Solvent-Selective Reactions of Alkyl Iodide with Sodium Azide for Radical Generation and Azide Substitution and Their Application to One-Pot Synthesis of Chain-End-Functionalized Polymers.

Abstract

Herein, a new reaction of an alkyl iodide (R-I) with an azide anion (N3-) to reversibly generate the corresponding alkyl radical (R•) is reported. Via this new reaction, N3- was used as an efficient catalyst in living radical polymerization, yielding a well-defined polymer-iodide. A particularly interesting finding was the solvent selectivity of this reaction; namely, R-I and N3- generated R• in nonpolar solvents, while the substitution product R-N3 was generated in polar solvents. Exploiting this unique solvent selectivity, a one-pot synthesis of polymer-N3 was attained. N3- 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-N3 in one pot. This one-pot synthesis was further applied to obtain N3-chain-end-functionalized polymer brushes on the surface, uniquely controlling the N3 coverage (number density). Using the chain-end N3, 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 N3-, thiocyanate (-SCN) and cyanate (-OCN) anions were also studied.