Herein, a new reaction of an alkyl iodide (R-I) with an azide anion (N-3(-)) to reversibly generate the corresponding alkyl radical (R center dot) is reported. Via this new reaction, N-3(-) was used as an efficient catalyst in living radical polymerization, yielding a welldefined polymer iodide. A particularly interesting finding was the solvent selectivity of this reaction; namely, R I and N-3(-) generated R center dot in nonpolar solvents, while the substitution product R N-3 was generated in polar solvents. Exploiting this unique solvent selectivity, a one-pot synthesis of polymer N-3 was attained. N-3(-) was first used as a catalyst for living radical polymerization in a nonpolar solvent to produce a polymer iodide and was subsequently used as a substitution agent in a polar solvent by simply adding the polar solvent, thereby transforming the polymer iodide to polymer N-3 in one pot. This one-pot synthesis was further applied to obtain N-3-chain-end-functionalized polymer brushes on the surface, uniquely controlling the N-3 coverage (number density). Using the chain-end N-3, the obtained linear and brush polymers were connected to functional molecules via an azide alkyne click reaction. The attractive features of this system include facile operation, access to unique polymer designs, and no requirement for using excess NaN3. In addition to N-3, thiocyanate (-SCN) and cyariate (-OCN) anions were also studied.