Abstract: The present invention provides an N-vinyl lactam polymer that is less likely to be colored (yellowing) even at high temperatures to maintain its color tone. The present invention provides an N-vinyl lactam polymer comprising a structural unit derived from an N-vinyl lactam monomer, the N-vinyl lactam polymer including a structural unit that has at least one of a hypophosphorous group and a group of hypophosphorous acid metal salt at a main chain terminal.

Abstract: The present invention provides an N-vinyl lactam polymer that is less likely to be colored (yellowing) even at high temperatures to maintain its color tone. The present invention provides an N-vinyl lactam polymer comprising a structural unit derived from an N-vinyl lactam monomer, the N-vinyl lactam polymer including a structural unit that has at least one of a hypophosphorous group and a group of hypophosphorous acid metal salt at a main chain terminal.

Abstract: To provide a continuous production method for producing a water-soluble polymer with a narrow molecular weight distribution with high efficiency. A continuous production method of a water-soluble polymer, comprising the steps of: circulating a circulation liquid containing a monomer having a polymerizable unsaturated bond through a reaction apparatus: having a tank and a circulation line comprising a piping circulating outside the tank, and thereby producing a water-soluble polymer continuously; and discharging part of the circulation liquid from a discharge line, wherein the circulation line is provided with a cooling device at least at one position.

Abstract: To provide a continuous production method for producing a water-soluble polymer with a narrow molecular weight distribution with high efficiency. A continuous production method of a water-soluble polymer, comprising the steps of: circulating a circulation liquid containing a monomer having a polymerizable unsaturated bond through a reaction apparatus: having a tank and a circulation line comprising a piping circulating outside the tank, and thereby producing a water-soluble polymer continuously; and discharging part of the circulation liquid from a discharge line, wherein the circulation line is provided with a cooling device at least at one position.

Abstract: A method for efficient production of a water-soluble porous polymer and a water-soluble porous polymer excelling in solubility in water are provided. A method for the production of the polymer is characterized by the fact that an aqueous monomer solution containing an ethylenically unsaturated monomer is polymerized while it is containing bubbles therein. The method can simplify the drying and crushing steps and the water-soluble porous polymer consequently obtained excels in solubility in water.