A subject-matter of the invention is alkoxyamines resulting from β-phosphorated nitroxides corresponding to the formula: in which R represents an alkyl radical having a number of carbon atoms ranging from 1 to 3, R1 represents a hydrogen atom or a residue: in which R3 represents an alkyl radical having a number of carbon atoms ranging from 1 to 20, and R2 represents a hydrogen atom, an alkyl radical having a number of carbon atoms ranging from 1 to 8, a phenyl radical, an alkali metal, such as Li, Na or K, H4N+, Bu4N+ or Bu3HN+, exhibiting a kinetic dissociation constant kd, measured at 120° C. by EPR, of greater than 0.05 s−1. These compounds can be used as initiators for the (co)polymerizations of at least one monomer which can be polymerized by the radical route.