Emulsion method
In this method, polymerization is done through free radicals, which is done in both hot and cold states. The product obtained by cold method in the presence of oil or in the presence of oil-soot has high linearity, narrow molecular distribution, high molecular mass and difficult processing. The product obtained by hot method is also highly branched and has a wide molecular mass distribution, good process ability and higher percentages of 1 and 2-vinyl.
Solution method
In this method is ion polymerization, the product of this method has high linearity, high flexibility and high abrasion and tear resistance against dynamic stresses.
Gel method
The product of this method has a weak percentage of chemical bonds during the polymerization reaction between the chains, which reduces the mobility of the chains and improves processability.
cooking methods
It is mainly done by sulfur vulcanization method. The cooking speed in the SBR is slower than the NR so the accelerator is used to increase the cooking speed.
Emulsion SBR (e-SBR)
It can be produced by free-radical emulsion polymerization of styrene and butadiene either at 50 to 60°C (hot emulsion SBR) or at about 5°C (cold emulsion SBR).
- The hot emulsion SBR process, which was developed first, leads to a more branched polymer than the cold emulsion process. SBR grades produced using this process have exception processing characteristics such as low mill shrinkage, good dimensional stability, and good extrusion characteristics.
- On the other hand, Cold SBR has a better abrasion resistance and, consequently, provides better tread wear and dynamic properties. It also exhibits superior mechanical properties such as tensile strength compared to grades produced by the hot emulsion polymerization route.
Key Features
- Green strength becomes low with increasing oil extension
- Low resilience and low tensile strength
- Outstanding resistance to abrasion
- Low resistance to oil, other hydrocarbon fluids and ozone
- Hot polymers are difficult to process with low green strength
- Poor tear strength
High styrene resins have good low-temperature properties but stiffen
Solution SBR (s-SBR)
Solution SBR is produced by termination-free*, anionic solution polymerization of styrene and butadiene with alkyl lithium initiator (e.g., butyllithium) in a hydrocarbon solvent, usually hexane or cyclohexane.
S-SBR grades have improved flexibility, performance, superior mechanical properties like tensile strength, low rolling resistance etc. especially when used in tires. Solution SBR has a narrower molecular weight distribution, higher molecular weight, and higher cis-1,4-polybutadiene content than emulsion polymerization SBR.
s-SBR rarely has more than 2% non-rubber materials in its finished form while e-SBR may have an emulsifier (soap) content of up to 5% and nonrubber materials sometimes in excess of 10%.
Key Features
- Good resilience and tensile strength
- Outstanding resistance to abrasion and fatigue
- Low resistance to oil, other hydrocarbon fluids and ozone
*It enables the synthesis of polymers with a very narrow molecular weight distribution and less chain branching.
