Salt sensitive aqueous emulsions

1. An aqueous emulsion comprising a water-dispersible copolymer which is non-dispersible in aqueous solutions containing 0.5% or more of an inorganic salt, wherein the water-dispersible copolymer comprises in percentages by weight:

(A) from about 10% to about 90% of an acidic ethylenically unsaturated monomer; and

(B) from about 10% to about 90% of an ethylenically unsaturated monomer selected from the group of monomer formulas consisting of:

(i) CH 2 ═C(R 1 )COR 2 ;

(ii) R 3 OOC—CH═CH—COOR 4 ;

(iii) CH 2 ═C(R 5 )OCOR 6 ;

(iv) CH 2 ═C(COOR 7 )CH 2 COOR 8 ;

(v) CH 3 CH═CHCOOR 9 ;

(vi) R 10 C 6 H 4 CR 11 ═CHR 11 ; and

(vii) R 12 CH═CHR 13 ;

wherein R 1 is hydrogen or methyl and R 2 is —OZ′ or —N(Z″)(Z″), wherein Z′ is an alkyl group having from 1 to 7 carbon atoms, and Z″ is independently selected from the group consisting of hydrogen and alkyl groups having from 1 to 6 carbon atoms; R 3 and R 4 are independently hydrogen or an alkyl group having from 1 to 7 carbon atoms, with the proviso that R 3 and R 4 are not both hydrogen; R 5 is hydrogen or methyl and R 6 is an alkyl group having from 1 to 7 carbon atoms; R 7 and R 8 are independently hydrogen or an alkyl group having from 1 to 7 carbon atoms, with the proviso that R 7 and R 8 are not both hydrogen; R 9 is an alkyl group having from 1 to 7 carbon atoms; R 10 and R 11 are hydrogen; R 12 and R 13 are independently selected from the group consisting of hydrogen, —CN, —NHCHO, —NHCOCH 3 , and an alkyl group having from 1 to 7 carbon atoms; and the copolymer has a weight average molecular weight greater than about 25,000 and is present in an amount from about 20% to about 70%.

2. The aqueous emulsion according to claim 1 , wherein the acidic ethylenically unsaturated monomer from (A) is a carboxylic acid group selected from the group consisting of acrylic acid, methacrylic acid, maleic acid, maleic acid half esters, maleic anhydride, itaconic acid, and crotonic acid.

3. The aqueous emulsion according to claim 1 , wherein the acidic ethylenically unsaturated monomer from (A) is a sulfonic acid group selected from the group consisting of styrene sulfonic acid, 2-acrylamido-2-methylpropane sulfonic acid, and sodium vinyl sulfonate.

4. The aqueous emulsion according to claim 1 , wherein the acidic ethylenically unsaturated monomer from (A) is a phosphoric acid group selected from the group consisting of styrene phosphoric acid, sodium vinyl phosphonate, and CH 2 ═C(CH 3 )COO(CH 2 ) n OPO 3 H, wherein n is from 2 to 4.

5. The aqueous emulsion according to claim 1 , wherein the ethylenically unsaturated monomer from (B) is (i) CH 2 ═C(R 1 )COR 2 , wherein R 1 is methyl and R 2 is —OZ′, wherein Z′ is an alkyl group having from 1 to 4 carbon atoms.

6. The aqueous emulsion according to claim 1 , wherein the ethylenically unsaturated monomer from (B) is (ii) R 3 OOC—CH═CH—COOR 4 , wherein R 3 and R 4 are independently an alkyl group having from 1 to 4 carbon atoms.

7. The aqueous emulsion according to claim 1 , wherein the ethylenically unsaturated monomer from (B) is (iii) CH 2 ═C(R 5 )OCOR 6 , wherein R 5 is methyl and R 6 is an alkyl group having from 1 to 4 carbon atoms.

8. The aqueous emulsion according to claim 1 , wherein the ethylenically unsaturated monomer from (B) is (iv) CH 2 ═C(COOR 7 )CH 2 COOR 8 , wherein R 7 and R 8 are independently an alkyl group having from 1 to 4 carbon atoms.

9. The aqueous emulsion according to claim 1 , wherein the ethylenically unsaturated monomer from (B) is (v) CH 3 CH═CHCOOR 9 , wherein R 9 is an alkyl group having from 1 to 4 carbon atoms.

10. The aqueous emulsion according to claim 1 , wherein the ethylenically unsaturated monomer from (B) is (vi) styrene.

11. The aqueous emulsion according to claim 1 , wherein the ethylenically unsaturated monomer from (B) is (vii) R 12 CH═CHR 13 , wherein R 12 and R 13 are independently hydrogen or methyl.