The present invention relates to a composition comprising 1) an aqueous dispersion of polymer particles having a core-shell morphology wherein the core protuberates from the shell and comprises less than 0.09 structural units of a phosphorus acid monomer, based on the weight of the core; and 2) pigment particles with a refractive index in the range of from 2.0 and 3.0, wherein the pigment volume concentration of the pigment particles is at least 11. The composition of the present invention is useful for improving block resistance in coatings applications.