Patent ID: 8252869

Claim:
A method of producing a crosslinked poly(meth)acrylic acid nitroxide compound including a repeating unit represented by formula (2): wherein in the formula (2), R represents a hydrogen atom or a methyl group, comprising: a nitroxidation step carried out in a state in which a crosslinked poly(meth)acrylic acid imino compound resulting from crosslinking of a poly(meth)acrylic acid imino compound including a repeating unit represented by formula (1) is dispersed in water: wherein in the formula (1), R represents the same group as that represented by R in said formula (2), wherein the crosslinked poly(meth)acrylic acid imino compound is crosslinked during polymerization for forming the poly (meth)acrylic acid imino compound in the presence of a crosslinking agent, the crosslinking agent being at least one selected from the group consisting of a (meth)acrylic acid-type polyfunctional compound, an allyl ether-type polyfunctional compound, and a vinyl-type polyfunctional compound, and the crosslinked poly(meth)acrylic acid imino compound is a powder having a median particle diameter of 1 mm or less.