Polymerisation of acrylonitrile will best take place by

Options

A. Cationic polymerisation
B. Anionic polymerisation
C. Free radical polymerisation
D. All of these

Answer

### Step-by-Step Solution:

1. **Understanding Acrylonitrile Structure**:
- Acrylonitrile has the chemical structure CH2=CH-CN. It contains a double bond between the first two carbon atoms and a cyano group (CN) attached to the last carbon.

2. **Identifying the Nature of the Cyano Group**:
- The cyano group (CN) is an electron-withdrawing group. This means it pulls electron density away from the double bond in acrylonitrile, making the adjacent carbon atom (the one with the double bond) electron-deficient.

3. **Formation of a Positive Charge**:
- Due to the electron-withdrawing effect of the CN group, the double bond can shift, creating a positive charge on the CH2 carbon atom. This charge makes it susceptible to nucleophilic attack.

4. **Choosing the Type of Polymerization**:
- Given that the CH2 carbon is electron-deficient, it can be attacked by an anion (a negatively charged species). Thus, the polymerization of acrylonitrile will best take place through anionic polymerization.

5. **Initiation Step**:
- In the initiation step, a strong base like NaNH2 can attack the CH2 carbon, leading to the formation of a reactive anion. This results in the formation of NH2-CH2-CH-CN.

6. **Propagation Step**:
- In the propagation step, another acrylonitrile molecule can react with the anion formed in the initiation step. The double bond shifts, allowing the new acrylonitrile molecule to bond, creating a longer chain of repeating units.

7. **Termination Step**:
- The polymerization process continues until a termination step occurs, where an H+ ion can react with the anion, stopping the polymerization process and resulting in the final polymer structure.

8. **Conclusion**:
- The polymerization of acrylonitrile occurs via anionic polymerization due to the electron-withdrawing nature of the cyano group, which facilitates the formation of a reactive anion that can initiate and propagate the polymer chain.

### Final Answer:
The polymerization of acrylonitrile will best take place by **anionic polymerization**.

---