Patent ID: 7700702

Claim:
An associative amphoteric polymer having a weight average molecular weight (M w ) greater than 50,000 g/mol consisting of: (a) between 0.005 and 10 mole % of at least one acrylamide-derived cationic monomer containing a hydrophobic chain and with the general formula: where R1, R2, R3, R4, R5, R6, independently, a hydrogen or an alkyl chain containing 1 to 4 carbons; Q: an alkyl chain containing 1 to 8 carbons; R7: an alkyl or arylalkyl chain containing 8 to 30 carbons; X: a counterion with a negative charge; (b) between 1 and 30 mole % of at least one anionic monomer containing acrylic, vinyl, maleic, fumaric or allyl functionalities and containing a group selected from carboxy, phosphonate or sulfonate and/or their ammonium salts or alkaline-earth metal salts or alkali metal salts; and (c) between 1 and 99 mole % of at least one acrylamide-derived non-ionic hydrosoluble monomer; wherein said amphoteric polymer is characterized by a monomeric molar ratio of x/y, in which x corresponds to the mole percentage of said cationic monomer containing a hydrophobic chain, y corresponds to the mole percentage of said anionic monomer, and y>x.