Emulsion polymer and process for preparing the same

An emulsion polymer comprising:

• (a) structural units of a polymerizable surfactant having the structure of formula (I),
• wherein R1 is a phenyl group or
• where R is an alkylene group;
• m1 is 1, 2, 3 or 4;
• R2 is an alkyl or a substituted alkyl;
• m2 is 0 or 1;
• A represents an alkylene group or a substituted alkylene group, having 2 to 4 carbon atoms;
• n is an integer in the range of from 1 to 30;
• and X represents —(CH2)a—SO3M or —(CH2)b—COOM, where a and b are each independently an integer of from 0 to 4, and M is an aminium ion having one ethylenically unsaturated bond;
• (b) structural units of an ethylenically unsaturated anionic monomer;
• and
• (c) structural units of an ethylenically unsaturated nonionic monomer;
• wherein polymer segments that comprise structural units of the ethylenically unsaturated anionic monomer and polymer segments that comprise structural units of the ethylenically unsaturated nonionic monomer together have the following Hansen solubility parameters:
• 16.42≤δD≤16.64, 2.87≤δP≤3.79, and 3.94≤δH≤4.57.