Several commercial trialkyl phosphines were tested as organic catalysts for the group transfer polymerization (GTP) of methyl methacrylate (MMA) and tert-butyl acrylate (tBA). Among them, only tris(2,4,6-trimethoxyphenyl)-phosphine (TTMPP) was able to bring about the "controlled/living" GTP of both monomers at room temperature, in bulk and/or in THF solution, using 1-methoxy-2-methyl-1-[(trimethylsilyl)oxy]prop-1-ene (MTS) as initiator. However, control of the polymerization appeared to be more difficult in the case of tBA compared to MMA. Poly[alkyl(meth)acrylate]s exhibiting dispersities <1.37 in bulk and <1.45 in THF, and molar masses in good accordance with the initial [monomer](0)/[MTS](0) molar ratio could thus be obtained in quantitative yields. Poly(methyl methacrylate)-b-poly(tert-butyl acrylate) block copolymers, with final dispersity <1.2 and controlled molar masses, were also synthesized by sequential TTMPP-catalyzed GTP. First order kinetics plot of the GTP of MMA revealed an induction period of a few hours, which strongly depended on the initial polymerization conditions. The tacticity of the final PMMA's (mm/mr/rr = 0.06/0.42/0.52) were very similar to that of an anionically derived PMMA. These data are in favor of the occurrence of a dissociative mechanism, forming minute amounts of true enolate-type propagating species, during the TTMPP-catalyzed GTP of MMA in THF. Analyses by C-13 and Si-29 NMR spectroscopy at room temperature of 1/1 molar MTS/TTMPP mixtures did not show the formation of enolate-type species.