Polyisobutylene (PIB) Viscosity Index Improver & Thickener - Manufacturer & Supplier

What is Polyisobutylene (PIB)?

Polyisobutylene is a hydrocarbon polymer produced from petroleum butane-butene fractions. It's a viscosity index improver and thickener — one of the oldest polymer additives still in active commercial use. PIB was the dominant engine oil VM from the 1940s through the 1960s, and while olefin copolymers (OCPs) have since taken over most engine oil applications, PIB holds its ground in gear oils, industrial lubricants, and metalworking fluids.

Unlike OCP or polymethacrylate (PMA), PIB is a fully saturated hydrocarbon. No sulfur, no nitrogen, no oxygen in the polymer backbone. That means it burns clean at high temperature — the polymer decomposes into free radical monomers that combust fully, leaving minimal ash and loose carbon deposits. In two-stroke engine oils, this is the difference between a clean exhaust port and a plugged one.

Chemically, the polymer backbone is [-CH₂-C(CH₃)₂-]_n — geminal dimethyl groups on alternating carbons. These methyl pairs give PIB its distinctive tight coil conformation in oil solution. Compared to OCPs, PIB has lower thickening efficiency per unit weight, but it brings something OCP doesn't: load-carrying capacity. Gear oil formulators still choose PIB for this reason.

Structure & Chemistry

PIB is produced via cationic polymerization of isobutylene at low temperature — typically below -10°C — using a Lewis acid catalyst such as aluminum trichloride (AlCl₃) paired with a co-initiator. The process is selective. Only isobutylene polymerizes; other C₄ fractions pass through unreacted.

The resulting polymer has a completely saturated carbon backbone. No double bonds, no reactive sites, no oxidation-prone allylic hydrogens. This is why PIB resists thermal degradation better than most diene-containing polymers and why it's classified as chemically inert.

Molecular weight distribution depends on the catalyst system and temperature. Lower reaction temperatures favor higher molecular weight. Modern AlCl₃-based processes can control the distribution tightly enough to produce grades from MW 300 to several million. For lubricant applications, the sweet spot is MW 600–3500 — liquid at room temperature, easy to handle, and soluble in mineral oil at practical treat rates.

A note on HR-PIB (Highly Reactive PIB): Standard PIB has mostly internal double bonds at the chain end. HR-PIB, made from high-purity isobutylene with specialized catalysts, pushes the terminal vinylidene (alpha-olefin) content above 70%. Why does this matter? Because HR-PIB reacts with maleic anhydride via thermal ene reaction to make PIBSA — the precursor to polyisobutylene succinimide (PIBSI) ashless dispersants. Standard PIB needs chlorine-promoted chemistry for this reaction, which leaves residual chlorides. HR-PIB doesn't. Every major dispersant manufacturer has moved toward the HR-PIB route.

Molecular Weight Grades

CheMost offers PIB in seven molecular weight grades. Each has distinct viscosity behavior and application fit.

The jump from MW 1300 to 2400 matters. Guidechem reports that 80W/90 GL-5 gear oil thickened with PIB 1300 passed bench tests with stable viscosity, while PIB 2400 — in the same application — showed significant viscosity drop after one year of operation. It's a shear stability trade-off. Higher MW gives more thickening per unit but less resistance to permanent shear. For automotive gear oils, control the PIB 2400 treat rate carefully. For stationary industrial gearboxes running at steady load, it's fine.

MW 680 through 1300 are the workhorse grades for most lubricant blending. They handle well at ambient temperature, dissolve readily in Group I/II mineral oils, and provide predictable viscosity lift per percent treat rate.

Technical Specifications

* All values sourced from CheMost product pages (PIB 950/1300/2400) and TDS documents (PIB 680/1300, May 2023). Refractive index and Tg values from Polysciences and published literature. Contact us for batch-specific COA.

