Preparation of Buna-S
-Also known as styrene-butadiene
–Buna-S name is derived from Bu-butadiene and Na-sodium/ natrium and S-styrene
-It is a replacement for natural rubber.
-It is derived from two monomers, styrene and butadiene. The mixture of these two monomers is polymerized by two basically different processes: from solution (S-SBR) or as an emulsion (E-SBR).
-It has good abrasion resistance and good aging stability when protected by additives.
-The styrene/butadiene ratio influences the properties of the polymer: with high styrene content, the rubbers are harder and less rubbery.
-It is the most commonly used synthetic rubber.
-It is a random co-polymer formed by the emulsion polymerization of a mixture of 1:3 butadiene and styrene in the presence of peroxide catalyst at 5 degree Celsius and therefore the product is called as cold rubber. The rubber obtained is also called Styrene butadiene rubber (SBR).
-It is vulcanized with sulfur. The rubber is slightly inferior to natural rubber in its physical properties.
1) It is used for the manufacture of passenger car tyres and treads, motor cycle and scooter tyres, cycle tyres and tubes.
2) They are also used for the manufacture of conveyor belts, foot-wares, shoe soles, hoses and electrical insulation.
-Polymerization of deines (molecules containing double bond) to form substitutes for rubber is the forerunner of the enormous present day plastic industry.
-Chloroprene was the first commercially successful rubber substitute produced in the United States.
-Chloroprene undergoing trans-polymerization to produce Synthetic Rubber, Polychloroprene
-The properties of Rubber so formed are determined by the nature of the substitutent groups. For example, Polychloroprene is inferior to natural rubber in some properties but superior in its resistance to oil, Organic Solvents. These differences are due to difference in nature of their monomers: Isoprene (for natural rubber) and Chloroprene (for synthetic rubber).
-Synthetic Rubber (also known as Gutta-Percha) was obtained by the free radical polymerization of Isoprene. The rubber so formed has all trans- Configuration. As a result of this, synthetic rubber has a highly regular zig-zag chain which cannot be stretched .This accounts for non-elasticity of Synthetic Rubber.
IMPORTANT QUESTION AND ANSWERS:
1) What is the IUPAC name of buna-S ?
2) What is the reason of non-elasticity of synthetic rubbers?
ANS) Synthetic Rubber is obtained by the free radical polymerization of Isoprene. The rubber so formed has all trans- Configuration. As a result of this, synthetic rubber has a highly regular Zigzag chain which cannot be stretched .This accounts for non-elasticity of Synthetic Rubber.
3) Which was the first rubber substitute?
ANS) Chloroprene was the first rubber substitute.
4) What is vulcanization?
ANS) Vulcanization is the process of introduction of Sulphur bridges between different chains by heating raw rubber with Sulphur at 373-415K. In the absence of catalyst the process of vulcanization is slow. Some additive such as Zinc Oxide is added to accelerate the rate of Vulcanization.
5) In what ways are vulcanized rubber different from natural rubbers?
ANS) Vulcanized rubber has
- excellent elasticity.
- Low water absorption tendency
- It is resistant to the action of organic solvents
- It is resistant to attack of oxidizing agents, which is opposite of natural rubber.