Patent ID: 7435783

Claim:
An aqueous polymer emulsion comprising water and swollen multi-stage emulsion polymer wherein the dry bulk density of the swollen multi-stage emulsion is: less than 0.74 g/cc when the swollen multi-stage emulsion polymer has a particle size of from 275 to 500 nm; less than 0.59 g/cc when the swollen multi-stage emulsion polymer has a particle size of from 501 to 750 nm; wherein said aqueous polymer emulsion is made by a process comprising: (a) providing an aqueous emulsion of (i) multi-stage emulsion polymer, comprising a core stage polymer and a shell stage polymer, wherein the core stage polymer comprises, as polymerized units, from 5 to 100 percent by weight, based on the weight of the core stage polymer, of hydrophilic monoethylenically unsaturated monomer, and from 0 to 95 percent by weight, based on the weight of the core stage polymer, of at least one nonionic monoethylenically unsaturated monomer; and wherein the shell stage polymer comprises, as polymerized units, at least 50 percent by weight of nonionic monoethylenically unsaturated monomer; (ii) monomer at a level of at least 0.5 percent by weight based on the weight of the multi-stage emulsion polymer; and (iii) swelling agent under conditions wherein there is no substantial polymerization of the monomer; and (b) reducing the level of monomer by at least fifty percent by polymerizing said monomer, wherein said multi-stage emulsion polymer additionally comprises an intermediate stage polymer that partially or fully encapsulates said core stage polymer and that is partially or fully encapsulated by said shell stage polymer, wherein said intermediate stage polymer comprises as polymerized units, (i) 0.3 to 20 percent by weight, based on the weight of said core stage polymer, at least one hydrophilic monoethylenically unsaturated monomer, (ii) 80 to 99.7 percent by weight, based on the weight of said core stage polymer, at least one nonionic monoethylenically unsaturated monomer.