Method for preparing pH-insensitive surfactant free polymer particle dispersion in aqueous medium

A method of making an aqueous dispersion of polymer particles comprising:

• reacting (i) an ethylenically unsaturated monomer selected from the group consisting of (meth)acrylates, styrenes, (meth)acrylamides, (meth)acrylonitriles, and mixtures thereof with (ii) a living macroinitiator, in an aqueous media and without a surfactant to effect polymerization of the ethylenically unsaturated monomer, wherein the macroinitiator, formed via nitroxide-mediated or reversible-addition-fragmentation-transfer (RAFT) polymerization, is a hydrophilic, pH-insensitive monomer, in polymerized form, selected from the group consisting of 2-acrylamido-2-methylpropanesulfonic acid (AMPS) and salts thereof and wherein said polymer particles have the formula R-{[(A)x(B)y]-[(C)m]p-Y}n or 1, where A is the hydrophilic, pH-insensitive monomer, B is a comonomer other than A and C, C is the ethylenically unsaturated monomer, Y is a terminal group selected from the group consisting of A, B, C and R, x≧1, y≧0, m≧1, n≧2, and p≧1, and A and B may appear in any order or sequence within the living macroinitiator, and R is of the formula (I) or (III):
• wherein R1 and R3, identical or different, represent a linear or branched alkyl group, with the number of carbon atoms in the alkyl group from 1 to 3;
• R2 represents a hydrogen atom or a linear or branched alkyl group having a number of carbon atoms in the alkyl group from 1 to 8, a phenyl group, an alkaline metal ion, or an ammonium ion;
• and Z represents an aryl group or a group of the formula Z1—[X—C(O)]n, in which, Z1 represents a polyfunctional structure where X is an oxygen atom, a nitrogen atom carrying a carbon group, a hydrogen atom, or a sulfur atom, n≧2, and said dispersion of polymer particles has a pH less than 7.