Polybutadiene Rubber (BR)
A glass transition of minus 107 degrees, the lowest of any common rubber, and abrasion resistance nothing else matches. It is also nearly unusable on its own, which is why you will never find a tyre made of it.
Molecular Structure
What is Polybutadiene Rubber (BR)?
Polybutadiene is butadiene polymerised through its 1 and 4 positions, leaving one double bond in the backbone for every four carbons. What matters commercially is the geometry of those double bonds. High-cis grades hold more than 96% of them in the cis configuration, and each cis unit puts a kink in the chain that prevents crystallisation and leaves the polymer extraordinarily mobile.
The result is a glass transition around −107 °C, lower than any other common rubber, and with it exceptional resilience, rebound and abrasion resistance. Neodymium catalysis gives the highest cis content and the most linear chains; cobalt gives a branched polymer that processes more easily; lithium initiation gives medium-cis or high-vinyl grades for different purposes.
The catch is that polybutadiene is difficult on its own. Wet grip is poor, tear strength is low, tack is minimal and green strength is inadequate for tyre building. It is therefore almost always a blend component — added to natural rubber and SBR to lift abrasion and fatigue performance without giving up the properties those polymers bring.
The second-largest use of polybutadiene has nothing to do with rubber goods. It is the rubber phase in high impact polystyrene and ABS, where dispersed BR particles arrest propagating cracks. Impact-modifier grades are specified on solution viscosity and cis content for that role, not on Mooney alone.
Quick Reference
Key Physical & Chemical Properties
Structure & Bonding
One double bond for every four backbone carbons, held in the cis configuration. Each cis unit kinks the chain, which prevents crystallisation and leaves the molecule free to coil and uncoil — the direct source of polybutadiene's very low glass transition and its resilience.
Chain segment — cis-1,4 units kinking the backbone
Structural Identity
- PolymerPolybutadiene rubber
- Repeat unit(C₄H₆)ₙ — butadiene
- Repeat unit mass54.09 g/mol
- Microstructurecis-1,4 above 96% in high-cis grades
- Effect of cisKinked chain, no crystallisation
- Glass transition≈ −107 °C — lowest common rubber
- Nd catalysedHighest cis, linear, best abrasion
- Co catalysedBranched, easier processing
- Li catalysedMedium cis or high vinyl
- CAS Number9003-17-2
- Specified byMooney, cis content, catalyst
Product Specifications
Chelora supplies Polybutadiene Rubber (BR) in standard and custom grades. Contact us for specification sheets tailored to your process.
| Polymer | Polybutadiene rubber |
|---|---|
| CAS Number | 9003-17-2 |
| Repeat unit | (C₄H₆)ₙ |
| cis-1,4 content | > 96% high-cis; 35 – 40% for lithium grades |
| Trans-1,4 content | ≤ 3% for high-cis grades |
| Vinyl (1,2) content | ≤ 2% high-cis; up to 70% for high-vinyl grades |
| Mooney viscosity ML(1+4) 100 °C | 35 – 55, grade dependent |
| Mooney relaxation | Reported — indicates degree of branching |
| Volatile matter (max) | ≤ 0.75 wt% |
| Ash (max) | ≤ 0.30 wt% |
| Gel content | Nil to trace |
| Antioxidant type | Staining or non-staining — specify |
| Solution viscosity (impact modifier grades) | Reported in styrene at declared concentration |
| Glass transition | ≈ −107 °C |
| Raw polymer density | 0.91 g/cm³ |
| Supply form | 35 kg bales, polyethylene film wrapped |
| Packaging | Palletised or crated bales, 1000 – 1200 kg |
| Transport classification | Not regulated as dangerous goods |
Downstream Applications & Derivatives
Key derivative chains and industrial uses of Polybutadiene Rubber (BR).
Tyre Tread & Sidewall
The largest outlet, always as a blend component with natural rubber and SBR. BR contributes abrasion resistance and fatigue life, which is what determines tread wear rating.
