The invention provides a process for preparing an aqueous polymer dispersion of a copolymer CP of at least two different monomers M1 and M2 by free-radical aqueous emulsion polymerization of the monomers M in the presence of at least one initiator, at least 80% of the monomers M and at least 75% of the initiator being supplied continuously to the polymerization reaction during its course, which comprises changing the rate at which the initiator is supplied to the polymerization reaction a number of times, or continuously, during the polymerization reaction. The invention further provides the polymer dispersions obtainable by this process, polymer powders prepared therefrom, and for the use of the dispersions and/or of the polymer powders to prepare pressure sensitive adhesives.