A process comprising contacting a stable aqueous dispersion of pre-formed polymer particles with a monomer emulsion under emulsion polymerization conditions to form a stable aqueous dispersion of pre-formed polymer particles protuberating from polymer particles arising from the polymerization of the monomer emulsion, wherein the pre-formed polymer particles comprise, based on the weight of the pre-formed polymer particles: a) 2 to 10 weight percent structural units of a phosphorus acid monomer or a salt thereof; b) from 0.2 to 20 weight percent structural units of a carboxylic acid monomer or a sulfur acid monomer or a salt thereof or a combination thereof; and c) from 0.1 to 30 weight percent structural units of a multiethylenically unsaturated monomer; and d) a sufficient proportion of structural units of one or more polymerizable ethylenically unsaturated bulk monomers so that the pre-formed polymer particles have a T g in the range of from -50 °C to 75 °C; and wherein the monomer emulsion comprises: a) less than 10 percent by weight of a phosphorus acid monomer and salts thereof, based on the weight percent of the structural units of phosphorus acid monomer or a salt thereof in the pre-formed polymer particles; b) from 0.1 to 4 weight percent of a carboxylic acid monomer or sulfur acid monomer or a salt thereof or combination thereof, based on total monomers in the monomer emulsion; c) less than 0.5 weight percent of a multiethylenically unsaturated monomer, based on total monomers in the monomer emulsion; and d) a sufficient proportion of one or more ethylenically unsaturated bulk monomers so that the polymer particles arising from the polymerization of the monomer emulsion have a T g in the range of from -20 °C to 75 °C; and wherein the weight-to-weight ratio of the monomers in the monomer emulsion to the pre-formed polymer is in the range of from 3:1 to 15:1; and wherein the solids content of the pre-formed polymer particles is in the range of from 30 to 50 weight percent, based on the weight of the stable aqueous dispersion of the pre-formed polymer particles. a) 2 to 10 weight percent structural units of a phosphorus acid monomer or a salt thereof; b) from 0.2 to 20 weight percent structural units of a carboxylic acid monomer or a sulfur acid monomer or a salt thereof or a combination thereof; and c) from 0.1 to 30 weight percent structural units of a multiethylenically unsaturated monomer; and d) a sufficient proportion of structural units of one or more polymerizable ethylenically unsaturated bulk monomers so that the pre-formed polymer particles have a T g in the range of from -50 °C to 75 °C; and a) less than 10 percent by weight of a phosphorus acid monomer and salts thereof, based on the weight percent of the structural units of phosphorus acid monomer or a salt thereof in the pre-formed polymer particles; b) from 0.1 to 4 weight percent of a carboxylic acid monomer or sulfur acid monomer or a salt thereof or combination thereof, based on total monomers in the monomer emulsion; c) less than 0.5 weight percent of a multiethylenically unsaturated monomer, based on total monomers in the monomer emulsion; and d) a sufficient proportion of one or more ethylenically unsaturated bulk monomers so that the polymer particles arising from the polymerization of the monomer emulsion have a T g in the range of from -20 °C to 75 °C; and