HIPS Impact Modifier
Dissolved in styrene before polymerisation, ending up as grafted rubber particles that give high impact polystyrene its toughness.
ABS Rubber Phase
The same role in ABS, where the grafted polybutadiene particles provide impact strength and, at the surface, the etchable phase that makes ABS electroplatable.
Golf Ball Cores
High-cis BR is the standard core material — the highest rebound resilience available in a solid elastomer, which translates directly into ball speed.
Conveyor Belt & Industrial
Belt covers, roll covers and industrial mouldings where abrasion is the wear mechanism, generally blended with natural rubber for tear strength.
Footwear Soling
Blended into sole compounds for abrasion resistance and low-temperature flexibility, particularly in cold-climate and performance footwear.
Why source Polybutadiene Rubber (BR) through Chelora Petrochem?
Verified Origin
Full origin certification and asset-backed supply chain documentation — no grey-market supply or unlabelled reclaim.
Grade Flexibility
Neodymium, cobalt and lithium catalysed grades supplied, plus impact modifier grades for HIPS and ABS. We match on cis content and catalyst system as well as Mooney.
Full Documentation
CoA covering Mooney, microstructure, volatiles and ash, SDS, REACH compliance, and solution viscosity data for impact modifier grades.
Logistics Support
Experienced in bale rubber logistics — palletised and crated bales with film wrapping, containerised delivery with attention to stack height and temperature, for Indian and international delivery.
Storage & Handling Guidelines
Always refer to the full SDS before handling. The following is a summary of key requirements.
- Store cool, dry and out of direct sunlight. Polybutadiene is more prone to cold flow than most bale rubbers because of its very low glass transition, and warm storage makes it markedly worse.
- Limit stack height strictly and keep storage time short. BR bales slump and knit under their own weight faster than SBR, and a tall pallet left through a warm season becomes a single block.
- Keep bales away from electric motors, welding equipment and other ozone sources. The backbone double bonds are readily attacked and surface cracking develops on stored stock.
- Rotate stock and record production dates. Gel formation over long storage is a real quality risk on high-cis grades and shows up as poor dispersion in the mixer.
- Specify antioxidant type up front. Staining grades discolour light-coloured goods and cannot be corrected once mixed.
- Segregate impact modifier grades from tyre grades. They are made to different microstructure and solution viscosity targets and are not interchangeable, despite looking identical as bales.
- Expect difficult mixing behaviour. BR has poor tack and green strength, and high-cis linear grades in particular incorporate filler slowly — mixing procedures developed for SBR usually need adjusting.
- Keep bales off concrete floors and away from external walls to avoid moisture pickup, which causes porosity in the cured article.
- Provide extraction at mixing and curing, and control the compounding ingredients rather than the polymer, which is where the occupational exposure actually sits.
Hazard Summary
Classification: polybutadiene rubber in bale form is not classified as hazardous under CLP. The polymer is inert. Occupational risk in rubber processing arises from compounding ingredients and process fume rather than from the elastomer.
Ozone attack in storage: polybutadiene has a backbone double bond every four carbons, which makes it among the more ozone-sensitive bale rubbers. Storage near electric motors, welding sets or any ozone generator produces surface cracking on the bale. Separation and ventilation are the controls.
Cold flow: with a glass transition near −107 °C, polybutadiene is far above its Tg at any storage temperature and flows under sustained load more readily than other bale rubbers. Overstacking causes bales to fuse, which is a productivity and manual handling problem.
Gel formation: long or warm storage can produce microgel that will not disperse in the mixer and shows as hard specks and poor filler distribution in the finished compound. Stock rotation is the practical control.
Compounding ingredients carry the hazard: carbon black, oils, accelerators and antidegradants each have their own classification. Assess the compound rather than the polymer, and note that some accelerator classes have been associated with nitrosamine formation during vulcanisation.
Vulcanisation fume: mixing and curing release oil volatiles and accelerator decomposition products. Rubber process fume is a recognised occupational exposure and local extraction at mixers, mills and presses is expected.
