Patent ID: 7943704

Claim:
A process for preparing emulsion polymer particles, comprising: preparing an aqueous emulsion of core stage particles, comprising: i) a seed; and ii) a swell seed comprising 55 to 100% by weight of at least one nonionically ethylenically unsaturated monomer and 0 to 40% by weight of at least one monoethylenically unsaturated hydrophilic monomer, based in each case on the total weight of a core stage polymer; enclosing the core stage particles in iii) a first shell comprising 85% to 99.9% by weight of at least one nonionically ethylenically unsaturated monomer and 0.1% to 15% by weight of at least one hydrophilic monoethylenically unsaturated monomer; and iv) a second shell ensheathing the first shell, comprising 85% to 99.9% by weight of at least one nonionically ethylenically unsaturated monomer and 0.1% to 15% by weight of at least one hydrophilic monoethylenically unsaturated monomer; to obtain unswollen core shell particles in the aqueous emulsion; adding v) at least one plasticizer monomer having a ceiling temperature of less than 181° C. to the aqueous emulsion of the swollen core shell particles; vi) neutralizing the aqueous emulsion of the swollen core shell particles to a pH of at least 7.5 with a base to obtain an aqueous emulsion of swollen core shell particles having a hollow core; enclosing the swollen core shell particles in vii) a third shell comprising 90% to 99.9% by weight of at least one nonionically ethylenically unsaturated monomer and 0.1% to 10% by weight of at least one hydrophilic monoethylenically unsaturated monomer; and viii) optionally further enclosing the enclosed swollen particles in at least one shell comprising at least one nonionically ethylenically unsaturated monomer and at least one hydrophilic monoethylenically unsaturated monomer; wherein a polymerization inhibitor or reducing agent is not added to the aqueous emulsion of the unswollen core shell particles.