The present invention relates to a process for preparing hydrophobically associating macromonomers M and to the novel macromonomers prepared by means of the process according to the invention. The macromonomers M comprise a copolymerizable, ethylenically unsaturated group and a polyether structure in block form, the latter consisting of a polyethyleneoxy block and a hydrophobic polyalkyleneoxy block consisting of alkyleneoxy units having at least 4 carbon atoms. Optionally, the macromonomers M may have a terminal polyethyleneoxy block. The macromonomers prepared by the process according to the invention are suitable for reaction with further monomers, especially with acrylamide, to give a water-soluble, hydrophobically associating copolymer.