Patent ID: 7504551

Claim:
A method of manufacturing color-stable superabsorbent polymer particles comprising the steps of: (a) forming a monomer mixture comprising: (i) at least one monomer capable of forming a superabsorbent polymer, (ii) a crosslinking agent, (iii) an initiator system comprising a sulfinic acid derivative having a structure wherein M is hydrogen, an ammonium ion, or a monovalent or a divalent metal ion of groups Ia, IIa, IIb, IVa, and VIIIb of the Periodic Table of the Elements; R 1 is OH or NR 4 R 5 , wherein R 4 and R 5 , independently, are H or C 1 -C 6 alkyl; R 2 is H or an alkyl, alkenyl, cycloalkyl, or aryl group, optionally having 1-3 substituents independently selected from the group consisting of C 1 -C 6 alkyl, OH, O—C 1 -C 6 alkyl, halogen, and CF 3 ; and R 3 is COOM, SO 3 M, COR 4 , CONR 4 R 5 , or COOR 4 , wherein M, R 4 , and R 5 are as defined above, or, if R 2 is unsubstituted or unsubstituted aryl, R 3 is H; and the salts thereof; or a mixture thereof; (iv) an optional photoinitiator, and (v) water; (b) polymerizing the monomer and the crosslinking agent in the monomer mixture to form a superabsorbent polymer hydrogel; (c) optionally subjecting the superabsorbent polymer hydrogel to a low dose of UV radiation; (d) comminuting the superabsorbent polymer hydrogel to provide superabsorbent hydrogel particles; and (e) drying the superabsorbent polymer hydrogel particles for a sufficient time at a sufficient temperature to provide the color-stable superabsorbent polymer particles, wherein the color-stable SAP particles, after storage for 30 days at 60° C. and 90% relative humidity, exhibit an HC60 color value of at least 60 and a maximum b-value of 10.