Question

The species which can best serve as an initiator for the cationic polymerization is:
A. \[LiAl{H_4}\]
B. \[HN{O_3}\]
C. \[AlC{l_3}\]
D. BaLi

Answer 1

Hint: Initiator in a chemical reaction can be understood as the chemical species that can react with the monomer to form an intermediate compound. This intermediate compound is capable of linking itself with many other similar monomeric molecules, thus resulting in the formation of a polymer. To put this in simpler terms, an initiator is basically that compound that reacts with the monomer to make it capable of forming polymeric molecules.

Complete step by step answer:
Before we move forward with the solution of the given question, let us first understand some important basic concepts.
Cationic polymerization can be understood as the chain growth polymerization in which the contributing monomer is made reactive with the help of a cationic initiator. To put it in simpler terms, cationic polymerization can be explained as an ionic polymerization reaction in which the kinetic chain carriers are cations.
Now that we have seen that for a cationic polymerization reaction, we would be requiring a cationic initiator, we can look through the options to find a cationic initiator or basically a Lewis acid. Lewis acids are chemical species that are electrophilic in nature, i.e. they accept lone pairs of electrons.
The molecular structures of the given compounds can be given as:
 \[LiAl{H_4}\]

 \[HN{O_3}\]

 \[AlC{l_3}\]

We can observe that Aluminium trichloride is the only Lewis acid in the given set of compounds.
Hence, the species which can best serve as an initiator for the cationic polymerization is \[AlC{l_3}\]

Hence, Option C is the correct option.

Note:
Initiators trigger chemical reactions. They are not true catalysts, as they become an integral part of the product; because of this they are instead considered to be co-reactants.