Highly efficient "click" functionalization of poly(3-azidopropyl methacrylate) prepared by ATRP

To prepare polymers with pendant functionality capable of participating in highly efficient Cu-I-atalyzed 1,3-dipolar cycloaddition of azide and alkynes, monomers with acetylene or azido groups were polymerized via controlled radical polymerization. Atom transfer radical polymerization (ATRP) of propargyl methacrylate (PgMA) resulted in high polydispersities (M-w/M-n > 3), multimodal molecular weight distributions, and cross-linked networks at moderate to high conversion. The poor results obtained with this monomer were presumably due to addition of the propagating radicals to the acetylene group, transfer reactions, and/or interference with the catalyst. A novel monomer, 3-azidopropyl methacrylate (AzPMA), was polymerized via ATRP with good control of the polymer molecular weight distribution and retention of chain functionality. Poly(3-azidopropyl methacrylate) was coupled with propargyl alcohol, propargyl triphenylphosphonium bromide, propargyl 2-bromoisobutyrate, and 4-pentynoic acid via a highly efficient "click" reaction in the presence of a Cu-I catalyst. The azido-functionalized polymer demonstrated enhanced reactivity as compared to small molecules with comparable structures. The ability of the coupling reactions to be conducted at room temperature without significant excess of reagents makes this an attractive alternative to preparing (co)polymers with high degrees of functionalization.