Patent ID: 7449439

Claim:
A water-soluble thickener comprising a water-soluble copolymer having a weight-average molecular weight of 6,000,000 or higher obtainable by polymerizing a monomer mixture which comprises 2-acrylamido-2-methylpropanesulfonic acid and/or a salt thereof and acrylic acid and/or a salt thereof and optionally other copolymerizable monomer components, wherein 2-acrylamido-2-methylpropanesulfonic acid and/or a salt thereof is present in an amount of 20 mol % or more of all the monomers, wherein the monomer mixture comprises a compound represented by the following formula (1): wherein n is an integer of 1 to 12, and/or a salt thereof as the other copolymerizable monomer components, wherein the amount of the compound of formula (1) and/or a salt thereof, is in the range of 0.1 to 20 mol % based on the total moles of all the monomers, and wherein the monomer mixture comprises 20 to 80 mol % of acrylic acid and/or salt thereof, based on the total moles of the monomers.