Fire: rubber burns readily once ignited with dense black smoke, high heat release and carbon monoxide. Bale stores are difficult to extinguish and warrant specific fire design and separation.
PPE minimum: gloves and safety footwear for bale handling; eye protection, gloves and respiratory protection appropriate to the compound at the mixer and mill.
Consult the full SDS for the polymer and, more importantly, the SDS for every compounding ingredient before mixing.
Frequently Asked Questions
Technical and commercial questions about Polybutadiene Rubber (BR) sourcing and specifications.
What is polybutadiene used for?
Around two-thirds goes into tyres, always as a blend component with natural rubber and SBR rather than on its own, contributing abrasion resistance and fatigue life. The next largest use is as the rubber phase in high impact polystyrene and ABS, where it is dissolved in the monomer before polymerisation. Beyond those, BR goes into golf ball cores for rebound resilience, and into conveyor belt covers, industrial mouldings and footwear soling where abrasion is the wear mechanism.
Why is cis content the key specification?
Because it determines whether the chain can crystallise. Each cis-1,4 unit puts a kink in the backbone, and a chain full of kinks cannot pack into an ordered structure, so it stays amorphous and mobile down to very low temperature. That gives polybutadiene its glass transition of around −107 °C — the lowest of any common rubber — and with it the resilience, rebound and abrasion resistance that are the reasons to use it. Trans units, by contrast, allow crystallisation and stiffen the polymer, so trans content is kept low. High-cis grades hold above 96%, and the small differences between 96% and 98% are commercially meaningful in tread compounds.
Why is BR always blended rather than used alone?
Because its weaknesses are as pronounced as its strengths. Wet grip is poor, since the very low glass transition means little energy dissipation at the frequencies that generate traction on wet roads. Tear strength is low, tack is minimal, and green strength is inadequate for a tyre to be built without falling apart before curing. Blending it into natural rubber and SBR compounds contributes abrasion resistance and fatigue life while those polymers supply the grip, tear strength and building tack. A tread compound might be 20 to 40% BR; it will never be 100%.
What is the difference between neodymium, cobalt and lithium catalysed BR?
Neodymium gives the highest cis content, around 98%, with linear chains and a narrow molecular weight distribution — the best abrasion resistance and fatigue life, which is why it commands a premium in tyre treads. Cobalt gives high cis with significant branching, which processes more easily and disperses filler faster at some cost in ultimate properties. Nickel sits between them. Lithium initiation is anionic rather than coordination polymerisation and produces medium-cis polymer around 35 to 40%, or high-vinyl grades where the 1,2 addition can be pushed above 50% for specialised tread applications. Impact modifier grades for HIPS and ABS are usually lithium catalysed, because chain end control and solution viscosity matter more there than cis content.
What is BR's role in HIPS and ABS?
It is the toughening phase. Polybutadiene is dissolved in styrene — or in styrene and acrylonitrile for ABS — before polymerisation begins. As the styrene polymerises, the two phases separate and the polybutadiene ends up as discrete particles dispersed through the glassy matrix, chemically grafted to it at the interface. When the finished material is struck, stress concentrates at those rubber particles and the matrix crazes in many small locations rather than forming one propagating crack, which absorbs a great deal of energy. In ABS the same particles serve a second purpose: chromic acid etching dissolves them at the surface, leaving the microscopic cavities that electroplating keys into.
What documentation does Chelora provide?
Every shipment includes a Certificate of Analysis covering Mooney viscosity with test conditions stated, cis, trans and vinyl microstructure, Mooney relaxation, volatile matter, ash and gel content, plus solution viscosity for impact modifier grades; a Safety Data Sheet to GHS and REACH format; REACH polymer compliance confirmation; antioxidant type declaration; an origin certificate; and destination-market certificates where required.
Request a quote or specification sheet
Talk to Chelora's sourcing team about Polybutadiene Rubber (BR) grade, volume, logistics, documentation, and lead times. We respond within one business day.
