Polyamino acid ester copolymers

A copolymer derived from polyaspartic acids, wherein at least 75% of the units present are selected from the group consisting of structural units having the general formula (I) and (II)

• (--NH--A(--COOR.sup.1)--C(O)--) (I)
• (--NH--B--C(O)--) (II)
• in which each structural element A is the same or different and each is a trifunctional hydrocarbon radical with 2 C atoms having the structure (A1) or (A2), ##STR7## wherein said copolymer contains at least three units having said formula (I), in which
• each R.sup.1 can have the meaning of R.sup.2, R.sup.3 or R.sup.4, where
• R.sup.2 represents one or more residues selected from the group consisting of alkali metals, alkaline earth metals, hydrogen, and ammonium of the formula (NR.sup.5 R.sup.6 R.sup.7 R.sup.8).sup.+, where R.sup.5 -R.sup.8 represent, independently of each other, hydrogen, alkyl or hydroxyalkyl,
• R.sup.3 represents identical or different, straight or branched, saturated or unsaturated alkyl residues R.sup.9 with 6-24 C atoms or radicals having the structure --X--R.sup.9, where X represents an oligo- or polyoxyalkylene chain with 1-100 oxyalkylene units,
• R.sup.4 represents identical or different, straight or branched, saturated or unsaturated alkyl residues with 1-5 C atoms,
• and in each case at least one residue R.sup.1 must have the meaning of R.sup.2 and at least one residue R.sup.1 must have the meaning of R.sup.3 or R.sup.4 ;
• and
• each unit (--NH--B--C(O)--) is a residue selected from the group consisting of protein-forming and nonprotein-forming amino acids, and the units (--NH--B--C(O)--) constitute not more than 20 wt %. of the copolymer.