An azido-containing monomer, a polymer containing monomeric units derived from the azido-containing monomer, and various articles containing a substrate and a coating layer of the polymer positioned on the substrate are provided. The azido groups, which are pendant groups of the polymer, can undergo a click chemistry reaction with an unsaturated compound such as those having a terminal —C≡CH group, a dibenzocyclooctyne-containing group, an unsaturated bicyclic olefinic group, or an amido group. The click chemistry reaction can be used to covalently attach a fluorescent or bioactive compound to the polymer.