Although μ-coordinating ligands such as LiCl are effective in promoting the well-controlled living anionic block copolymerization of methyl methacrylate (MMA) and tert-butylacrylate (tBuA), whichever monomer is first polymerized, it has been previously shown that a copolymerization of mixtures of these two monomers does not proceed as expected, giving poor results in terms of both conversion and molecular weight distribution: that was accounted for by the easy back-biting nucleophilic attack of a highly sensitive methyl ester group by a moderately hindered PtBuA anion. It is now reported that such a situation can be completely modified, when a cation-binding σ-ligand, i.e., dibenzo-18-CE-6, is used in chelating a sodium counterion and surrounding it with a steric barrier, blocking a large enough space area around the ion pair