An aqueous polymer dispersion, comprising: (i) an emulsion polymer having a weight average molecular weight of from 2,000 to 30,000 daltons, wherein the emulsion polymer comprises as polymerized units, based on the dry weight of the emulsion polymer, (a) from 10% to 90% by weight of an ethylenically unsaturated ionic monomer, (b) from 5% to 90% by weight of a photosensitive monomer, wherein the photosensitive monomer comprises a substituted styrene, a benzophenone derivative, or mixtures thereof; wherein the substituted styrene has the structure of formula, wherein R 1, R 2, and R 3 are each independently selected from the group consisting of H, an alkyl, an alkoxy, and a (hetero)aryl; and R 4 is H or an alkyl; and wherein the benzophenone derivative has the structure of formula,, or, wherein, in formula, R 1 is H or methyl; R 2 is -O- or -NH-; R 3 has the following structure Z, wherein R 7, R 8, and R 9 are each independently H or methyl, n is an integer of from 0 to 200, and o and p are each independently an integer of from 0 to 2; R 4 is -O-, -NH-, -O-CO-O-, -CO-, -NH-CO-O-, -NH-CO-NH-, or -S-; R 5 is H, a halogen, or a C 1 -C 20 moiety optionally substituted by oxygen, nitrogen, sulphur, or combinations thereof; m is an integer of from one to 4; and R 6 is an alkyl, an aryl, or a heterocyclyl; wherein, in formula and/or, R 10 is H or methyl; and R 11 and R 12 are each independently selected from the group consisting of H, an alkyl, an alkoxy, and a (hetero)aryl (c) from 0 to 85% by weight of an ethylenically unsaturated nonionic monomer; and (ii) from 3.5% to 50% by weight of TEMPO and/or a derivative thereof, based on the total dry weight of the aqueous polymer dispersion, wherein TEMPO and/or its derivative have the structure of formula: wherein R is H, -OH, an alkyl, an alkoxy, or a (hetero)aryl. (i) an emulsion polymer having a weight average molecular weight of from 2,000 to 30,000 daltons, wherein the emulsion polymer comprises as polymerized units, based on the dry weight of the emulsion polymer, (a) from 10% to 90% by weight of an ethylenically unsaturated ionic monomer, (b) from 5% to 90% by weight of a photosensitive monomer, wherein the photosensitive monomer comprises a substituted styrene, a benzophenone derivative, or mixtures thereof; wherein the substituted styrene has the structure of formula, wherein R 1, R 2, and R 3 are each independently selected from the group consisting of H, an alkyl, an alkoxy, and a (hetero)aryl; and R 4 is H or an alkyl; and wherein the benzophenone derivative has the structure of formula,, or, wherein, in formula, R 1 is H or methyl; R 2 is -O- or -NH-; R 3 has the following structure Z, wherein R 7, R 8, and R 9 are each independently H or methyl, n is an integer of from 0 to 200, and o and p are each independently an integer of from 0 to 2; R 4 is -O-, -NH-, -O-CO-O-, -CO-, -NH-CO-O-, -NH-CO-NH-, or -S-; R 5 is H, a halogen, or a C 1 -C 20 moiety optionally substituted by oxygen, nitrogen, sulphur, or combinations thereof; m is an integer of from one to 4; and R 6 is an alkyl, an aryl, or a heterocyclyl; wherein, in formula and/or, R 10 is H or methyl; and R 11 and R 12 are each independently selected from the group consisting of H, an alkyl, an alkoxy, and a (hetero)aryl (c) from 0 to 85% by weight of an ethylenically unsaturated nonionic monomer; and (a) from 10% to 90% by weight of an ethylenically unsaturated ionic monomer, (b) from 5% to 90% by weight of a photosensitive monomer, wherein the photosensitive monomer comprises a substituted styrene, a benzophenone derivative, or mixtures thereof; wherein the substituted styrene has the structure of formula, wherein R 1, R 2, and R 3 are each independently selected from the group consisting of H, an alkyl, an alkoxy, and a (hetero)aryl; and R 4 is H or an alkyl; and wherein the benzophenone derivative has the structure of formula,, or, wherein, in formula, R 1 is H or methyl; R 2 is -O- or -NH-; R 3 has the following structure Z, wherein R 7, R 8, and R 9 are each independently H or methyl, n is an integer of from 0 to 200, and o and p are each independently an integer of from 0 to 2; R 4 is -O-, -NH-, -O-CO-O-, -CO-, -NH-CO-O-, -NH-CO-NH-, or -S-; R 5 is H, a halogen, or a C 1 -C 20 moiety optionally substituted by oxygen, nitrogen, sulphur, or combinations thereof; m is an integer of from one to 4; and R 6 is an alkyl, an aryl, or a heterocyclyl; wherein, in formula and/or, R 10 is H or methyl; and R 11 and R 12 are each independently selected from the group consisting of H, an alkyl, an alkoxy, and a (hetero)aryl (c) from 0 to 85% by weight of an ethylenically unsaturated nonionic monomer; and (ii) from 3.5% to 50% by weight of TEMPO and/or a derivative thereof, based on the total dry weight of the aqueous polymer dispersion, wherein TEMPO and/or its derivative have the structure of formula: wherein R is H, -OH, an alkyl, an alkoxy, or a (hetero)aryl.