Acrylic amphoteric polymers

Claim 1

In a process for preparing an amphoteric polymer comprising polymerizing these monomers by solution or emulsion polymerization: (a) 20 to 90 mol percent of the methyl ester of acrylic acid, (b) 10 to 30 mol percent of N,N-dimethylamino-ethyl methacrylate or N,N-diethylaminoethyl methacrylate, and (c) 0 to 70 mol percent of at least one member selected from the group consisting of C 1-8 alkyl methacrylate, 2-hydroxyethyl acrylate, 2-hydroxyethyl methacrylate, 2-hydroxypropyl acrylate, and 2-hydroxypropyl methacrylate; the improvement which comprises hydrolyzing the polymer in aqueous base to selectively convert acryate ester groups to carboxylate salt groups, thereby forming an amphoteric polymer characterized by: (i) a molar ratio of hydrolyzed polymer units derived from monomer (a) which contains carboxylate salt groups, to polymer units derived from monomer (b), of at least 2 to 1, (ii) a degree of polymerization of about 50 to 300 and (iii) substantially no betaine-type contaminant.