Question

The structure of Buna-S polymer is

• A. \(\left[-CH_2-CH=CH-CH_2-CH(C_6H_5)-CH_2-\right]_n\)
• B. \(\left[-CH_2-CH=CH-CH_2-CH(CN)-CH_2-\right]_n\)
• C. \(\left[-CH_2-C(Cl)=CH-CH_2-\right]_n\)
• D. \(\left[-NH-CO-NH-CH_2-\right]_n\)

Hint:

Buna-S is made from butadiene and styrene; therefore, its structure contains a phenyl group \((C_6H_5)\).

Answer 1

The Correct Option is A

Step 1: Understanding the Question:
The question asks to identify the chemical structure of Buna-S, which is a common synthetic rubber.
"Buna-S" is a copolymer, meaning it is made from two different types of monomers.
Step 2: Detailed Explanation:

Monomers of Buna-S:
The name is derived from its components:
- Bu stands for \(1,3\)-Butadiene (\(CH_2=CH-CH=CH_2\)).
- Na represents Sodium (\(Na\)), which was originally used as the catalyst for polymerization.
- S stands for Styrene (Vinylbenzene, \(C_6H_5-CH=CH_2\)).

Polymerization Reaction:
Buna-S is formed by the copolymerization of \(1,3\)-butadiene and styrene in the presence of an initiator or catalyst.
In the polymer chain, the butadiene units undergo addition at the \(1\) and \(4\) positions, resulting in a double bond in the middle of the unit.

The Resulting Structure:
The repeating unit consists of a butadiene fragment \((-CH_2-CH=CH-CH_2-)\) and a styrene fragment \((-CH(C_6H_5)-CH_2-)\) connected together.
Option (A) shows the correct repeating unit:
\([ -CH_2 - CH = CH - CH_2 - CH(C_6H_5) - CH_2 - ]_n\)

Comparison with other options:
- Option (B) typically shows Buna-N, where Styrene is replaced by Acrylonitrile (\(-CN\) group).
- Option (C) usually depicts Neoprene (Polychloroprene), characterized by a chlorine atom on the chain.
- Option (D) shows a different polymer like Urea-formaldehyde or a simple addition polymer.

Step 3: Final Answer:
The structure of Buna-S is represented by the copolymer unit of \(1,3\)-butadiene and styrene as shown in option (A).