One-Step Synthesis of Azlactone-Functionalized SG1-Based Alkoxyamine for Nitroxide-Mediated Polymerization and Bioconjugation

The one-step synthesis of azlactone-functionalized SG1-based alkoxyamine (AzSG1) for the design of functional polymers by nitroxide-mediated polymerization (NMP) is reported. At 347.7 K, its dissociation rate constant, k_d, was determined to be 2.72 × 10^–4 s^–1, leading to an activation energy, E_a, of 119.5 kJ mol^–1, which represents the lowest value ever reported for a secondary SG1-based alkoxyamine without any activation by an external stimulus. This was ascribed to enhanced stabilization of the released radical compared to other secondary alkyl radicals. The AzSG1 alkoxyamine was successfully used for the NMP for styrene, n-butyl acrylate, and methyl methacrylate with the addition of a small amount of acrylonitrile as a comonomer, without the need for free SG1. In all cases, first-order kinetics, good control with low dispersities (Đ = 1.2–1.4), and high living chain fractions (LF ∼90%) were obtained. As a proof of concept, the conjugation of azlactone-functionalized polymers to benzylamine and lysozyme was successfully demonstrated. This work may be of high interest for conjugation as the azlactone functionality is also known to react with other nucleophiles such as alcohols or thiols.