A process for preparing an aqueous dispersion of first and second acrylic-based polymer particles, wherein the first polymer particles each comprise a shell with a protuberating phosphorus acid functionalized core, and wherein none of the second polymer particles comprise a protuberating core; wherein the weight-to-weight ratio of the polymer particles with the protuberating cores to the polymer particles without the protuberating cores is in the range of 30:70 to 68:32; wherein the volume average particle size of the polymer particles with the protuberating core is in the range of from 110 nm to 160 nm (as determined by Asymmetric Flow Field Flow Fractionation); and the volume average particle size of the particles without a protuberating core is in the range of from 70 to 140 nm (as determined by Asymmetric Flow Field Flow Fractionation); wherein the composition of the shells of the first polymer particles is identical to the composition of the second polymer particles; wherein the ratio of volume average particle size of the protuberating core particles to the non-protuberating core particle diameters is from 1.45:1 to 0.9:1; comprising the steps of: a) preparing an aqueous dispersion of first seed polymer particles by emulsion polymerization of first monomers comprising i) methyl methacrylate or styrene or a combination thereof; ii) one or more acrylates selected from the group consisting of ethyl acrylate, butyl acrylate, 2-propylheptyl acrylate, and 2-ethylhexyl acrylate; iii) a phosphorus acid monomer or a salt thereof; and optionally a carboxylic acid monomer or a sulfur acid monomer, or salts thereof or combinations selected from: acrylic acid, methacrylic acid, and itaconic acid, and salts thereof; sulfoethyl methacrylate, sulfopropyl methacrylate, styrene sulfonic acid, vinyl sulfonic acid, vinylbenzensulfonic acid and 2-acrylamido-2-methyl propanesulfonic acid, and salts thereof; b) preparing an aqueous dispersion of second seed polymer particles by emulsion polymerization of second monomers comprising i) methyl methacrylate or styrene or a combination thereof; ii) one or more acrylates selected from the group consisting of ethyl acrylate, butyl acrylate, 2-propylheptyl acrylate, and 2-ethylhexyl acrylate; and less than 0.5 weight percent of a phosphorus acid monomer, based on the weight of the second monomers; and optionally a carboxylic acid monomer or a salt thereof; and optionally a sulfur acid monomer or a salt thereof; c) mixing the aqueous dispersions of the first and second seed polymer particles at a first-to-second seed polymer particles weight-to-weight ratio of from 1:2 to 10:1 to form a mixture of first and second seed polymer particles; then d) contacting the mixture of first and second seed polymer particles with a monomer emulsion under emulsion polymerization conditions to form polymer particles with a protuberating phosphorus acid functionalized core and polymer particles without a protuberating core. a) preparing an aqueous dispersion of first seed polymer particles by emulsion polymerization of first monomers comprising i) methyl methacrylate or styrene or a combination thereof; ii) one or more acrylates selected from the group consisting of ethyl acrylate, butyl acrylate, 2-propylheptyl acrylate, and 2-ethylhexyl acrylate; iii) a phosphorus acid monomer or a salt thereof; and optionally a carboxylic acid monomer or a sulfur acid monomer, or salts thereof or combinations selected from: acrylic acid, methacrylic acid, and itaconic acid, and salts thereof; sulfoethyl methacrylate, sulfopropyl methacrylate, styrene sulfonic acid, vinyl sulfonic acid, vinylbenzensulfonic acid and 2-acrylamido-2-methyl propanesulfonic acid, and salts thereof; b) preparing an aqueous dispersion of second seed polymer particles by emulsion polymerization of second monomers comprising i) methyl methacrylate or styrene or a combination thereof; ii) one or more acrylates selected from the group consisting of ethyl acrylate, butyl acrylate, 2-propylheptyl acrylate, and 2-ethylhexyl acrylate; and less than 0.5 weight percent of a phosphorus acid monomer, based on the weight of the second monomers; and optionally a carboxylic acid monomer or a salt thereof; and optionally a sulfur acid monomer or a salt thereof; c) mixing the aqueous dispersions of the first and second seed polymer particles at a first-to-second seed polymer particles weight-to-weight ratio of from 1:2 to 10:1 to form a mixture of first and second seed polymer particles; then d) contacting the mixture of first and second seed polymer particles with a monomer emulsion under emulsion polymerization conditions to form polymer particles with a protuberating phosphorus acid functionalized core and polymer particles without a protuberating core.