Self-polymerization of mono-aziridine (or azetidine) and multi-aziridine (or azetidine) containing compounds with vinyl group containing organic acid, such as acrylic acid (AA), 2-methylenesuccinic acid, 2,3-dimethylenesuccinic acid and etc, at ambient temperature results in the new type of cross-linked and linear type copolymers, respectively. The polymerization of multi-functional aziridine (or azetidine) containing compounds with vinyl group containing organic acid results in the formation of high cross-linked polymers. The self-polymerization takes place at ambient temperature and the resultants, cross-linked polymeric networked materials, are solvent insoluble and potential for adhesive, composite matrix and other applications. These insoluble materials are hydrolyzed in an acidic or basic condition to form the water soluble β-amino acids. A linear poly(β-aminoester) is obtained from the self-polymerization of vinyl group containing organic acid with mono-aziridine (or azetidine) containing compound at ambient temperature. poly(β-aminoester) is applicable for gene transfer, controlled drug release and other applications. This self-polymerization process offers a convenient route for preparing poly(β-aminoesters).