A process for chemically-modifying the surface of a polymer particle, comprising the following sequential steps: (a) providing an aqueous emulsion comprising (i) a multistage emulsion polymer comprising a core stage polymer and a shell stage polymer, wherein said core stage polymer comprises, as polymerized units, from 5% to 100% by weight, based on the weight of said core stage polymer, of hydrophilic monoethylenically unsaturated monomer, and from 0% to 95% by weight, based on the weight of said core stage polymer, of at least one nonionic monoethylenically unsaturated monomer; and wherein said shell stage polymer comprises, as polymerized units, at least 50% by weight of nonionic monoethylenically unsaturated monomer; and (ii) a monomer at a level of at least 0.5% by weight based on the weight of said multistage emulsion polymer; under conditions wherein there is no polymerization of said monomer; and (b) reducing the level of said monomer (ii) by at least 50% by polymerizing said monomer; characterized in that: said monomer (ii) is nonionic monomer; and said aqueous emulsion additionally comprises (iii) at least one surface-modifying chemical capable of chemically bonding with said monomer;. (a) providing an aqueous emulsion comprising (i) a multistage emulsion polymer comprising a core stage polymer and a shell stage polymer, wherein said core stage polymer comprises, as polymerized units, from 5% to 100% by weight, based on the weight of said core stage polymer, of hydrophilic monoethylenically unsaturated monomer, and from 0% to 95% by weight, based on the weight of said core stage polymer, of at least one nonionic monoethylenically unsaturated monomer; and wherein said shell stage polymer comprises, as polymerized units, at least 50% by weight of nonionic monoethylenically unsaturated monomer; and (ii) a monomer at a level of at least 0.5% by weight based on the weight of said multistage emulsion polymer; under conditions wherein there is no polymerization of said monomer; and (i) a multistage emulsion polymer comprising a core stage polymer and a shell stage polymer, wherein said core stage polymer comprises, as polymerized units, from 5% to 100% by weight, based on the weight of said core stage polymer, of hydrophilic monoethylenically unsaturated monomer, and from 0% to 95% by weight, based on the weight of said core stage polymer, of at least one nonionic monoethylenically unsaturated monomer; and wherein said shell stage polymer comprises, as polymerized units, at least 50% by weight of nonionic monoethylenically unsaturated monomer; and wherein said core stage polymer comprises, as polymerized units, from 5% to 100% by weight, based on the weight of said core stage polymer, of hydrophilic monoethylenically unsaturated monomer, and from 0% to 95% by weight, based on the weight of said core stage polymer, of at least one nonionic monoethylenically unsaturated monomer; and wherein said shell stage polymer comprises, as polymerized units, at least 50% by weight of nonionic monoethylenically unsaturated monomer; and (ii) a monomer at a level of at least 0.5% by weight based on the weight of said multistage emulsion polymer; under conditions wherein there is no polymerization of said monomer; and (b) reducing the level of said monomer (ii) by at least 50% by polymerizing said monomer; characterized in that: said monomer (ii) is nonionic monomer; and said aqueous emulsion additionally comprises (iii) at least one surface-modifying chemical capable of chemically bonding with said monomer;. said monomer (ii) is nonionic monomer; and said aqueous emulsion additionally comprises (iii) at least one surface-modifying chemical capable of chemically bonding with said monomer;.