Disclosed are copolymers based on aspartic acid or its precursor molecules and methods of their production. The copolymers are water-soluble over a wide range of composition and molecular weight. Their preparation involves conversion of a polysuccinimide to copolymers of defined composition, containing aspartate and succinimide residues and/or residues of asparagine. In particular, the copolymers include water-soluble terpolymers of aspartate, asparagine, and succinimide.