Which of the following are not used as chain transfer agents ?

Options

A. `C Cl_(4)`
B. `C Br_(4)`
C. Benzoquinone
D. Benzoyl peroxide

Explanation

To determine which of the given options are not used as chain transfer agents, we will analyze each option based on their chemical properties and typical applications in polymer chemistry.

### Step 1: Understand Chain Transfer Agents
Chain transfer agents are substances that can terminate the growth of a polymer chain and create new active sites for polymerization. They typically contain at least one weak chemical bond that can break during the reaction, allowing for the transfer of the growing polymer chain.

### Step 2: Analyze Each Option
1. **C-Cl4 (Carbon Tetrachloride)**:
- Carbon tetrachloride is a halocarbon and is known to be used as a chain transfer agent due to the presence of weak C-Cl bonds.
- **Conclusion**: C-Cl4 can be used as a chain transfer agent.

2. **CBR (Carbon Tetrabromide)**:
- Similar to C-Cl4, carbon tetrabromide is also a halocarbon with weak C-Br bonds. It is commonly used as a chain transfer agent in polymerization processes.
- **Conclusion**: CBR can be used as a chain transfer agent.

3. **Benzoquinone**:
- Benzoquinone does not have weak bonds suitable for chain transfer. It is primarily used as an oxidizing agent and does not function as a chain transfer agent.
- **Conclusion**: Benzoquinone cannot be used as a chain transfer agent.

4. **Benzoil Peroxide**:
- Benzoil peroxide is primarily used as an initiator in free radical polymerization rather than as a chain transfer agent. It decomposes to generate free radicals but does not facilitate chain transfer.
- **Conclusion**: Benzoil peroxide cannot be used as a chain transfer agent.

### Step 3: Final Answer
Based on the analysis, the substances that are **not used as chain transfer agents** are:
- Benzoquinone
- Benzoil peroxide

Thus, the correct answer is options 3 and 4.

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