Technical Specifications
| Property | Unit | Typical Value | Test Method |
|---|---|---|---|
| Appearance | Light yellow liquid | Visual | |
| Density @ 20 °C | kg/m³ | 1005 | ASTM D4052 |
| Viscosity @ 40 °C | mm²/s | 3.5 | ASTM D445 |
| Sulfur Content | % | 45 | ASTM D4951 |
| Flash Point | °C | 100 | ASTM D93 |
| Copper Corrosion (121 °C, 3 h) | rating | 2e | ASTM D130 |
| Weld Load P_D (3% in oil) | kg | 650 | ASTM D2596 |
| Moisture Content | % | 0.03 | ASTM D95 |
| Mechanical Impurities | % | 0.03 | ASTM D473 |
| Base-Oil Solubility | Mineral Group I, II, III >3% | — |
* 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 · sulfur carrier
R–Sₓ–R (polysulfide-bridged isobutylene oligomers)
Sulfurized isobutylene is a UVCB sulfur carrier: isobutylene oligomers bridged by active polysulfide (–Sₓ–) chains that release sulfur to form the EP iron-sulfide film.
What Is Sulfurized Isobutylene (T321)?
CheMost-T321 is a high-activity sulfurized isobutylene — a chlorine-free extreme-pressure (EP) additive built from isobutylene oligomers carrying a very high sulfur content (45%). It is supplied as a light yellow liquid and is used as a primary EP additive in automotive and industrial gear oils, where it carries the high contact loads that would otherwise cause scuffing and seizure.
Sulfurized isobutylene belongs to the family of sulfur carriers — organic molecules that hold sulfur in active polysulfide (–Sₓ–) bridges and release it at the hot, highly loaded metal contact to form a sacrificial iron-sulfide film. That film prevents adhesive wear, scuffing and cold welding under boundary lubrication. T321’s high active-sulfur content makes it a strong EP carrier, demonstrated by a P_D weld load of 650 at 3% treat (ASTM D2596).
CheMost-T321 is made by a high-pressure synthesis process, which gives better extreme-pressure and wear performance than normal-pressure sulfurized isobutylene, with a lighter colour and good antioxidant capacity. Because it is chlorine-free, it is a clean replacement for chlorinated-paraffin EP chemistry. For metalworking-fluid duty, the olefin-based sulfurized olefin is the companion grade.
How Sulfurized Isobutylene Works
EP iron-sulfide film
At the hot, highly loaded contact the active polysulfide bridges release sulfur that reacts with the steel to form a low-shear iron-sulfide layer — preventing adhesive wear, scuffing and welding under extreme pressure.
High sulfur, high activity
At 45% sulfur with high activity, a small treat delivers strong load-carrying capacity — the P_D weld load reaches 650 at 3% addition (ASTM D2596).
High-pressure synthesis
The high-pressure manufacturing route gives better EP and wear performance than normal-pressure sulfurized isobutylene, in a lighter-coloured product.
Chlorine-free, with antioxidancy
Contains no chlorine — a clean replacement for chlorinated-paraffin EP — and carries good antioxidant capacity that supports oil life.
Active Sulfur & Yellow-Metal Compatibility
Sulfur carriers are classed by how readily their sulfur reacts: active sulfur gives the strongest EP but is corrosive to copper and yellow metals, while inactive grades are gentler but lower in EP. T321 is a high-activity grade (ASTM D130 copper corrosion 2e), so it delivers strong EP for steel-on-steel gear contacts but is aggressive to copper and bronze. Where yellow metals are present, pair it with a copper metal deactivator such as benzotriazole, or moderate the active-sulfur level — the standard way to balance EP against yellow-metal corrosion.
Applications
CheMost-T321 is used as the EP component in formulations targeting the duties below, where high load-carrying capacity is the priority:
Automotive & industrial gear oils
The core application — the high-sulfur EP carrier in hypoid and industrial gear oils that must resist scuffing and seizure under shock and high load.
