The present invention relates to a method of preparing an aqueous dispersion of multistage polymer particles comprising contacting under emulsion polymerization conditions and in a staged fashion an aqueous dispersion of carboxylic acid functionalized core polymer particles with first monomers and second monomers. The core comprises structural units of a high T_ghydrophobic monomer and/or the first monomers comprise a high T_ghydrophobic monomer, and the second monomers comprise at least 80 percent styrene. The high T_ghydrophobic monomer is cyclohexyl methacrylate, isobornyl methacrylate, 4-t-butyl methacrylate,t-butylstyrene, orn-butyl methacrylate, or a combination thereof. The multistage polymer particles are useful as opaque polymers, which are used in pigmented coating formulations to reduce the load of TiO₂. The particles exhibit excellent collapse resistance and unusually low dry bulk density, and do not require acrylonitrile to achieve this desired combination of properties.