The intermediate never formed during chain growth polymerization is

Options

A. `-overset("| ")underset("| ")(C^(-))`
B. `-overset("| ")underset("| ")(C^(o+))`
C.
D. `-overset("| ")underset("| ")(C^(.))`

Answer

To solve the question regarding which intermediate is never formed during chain growth polymerization, we will analyze the types of intermediates involved in this process.

### Step-by-Step Solution:

1. **Understanding Chain Growth Polymerization**:
- Chain growth polymerization involves the sequential addition of monomer units to a growing polymer chain. This process can occur through various mechanisms: free radical, cationic, or anionic polymerization.

2. **Identifying Intermediates**:
- In chain growth polymerization, the common intermediates formed are:
- **Carbocations**: Formed in cationic polymerization when a positively charged carbon atom is generated.
- **Carbanions**: Formed in anionic polymerization when a negatively charged carbon atom is generated.
- **Free Radicals**: Formed in free radical polymerization, which are highly reactive species with unpaired electrons.

3. **Examining the Options**:
- The question presents several intermediates, and we need to determine which one is not formed during any of the chain growth polymerization mechanisms.
- **Carbocation**: Can be formed during cationic polymerization.
- **Carbanion**: Can be formed during anionic polymerization.
- **Free Radical**: Can be formed during free radical polymerization.
- **Carbene**: A carbene is a neutral species containing a carbon atom with only six valence electrons (R2C:), which is not typically involved in chain growth polymerization.

4. **Conclusion**:
- Among the intermediates listed, **carbene** is the one that is never formed during chain growth polymerization. Therefore, the answer to the question is option 3: **Carbene**.

### Final Answer:
The intermediate that is never formed during chain growth polymerization is **Carbene**.

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