AbstractA method of the control of copolymer endgroups in a solution‐suspension copolymerization process was elaborated. The method is based on the utilisation of an initiating system containing three components: S2O2‐8 /HSO‐3 /Fe2+, their ratio and the ratio S2O2‐8 /comonomer mixture being optimized. In this way it is possible to control the content of endgroups of the copolymer, the saturation value, the M̄n values and polydispersity, without using comonomers with polar groups –SO3H or –OSO3H. Due to their conformational peculiarities and their packing manner in concentrated solutions, the macromolecular chains with a high endgroup content behave much better during the solving and spinning processes.Thus, an increase of the content of copolymer endgroups favours not only the tinctorial properties, but also the spinnability of the spinning dopes obtained from the respective copolymers.The proposed method for the copolymer endgroup control is more economical than the utilization of the comonomers with polar groups.