Aqueous dispersion of multi-stage polymeric particles and process of making the same

1. An aqueous dispersion of multi-stage polymeric particles comprising a polymer and an oligomer,

wherein the polymer comprises,

(a1) structural units of a functional monomer mixture, comprising,

(i) 0.5% by weight or more of structural units of an α, β-ethylenically unsaturated carboxylic acid,

(ii) structural units of methyl acrylamide and/or sodium styrene sulfonate, and optionally

(iii) structural units of acrylamide;

wherein the total amount of (i), (ii), and (iii) is 2% by weight or more;

(a2) structural units of an alkyl ester of (meth)acrylic acid; and optionally,

(a3) structural units of a vinyl aromatic monomer;

wherein the oligomer has a weight average molecular weight of from 1,000 to 60,000 g/mol and comprises:

(b1) 0.1% by weight or more of structural units of an alkoxylated (meth)acrylate having the structure of formula (I),

wherein R 1 is H or CH 3 , R 2 is H or a C 1 -C 6 alkyl group, R 3 and R 4 are each independently H or CH 3 , m is an integer of from 8 to 50, and n is an integer of from 0 to 6; and optionally

(b2) structural units of a vinyl aromatic monomer;

wherein the structural units of the vinyl aromatic monomer in the multi-stage polymeric particles are present in a combined amount of 5% by weight or more; and

wherein the multi-stage polymeric particles comprise from 1% to 30% by weight of the oligomer; with percent by weight values relative to the weight of the multi-stage polymeric particles.

2. The aqueous dispersion of claim 1 , wherein the alkoxylated (meth)acrylate has the structure of formula (I), wherein n is 0 and m is an integer of from 15 to 35.

3. The aqueous dispersion of claim 1 , wherein the total amount of (i), (ii) and (iii) in the polymer is in the range of from 2.1% to 5%, by weight based on the weight of the multi-stage polymeric particles.

4. The aqueous dispersion of claim 1 , wherein the polymer comprises (i) from 0.5% to 5% of structural units of the α, β-ethylenically unsaturated carboxylic acid, and (ii) from 0.1% to 5% of structural units of methyl acrylamide and/or sodium styrene sulfonate.

5. The aqueous dispersion of claim 1 , wherein the polymer comprises from zero to 4% by weight of structural units of acrylamide.

6. The aqueous dispersion of claim 1 , wherein the polymer further comprises structural units of a phosphorous-containing acid monomer and/or salts thereof.

7. The aqueous dispersion of claim 1 , wherein the oligomer is present, based on the weight of the multi-stage polymeric particles, in an amount of from 3% to 15% by weight.

8. The aqueous dispersion of claim 1 , wherein the oligomer comprises, based on the weight of the multi-stage polymeric particles, from 0.3% to 5% by weight of structural units of the alkoxylated (meth)acrylate.

9. A process of preparing an aqueous dispersion of multi-stage polymeric particles by multi-stage free-radical polymerization, comprising at least one stage forming a polymer and at least one stage forming an oligomer in the presence of a chain transfer agent;

wherein the polymer comprises,

(a1) structural units of a functional monomer mixture, comprising,

(i) 0.5% by weight or more of structural units of an α, β-ethylenically unsaturated carboxylic acid,

(ii) structural units of methyl acrylamide and/or sodium styrene sulfonate, and optionally

(iii) structural units of acrylamide;

wherein the total amount of (i), (ii), and (iii) is 2% or more;

(a2) structural units of an alkyl ester of (meth)acrylic acid; and optionally,

(a3) structural units of a vinyl aromatic monomer; and

wherein the oligomer has a weight average molecular weight of from 1,000 to 60,000 g/mol and comprises:

(b1) 0.1% by weight or more of structural units of an alkoxylated (meth)acrylate having the structure of formula (I),

wherein R 1 is H or CH 3 , R 2 is H or a C 1 -C 6 alkyl group, R 3 and R 4 are each independently H or CH 3 , m is an integer of from 8 to 50, and n is an integer of from 0 to 6; and optionally

(b2) structural units of a vinyl aromatic monomer;

wherein the structural units of the vinyl aromatic monomer in the multi-stage polymeric particles are present in a combined amount of 5% by weight or more; and

wherein the multi-stage polymeric particles comprise from 1% to 30% by weight of the oligomer; with percent by weight values relative to the weight of the multi-stage polymeric particles.

10. An aqueous coating composition comprising the aqueous dispersion of multi-stage polymeric particles of claim 1 .

11. The aqueous coating composition of claim 10 , being substantially free of anti-freezing agents.