R is one of the monomers for the formation of a polymer called 

$$\begin{gathered} {\mathrm{CH}}_3-{\mathrm{C}}_6{\mathrm{H}}_4-{\mathrm{NO}}_2\underset{\left(\mathrm{ii}\right) {\mathrm{H}}^{+}}{\overset{\left(\mathrm{i}\right) {\mathrm{KMnO}}_4/{\mathrm{OH}}^{-}}{\to }}\underset{\mathrm{P}}{\mathrm{COOH}-{\mathrm{C}}_6{\mathrm{H}}_4-{\mathrm{NO}}_2}\underset{\left(\mathrm{ii}\right) {\mathrm{NaNO}}_2/\mathrm{HCl}, 0°\mathrm{C}}{\overset{\left(\mathrm{i}\right) \mathrm{Zn}/\mathrm{HCl}}{\to \underset{\mathrm{Q}}{\mathrm{COOH}-{\mathrm{C}}_6{\mathrm{H}}_4-{\mathrm{N}}_2^{+}{\mathrm{Cl}}^{-}}}} \\ \underset{\mathrm{Q}}{\mathrm{COOH}-{\mathrm{C}}_6{\mathrm{H}}_4-{\mathrm{N}}_2^{+}{\mathrm{Cl}}^{-}}\underset{\left(\mathrm{ii}\right) {\mathrm{H}}^{+}/{\mathrm{H}}_2\mathrm{O}}{\overset{\left(\mathrm{i}\right) \mathrm{CuCN}}{\to }}\underset{\mathrm{R}}{\mathrm{COOH}-{\mathrm{C}}_6{\mathrm{H}}_4-\mathrm{COOH}} \end{gathered}$$

Formation of terylene or dacron by the interaction of ethylene glycol and terephthalic acid, and Product R formed in the above reaction is terephthalic acid.