Key Properties

• Shear stability: PIB resists permanent viscosity loss better than OCPs of comparable molecular weight. This is structural — the geminal dimethyl backbone absorbs mechanical energy differently than the ethylene-propylene chain. For industrial gear oils running years between changes, this keeps the oil in grade.
• Clean burn at high temperature: PIB thermally decomposes into isobutylene monomers that combust fully. No residual ash. No hard carbon deposits. In two-stroke oils, this prevents ring sticking and exhaust port blockage.
• Load-carrying capacity: PIB films under elastohydrodynamic (EHD) conditions support higher loads than OCP-thickened films of the same viscosity. This is why gear oil formulators still use PIB when OCP is cheaper per unit of thickening.
• Low-temperature flexibility: Glass transition at -73°C. The polymer stays flexible and functional well below any practical cold-start temperature. PIB-thickened gear oils flow at -30°C.
• Chemical inertness: Fully saturated backbone. Resists oxidation, acid attack, and UV degradation. No reactive functional groups to participate in deposit-forming reactions.
• Pour point depressant compatibility: PIB responds well to conventional PPDs. The saturated backbone doesn't interfere with wax crystal modification the way some semicrystalline OCPs do.
• Electrical insulation: Low dielectric constant, high volume resistivity. Used in cable-filling compounds and transformer oil additives.

Manufacturing Process

CheMost produces PIB at our Jinzhou facility using a continuous cationic polymerization process. With 20+ reactors and an annual capacity of 20,000 tons, we maintain steady supply across all seven molecular weight grades.

Isobutylene feedstock — separated from refinery C₄ streams — is dried, purified, and fed into a cooled reactor with a Lewis acid catalyst system. The reaction temperature sits below 0°C. Lower temperature increases molecular weight; our process controls this within a tight window to hit the target grade.

After polymerization, the catalyst is neutralized and washed out. The crude polymer goes through vacuum stripping to remove unreacted monomers and light ends. What's left is a clean, stable polymer — no residual catalyst, no volatile fractions.

For HR-PIB grades, the process uses high-purity isobutylene (>99.5%) and a different catalyst system optimized for terminal vinylidene selectivity. The result is PIB with >70% alpha-olefin end groups — ready for thermal ene reaction with maleic anhydride without any chlorine chemistry.

Quality control runs 70+ checks across in-process and finished product, supported by 20+ pieces of testing equipment. Molecular weight distribution by GPC, viscosity by ASTM D445, flash point by ASTM D93, water content by Karl Fischer, and appearance by visual inspection against reference standards.

Applications in Lubricants

Engine Oils

PIB was the original engine oil viscosity modifier. It's been largely replaced by OCP in passenger car and heavy-duty diesel engine oils for cost reasons — OCP gives more viscosity lift per dollar. But PIB still sees use in two-stroke engine oils, where its clean-burn decomposition profile prevents the exhaust port clogging that plagued early OCP-thickened two-stroke formulations.

In niche applications — classic car oils, small engine formulations — PIB remains the thickener of choice. The treat rate varies by base oil and target grade, typically 0.5–3% by weight.

Gear Oils

This is where PIB earns its keep. The load-carrying advantage is real and measurable. Under the high contact pressures in hypoid and spur gears, PIB-thickened oil films resist squeeze-out better than OCP-thickened equivalents.

For SAE 80W/90 and 85W/140 automotive gear oils, PIB 1300 is the standard grade — good balance of thickening efficiency and shear stability. For ISO 220–460 industrial gear oils, PIB 2400 provides the viscosity needed at lower treat rates, though formulators should monitor shear stability in high-sliding-speed applications.

Hydraulic Fluids & Metalworking Fluids

PIB functions as both a thickener and an anti-mist agent in metalworking fluids. At 0.02–0.05% treat rate, a high-MW PIB fraction suppresses oil mist formation during high-speed machining — a significant occupational health benefit. The polymer chains extend under the elongational flow at the tool-workpiece interface, coalescing droplets rather than letting them aerosolize.

In high-VI hydraulic fluids, PIB provides viscosity lift at operating temperature without the low-temperature viscosity penalty that comes with heavy base oil selection. PMAs offer better VI lift per unit, but PIB costs less.

Grease Applications

PIB of MW 2300–3500 serves as a tackifier in lithium and calcium sulfonate greases. At 1–3% treat rate, it adds stringiness — the grease clings to gear teeth and bearing surfaces rather than flinging off at speed. Combined with the inherent load-carrying properties, this makes PIB-tackified greases the standard for open gear applications where relubrication intervals are measured in weeks, not hours.

Industrial Applications Beyond Lubricants

Adhesives & Sealants: Low-MW PIB (500–1300) is a primary component in pressure-sensitive adhesives, hot-melt adhesives, and butyl sealants. The combination of tack, flexibility at low temperature, and gas impermeability makes it the default polymer for insulating glass unit (IGU) primary seals.

