-lasting oil TBN.
Like all phenolic antioxidants it is a primary antioxidant: the hindered phenol –OH donates a hydrogen to a peroxy radical, breaking the oxidation chain. What sets AO135 apart from a simple phenol such as BHT is its size. The bulky branched-alkyl ester makes the molecule large and very low in volatility, so it stays dissolved in the oil and keeps working at high temperature, where small-molecule phenolics evaporate or break down.
Because it is supplied 100% active and liquid, it meters cleanly with no solvent carried into the blend. The data sheet recommends it for use with the aminic antioxidant AO57 — the amine + phenol pairing explained below.
How AO135 Works
Hindered-phenol radical trap
The di-tert-butyl-shielded phenolic –OH donates a hydrogen to a propagating peroxy radical, converting it to a stable species and terminating the autoxidation chain — the primary-antioxidant mechanism.
Low volatility, high persistence
The high molecular weight and bulky branched-alkyl ester give very low volatility, so the antioxidant stays in the oil through high-temperature, long-drain service instead of evaporating like a light phenol.
Deposit & piston-cleanliness control
By suppressing oxidation it limits the varnish, sludge and deposits that form as oil ages, helping keep pistons clean and protecting the oil’s base reserve (TBN) over the drain interval.
100% active, easy to meter
Supplied 100% active and liquid, it blends accurately with no carrier solvent — and pairs with an aminic antioxidant for heterosynergistic, broad-temperature protection.
Antioxidant Types Compared — Where AO135 Fits
Lubricant antioxidants split into aminic and phenolic primary types plus liquid/solid forms. The table places AO135 against CheMost’s other antioxidant grades so you can pick by temperature, form and synergy. All figures are from each grade’s data sheet.
| Grade | Class | Form | Key spec | Temperature niche |
|---|---|---|---|---|
| AO135 (this page) | Phenolic ester (HMW) | Liquid | 100% active | High-temp, low-volatility |
| AO57 | Aminic (alkylated diphenylamine) | Liquid | N 4.58% · TBN 198 | High-temperature primary AO |
| BHT | Phenolic (simple) | Solid | Purity 99.9% | Low–moderate temperature |
| AO52 | Phenolic (mixed blend) | Liquid | Free phenol 0.5% | Low-end industrial / turbine |
Within the phenolics, AO135 is the high-temperature, low-volatility choice; BHT and AO52 are the simpler, lower-cost options for cooler service. For the broadest protection, run AO135 with the aminic AO57.
Applications
CheMost-AO135 is used as the high-temperature, low-volatility phenolic antioxidant in formulations targeting the duties below:
Passenger-car & heavy-duty engine oils
Deposit control and piston cleanliness in gasoline and diesel engine oils, where its low volatility keeps the antioxidant working at ring-zone temperatures.
Industrial & circulating oils
Long-life oxidation protection for hot-running industrial, circulating and gear oils that need a phenolic that will not boil off.
Long-drain / TBN-retention service
Where extended drain intervals demand that the base reserve be protected, AO135 slows oxidative acid build-up to help retain oil TBN.
Finished-oil performance approvals (e.g. API, ACEA or OEM engine-oil specifications) belong to the fully formulated oil, not to an individual antioxidant component.
Treat Rate
The data sheet specifies the product but not a per-application dosage, so the figures below are indicative, derived from the chemistry and our formulating experience — confirm the final level.
First-order estimate. As a high-molecular-weight liquid phenolic, AO135 is used at roughly 0.25–1.5%, dosed to the oxidation target (RBOT/RPVOT, ASTM D2272). Being 100% active, the treat figure is the active figure — there is no solvent to discount.
AO135 is usually paired with an aminic antioxidant such as AO57 so the phenol/amine couple covers both moderate and high temperature; each then runs at a lower level than it would alone. The exact level depends on the oxidation target, the base oil and the rest of the package.
Treat rates are indicative, not fixed dosages. CheMost can provide formulation and treat-rate support on request.
Formulating With AO135 — Complementary Additives
Aminic antioxidant (AO57)
The headline pairing: amine and phenol trap radicals by different mechanisms and regenerate one another (heterosynergism), giving broad-temperature oxidation life. The data sheet recommends AO135 with AO57.
ZDDP
ZDDP is a secondary antioxidant that decomposes peroxides and adds antiwear, complementing AO135’s primary radical-trapping in engine and industrial oils.
Metal deactivator (BTA)
A metal deactivator passivates copper and yellow metals that would otherwise catalyse oxidation, sparing the antioxidant reserve.
Simple phenolic (BHT)
For cooler service or cost-driven blends, a simpler phenolic such as BHT or liquid AO52 can supplement or replace part of the HMW phenol.
Documentation, Qualification & Regulatory Support
Standard documentation — Certificate of Analysis (COA, per shipment), Technical Data Sheet (TDS) and Safety Data Sheet (SDS, GHS/CLP) — is provided. The full TDS is available on request rather than as a public download. Additional support is available on request:
Regulatory documentation
REACH, TSCA and country-specific market-registration documentation support available on request.
Third-party inspection
SGS / Intertek / BV pre-shipment inspection can be arranged on request.
Custom grades & packaging
Custom packaging and grades on request.
Formulation support
Antioxidant-system and treat-rate guidance from our technical team.
Packaging & Supply
CheMost-AO135 is stocked and shipped worldwide, with a typical lead time of 1–15 days and a 36-month shelf life at ambient temperature. Samples and quotations are answered within 12 hours.
Packaging
180 kg metal drum · 900 kg IBC tank.
Minimum order
1 drum / 1 IBC — contact us for your quantity.
Incoterms
FOB · CIF · EXW, to suit your freight arrangement.
Loading ports
All major Chinese ports.
Frequently Asked Questions
What is a high molecular weight phenolic antioxidant?
It is a large, low-volatility hindered-phenol — here the C7–9 branched-alkyl ester of 3-(3,5-di-tert-butyl-4-hydroxyphenyl)propionic acid (CAS 125643-61-0), supplied 100% active and liquid. The phenolic –OH traps free radicals; the high molecular weight keeps it in the oil at high temperature.
Why use AO135 instead of BHT?
BHT is a small, volatile phenol that loses effectiveness at high temperature. AO135 is a high-molecular-weight phenol ester with very low volatility, so it stays in the oil and protects through hot, long-drain service — at the cost of being a more specialised additive. For cool service, BHT is the cost-effective choice.
Is it really 100% active?
Yes — the data sheet reports 100% purity (GC), so it carries no diluent. The treat figure is the active figure, and there is no carrier solvent to account for in the blend.
What treat rate should I use?
As a high-molecular-weight liquid phenolic, AO135 is typically used at about 0.25–1.5%, dosed to the oxidation target and usually paired with the aminic AO57. The exact level depends on the oxidation requirement, the base oil and the rest of the package; our technical team can assist.
How is it supplied, and how fast can I get a sample?
It is supplied as a colourless-to-light-yellow liquid in 180 kg metal drums and 900 kg IBC tanks with a 36-month shelf life, and shipped worldwide. As a manufacturer and sourcing partner (Est. 2013), CheMost answers sample and quotation requests within 12 hours.