Acetylation of crude reaction products containing polymeric colorants

The process which comprises:

• (a) contacting a liquid mixture comprising 0.1 to 10% by weight of polymeric colorant containing anionic water-solubilizing groups selected from the group consisting of sulfonate groups, carboxylate groups, sulfamate groups and phosphonate groups;
• and comprising a nonchromophoric organic polymer backbone to which is covalently bonded a plurality of units of organic chromophore and a plurality of residual primary or secondary alkyl nitrogens, 60-98% by weight aqueous solvent, 0.2-30% by weight unattached organic chromophore and byproducts of the polymeric colorant preparation, with from 1 to 6 equivalents of acetic anhydride per mole of primary and secondary alkyl amines on said polymeric colorant, said contacting being effected at a pH of 9.13, a temperature of from 0.degree. to 10.degree. C. and for a time of from 1 to 60 minutes, thereby acetylating said primary and secondary alkyl amines to amides and forming an acetylated polymeric colorant in which the number of said primary or secondary alkyl nitrogens present in acetylated form as amides is at least twice the number of said primary or secondary alkyl nitrogens present as unacetylated amines and the number of anionic water-solubilizing groups is at least three times the number of said residual primary or secondary alkyl nitrogens present as unacetylated amines, and
• (b) recovering said acetylated polymeric colorant.