This invention provides a multistage emulsion polymer including, as copolymerized units: from 0.5% to 5%, by weight P-acid monomer, based on the weight of the emulsion polymer; from 0% to 0.05% by weight multiethylenically unsaturated monomer, based on the weight of the emulsion polymer; and at least one second monoethylenically unsaturated monomer; the emulsion polymer having a calculated Tg of from −20° C. to 50° C.; the emulsion polymer is formed by the “pulsed” addition of 75% to 100% of the P-acid monomer during a stage including from 10% to 50% of the total monomer weight, preferably added during the relatively early stages of the polymerization. A multistage polymer/TiO2 composite particle and an aqueous coating composition including the composite particle are also provided.