The synthesis of carboxylated derivatives of poly(isobutylene-co-isoprene) (isobutylene-isoprene rubber, IIR) with substitution levels ranging from 1-4 mol% and different spacer lengths was accomplished by azide-alkyne Huisgen cycloaddition. Azido-functionalized IIR was first prepared by reacting brominated IIR to full conversion with sodium azide in a tetrahydrofuran/N,Ndimethylacetamide 90:10 mixture. The click reaction of the azido-functionalized IIR with acetylenic acids, using the copper(I) bromide/N,N,N′,N″,N″-pentamethyldiethylenetriamine catalyst system in tetrahydrofuran, gave the carboxylated IIRs. The products were characterized by 1 H NMR and FT-IR spectroscopy, and their molecular weight was determined by size exclusion chromatography analysis. The conversion to carboxylated groups reached up to 100%, as determined by NMR spectroscopy, but was highly dependent on the type of solvent and the amounts of catalyst and reactants used in the procedures.