A process for preparing an aqueous dispersion of neutralized multistage polymer particles comprising the steps of: 1) contacting under emulsion polymerization conditions a) an aqueous dispersion of first polymer particles comprising from 25 to 65 weight percent structural units of a carboxylic acid monomer, from 40 to 75 weight percent structural units of a nonionic monomer with b) first monomers comprising, based on the weight of the first monomers, i) from 80 to 99.5 weight percent styrene or methyl methacrylate or a combination thereof, and ii) from 0.5 to 20 weight percent of a carboxylic acid monomer; to form an aqueous dispersion of 2-stage polymer particles; then 2) contacting under emulsion polymerization conditions the aqueous dispersion of the 2-stage polymer particles with second monomers comprising, based on the weight of the second monomers a) from 1 to 60 weight percent methyl methacrylate, b) from 35 to 98.5 weight percent n -butyl acrylate, 2-ethylhexyl acrylate, ethyl acrylate, or n -butyl methacrylate, or a combination thereof; c) from 0.5 to 5 weight percent of a carboxylic acid monomer; and d) less than 20 weight percent styrene, to convert the 2-stage polymer particles to unneutralized 3-stage polymer particles; then 3) neutralizing the unneutralized aqueous dispersion of the 3-stage polymer particles with a base to form an aqueous dispersion of neutralized 3-stage polymer particles having an average particle size in the range of 150 nm to 400 nm; wherein the weight-to-weight ratio of the first polymer particles to the first and second monomers is in the range of from 1:2 to 1:9; and the weight-to-weight ratio of the first monomers to second monomers is in the range of from 3:2 to 1:8; wherein the first and second monomers form a shell having a calculated T g of less than 50 °C. 1) contacting under emulsion polymerization conditions a) an aqueous dispersion of first polymer particles comprising from 25 to 65 weight percent structural units of a carboxylic acid monomer, from 40 to 75 weight percent structural units of a nonionic monomer with b) first monomers comprising, based on the weight of the first monomers, i) from 80 to 99.5 weight percent styrene or methyl methacrylate or a combination thereof, and ii) from 0.5 to 20 weight percent of a carboxylic acid monomer; to form an aqueous dispersion of 2-stage polymer particles; then 2) contacting under emulsion polymerization conditions the aqueous dispersion of the 2-stage polymer particles with second monomers comprising, based on the weight of the second monomers a) from 1 to 60 weight percent methyl methacrylate, b) from 35 to 98.5 weight percent n -butyl acrylate, 2-ethylhexyl acrylate, ethyl acrylate, or n -butyl methacrylate, or a combination thereof; c) from 0.5 to 5 weight percent of a carboxylic acid monomer; and d) less than 20 weight percent styrene, to convert the 2-stage polymer particles to unneutralized 3-stage polymer particles; then 3) neutralizing the unneutralized aqueous dispersion of the 3-stage polymer particles with a base to form an aqueous dispersion of neutralized 3-stage polymer particles having an average particle size in the range of 150 nm to 400 nm;