Process for production of water-soluble (meth)acrylic polymers, water-soluble (meth) acrylic polymers, and use thereof

A (meth)acrylic acid based water-soluble polymer having a content of groups in neutralized state of less than 20 mole percent, where the sum total of acid groups and groups in neutralized state contained in the (meth)acrylic acid based water-soluble polymer is taken as 100 mole percent,

• wherein an intrinsic viscosity of a neutralized product obtained by neutralization of all acid groups of the said polymer in a 2 N aqueous solution of sodium hydroxide at 30° C. is 30 to 120 ml/mmol, and
• wherein an insoluble matter content in deionized water is less than 5% by mass,
• said insoluble matter content being the value determined by adding 1.0 g of said (meth)acrylic acid based water-soluble polymer to 500 g of deionized water, stirring the mixture at 25° C. for 2 hours, filtering the mixture through a 32-mesh filter, separating the insoluble matter in hydrous state and making a calculation according to the following formula:
• Insoluble matter content (% by mass)={mass (g) of insoluble matter/500 (g)}×100.