Process for preparing highly water absorbent resin

A process for preparing a water absorbent resin, which consists essentially of:

• (1) neutralizing acrylic acid with an aqueous alkali metal hydroxide to a neutralization degree ranging from 50 to 100% based on the total number of moles of the acid employed and polymerizing it by a reverse phase suspension polymerization to provide a 50 to 100% neutralized polymer;
• (2) dehydrating the polymer until its water content reaches 25% by weight or less based on the weight of the polymer through an azeotropic distillation under reflux of a solvent selected from the group consisting of n-hexane, n-heptane, benzene, xylene, toluene, cyclopentane and cyclohexane;
• (3) crosslinking the dehydrated polymer by adding a mixture of a hydrophilic crosslinking agent containing at least two epoxy groups in an amount ranging from 0.05 to 5.0% by weight and water in an amount ranging from 7.0 to 25.0% by weight, both amounts being based on the weight of the dehydrated polymer;
• (4) dehydrating the crosslinked polymer until 60% by weight or more of the amount of water added in step (3) above is removed through a continued azeotropic distillation under reflux of the solvent present in step (2);
• and
• (5) recovering the crosslinked and dehydrated polymer by filtration.