A process for removing metallic impurities from a product mass flow comprising water-absorbing polymer particles by means of bar magnets, wherein the water-absorbing polymer particles comprise a surfactant and have direct contact with the bar magnets.

A process for removing metallic impurities from a product mass flow comprising water-absorbing polymer particles by means of bar magnets, wherein the water-absorbing polymer particles comprise a surfactant and have direct contact with the bar magnets.

A process for producing water-absorbing polymer particles having high free swell rate and high centrifuge retention capacity with simultaneously high permeability of the swollen gel bed by polymerization of an aqueous monomer solution in a polymerization reactor having at least two shafts (kneaders) which rotate in an axially parallel manner, subsequent extrusion at high temperatures and thermal surface postcrosslinking.

A process for producing water-absorbing polymer particles having high free swell rate and high centrifuge retention capacity with simultaneously high permeability of the swollen gel bed by polymerization of an aqueous monomer solution in a polymerization reactor having at least two shafts (kneaders) which rotate in an axially parallel manner, subsequent extrusion at high temperatures and thermal surface postcrosslinking.

A process for producing water-absorbing polymer particles by polymerizing droplets of a monomer solution, where the monomer solution comprises at least two initiators, one of the initiators is a peroxide with the exception of persulfate, and the molar ratio of peroxide to further initiator is at least 1:8, the water-absorbing polymer particles themselves, and hygiene articles comprising these water-absorbing polymer particles.

A process for producing water-absorbing polymer particles by polymerizing droplets of a monomer solution, where the monomer solution comprises at least two initiators, one of the initiators is a peroxide with the exception of persulfate, and the molar ratio of peroxide to further initiator is at least 1:8, the water-absorbing polymer particles themselves, and hygiene articles comprising these water-absorbing polymer particles.

A method for producing a polyvinylphosphonic acid copolymer may control a rise in internal temperature in the reaction system during polymerization and may allow synthesis of a copolymer as a polymer solution. A method for producing a polyvinylphosphonic acid copolymer may include polymerizing a compound of formula (1) and a compound of formula (2) in presence of a radical polymerization initiator and in a water-containing solvent:

##STR00001##

wherein R.sup.1 and R.sup.2 are independently —OH, —O.sup.−, or —O.sup.−M.sup.+(M.sup.+ being a counter ion), R.sup.3 is —OH, —O.sup.−, —O.sup.−M.sup.+, or an optionally substituted alkoxy group having 1 to 10 carbon atoms (M.sup.+ being a counter ion), and R.sup.4 is an optionally substituted alkoxy group having 1 to 10 carbon atoms, R.sup.3 and R.sup.4 optionally forming a ring together with an adjacent phosphorus atom when both R.sup.3 and R.sup.4 are alkoxy groups.

A method for producing a polyvinylphosphonic acid copolymer may control a rise in internal temperature in the reaction system during polymerization and may allow synthesis of a copolymer as a polymer solution. A method for producing a polyvinylphosphonic acid copolymer may include polymerizing a compound of formula (1) and a compound of formula (2) in presence of a radical polymerization initiator and in a water-containing solvent:

##STR00001##

wherein R.sup.1 and R.sup.2 are independently —OH, —O.sup.−, or —O.sup.−M.sup.+(M.sup.+ being a counter ion), R.sup.3 is —OH, —O.sup.−, —O.sup.−M.sup.+, or an optionally substituted alkoxy group having 1 to 10 carbon atoms (M.sup.+ being a counter ion), and R.sup.4 is an optionally substituted alkoxy group having 1 to 10 carbon atoms, R.sup.3 and R.sup.4 optionally forming a ring together with an adjacent phosphorus atom when both R.sup.3 and R.sup.4 are alkoxy groups.

Provided is a method of producing a polycarboxylic acid-based polymer, the method including adding a monomer composition containing an unsaturated monocarboxylic acid-based monomer and/or an unsaturated dicarboxylic acid-based monomer to a reaction vessel to perform a polymerization reaction, which enables effective suppression of the foaming of a polymerization reaction liquid. The method of producing a polycarboxylic acid-based polymer of the present invention is a method of producing a polycarboxylic acid-based polymer, the method including adding a monomer composition containing an unsaturated monocarboxylic acid-based monomer and/or an unsaturated dicarboxylic acid-based monomer to a reaction vessel to perform a polymerization reaction, the method further including adding a defoaming agent by a time when 100 mass % of a total amount of the monomer composition is added.

Disclosed are a method of preparing a superabsorbent polymer, including adding a superabsorbent polymer with a water dispersion solution containing particles having i) a BET specific surface area of 300 to 1500 m.sup.2/g and ii) a porosity of 50% or more, and a superabsorbent polymer prepared by the method.