Aqueous polymer dispersion and process of making the same

1. An aqueous dispersion of a multistage polymer, wherein the multistage polymer comprises:

(A) a polymer A comprises as polymerized units, based on the weight of the polymer A,

(a1) from 75% to 92% by weight of a hydrophilic (meth)acrylic acid alkyl ester;

(a2) from 2.1% to 10% by weight of a carbonyl-containing functional monomer; and

(a3) from 5% to 15% by weight of an acid monomer comprising from 4% to 14% by weight of an α, β-ethylenically unsaturated carboxylic acid and from 1% to 9% by weight of a phosphorous-containing acid monomer, and

wherein the polymer A has a number average molecular weight of from 3,000 to 100,000; and

(B) a polymer B comprises as polymerized units, based on the weight of the polymer B,

(b1) from 81% to 99% by weight of a hydrophobic monomer selected from a vinyl aromatic monomer, a hydrophobic (meth)acrylic acid alkyl ester, or mixtures thereof;

(b2) from 0.8% to 10% by weight of a carbonyl-containing functional monomer; and

(b3) from 0 to 15% by weight of a hydrophilic monomer;

wherein the polymer B has a glass transition temperature at least 40° C. lower than that of the polymer A, and the weight ratio of the polymer A to the polymer B is from 25:75 to 50:50.

2. The aqueous dispersion of claim 1 , wherein the carbonyl-containing functional monomers (a2) and (b2) are each independently selected from diacetone acrylamide.

3. The aqueous dispersion of claim 1 , further comprising from 0.5% to 10% by weight of a polyfunctional carboxylic hydrazide containing at least two hydrazide groups per molecule, based on the total weight of the polymer A and polymer B.

4. The aqueous dispersion of claim 3 , wherein the polyfunctional carboxylic hydrazide is selected from adipic dihydrazide, oxalic dihydrazide, isophthalic dihydrazide, polyacrylic polyhydrazide, or mixtures thereof.

5. The aqueous dispersion of claim 1 , wherein the phosphorous-containing acid monomer is selected from phosphoethyl (meth)acrylate, phosphopropyl (meth)acrylate, phosphobutyl (meth)acrylate, or mixtures thereof.

6. The aqueous dispersion of claim 1 , wherein the hydrophilic (meth)acrylic acid alkyl ester is selected from methyl (meth)acrylate, ethyl (meth)acrylate, or mixtures thereof.

7. The aqueous dispersion of claim 1 , wherein the hydrophobic monomer is selected from styrene or substituted styrene, butyl (meth)acrylate, iso-butyl (meth)acrylate, 2-ethylhexyl acrylate, lauryl (meth)acrylate, stearyl (meth)acrylate, or mixtures thereof.

8. The aqueous dispersion of claim 1 , wherein the polymer A has a number average molecular weight of from 3,000 to 30,000.

9. The aqueous dispersion of claim 1 , wherein the weight ratio of the polymer A to the polymer B is from 30:70 to 40:60.

10. The aqueous dispersion of claim 1 , wherein the polymer A has a glass transition temperature of from 60 to 110° C., and the polymer B has a glass transition temperature of −20° C. or higher.

11. The aqueous dispersion of claim 1 , wherein the polymer A comprises as polymerized units, based on the weight of the polymer A,

(a1) from 80% to 90% by weight of the hydrophilic (meth)acrylic acid alkyl ester;

(a2) from 3% to 6% by weight of the carbonyl-containing functional monomer; and

(a3) from 7% to 13% by weight of the acid monomer comprising from 4% to 10% by weight of the α, β-ethylenically unsaturated carboxylic acid and from 3% to 6% by weight of the phosphorous-containing acid monomer; and

the polymer B comprises as polymerized units, based on the weight of the polymer B,

(b1) from 81% to 99% by weight of the hydrophobic monomer selected from a vinyl aromatic monomer, a hydrophobic (meth)acrylic acid alkyl ester, or mixtures thereof;

(b2) from 2.5% to 10% by weight of the carbonyl-containing functional monomer; and

(b3) from 0 to 15% by weight of the hydrophilic monomer.

12. An aqueous coating composition comprising the aqueous dispersion of claim 1 .

13. A process of preparing an aqueous dispersion of a multistage polymer by a multistage free-radical polymerization, comprising:

(i) preparing a polymer A in an aqueous medium by a free-radical polymerization in the presence of a chain transfer agent and neutralizing the obtained polymer A to a pH value of at least 6, wherein the polymer A comprises as polymerized units, based on the weight of the polymer A,

(a1) from 75% to 92% by weight of a hydrophilic (meth)acrylic acid alkyl ester;

(a2) from 2.1% to 10% by weight of a carbonyl-containing functional monomer; and

(a3) from 5% to 15% by weight of an acid monomer comprising from 4% to 14% by weight of an α, β-ethylenically unsaturated carboxylic acid and from 1% to 9% by weight of a phosphorous-containing acid monomer; and

(ii) preparing a polymer B in the presence of the polymer A obtained from step (i) by a free-radical polymerization, wherein the polymer B comprises as polymerized units, based on the weight of the polymer B,

(b1) from 81% to 99% by weight of a hydrophobic monomer selected from a vinyl aromatic monomer, a hydrophobic (meth)acrylic acid alkyl ester, or mixtures thereof;

(b2) from 0.8% to 10% by weight of a carbonyl-containing functional monomer; and

(b3) from 0 to 15% by weight of a hydrophilic monomer; and

wherein the polymer B has a glass transition temperature at least 40° C. lower than that of the polymer A, and the weight ratio of the polymer A to the polymer B is from 25:75 to 50:50.

14. A process of preparing an aqueous dispersion of a multistage polymer by a multistage free-radical polymerization, comprising:

(i) preparing a polymer B in an aqueous medium in the presence of a surfactant by a free-radical polymerization, wherein the polymer B comprises as polymerized units, based on the weight of the polymer B,

(b1) from 81% to 99% by weight of a hydrophobic monomer selected from a vinyl aromatic monomer, a hydrophobic (meth)acrylic acid alkyl ester, or mixtures thereof;

(b2) from 0.8% to 10% by weight of a carbonyl-containing functional monomer; and

(b3) from 0 to 15% by weight of a hydrophilic monomer; and

(ii) preparing a polymer A by a free-radical polymerization in the presence of a chain transfer agent and neutralizing the obtained multistage polymer to a pH value of at least 7, wherein the polymer A comprises as polymerized units, based on the weight of the polymer A,

(a1) from 75% to 92% by weight of a hydrophilic (meth)acrylic acid alkyl ester;

(a2) from 2.1% to 10% by weight of a carbonyl-containing functional monomer; and

(a3) from 5% to 15% by weight of an acid monomer comprising from 4% to 14% by weight of an α, β-ethylenically unsaturated carboxylic acid and from 1% to 9% by weight of a phosphorous-containing acid monomer; and

wherein the polymer B has a glass transition temperature at least 40° C. lower than that of the polymer A, and the weight ratio of the polymer A to the polymer B is from 25:75 to 50:50.