Polymer in multicoat color and/or effect paint systems

A pigmented aqueous basecoat material comprising at least one polymer comprising the reaction product of

• (a) dimer fatty acids with
• (b) at least one polyether of general structural formula (I)
• where R is a C3 to C6 alkylene radical and n is selected accordingly such that said polyether has a number-average molecular weight of 450 to 2200 g/mol, components (a) and (b) are used in a molar ratio of 0.7/2.3 to 1.3/1.7, and the resulting polymer has a number-average molecular weight of 1500 to 5000 g/mol and an acid number of <10 mg KOH/g,
• wherein the pigmented aqueous basecoat material is effective to form a film upon application to a substrate.

A method of promoting adhesion, comprising adding a polymer to a pigmented aqueous basecoat material, the polymer comprising the reaction product of

• (a) dimer fatty acids with
• (b) at least one polyether of general structural formula (I)
• where R is a C3 to C6 alkylene radical and n is selected accordingly such that said polyether has a number-average molecular weight of 450 to 2200 g/mol, components (a) and (b) are used in a molar ratio of 0.7/2.3 to 1.3/1.7, and the resulting polymer has a number-average molecular weight of 1500 to 5000 g/mol and an acid number of <10 mg KOH/g,
• wherein when the polymer is incorporated into the pigmented aqueous basecoat material, the pigmented aqueous basecoat material is effective to form a film upon application to a substrate.

A pigmented aqueous basecoat material comprising at least one polymer comprising the reaction product of

• (a) dimer fatty acids consisting of at least 90% by weight of dimeric molecules and less than 5% by weight of trimeric molecules with
• (b) at least one polyether of general structural formula (I)
• where R is a C3 to C6 alkylene radical and n is selected accordingly such that said polyether has a number-average molecular weight of 450 to 2200 g/mol, components (a) and (b) are used in a molar ratio of 0.7/2.3 to 1.3/1.7, and the resulting polymer has a number-average molecular weight of 1500 to 5000 g/mol and an acid number of <10 mg KOH/g,
• wherein the pigmented aqueous basecoat material is effective to form a film upon application to a substrate.