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How is styrene-butadiene rubber made?
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Truck tires being removed from their molds.
Styrene-butadiene rubber (SBR) is a synthetic rubber produced by copolymerizing styrene and butadiene, typically in a ratio of 25 percent styrene to 75 percent butadiene.12
The production process generally utilizes one of two methods:
- Emulsion Polymerization: This is the most common method. The monomers are emulsified in water using a soap-like surfactant. A water-soluble free-radical catalyst is added to initiate the reaction. This process can be conducted "hot" (at 50 °C) or "cold" (at 5 °C), with the latter producing more linear, higher molecular weight polymers that improve tire performance.13
- Solution Polymerization: The monomers are dissolved in a hydrocarbon solvent and polymerized using an organometallic catalyst, such as butyllithium. This method allows for more precise control over the placement of monomer units and the structure of the polymer chain.3
Following polymerization, the resulting polymer chains are cross-linked through vulcanization to provide the material with its final elastic properties.14