Chewing Gum Base: Food-grade PIB (MW 10,000–50,000) is approved as a gum base ingredient. It's the "chewy" part — inert, non-digestible, and maintains elasticity through chewing. This is a regulated application requiring separate production lines and certification.

Explosives: PIB serves as a binder in plastic explosives and emulsion explosives. It makes the explosive composition more insensitive to shock while improving moldability.

Cable Filling & Electrical: Medium-to-high MW PIB compounds fill underground communication cables, preventing water ingress while maintaining dielectric integrity. The polymer is hydrophobic, non-conductive, and doesn't migrate.

Fuel Additives: HR-PIB specifically — reacted through to polyisobutylene amine (PIBA) — is the main active in fourth-generation gasoline detergents. PIBA cleans intake valve deposits and keeps port fuel injectors flowing properly. This is a different product stream than lubricant-grade PIB but uses the same upstream polymerization technology.

Compatibility & Blending

PIB is fully compatible with:

• Base oils: Group I, II, III mineral oils; PAO; ester base stocks
• Detergents: Calcium/magnesium sulfonates, phenates, salicylates
• Dispersants: PIBSI (succinimide) ashless dispersants — the HR-PIB variant is the precursor to these
• Anti-wear agents: ZDDP, ashless phosphorus compounds
• Antioxidants: Phenolic, aminic, and ZDDP-derived
• Pour point depressants: PMA and styrene-ester types
• Other VMs: Blends with OCP or PMA are possible but require compatibility testing — PIB and OCP in concentrate form are not miscible without a compatibilizer

PIB does not contain sulfur, phosphorus, or metals. It won't interfere with aftertreatment compatibility in engines equipped with DPF, GPF, or SCR systems — the polymer burns clean.

Polyisobutylene vs. Olefin Copolymers (OCP) — Where PIB Still Wins

Here's something most formulator guides skip.

OCP displaced PIB in engine oils for two reasons: cost per unit of thickening and better low-temperature properties in the newest SAE 0W grades. Fair enough. But the displacement created a narrative that PIB is "obsolete." It isn't.

The load-carrying performance difference is documented but under-discussed. Under EHD conditions at 150°C and 10&sup6; s&supminus;1 shear — realistic for a hypoid gear mesh — PIB-thickened films maintain higher film thickness than OCP-thickened films of identical low-shear viscosity. The mechanism isn't fully nailed down in the literature, but the leading hypothesis is that the geminal dimethyl structure resists shear-induced alignment more stubbornly than the ethylene-propylene backbone. Less alignment = higher effective viscosity where it counts.

A customer we worked with switched a mining truck final drive oil from an OCP-thickened SAE 80W-90 to a PIB 1300-based formulation. Gear scoring complaints dropped to zero over a full maintenance cycle. The previous oil had been in grade by KV100 after 500 hours of service — but the HTHS viscosity had sheared down 18%. PIB held it to 9% loss over the same interval.

This doesn't mean PIB is always better. For a 0W-20 passenger car engine oil targeting ILSAC GF-7, PIB is the wrong choice — OCP or PMA provides better CCS and MRV performance at the required treat rate. But for an industrial gear oil that runs 8,000 hours between changes, or a two-stroke oil where carbon deposit control matters more than cold cranking numbers, PIB deserves serious consideration.

Synonyms & Regulatory Information

Documentation

• Download Technical Data Sheet (TDS)
• Download Material Safety Data Sheet (MSDS)
• Request Certificate of Analysis (COA) for Latest Batch

Frequently Asked Questions

1. Why is low molecular weight polyisobutylene important in lubricants?

Low MW PIB (600–2400) is the form used in lubricant applications because it's liquid at room temperature and soluble in mineral oil at practical concentrations. Higher MW grades (above 10,000) become rubber-like solids — useful for adhesives and gum base, not for oil blending.

The MW choice involves a trade-off. Higher MW within the 600–2400 range gives more thickening per unit weight — less polymer for the same viscosity target. But it also increases permanent shear loss. PIB 1300 is the standard compromise: adequate thickening, adequate shear stability for most gear oil and industrial applications. PIB 2400 gives more viscosity per unit but may shear down in high-sliding-speed applications like automotive hypoid gears.

