Metal-Free Fast Azidation by Using Tetrabutylammonium Azide: Effective Synthesis of Alkyl Azides and Well-Defined Azido-End Polymethacrylates

An effective method to synthesize azido-end polymethacrylates from tetrabutylammonium azide (BNN₃) in a nonpolar solvent (toluene) was developed. Several low-mass alkyl halides were reacted with BNN₃ in toluene as model reactions and the rate constants of these reactions were determined, to confirm fast BNN₃ azidation for tertiary and secondary halides. The end-group transformation of halide-end polymethacrylates was effective and nearly quantitative. Notably, the combination of organocatalyzed living (or reversible deactivation) radical polymerization and BNN₃ azidation enabled the metal-free synthesis of azido-end polymethacrylates, including single-azido-end and multi-azido-end functional homopolymers and block copolymers. The rapid and quantitative reaction without the requirement for a large excess of BNN₃, metal-free and polar-solvent-free nature, and broad polymer scope are attractive features of this azidation.