Process for preparing absorbent polymers

Claim 2

A process for preparing an absorbent polymer composition comprising the steps of: (a) preparing a dispersion of an effective amount of a crosslinking monomer and a dispersing agent in an aqueous solution of a water-soluble α,β-ethylenically unsaturated carboxylic acid monomer which is at least partially neutralized, (b) subjecting the dispersion to reactive conditions so as to polymerize the neutralized or partially neutralized carboxylic acid and crosslinking monomer, wherein the dispersing agent does not reduce the surface tension of a supernatant solution of 1 g of the polymerized monomer in 200 ml of a 0.9 percent aqueous sodium chloride below 60 dynes/cm (6 pascals).

Claim 3

A process as claimed in Claim 1 wherein the crosslinking monomer is trimethylolpropane­triacrylate or diethylene glycol diacrylate; the water-soluble ethylenically unsaturated monomer is acrylic acid, methacrylic acid, or alkali metal salts of these acids and the dispersing agent is carboxymethyl-cellulose suspending aids or polyvinyl alcohol.

Claim 4

A process as claimed in Claim 1 wherein the crosslinking monomer present in the dispersion is polymerized in an amount ranging from 0.0001 to 5 parts by weight based on 100 parts by weight of water-soluble monomer.

Claim 5

A process as claimed in Claim 1 wherein the dispersion further comprises water soluble alkyl esters of unsaturated carboxylic acids and an effective amount of one or more vinyl addition polymerization initiators.

Claim 6

A process as claimed in Claim 1 wherein the water-soluble ethylenically unsaturated monomer is present in an amount ranging from 10 percent to 80 percent based on the total weight of the aqueous monomer dispersion.

Claim 7

A process as claimed in Claim 4 wherein the initiator is sodium persulfate, ammonium persulfate, potassium persulfate, hydrogen peroxide, azo-bis compounds or redox-type initiators and is present in the dispersion in an amount of from 0.01 to 1.0 weight percent based on the total weight of monomer reactants.

Claim 8

A process as claimed in of Claim 1 wherein the dispersion is prepared by contacting an aqueous solution of crosslinking monomer, ethylenically unsaturated monomer, and the dispersing agent with a basic material effective to neutralize the acid groups of the water-soluble ethylenically unsaturated monomer.

Claim 9

A process as claimed in Claim 7 wherein the basic material used to neutralize the monomer mixture is sodium hydroxide, potassium hydroxide or sodium carbonate and is used in an amount effective to neutralize at least 20 percent of the acid groups of the water-soluble ethylenically unsaturated monomer.

Claim 10

A process for preparing an absorbent polymer composition comprising the steps of (1) forming an aqueous solution of a crosslinking monomer in a water-soluble ethylenically unsaturated monomer in the presence of an amount of a dispersing agent effective to maintain the dispersion of the crosslinking monomer after the water-soluble monomer has been neutralized, the dispersing agent being chosen such that the surface tension of a supernatant solution of 1 g of the polymerized monomer in 200 ml of a 0.9 percent sodium chloride is not less than 60 dynes/cm (6 pascals) as measured on a Du Nouy tensiometer, (2) neutralizing the monomer solution with an amount of basic material sufficient to neutralize a substantial portion of the monomer solution, (3) adding one or more vinyl addition polymerization initiators to the neutralized monomer solution, and then (4) subjecting the neutralized solution to polymerization conditions.

Claim 11

A process for preparing an absorbent polymer composition comprising the steps of (1) forming an aqueous solution of a crosslinking monomer in a water-soluble ethylenically unsaturated monomer in the presence of an amount of a dispersing agent effective to maintain the dispersion of the crosslinking monomer after the water-soluble monomer has been neutralized, the dispersing agent being chosen such that the surface tension of a supernatant solution of 1 g of the polymerized monomer in 200 ml of a 0.9 percent sodium chloride is not less than 60 dynes/cm (6 pascals) as measured on a Du Nouy tensiometer, (2) neutralizing the monomer solution with an amount of basic material sufficient to neutralize a substantial portion of the monomer solution, (3) adding one or more vinyl addition polymerization initiators to the neutralized monomer solution, and then (4) subjecting the neutralized solution to polymerization conditions.

Claim 12

A process for preparing an absorbent polymer composition comprising the steps of (1) dissolving a crosslinking monomer in an aqueous solution of water-soluble α,β-ethylenically unsaturated monomer, (2) neutralizing the monomer solution with an amount of basic material sufficient to neutralize a substantial portion of the monomer solution, (3) introducing into the neutralized solution an amount of a dispersing agent effective to maintain the dispersion of crosslinking monomer in the neutralized monomer solution, the dispersing agent being chosen such that the surface tension of a supernatant solution of 1 g of the polymerized monomer in 200 ml of a 0.9 percent sodium chloride is not less than 60 dynes/cm (6 pascals), (4) adding one or more vinyl addition polymerization initiators to the neutralized monomer solution, and then (5) subjecting the solution to polymerization conditions.

Claim 13

A process for preparing an absorbent polymer composition comprising the steps of (1) dissolving a crosslinking monomer in an aqueous solution of water-soluble α,β-ethylenically unsaturated monomer, (2) neutralizing the monomer solution with an amount of basic material sufficient to neutralize a substantial portion of the monomer solution, (3) introducing into the neutralized solution an amount of a dispersing agent effective to maintain the dispersion of crosslinking monomer in the neutralized monomer solution, the dispersing agent being chosen such that the surface tension of a supernatant solution of 1 g of the polymerized monomer in 200 ml of a 0.9 percent sodium chloride is not less than 60 dynes/cm (6 pascals), (4) adding one or more vinyl addition polymerization initiators to the neutralized monomer solution, and then (5) subjecting the solution to polymerization conditions.