In this thesis, the ring-opening polymerization by a monomer activation strategy of heterocyclic monomers such as lactams and aziridines was investigated. In the first part, we described that covalently activated aziridines, i.e. N-sulfonyl aziridines, could be subjected to the N-heterocyclic carbene organocatalyzed ring-opening polymerization (NHC-OROP) in a living/controlled manner. Secondary activated amine, non-activated secondary amine as well as functional initiators were used to promote the ring-opening polymerization of N-activated aziridines. The high tolerance to various chemical functions and the high level of control of the so-called NHC-OROP have allowed the synthesis of well-defined and original aziridine-based block copolymers. On the other hand, the simultaneous combination of anionic ring-opening of ε-caprolactam and condensation reactions of aminobenzoate derivatives was shown to occur in a « one-step » bulk copolymerization allowing the preparation of aliphatic-aromatic copolyamides with enhanced thermal properties (including the glass transition temperature). Alternatively, other methodologies such as covalent activation of lactams with electron withdrawing group or the hydrogen transfer polymerization of acrylamide derivatives were investigated for the synthesis of new polyamides.