Question

Arrange the following monomers in order of decreasing ability to undergo cationic polymerisation.
I. $C{H_2} = CH - {C_6}{H_{4}}(N{O_{2}})$
II. ${\mathbf{C}}{{\mathbf{H}}_{\mathbf{2}}} = {\mathbf{CH}} - {{\mathbf{C}}_{\mathbf{6}}}{{\mathbf{H}}_{\mathbf{4}}}({\mathbf{C}}{{\mathbf{H}}_{\mathbf{3}}})$
III. ${\mathbf{C}}{{\mathbf{H}}_{\mathbf{2}}} = {\mathbf{CH}} - {{\mathbf{C}}_{\mathbf{6}}}{{\mathbf{H}}_{\mathbf{4}}}({\mathbf{OC}}{{\mathbf{H}}_{\mathbf{3}}})$
A.${\text{I > II > III}}$
B.${\text{II > I > III}}$
C.${\text{III > II > I}}$
D.${\text{I > III > II}}$

Answer 1

To answer this question, you should recall the concept of cationic polymerization. Cationic polymerizations are initiated by electrophilic agents such as the halo hydric acids. You know that Lewis acids are defined as electron acceptors and have the ability to generate carbonium ions and can also initiate polymerization.

Complete Step by step solution:
We know that monomer activation for cationic polymerization takes place by the help of electron releasing groups as such as $- C{H_3}, - OC{H_3}$ showing ${\text{ + I}}$ effect as it stabilizes the carbocation formed.
On the other hand, $- N{O_2}$ ​ is an electron-withdrawing group. So, it reduces the stability of carbocation formed. Thus, the correct order should be:
${\mathbf{C}}{{\mathbf{H}}_{\mathbf{2}}} = {\mathbf{CH}} - {{\mathbf{C}}_{\mathbf{6}}}{{\mathbf{H}}_{\mathbf{4}}}({\mathbf{OC}}{{\mathbf{H}}_{\mathbf{3}}})$> ${\mathbf{C}}{{\mathbf{H}}_{\mathbf{2}}} = {\mathbf{CH}} - {{\mathbf{C}}_{\mathbf{6}}}{{\mathbf{H}}_{\mathbf{4}}}({\mathbf{C}}{{\mathbf{H}}_{\mathbf{3}}})$> $C{H_2} = CH - {C_6}{H_{4}}(N{O_{2}})$ which is ${\text{III > II > I}}$
Hence, we can conclude that the correct answer to this question is option C.

Note: You should know that Lewis acid require a co-initiator such as ${{\text{H}}_{\text{2}}}{\text{O}}$ or an organic halogen compound. This process occurs fast in presence of either a proton donor such as water, alcohol, and organic acids or a cation donor such as t-butyl chloride or triphenylmethyl fluoride. Actually, the proton donor or cation donor is referred to as the initiator while the Lewis acid is the co-initiator, since it is the donors which ultimately supply the proton or cation which adds to the monomer that initiates polymerization. Another important point to know is that within the cationic system is that the overall rate of polymerization and its relationship to temperature. Cationic polymerizations are normally conducted at low temperatures, and tend to go explosively fast in some cases. In most reactions, it is common for the rate of the reaction to increase with an increase in temperature.