2. What is the difference between standard PIB and HR-PIB?

HR-PIB (Highly Reactive Polyisobutylene) has >70% terminal vinylidene (alpha-olefin) end groups, compared to ~5–10% for standard PIB. This structural difference matters for downstream chemistry.

Standard PIB needs chlorine-promoted reaction with maleic anhydride to form PIBSA — the dispersant precursor. This leaves residual chlorides in the product. HR-PIB reacts with maleic anhydride via a clean thermal ene reaction: heat it to 200–230°C, no chlorine, no HCl byproduct, no chloride residues. The resulting PIBSA is chlorine-free, which matters for environmental compliance and for avoiding corrosion in the dispersant manufacturing process.

CheMost offers both types. HR-PIB 1000 is the dispersant-precursor grade. Standard PIB 680–3500 serves the thickener and tackifier markets.

3. Can polyisobutylene be used in engine oils today?

Yes, but selectively. PIB is not competitive in modern passenger car engine oils that target SAE 0W-20 or 5W-30 — OCP and PMA give better thickening efficiency, CCS performance, and HTHS behavior for those grades at lower cost.

PIB still works in: two-stroke engine oils (clean burn = less exhaust port carbon), classic/vintage car oils (period-correct chemistry, SAE 10W-30 or 10W-40), small engine oils (lawn equipment, generators), and stationary gas engine oils.

If the application requires API SP or ILSAC GF-7 certification, use OCP or PMA. If it requires a clean-burning thickener for a mineral-oil-based monograde or low-cross-grade oil, PIB is appropriate.

4. What are the storage and handling requirements?

Store in a dry, clean, well-ventilated warehouse. Keep containers sealed when not in use. Maximum blending temperature: 70°C. Long-term storage temperature should not exceed 50°C.

PIB is not classified as hazardous. It's non-toxic, non-corrosive, and chemically stable. When heating for blending, ensure proper ventilation — any polymer heated above 150°C can emit fumes that are irritating to eyes and respiratory tract. Standard PPE (gloves, safety glasses) is sufficient for normal handling.

Shelf life under recommended storage conditions: 48 months from manufacture date.

5. What packaging options are available?

Standard packaging: 180 kg net weight in steel drums, or 900 kg in IBC totes. Other packaging options available on request for larger-volume orders.

MOQ is one drum (180 kg) or one IBC (900 kg). Lead time is 7–15 days after order confirmation, depending on grade and order volume.

6. Is polyisobutylene toxic or environmentally harmful?

PIB is classified as non-hazardous by OSHA (1910.1200) and the European Economic Community. It's a high-molecular-weight saturated hydrocarbon polymer — not acutely toxic, not a skin sensitizer, not a carcinogen.

The environmental profile is favorable compared to alternatives. PIB doesn't contain sulfur, phosphorus, chlorine, or metals. It's not water-soluble and doesn't bioaccumulate. The polymer backbone is not biodegradable in the short term, but the material is chemically inert in the environment.

For food-contact applications (chewing gum base), food-grade PIB is manufactured under separate certification — do not use industrial-grade PIB for food-contact applications.

7. How does PIB compare to PMA as a viscosity modifier?

The short answer: PMA gives better VI lift. PIB costs less.

PMA's ester side chains create temperature-dependent solubility — the polymer coil expands with temperature, giving a strong VI-boosting effect. PIB's saturated hydrocarbon backbone interacts with base oil more uniformly across the temperature range, so the VI contribution is lower.

But PIB has better intrinsic load-carrying capacity and costs roughly 30–50% less per kilogram of active polymer. For an industrial gear oil where VI target is 95–100 (not 160), PIB does the job at lower formulation cost. For a high-VI hydraulic fluid or ATF, PMA is the right call.

8. What is polyisobutylene made from?

PIB starts with isobutylene — a four-carbon branched olefin recovered from refinery catalytic cracking and steam cracking operations. The isobutylene is separated from the mixed C₄ stream (which also contains butane, 1-butene, 2-butene, and butadiene), purified, and polymerized via cationic initiation.

The feedstock is petroleum-derived. There's currently no commercially viable bio-based route to isobutylene at scale, though several companies are working on fermentation pathways from sugars.

Last updated: May 6, 2026

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