A new synthetic route for high-performance biopolyamides with a rigid N-substituted pyrrolidone ring was developed from the biomonomer itaconic acid (IA), which was mass-produced by the fermentation of Aspergillus terreus. We used salt-type monomers composed of diacidic IA and diamines. These salts thermally converted into polyamides in the presence of sodium dihydrogen phosphate through the aza-Michael addition, followed by intramolecular cyclization to create a pyrrolidone ring in the polymer main chain. Polyamides with molecular weights ranging over 28 000 showed T-g values over 87 degrees C, which were higher than conventional polyamides (around 57 degrees C). The Young's modulus and mechanical strength of these polyamides also showed high values of 430-2800 MPa and 90-165 MPa, respectively. In addition, the polyamides became soluble in water by ring-opening reaction of the pyrrolidone, which led to environmental corrosion by landfill or ultraviolet irradiation.