Difference Between Buna-N and Buna-S
Buna-N and Buna-S are two of the most widely used synthetic elastomers (rubbers) in modern industrial chemistry. While both polymers leverage butadiene as a core foundational monomer unit, they are synthesized using entirely different secondary comonomers, fundamentally changing their chemical properties and end-use applications.
Comparison Matrix
| Property / Feature | Buna-N (Nitrile Rubber) | Buna-S (Styrene-Butadiene Rubber) |
|---|---|---|
| Monomers | 1,3-Butadiene and Acrylonitrile (CH₂=CH-CN) | 1,3-Butadiene and Styrene (C₆H₅CH=CH₂) |
| Structure |  |
 |
| Chemical Resistance | Excellent resistance to oils, petroleum products, fuels, and acids. | Poor oil resistance; swells heavily upon contact with hydrocarbons. |
| Mechanical Properties | Superior resistance to wear and abrasion, though less elastic overall. | High load-bearing capabilities, high elasticity, and structural strength. |
| Primary Drawback | Relatively poor flexibility at extremely low temperatures. | Oxidizes and degrades readily when exposed to ozone or UV radiation. |
| Common Uses | Oil seals, fuel hoses, aircraft gaskets, and disposable medical gloves. | Automobile vehicle tires, footwear soles, conveyor belts, and cable insulation. |
Synthesis of Buna-N
Buna-N is generated through the emulsion copolymerization of 1,3-butadiene and acrylonitrile in varying proportions. The 'N' explicitly designates the Nitrile functionality provided by the acrylonitrile unit. Increasing the ratio of acrylonitrile directly increases the rubber's structural resistance to volatile oils and solvents, but conversely makes the product less flexible at colder operating temperatures.
Synthesis of Buna-S
Buna-S is formed through the copolymerization of 1,3-butadiene with styrene (typically in a 3:1 ratio ratio). The 'S' represents Styrene. This material serves as a scalable, cost-efficient substitute for natural tree rubber due to its high vulcanization strength and robust structural endurance during mechanical rolling operations.
Related Topic Preparation, Properteis and Applications of Buna-N and Buna-S
Which comonomer gives Buna-N its characteristically high resistance to petroleum fuels and organic solvents?
A. Styrene
B. Acrylonitrile
C. Isoprene
D. Neoprene
Show Answer
Option B is the correct answer.
Acrylonitrile supplies the polar nitrile (-CN) group that actively repels nonpolar hydrocarbons, preventing the polymer matrix from swelling or degrading in contact with oils.
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