Question

In which of the following chain termination step is absent?

• A. Polymerisation of $ \text{C}_6\text{H}_5\text{CH}=\text{CH}_2 $ by RLi
• B. Polymerisation of $ \text{C}_6\text{H}_5\text{CH}=\text{CH}_2 $ by $ \text{BF}_3 $ and $ \text{H}_2\text{O} $
• C. Polymerisation of $ \text{C}_6\text{H}_5\text{CH}=\text{CH}_2 $ by $ \text{SO}_3 $ and $ \text{H}_2\text{O} $
• D. Polymerisation of $ \text{C}_6\text{H}_5\text{CH}=\text{CH}_2 $ by $ (\text{C}_6\text{H}_5\text{COO})_2 $

Hint:

Living polymerization (anionic) ideally proceeds without termination.

Answer 1

The Correct Option is A

In polymer chemistry, chain termination is a crucial step that ends the polymerization process. It is usually observed in radical polymerizations and ionic polymerizations involving cations or anions. Let's evaluate the given options to identify which lacks a chain termination step:

• Polymerisation of $\text{C}_6\text{H}_5\text{CH}=\text{CH}_2$ by RLi: This involves anionic polymerization. In anionic polymerizations, particularly when initiated by organolithium compounds like RLi, there is typically no chain termination step because the process can propagate indefinitely. Hence, there is no natural terminator in such reactions unless an intentional quenching agent is added.
• Polymerisation of $\text{C}_6\text{H}_5\text{CH}=\text{CH}_2$ by $\text{BF}_3$ and $\text{H}_2\text{O}$: This is an example of cationic polymerization initiated by Lewis acids. Chain termination may occur due to the formation of inactive species or transfer reactions.
• Polymerisation of $\text{C}_6\text{H}_5\text{CH}=\text{CH}_2$ by $\text{SO}_3$ and $\text{H}_2\text{O}$: This involves strong electrophiles, and termination can occur by various means, including transfer reactions.
• Polymerisation of $\text{C}_6\text{H}_5\text{CH}=\text{CH}_2$ by $(\text{C}_6\text{H}_5\text{COO})_2$: This is radical polymerization typically initiated by peroxide initiators. Chain termination is an inherent part of radical polymerization through radical coupling or disproportionation.

Conclusively, the polymerization of $\text{C}_6\text{H}_5\text{CH}=\text{CH}_2$ by RLi lacks a chain termination step naturally, hence it is the correct choice where chain termination is absent.