Patent ID: 8481159

Claim:
Water-absorbent polymer particles prepared by polymerizing droplets of a monomer solution comprising a) at least one ethylenically unsaturated monomer which bears acid groups and optionally is at least partly neutralized, b) at least one crosslinker, c) at least one initiator, d) optionally one or more ethylenically unsaturated monomer copolymerizable with the monomer mentioned under a), e) optionally one or more water-soluble polymer, and f) water, in a surrounding heated gas phase and flowing the gas cocurrent through a polymerization chamber, wherein a temperature of the gas leaving the polymerization chamber is 130° C. or less, a gas velocity inside the polymerization chamber is at least 0.5 m/s, and the droplets are generated by using a droplet plate having a multitude of bores, wherein the polymer particles have a mean sphericity from 0.86 to 0.99, a bulk density of at least 0.58 g/cm 3 , and an average particle diameter from 250 to 550 μm, wherein a particle diameter distribution is less than 0.7 and a ratio of particles having one cavity to particles having more than one cavity is less than 1.0.