Chapter 26, Problem 26.51P

Interpretation Introduction

Interpretation:

When treated with acid, $\text{aziridine}$ will undergo ring-opening polymerization to produce branched $\text{polyethylenimine}$. The mechanism that shows how a tetramer can be produced is to be drawn in which three monomers form a chain and the fourth forms a branch.

Concept introduction:

Acid promotes a cationic polymerization. The basic $\text{N}$ of the $\text{aziridine}$ is protonated first, then the nucleophilic $\text{N}$ of another aziridine attacks the $\text{C}$ atom of a positively charged ring in an ${\text{S}}_{\text{N}}\text{2}$ step to open the ring. In a growing chain, branching can occur when a nucleophilic $\text{N}$ in the middle of the chain attacks a protonated $\text{aziridine}$ ring. The mechanism shows how a tetramer is produced in which three monomers form a chain and the fourth forms a branch.