FIELD: organic chemistry. SUBSTANCE: invention proposes polyimides or their polypeptide hydrolyzates exhibiting biological degradability at least 80% that can be used as a modifying addition in detergent composition. The indicated polyimides or their polypeptide hydrolyzates are obtained by polycondensation of aspartic acid followed by, if necessary, hydrolysis of the obtained product in the presence of "acid" catalyst taken from the group: sulfuric, phosphoric, sulfurous, sulfonic acids, organic phosphonic or sulfoacid containing 1-25 carbon atoms, hydrochloric acid, salts of these acids or salts of these acids and aspartic acid, acid salts of sulfuric, phosphoric or phosphorous acid, Lewis acid at molar ratio "acid catalyst" : aspartic acid = (0.005-10):1. EFFECT: improved method of synthesis. 10 cl, 49 ex, 5 tbl, 1 dwg
