Synthesis of cobalt(II)-α-diimines complexes and their activity as mediators in organometallic mediated radical polymerization of vinyl acetate

Abstract: This study describes the synthesis and characterization of three α-diimine-cobalt complexes of the type [CoCl₂(R-DAB)] (R-DAB = RNCHCHNR; R = Mes, Dipp and Dipp^∗) and their application as mediators for the cobalt-mediated radical polymerization (CMRP) of vinyl acetate (VAc) using 2,2′-Azobis(2-methylpropionitrile) (AIBN) as initiator. The complexes were characterised by elemental analyses, FTIR, UV–Vis, electron paramagnetic resonance spectroscopy, cyclic voltammetry, and computational methods. The systematic variation of the reaction conditions, such as [initiator]/[Co] and [monomer]/[Co] molar ratios at 65 °C, affected the polymerization rates and the molecular weights, reaching a certain level of control. The VAc polymerization was initiated by AIBN in the presence of DMSO using the α-diimine-cobalt complexes as mediators with [DMSO]/[Co] = 1 at 65 °C. The control over the polymer produced was not improved after the addition of DMSO. Kinetics studies and computational investigations support a tailorable cobalt complex reactivity mainly altered by steric factors of the α-diimine ligands.

Authors: Beatriz A. Riga, Marina D. Neves, Antonio E. H. Machado, Diesley M. S. Araújo, Jhonathan R. Souza, Otaciro R. Nascimento, Vinícius T. Santana, Carla C. S. Cavalheiro, Valdemiro P. Carvalho-Jr & Beatriz E. Goi.