Polymeric micelles are potentially useful in a wide range of applications including chiral separation with amino acid-based molecular micelles (polymeric surfactants) utilized as pseudostationary phases in capillary electrophoresis, environmental condition-independent micellization, and nano drug delivery vectors to name a few. However, these applications have not been commercially realized due to the difficulty of reproducing vacuum UV-initiated radical polymerizations. A typical monomer (surfactant) consists of a terminal alkene on the hydrophobic tail which is activated to trigger the initiation of a free radical polymerization. However, traditional radical polymerization approaches do not preserve the micellar superstructure during the propagation steps. This research is investigating a new approach for initiating a radical polymerization using reaction conditions that do not perturb the micellar superstructure. Metal complexes of Co and Fe can selectively initiate radical formation on alkenes by acting as Lewis acids for an atom transfer-based mechanism. In order for this reaction to be feasible at room temperature, a requirement for micelles, the metal complex must have a weak ligand field and thus be high spin (4). To that end, we synthesized acetylacetone (acac) complexes of Co(II) and Fe(II) in this work, which could be electrochemically oxidized to initiate metal-hydrogen atom transfer (MHAT) reactions. The reaction can be monitored using UV-Vis spectroelectrochemistry to ensure quantitative conversion to M(III) complexes, which are capable of abstracting H-atoms from RSi-H compounds in solution. Once the initiator electrosynthesis is complete, the MHAT can then be introduced to a micellar solution to initiate radical polymerization under alkaline conditions. Following polymerization, the polymeric micelles can be isolated and purified for subsequent characterization and use.

Novel method for polymeric micelle synthesis using electrochemical metal hydride atom transfer initiator

ACS Spring 2022

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