An aqueous composition that contains an aqueous dispersion of a copolymer of (i) 95-98% by weight of one or more monoethylenically unsaturated monomer; and (ii) 2-5% by weight of a beta-dicarbonyl monomer or cyanocarbonyl monomer, which may be in the enamine form, whereby the beta-dicarbonyl monomer or cyanocarbonyl monomer (ii) is added by staged feed of the said monomer during the second half, by weight, of the feed of monomers (i); and a photoinitiator present in the range of 0.1-1% by weight based upon the total weight of copolymer.