`SBR(GRS,Buna-S,Cold Rubber)is obtained by free radical intiator.The most commenly used free radical initiator is:

Options

A. Buta`-1,3-` dinene `(70%)` and `30%` phenyl ethene (styrene)
B. Chloroprene and styrene
C. Vinyl acetylene and styrene
D. Isoprene and `1,3-` butadiene

Answer

To solve the question regarding the most commonly used free radical initiator for the production of SBR (Styrene-Butadiene Rubber), we can follow these steps:

### Step-by-Step Solution:

1. **Understanding SBR**:
- SBR stands for Styrene-Butadiene Rubber, which is a copolymer made from the polymerization of styrene and butadiene.
- The chemical formula for butadiene is C4H6 (1,3-butadiene) and for styrene is C8H8.

2. **Identifying the Process**:
- SBR is synthesized through a process called copolymerization, which involves the reaction of two different monomers (styrene and butadiene) to form a polymer.

3. **Role of Free Radical Initiators**:
- Free radical initiators are substances that help in initiating the polymerization process by generating free radicals. These free radicals react with the monomers to start the chain reaction that leads to polymer formation.

4. **Common Free Radical Initiators**:
- The question asks for the most commonly used free radical initiator. Among the options typically used in polymer chemistry, benzoyl peroxide is a well-known free radical initiator.

5. **Analyzing the Given Options**:
- The options provided in the question include various combinations of monomers and initiators.
- The correct answer should indicate a combination that is commonly used in the production of SBR.

6. **Selecting the Correct Option**:
- Based on the analysis, the first option, which mentions "buta-1,3-diene 70% and 30% phenyl ethene (styrene)," is the correct choice as it represents the correct monomer composition for SBR.

### Final Answer:
The most commonly used free radical initiator for the production of SBR (Buna-S) is **buta-1,3-diene 70% and 30% phenyl ethene (styrene)**.

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