Adhesion promoters for aqueous coating compositions

A copolymer obtained by copolymerization of at least three ethylenically unsaturated monomers each different from one another,

• wherein
• the copolymer has at least three structural units (S1), (S2), and (S3) each different from one another,
• each structural unit (S1) has at least one branched alkyl group having at least 11 carbon atoms,
• each structural unit (S2) has at least one urea group bonded via a C1-10 alkylene group, of the formula (I):
• wherein:
• X is O or S,
• A is a C1-10 alkylene group, and
• R1, R2 and R3 each independently of one another are H or a C1-10 alkyl radical,
• or
• R1 and R2 together are —(CR4R5)n— and R3 is H or a C1-10 alkyl radical, where R4 and R5 each independently of one another are H or a C1-6 alkyl radical, and n is an integer from 2 to 5, and
• each structural unit (S3) has at least one functional group selected from the group consisting of a carboxyl group, hydroxyl group, thiol group, amino group, epoxide group, and a mixture thereof.