The invention concerns an aqueous polymer dispersion, prepared from a monomer composition comprising: (A) 50 to 99.99 parts by weight of at least an acrylic or methacrylic ester derived from acrylic or methacrylic acid and an alcohol having 1 to 12 carbon atoms; (B) 0 to 40 parts by weight of at least a vinylaromatic monomer; (C) 0 to 5 parts by weight of at least a short-chain .alpha.,.beta.-unsaturated mono- or polycarboxylic acid; (D) 0.01 to 5 parts by weight of at least an ethylenically unsaturated alpha-beta monomer compound (D), comprising at least a carbonyl group having at least a hydrogen atom borne in position alpha of said carbonyl (diacetone acrylamide), for 100 parts by weight of monomers (A)+(B)+(C)+(D), 80 to 98 wt. % of monomer components having been added to a reaction medium already containing a totally or partly polymerized pre-emulsion representing 2 to 20 wt. % of the final global proportion of monomer components in the dispersion finally obtained.