The invention relates to novel cross-linkable monomers that may be polymerized with ethylenically unsaturated comonomers to form cross-linkable copolymers. Said copolymers may particularly be used in the form of aqueous dispersions as formaldehyde-free adhesives or as coatings with good water resistance. The cross-linkable monomer is a compound in acid or salt form comprising an anion of the formula (I) and one or more cations for producing electrical neutrality, where R1 and R2 represent, independently of one another, hydrogen alkyl, cycloalkyl, aryl, aralkyl, —COOR5, —COO− cat+ or —CON(R6R7), R6 and R7 represent, independently of one another, hydrogen, alkyl, or aryl, cat+ represents a monovalent cation, and one of the groups R1 or R2 may also represent a group —X—R4—CR5(OH)SO3−), wherein X, R4, and R5 assume one of the meanings listed below, R3 represents hydrogen, alkyl, or aryl, X is selected from the group of direct C—C bond, —O—, —CH2—O—, —CH2—NR8—, —COO— or —CONR8—, R8 represents hydrogen, alkyl, or aryl, R4 represents alkylene, polyoxyalkylene, cycloalkylene, or arylene, and R5 represents hydrogen, alkyl, cycloalkyl, or aryl.