Metalworking fluids
Heavy-duty cutting, forming and drawing oils where a strong sulfur EP carrier extends tool life under boundary lubrication.
Greases & high-load lubricants
EP/antiwear performance in greases and specialty lubricants for heavily loaded steel components.
Finished-oil performance approvals (e.g. API GL-5, AGMA, FZG ratings) belong to the fully formulated gear oil, not to an individual additive component.
Treat Rate
The data sheet reports a performance point (P_D weld load 650 at 3% in oil, ASTM D2596) rather than a fixed dosage, so the figures below are indicative — confirm the final level for your formulation.
First-order estimate. Sulfur-carrier EP additives are typically dosed around 1–5% in gear and metalworking oils, trimmed up to the target FZG / four-ball load result and down to the copper-corrosion limit. With T321’s high activity, the 3% point already delivers a 650 weld load — so the level is set as much by the yellow-metal corrosion cap as by the EP target.
In a gear-oil package the sulfur carrier is balanced against a phosphorus EP/antiwear additive (the classic S–P synergy) and a copper deactivator. The exact level depends on the load rating sought, the metals present and the rest of the additive system.
Treat rates are indicative, not fixed dosages. CheMost can provide formulation and treat-rate support on request.
Formulating With T321 — Complementary Additives
Phosphorus EP / antiwear (TPPT)
Sulfur and phosphorus EP/AW chemistries act in synergy: the sulfur carrier handles extreme-pressure welding while the phosphorus additive builds the antiwear film — the backbone of every gear-oil EP system.
Benzotriazole (metal deactivator)
BTA passivates copper and yellow metals, offsetting the active sulfur’s copper corrosion so the EP level can be raised without staining bronze components.
Sulfurized olefin
The olefin-based sulfur carrier is the metalworking-oriented sibling; the two sulfur carriers can be combined to tune activity, viscosity and EP level.
Antioxidants
Antioxidants extend oil life under the high temperatures of loaded gear contacts, complementing T321’s own antioxidant capacity.
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 activity/sulfur levels and packaging — metal drum, IBC, ISO tank.
Formulation support
EP/AW balancing and treat-rate guidance from our technical team.
Packaging & Supply
CheMost-T321 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
200 kg metal drum · 1000 kg IBC tank.
Minimum order
1 drum or 1 IBC — no minimum order value.
Incoterms
FOB · CIF · EXW, to suit your freight arrangement.
Loading ports
All major Chinese ports.
Frequently Asked Questions
What is sulfurized isobutylene used for?
It is a high-sulfur extreme-pressure (EP) additive (CAS 68511-50-2) used mainly in automotive and industrial gear oils, and in heavy-duty metalworking fluids. Its active polysulfide sulfur reacts with the steel surface under high load to form a protective iron-sulfide film that prevents scuffing, seizure and welding. CheMost-T321 contains 45% sulfur and is chlorine-free.
Why is T321 made by a high-pressure process?
The high-pressure synthesis route gives sulfurized isobutylene with better extreme-pressure and wear performance than the normal-pressure method, along with a lighter colour and good antioxidant capacity. At 3% in oil it reaches a P_D weld load of 650 (ASTM D2596).
Is it corrosive to copper and yellow metals?
T321 is a high-activity sulfur carrier (ASTM D130 copper corrosion 2e), so it is aggressive to copper and bronze. That is normal for a high-EP active grade — where yellow metals are present, pair it with a copper metal deactivator such as benzotriazole or moderate the active-sulfur level to balance EP against corrosion.
Is sulfurized isobutylene chlorine-free?
Yes — CheMost-T321 contains no chlorine, making it a clean replacement for chlorinated-paraffin EP additives in gear oils and metalworking fluids.
How is it supplied, and how fast can I get a sample?
It is supplied in 200 kg metal drums and 1000 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.