This study describes the synthesis and characterization of three α-diimine-cobalt complexes of the type [CoCl2(R-DAB)] (R-DAB = R–N[dbnd]CH–CH[dbnd]N–R; 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.