Colouring linear polyesters

Linear polyesters are coloured by effecting the polymerization of the polyester-forming compounds in the presence of a dyestuff of formula where D is a polycyclic dyestuff radical which consists of or includes a group of at least three condensed rings; Y is -NH- or -S-; R represents a substituted or unsubstituted alkyl radical or a cyclohexyl radical; n is 1 to 3; m is 1 to 4; and the benzene ring may be further substituted by chlorine or bromine atoms. The preferred polyesters are those obtained by reacting terephthalic acid or an ester thereof with a glycol of formula HO-(CH2)x-OH (where x = 2-10) or with 1:4-di(hydroxy-methyl)cyclohexane. In the dyestuff D may be an anthraquinone, 11:91-anthrapyridone, 11:91 - anthrapyrimidine, isothiazoloanthrone, pyrazoleanthrone, 31:41-phthaloylacridone or phthaloyl perinone radical. The dyestuff radical may be substituted, e.g. by chlorine, bromine, carboxylic acid, lower alkyl, lower alkoxy, hydroxy, amino, N-lower alkylamino or acylamino groups. Most preferred dyestuffs are those of formula where T1, T2, and T3 are hydrogen atoms or groups of formula where R1 is a lower alkyl radical. In examples, the dyestuff previously wetted with ethylene glycol is incorporated into a monomer obtained by reacting dimethyl terephthalate with ethylene glycol or the dyestuff is incorporated initially with the dimethyl teraphthalate and the ethylene glycol.