The polymerization of n-butyl acrylate initiated by ester enolates in the presence of tetraalkylammonium halide-trialkylaluminum complexes, R4N[AlnR ' X-3n] (n = 1, 2), in toluene has a controlled character at -78 degreesC only for selected combinations of the complex. Quantitative monomer conversions are usually reached with Me4N[(AlnBu3nCl)-Cl-i] leading to polymers with narrow molecular weight distributions (.)(M-W/M-n < 1.2). Kinetic investigations show a complex mechanism of the polymerization, implying an equilibrium between at least two active species. Besides, various acrylate homopolymers and block copolymers (PMMA-b-polyacrylate) can be synthesized with this new initiating system.