Method for producing leather

In a process for the production of leather, pelts, pickled pelts or semifinished products are treated with at least one polymer which is obtainable by copolymerization of at least one ethylenically unsaturated dicarboxylic anhydride (A), derived from at least one dicarboxylic acid of 4 to 8 carbon atoms, at least one vinylaromatic compound (B) and optionally at least one ethylenically unsaturated monomer (C) which differs from (A) and has a hetero atom, reaction with at least one compound (D) of the formula Ia or Ib at least 0.55 equivalent, based on (A), of (D) being used, and optionally hydrolysis with water or aqueous alkaline solution, where, in formulae Ia and Ib, the variables are defined as follows: A1 are identical or different and are C2-C6-alkylene R1 is linear or branched C1-C20-alkyl, and n is an integer from 6 to 200.